I am considering a Wilwood Master Cylinder instead of an OEM

there is no other master cylinder make that is new and made in the usa guaranteed. The AC Delco may arrive with the usa stamp or may not and the listings at summit and amazon say mexico. Shipping date is October and Summit said they may push that date further out or back order. Centric is China. A Premium also China. Raybestos is made in mexico and has the the best shipping date of just a few days. Same with front calipers.

Wilwood's are new and made in the USA.


Just got off the tech phone support line and they say they do not have a list of master cylinders for different makes and models

and therefore don't have a specific model intended for fiero and that there units are universal

They offer the following check list of questions to help determine the best unit:

Piston size and number of pistons in calipers

Master Cylinder bore size OEM

Brake Booster with Dual Diaphram

8 inch diameter diaphram

and Minimum 18 inches of vacuum at idle

And finally:

the pedal ratio (calculated using a pdf from Wilwood)

https://shop.wilwood.com/bl...and-how-to-find-them

Has anyone determined the best Wilwood unit for fiero's

They suggested the 260-8555 fwiw


Joe k

[This message has been edited by Signupacct (edited 09-24-2024).]

quote Originally posted by Signupacct: I am considering a Wildwood Master Cylinder instead of an OEM there is no other master cylinder make that is new and made in the usa guaranteed. The AC Delco may arrive with the usa stamp or may not and the listings at summit and amazon say mexico. Shipping date is October and Summit said they may push that date further out or back order. Centric is China. A Premium also China. Raybestos is made in mexico and has the the best shipping date of just a few days. Same with front calipers. Wildwood's are new and made in the USA. Just got off the tech phone support line and they say they do not have a list of master cylinders for different makes and models and therefore don't have a specific model intended for fiero and that there units are universal They offer the following check list of questions to help determine the best unit: Piston size and number of pistons in calipers Master Cylinder bore size OEM Brake Booster with Dual Diaphram 8 inch diameter diaphram and Minimum 18 inches of vacuum at idle And finally: the pedal ratio (calculated using a pdf from Wildwood) https://shop.wilwood.com/bl...and-how-to-find-them Has anyone determined the best Wildwood unit for fiero's They suggested the 260-8555 fwiw Joe k

their suggestions are usually pretty good. do tell them the bolt holes size needs to fit an s10 blazer since a few gm cars do use a different bolt hole pattern. just so happens the fiero and most of the late 80s-early 90s gms share until they got abs

I will measure it later today but from memory the bore size of the Fiero master cylinder is either 1 1/8" or 1 1/4".

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

quote Originally posted by Dennis LaGrua: I will measure it later today but from memory the bore size of the Fiero master cylinder is either 1 1/8" or 1 1/4".

it should just be 1 inch. that's what I'm measuring off of a few junked ones and one that was slated to go Into a car soon

You should share the year of the Fiero, as 84-87 are different than the 88s.
All the Fiero brake masters have quick take up features, which I doubt Wilwood has. This will likely mean more dead pedal travel.

84-87 is 25.4mm or 1":


88 is 23.8mm or 15/16"


If you go larger than stock, the pedal will be harder to press, have less travel, less clamp force at the calipers, and less overall braking force for a given pedal input force.
If you go smaller than stock, then pedal will be easier to press, have more travel, higher clamp force at the calipers, and more overall braking force for a given pedal input force.

For 99.9% of people, it would be best to stick with the stock diameter.

Sorry about not mentioning the year


It is a 1987 Pontiac Fiero GT with a V6

I hope that helps


I am interested in as close to oem on bore size as is possible unless the community thinks that a slightly smaller diameter might enhance brake pressure at the calipers etc.


Otherwise yes I would like OEM as close as possible

the calipers and pads are OEM no modification or conversions here.

So far the only deviations in this brake job are the SS brake lines and the wildwood proportion valve replacing the OEM proportion valve and went with the

https://www.wilwood.com/mas...rod?itemno=260-11179

only mildly irritated that wildwood won't say which unit is best fit to replace OEM

any help here is appreciated

Joe k

Here is the measurement from a Fiero MC rebuilding kit.



