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S 10 brake booster causing spongy pedal? by Rickady88GT
Started on: 10-07-2021 09:57 PM
Replies: 27 (364 views)
Last post by: fieroguru on 10-17-2021 02:26 PM
Rickady88GT
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Report this Post10-07-2021 09:57 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
My 88 has a good pedal feel with engine off, but start the engine and the pedal gets spongy. I know the booster takes out some petal feel, and that the pedal will go down a bit, but this seems extreme. So does the booster go bad like this?
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Report this Post10-07-2021 10:17 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
If this has developed over time, it likely is the rear brake calipers having too large of a gap between the pads and the rotors.

The parking brake self adjuster inside the caliper pistons probably are not working like they are supposed to.
If these do not adjust, then as the pads wear, the gap between the pads and rotors increases. This will give you a very soft pedal for the first portion of travel as the pads are pushed through the excess gap. The pedal firms up when the pads contact the rotor.
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Report this Post10-07-2021 11:25 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by fieroguru:

If this has developed over time, it likely is the rear brake calipers having too large of a gap between the pads and the rotors.

The parking brake self adjuster inside the caliper pistons probably are not working like they are supposed to.
If these do not adjust, then as the pads wear, the gap between the pads and rotors increases. This will give you a very soft pedal for the first portion of travel as the pads are pushed through the excess gap. The pedal firms up when the pads contact the rotor.


Thanks, I actually have the rear wheels off and bleeding the brakes. I did not notice that much of a gap. The gap is so slight that you can barely see light through it. Same with the front. The pedal feels ok with the engine off, no vacuum to the booster. Start the engine and instantly the brake suck. (In my opinion) I am just not sure what is in-between the pedal and master, so not really sure if this booster is an issue?
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Report this Post10-08-2021 12:02 AM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
After bleeding the brakes, I feel like something is still not right. I think I will replace the master. It feels like the pedal creeps down as I hold pressure on it. No leaks anywhere, so if the pedal is creeping down then fluid must be pushing back past the cups.
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Report this Post10-08-2021 12:41 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
Spongy & Low pedal do not mean same.
See my Cave, Brake Service
Can have either or both at same time...

You took MC out to replace the booster now spongy pedal = air in the lines or MC itself.
See my Cave, Bleeding MC notes as to why you "bench bleed" them.

Low pedal often is rear brake problems. See my Cave, Rear Brakes

But Low pedal can be cause replacement booster w/ wrong adjustment on output rod that push the MC.
Need to find or make special tool to set clearance right or will have low pedal or worse problems w/ MC not fully return to rest position.
Output rod likely has clearance of some X 100th to 1000th of inch to make MC fully returns but not cause low pedal. tool(s) in FSM and other doc's to set the output rod is setup for this w/o publishing the tool design or clearance value.

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Report this Post10-08-2021 02:44 AM Click Here to See the Profile for SemperFi18Send a Private Message to SemperFi18Edit/Delete MessageReply w/QuoteDirect Link to This Post
Check your proportioning valve before you mess with the master. If you ever bled the brakes to quickly (quick loss of pressure) either front or back, that valve closes off that part of the brakes as a safety. Pull the sensor off the valve and you should see a gap that the pin from the sensor sets in. If it's moved front or back you can move it with a narrow pick.

Pulled my hair out for weeks with this issue, spongy pedal because you only have half your brakes. Once I checked that valve I fixed it in two minutes. Gravity bleed after that
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Report this Post10-08-2021 06:39 AM Click Here to See the Profile for RaydarClick Here to Email RaydarSend a Private Message to RaydarEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by SemperFi18:

Check your proportioning valve before you mess with the master. If you ever bled the brakes to quickly (quick loss of pressure) either front or back, that valve closes off that part of the brakes as a safety. Pull the sensor off the valve and you should see a gap that the pin from the sensor sets in. If it's moved front or back you can move it with a narrow pick.