------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

[This message has been edited by Dennis LaGrua (edited 09-24-2024).]

Dennis


thank you for posting. Is that a MC rebuild kit by GM or genuine gm parts and it was the size for your OEM master cylinder ?

The diameter is not only key to making a selection of a unit from wilwood but also making sure that the correct diameter is obtained when buying a oem replacement.

Centric's are made in China so why would I want to trust their diameter in the centric graphic that was shared in a post, well intended as it may have been.

Does anyone have documentation from factory technical materials indicating what the diameter is ?

I have checked all of mine and I have not found anything in the manuals and other documentation that I have

Does anyone have WHAT THEY KNOW IS a oem master cylinder that they know was put on at the factory?

My Duralast reman (which I'm returning and trying to go with a new oem unit) measures 1.4350 inches and that is 36.45 mm. Very close to your measurement. Mine is a Duralast part # NM1988.

Duralast being autozone isn't any more reliable a source for accuracy then Centric.

In other posts it is noted that you DO NOT WANT TO GO WITH A LARGER DIAMETER PISTON SIZE as it will result in less breaking power.

And other posts say, be sure you don't inadvertently get the larger diameter bore

I wish I still had the unit that was on my car before I started this brake job from h _ _ _ ! but I turned it in for the core already.

I have a New OEM Raybestos MC39572 on the way that they say is made in Mexico and looked up the specs and it doesnt say the piston diamter

Anyone ?


Joe k

[This message has been edited by Signupacct (edited 09-26-2024).]

It is apparent I need to further explain what a Quick take up master does...

The Fiero masters have a stepped bore (two separate bore sizes) where the larger bore is only used to move the caliper pads to the rotors.
Once the pads make contact there is a pressure bypass on the large bore and the smaller bore takes over for actual braking pressure.
The smaller bore is then the source for all brake pressure through the system - not the larger one.
This was done to allow the pads to retract further from the rotors for fuel economy.
You can use a quick take up master with almost any caliper.
However, using a standard bore master on calipers designed for the quick take up master will have more dead pedal as the smaller master bore will be the only thing moving the pads to the rotor and it will take more travel than the larger bore would.

So if you have an 84-87 and looking for a non-stepped master from another supplier, you would need the 1" diameter one.
However, doing this will result in more dead pedal travel as you will eliminate the quick take up feature.
Going to a larger bore would reduce the dead pedal travel some, but at the expense of brake line pressure and result in less braking force, making the conversion a brake downgrade.

The 84-87 Raybestos bore diameter size is 26.400mm.

But the Centric brand MC says the bore is 25.4mm = 1”.

I can’t confirm because I never measured these 2 MC to actually see it.

These measurements are listed on RockAuto website.

------------------
fierogt28

88 GT, Loaded, 5-speed.
88 GT, 5-speed. Beechwood interior, All original.

Hard to figure out. I got that new piston assembly out of a Raybestos box and the measurements are shown here in this thread.. The last MC that I replaced was AC Delco. marked USA but who knows? Have had good luck with Chinese Centric products so may go with that next time. All the major brands are Chinese made. Its just strange that a large US company like Wilwood cannot recommend a direct replacement. If the replacement had a 1.43" bore it may work OK. With the S-10 brake booster you would probably not notice much difference in pedal feel.

------------------
" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Spintech/Hedman Exhaust, P-log Manifold, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, Champion Radiator, S10 Brake Booster, HP Tuners VCM Suite.
"THE COLUSSUS"
87GT - ALL OUT 3.4L Turbocharged engine, Garrett Hybrid Turbo, MSD ign., modified TH125H
" ON THE LOOSE WITHOUT THE JUICE "

While I appreciate the effort to buy American made products where possible, in this case it seems like one would be better of buying a quality rebuilt master cylinder that is designed for the car.

Yes I wish I could change the wording on this thread becuase I am becoming less enthusiastic on the Wilwood simply becuase they will not issue out a parts compatibility recommendation on the fiero.

Well as for remans I been to that rodeo and got the t shirt. In another post I mentioned that if the cars were just 5 or 7 or even 10 years old then a reman unit is likely not entirely worn and a rebuilding can make more sense. But over time as the units are used the surfaces wear and then rebuiding takes even more to smooth out and thus less likely to be a reliable option. Especially now that some oem units are almost 40 years old. And the core charge attracts all kinds of candidate for the reman process and the reman factory is more oriented to GET ANOTHER UNIT OUT THE DOOR kind of thing.

SOOOO! then what is the highest on the pecking order for new units. Made in the USA OEM specs. Ok let's go there. First Made in the USA: not a guarantee that any NEW unit will be made in USA and so then next down from there is Mexico and then from there China. Why USA is likely best choice, because they are more likely to appreciate what the product promises to be, an OEM replacement and likely to have the OEM specs and not have a language barrier to interpreting it. Then why Mexico over China, well some just over the border manuafacturing still has US oversight, more so then China with a language barrier.Everything is a crap shoot these days but these are my thoughts so far.

[This message has been edited by Signupacct (edited 09-26-2024).]

quote Originally posted by fieroguru: It is apparent I need to further explain what a Quick take up master does... The Fiero masters have a stepped bore (two separate bore sizes) where the larger bore is only used to move the caliper pads to the rotors. Once the pads make contact there is a pressure bypass on the large bore and the smaller bore takes over for actual braking pressure. The smaller bore is then the source for all brake pressure through the system - not the larger one. This was done to allow the pads to retract further from the rotors for fuel economy. You can use a quick take up master with almost any caliper. However, using a standard bore master on calipers designed for the quick take up master will have more dead pedal as the smaller master bore will be the only thing moving the pads to the rotor and it will take more travel than the larger bore would. So if you have an 84-87 and looking for a non-stepped master from another supplier, you would need the 1" diameter one. However, doing this will result in more dead pedal travel as you will eliminate the quick take up feature. Going to a larger bore would reduce the dead pedal travel some, but at the expense of brake line pressure and result in less braking force, making the conversion a brake downgrade.

dont know why my browser is just now showing your post and that's ok

thank you for your explanation.

So after reviewing the specs on the Rock Auto site as I noted which say 1.0 for some units and which say 1.4 for other units and noting the Raybestos cited 1.0 in the description I received my Raybestos and when I opened it I noted that the diameter of the unit is 1.4 mm

So Im guessing that 1.4 is the measurement at the top of the piston and then further into the unit it is 1.0 and that is what counts ?

I am now figuring out how to get to ogre's cave to find data there.


Joe k

[This message has been edited by Signupacct (edited 09-27-2024).]

quote Originally posted by Signupacct: So Im guessing that 1.4 is the measurement at the top of the piston and then further into the unit it is 1.0 and that is what counts ?

All Fiero masters have 2 bore diameters.
The 36mm (or 1.4") is the diameter of the quick take up bore and this has nothing to do with brake pressure, it is for pad movement only.
https://fierocave.shorturl.com/index.htm

For the 84-87, the smaller bore is 1" and this what what actually provides the brake pressure. This is confirmed with the chart on this page:
https://fierocave.shorturl.com/index.htm

On the 88 Fieros this smaller bore is 15/16".

Wilwood does not offer any master cylinders with the quick take-up stepped bore setup, so they can't offer a stock replacement for the Fiero without it having some type of negative performance (more dead pedal travel or less overall braking force).

If I needed one for an 84-87, I would buy this one:
https://www.summitracing.co...odel/fiero/year/1987

[This message has been edited by fieroguru (edited 09-27-2024).]

quote Originally posted by fieroguru: calipers designed for the quick take up master

According to my understanding, basically all calipers use square seals.

Would a low-drag caliper have a seal with a larger square section?

quote Originally posted by pmbrunelle: According to my understanding, basically all calipers use square seals. Would a low-drag caliper have a seal with a larger square section?

My understanding is that the seal surface on the piston is the same, but the seal surface within the caliper is more of a wedge shape with a little more clearance along the sides.
http://www.remaninc.com/pdfs/lowdragcalipers.pdf

I have taken Fiero calipers apart a few times. The seal was square. I didn't pay much attention to the groove (it's hard to inspect that area anyway).

I don't know if a conical groove requires a matching conical seal, or if it works with a square seal.