Not to discount your remedy. Obviously, it worked.
But if the valve is moved far enough to affect your brake system, shouldn't it be tripping the sensor and turning the brake light on?
Asking because I've been chasing a "fronts lock up long before the rears" situation for a long time. (Yeah... I know that's how they're supposed to work. But not to the extent I'm seeing, I don't think.)
My pedal feels fine. Brakes are freshly bled, with no real change.
The only difference is the front pads are supposedly OEM. Bought loaded NOS front calipers. The rears are... something else. But the fronts do make a lot more dust.

[This message has been edited by Raydar (edited 10-08-2021).]

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Report this Post10-08-2021 09:51 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Raydar:
Not to discount your remedy. Obviously, it worked.
But if the valve is moved far enough to affect your brake system, shouldn't it be tripping the sensor and turning the brake light on?
Asking because I've been chasing a "fronts lock up long before the rears" situation for a long time. (Yeah... I know that's how they're supposed to work. But not to the extent I'm seeing, I don't think.)
My pedal feels fine. Brakes are freshly bled, with no real change.
The only difference is the front pads are supposedly OEM. Bought loaded NOS front calipers. The rears are... something else. But the fronts do make a lot more dust.
Yes, when the balance bar moves the brake light should be On when the Key is On.

The bar isn't easy to move for bleeding and even many times driving w/ minor system leaks unless maybe you panic stop for whatever reason.

Balance bar Does Not close off a line w/ low pressure. In fact if the front has a leak etc will Open the rear to full pressure bypassing the prop valve.
If air got in the prop section and bar moves to front then may never get air out of that w/o bar reset automatic or manual. It doesn't block the prop valve but little or no flow when in bypass to push air out of the prop section.
Bar auto resets but often need to "slam" the pedal a couple to several times to spike system pressure until it centers and light off. If have air in the system maybe hard or impossible to auto reset depending how much air in there.

If balance bar blocks a line, then the combi-valve have other problems.

See my Cave, Combination Valve
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mmeyer86gt/gtp
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Report this Post10-08-2021 11:15 AM Click Here to See the Profile for mmeyer86gt/gtpClick Here to Email mmeyer86gt/gtpSend a Private Message to mmeyer86gt/gtpEdit/Delete MessageReply w/QuoteDirect Link to This Post
I had this problem too. It turned out to be a brake bleeder split in a caliper causing air to get into the system.
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Report this Post10-08-2021 11:56 AM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
If the bar moves, shouldn't I be able to use an Ohm multimeter to check it, without removing it? It reads open right now, this is what I expect from a normal poison. If the bar moved shouldn't I get resistance?
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Report this Post10-08-2021 12:02 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
All 4 calipers appear to be working fine. I religiously use my parking brake. It is in good working order. They wear the pads about the same, left to right and front to rear. With the exception of the rears have slightly more wear on the outside pads. But rears wore exactly the same.
I do not remember attempting to bleed the proportioning valve?
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Report this Post10-08-2021 12:58 PM Click Here to See the Profile for 82-T/A [At Work]Send a Private Message to 82-T/A [At Work]Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:

My 88 has a good pedal feel with engine off, but start the engine and the pedal gets spongy. I know the booster takes out some petal feel, and that the pedal will go down a bit, but this seems extreme. So does the booster go bad like this?


Lots of things, but I basically concur with everything Ogre has said. Here are some instances where I found spongy brakes to be caused:

1 - Old flexible brake lines (between the steel lines and the calipers.
2 - Worn pads = greater distance
3 - Air in brake lines
4 - Failing master cylinder, e.g. the piston seal is corroding allowing fluid to escape.
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Report this Post10-08-2021 01:18 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 82-T/A [At Work]:


Lots of things, but I basically concur with everything Ogre has said. Here are some instances where I found spongy brakes to be caused:

1 - Old flexible brake lines (between the steel lines and the calipers.
2 - Worn pads = greater distance
3 - Air in brake lines
4 - Failing master cylinder, e.g. the piston seal is corroding allowing fluid to escape.

Yah, I also agree in theory, but in practice it is a little more difficult to trace it down. The lines are SS, and the pads look new with no visible gap. VERY slight drag on every disk, only enough to hear it drag. The park brake holds the car in place on an incline.
Air in the master or proportioning valve is a possibility as well as bad cups in the master.

[This message has been edited by Rickady88GT (edited 10-08-2021).]

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mmeyer86gt/gtp
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Report this Post10-08-2021 02:36 PM Click Here to See the Profile for mmeyer86gt/gtpClick Here to Email mmeyer86gt/gtpSend a Private Message to mmeyer86gt/gtpEdit/Delete MessageReply w/QuoteDirect Link to This Post
how old are the ss brake lines
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Rickady88GT
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Report this Post10-08-2021 03:45 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by mmeyer86gt/gtp:

how old are the ss brake lines


10 years?
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Report this Post10-08-2021 04:27 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:
If the bar moves, shouldn't I be able to use an Ohm multimeter to check it, without removing it? It reads open right now, this is what I expect from a normal poison. If the bar moved shouldn't I get resistance?
Yes. The 2 pins Will show a "short"/close reading 0Ω when the bar moves.

Bar middle is sealed by "o-rings" and never get brake fluid there so the Switch never sees system pressure.
Can check/replace w/o causing other brake issues But don't leave switch hole open to air for hours to days either.
Any Tiny amount of fluid getting in the bar middle draws water from air and can drop crap in there.
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Report this Post10-08-2021 10:31 PM Click Here to See the Profile for 82-T/A [At Work]Send a Private Message to 82-T/A [At Work]Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:

10 years?


My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.

My thought though... master cyl... the "cups" as you said (didn't know that's what they were called). I had a Fiero sit for a long time, and I reused the same master cyl (which was new a couple of years before I let it sit) and no matter how much I bled the lines, it still felt spongy. Just a thought...
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Report this Post10-08-2021 11:47 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 82-T/A [At Work]:
My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.
Not when have "real" SS soft lines because inner core is Teflon tube.

That said... SS soft lines in street cars have never been good idea no matter how much BS is published by the makers.
And while newer ones labeled as DOT sets, that cert is Voided as soon as you add anything to support/protect the hose like many use zip ties and other things to keep the hose away from tires etc. That also Voids most SS soft line Warranties too even when they come w/ the hoses.

When replace old OE "Rubber" or SS lines get sae j1401 "rubber" hose.
Uses same hardware as OE w/ much better "rubber" hose. Often sold as "pro grade" parts.
See https://www.fiero.nl/forum/Forum2/HTML/129208.html
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Report this Post10-09-2021 09:34 AM Click Here to See the Profile for 82-T/A [At Work]Send a Private Message to 82-T/A [At Work]Edit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

[QUOTE]Originally posted by 82-T/A [At Work]:
My thought also here... I wouldn't go replacing them necessarily... but they technically aren't stainless steel, but instead rubber hoses with steel braiding around them. They can still swell and expand.
Not when have "real" SS soft lines because inner core is Teflon tube.

That said... SS soft lines in street cars have never been good idea no matter how much BS is published by the makers.
And while newer ones labeled as DOT sets, that cert is Voided as soon as you add anything to support/protect the hose like many use zip ties and other things to keep the hose away from tires etc. That also Voids most SS soft line Warranties too even when they come w/ the hoses.

When replace old OE "Rubber" or SS lines get sae j1401 "rubber" hose.
Uses same hardware as OE w/ much better "rubber" hose. Often sold as "pro grade" parts.
See https://www.fiero.nl/forum/Forum2/HTML/129208.html[/QUOTE]


OGRE, are there any "stainless" brake lines you recommend at all for a car that you were completely restoring / rebuilding? Or would you just use the rubber lines you mentioned in the link?
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Mickey_Moose
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Report this Post10-12-2021 02:11 PM Click Here to See the Profile for Mickey_MooseClick Here to visit Mickey_Moose's HomePageClick Here to Email Mickey_MooseSend a Private Message to Mickey_MooseEdit/Delete MessageReply w/QuoteDirect Link to This Post
I recently had this problem as well. I just had to remove the master and bench bleed it properly - all is good since doing that at the start of the year.

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Report this Post10-12-2021 07:35 PM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by 82-T/A [At Work]:
OGRE, are there any "stainless" brake lines you recommend at all for a car that you were completely restoring / rebuilding? Or would you just use the rubber lines you mentioned in the link?
For all street cars...
Always use the SAE j1401 "rubber" hose whenever possible. This is DOT rated with same OE hardware including bracket in the middle most vehicles need.
Many New cars have this as OE when made at whatever factory.

"Old" DOT "rubber" next because have correct hardware. This "Old type" DOT rubber is a lot better then SS hype claims and easily last another 10 15 or more years for most cars.

New "old type" DOT rubber and SAE sets look same but SAE hose marked both DOT and SAE J1401.

Most think SS lines are better have no clue have many problems even w/ "DOT Approved" sets and not just having universal end(s) and missing support bracket.
Yes, Either "Rubber" can wear out but so can SS lines but the Hype Train never will tell you that. Worse Most DOT SS have clear plastic that hates UV etc and when that cracks let dirt and other road crap attacking the SS and/or the liner.
IOW Crack cover on SS lines is as bad or often worse then cracks on rubber hose.
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Report this Post10-12-2021 08:46 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Mickey_Moose:

I recently had this problem as well. I just had to remove the master and bench bleed it properly - all is good since doing that at the start of the year.


This is exactly what am am doing right now. The combination value came off as well. The proportion valve just seemed strange that it wouldn't bleed like I thought it should? So I took it apart and the cup seal on the spring loaded proportion value was stuck in the boar as I removed the red plunger. The boars of the valve body were in good shape after cleaning, but gummed up pretty bad as it was. So, I got it cleaned up and am now bleeding the system.
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Report this Post10-12-2021 08:49 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post

Rickady88GT

10081 posts
Member since Dec 2002
 
quote
Originally posted by theogre:

[QUOTE]Originally posted by 82-T/A [At Work]:
OGRE, are there any "stainless" brake lines you recommend at all for a car that you were completely restoring / rebuilding? Or would you just use the rubber lines you mentioned in the link?

 
quote

For all street cars...
Always use the SAE j1401 "rubber" hose whenever possible. This is DOT rated with same OE hardware including bracket in the middle most vehicles need.
Many New cars have this as OE when made at whatever factory.

"Old" DOT "rubber" next because have correct hardware. This "Old type" DOT rubber is a lot better then SS hype claims and easily last another 10 15 or more years for most cars.

New "old type" DOT rubber and SAE sets look same but SAE hose marked both DOT and SAE J1401.

Most think SS lines are better have no clue have many problems even w/ "DOT Approved" sets and not just having universal end(s) and missing support bracket.
Yes, Either "Rubber" can wear out but so can SS lines but the Hype Train never will tell you that. Worse Most DOT SS have clear plastic that hates UV etc and when that cracks let dirt and other road crap attacking the SS and/or the liner.
IOW Crack cover on SS lines is as bad or often worse then cracks on rubber hose.


Thanks for the info, my next set of lines will not be SS. Standard will work just fine for me.

[This message has been edited by Rickady88GT (edited 10-12-2021).]

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Report this Post10-12-2021 11:08 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
Got it all together and did the bleeding as best I could. I gravity beed the brakes one at a time then bleed them with the pedal. They feel better but not what I had in mind. I feel like they should be more solid.
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Report this Post10-14-2021 11:32 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:
Got it all together and did the bleeding as best I could. I gravity beed the brakes one at a time then bleed them with the pedal. They feel better but not what I had in mind. I feel like they should be more solid.
Duh. When you Add booster power, you feel less w/ your foot. Is like having a longer pedal arm adding more leverage.

Or worse comparing old booster w/ problems to any new booster.

And That's assuming the rest of brake parts still don't have problems like Slider w/o or wrong lube and more covered in cave.
Everything in brake section of the cave covers 88 but have to account for really minor differences to mount the calipers and pads etc.
Like Still uses same type MC and rear pistons but different sizes.

[This message has been edited by theogre (edited 10-14-2021).]

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Report this Post10-14-2021 07:00 PM Click Here to See the Profile for Rickady88GTClick Here to Email Rickady88GTSend a Private Message to Rickady88GTEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by theogre:

Duh. When you Add booster power, you feel less w/ your foot. Is like having a longer pedal arm adding more leverage.

I was talking about the pedal feel with the engine off.
There is clearly something else that needs to be addressed.
I have not driven the car sense I started this brake job.
I had hoped that bench bleeding would help.
 
quote



And That's assuming the rest of brake parts still don't have problems like Slider w/o or wrong lube and more covered in cave.

The sliders are fine. They are not sticking or rough, they are smooth.
 
quote

Everything in brake section of the cave covers 88 but have to account for really minor differences to mount the calipers and pads etc.
Like Still uses same type MC and rear pistons but different sizes.


I have clicked on a couple of links for the cave, in various threads and the page said something like it is a dead link?

[This message has been edited by Rickady88GT (edited 10-14-2021).]

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Report this Post10-17-2021 11:45 AM Click Here to See the Profile for theogreClick Here to visit theogre's HomePageSend a Private Message to theogreEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:
1. I was talking about the pedal feel with the engine off.
There is clearly something else that needs to be addressed.
I have not driven the car sense I started this brake job.
I had hoped that bench bleeding would help.

2. I have clicked on a couple of links for the cave, in various threads and the page said something like it is a dead link?
1. Engine off then Pedal Feel is useless. Plus actually stop the car with pedal or using P-brake properly is very hard pedal often need both feet to push the pedal w/o vacuum in the booster.

Worse If you bought Used Booster as that thing maybe bad. Bad diaphragm(s) bad/weak spring etc.

Test w/o engine running need a vac pump.
Small Mityvac and similar work but can take a long time to pump down a big part like the booster.
Electric pumps are good but need carefully attention to Not pump too much.
Boosters need ~ 18 - 22 in-Hg same "normal" vac from an engine at idle or cruise. Do Not pump down like AC that need max vac from most E-pumps.
Unplug vac line up front and use spare hose(s) etc to make whatever pump to fit plastic valve on booster case.

2. Old cave links years ago are dead because Comcast and other ISP killed them. Use link above and other links < ~ 5 years old or search archive.org
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Report this Post10-17-2021 02:26 PM Click Here to See the Profile for fieroguruSend a Private Message to fieroguruEdit/Delete MessageReply w/QuoteDirect Link to This Post
 
quote
Originally posted by Rickady88GT:
My 88 has a good pedal feel with engine off, but start the engine and the pedal gets spongy. I know the booster takes out some petal feel, and that the pedal will go down a bit, but this seems extreme. So does the booster go bad like this?


When the booster fails, you will not feel a difference in the brake pedal when the engine is on/off. The pedal will be super hard at all times and braking performance will be about 1/3 of normal.

This thread has a lot of measured results from the stock brake booster and S10 brake booster at various pedal forces so you can see exactly how much assist the stock and S10 booster create.
https://www.fiero.nl/forum/...0323-2-121747-2.html

Without the engine running, the pedal should be as hard a brick with very limited movement. If you stand on the pedal and put 100 lbs force to it, the resulting front caliper line pressure will be about 475 PSI.

When you turn on the engine with the the stock brake booster, the same 100 lb force of brake pedal will create 1475 psi, which means the stock fiero booster generates 1000 psi of assist. This is enough to flex hoses as well as brake pads and the reason the pedal feels a lot softer with the engine running.

With the S10 booster at the same 100 lb force on the pedal, you will get 1700 psi line pressure or an increase of 15%. At low pedal forces, the S10 booster gain vs. stock 88 is up to 40%, which will make the pedal feel softer vs. stock when the engine is running. Most of the time people install the S10 booster so they can press the pedal less for the same stopping performance.

Pad compound can also make a significant difference. The carbomet pads were very hard, which gave a super firm pedal even with stock brake assist. Wagner thermoquiets were much more compressible and made the firm pedal feel spongy - They also didn't have the same initial bite or overall performance, so they didn't stay on the car long.

The pedal getting softer when the engine running is normal - that is the booster providing assist.
The pedal being even more soft with the engine running after the S10 booster install is normal - it is a larger booster with more assist.
If you changed brake pads as part of this change, they could be softer than the ones on the car originally and contributing to the soft pedal feel.
If the brakes are engaging further down in the pedal travel, that could be air in the system or the caliper pads too far from the rotors.
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