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88 rear caliper piston rebuild- see pictures by cam-a-lot
Started on: 11-17-2019 07:22 PM
Replies: 8 (429 views)
Last post by: FX on 11-19-2019 10:16 AM
cam-a-lot
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Report this Post11-17-2019 07:22 PM Click Here to See the Profile for cam-a-lotSend a Private Message to cam-a-lotEdit/Delete MessageReply w/QuoteDirect Link to This Post
I recently had a leaking caliper and decided to order a rebuilt caliper from TFS. It arrived and it looks great. It is the unpainted one in the photo. The piston is original, as they are apparently not available anymore.

In the meantime, a local caliper rebuild shop told me that he can rebuild 88 calipers (seemed confident and says he is aware of the differences between 84-87 Fiero calipers and the 88 ones) and he says the pistons are the same. I realize that they are officially slightly different and were a different part number

I have installed one of his rebuilt calipers in my car and so far so good. No leaks and it seems to be working fine.

Just wondering if anyone agrees or disagrees with his assessment that the pistons from earlier Fieros would work fine. The face on his pistons is clearly different (the red painted one in the picture)

I have only driven the car once since the install and it is now stored for the winter, but it seemed to work fine and so far has not leaked. Does anyone recognize the piston on the red one?


thoughts?

[This message has been edited by cam-a-lot (edited 11-17-2019).]

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cam-a-lot
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Report this Post11-18-2019 08:50 AM Click Here to See the Profile for cam-a-lotSend a Private Message to cam-a-lotEdit/Delete MessageReply w/QuoteDirect Link to This Post
Any opinions on the difference between these pistons?
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FX
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Report this Post11-18-2019 12:33 PM Click Here to See the Profile for FXSend a Private Message to FXEdit/Delete MessageReply w/QuoteDirect Link to This Post
Cam-a Lot. Calipers are very easy to rebuild. The kit consists of a new O-ring seal, and a new boot. Just pop the piston out with compressed air, hone the bore, clean the piston up really good, install the new O-ring using brake fluid for lubrication to slide the piston back in, install new dust boot, and reassemble.

[This message has been edited by FX (edited 11-18-2019).]

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cam-a-lot
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Report this Post11-18-2019 12:58 PM Click Here to See the Profile for cam-a-lotSend a Private Message to cam-a-lotEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks for the reply

My question was whether or not the piston in the picture (red caliper) was familiar to anyone else, since apparently the 88 piston is no longer available.
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theogre
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Report this Post11-18-2019 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
"Red" is "New Type" piston w/ notches for stamped SS pad clip for 84-87 Fiero and likely others.
CLICK FOR FULL SIZE

84-87 Fiero rear piston Is Not same total diam as 88. Only same in the guts for E-brake function.

Piston Size: 47.75mm (1.88") 88 Front and Rear
Piston Size: 47.57mm (1.87") 84-87 Rear
Piston Size: 49.05mm (1.93") 84-87 Front
From Cardone.com
88 MC size: 24mm (0.9448818898") per ACDelco

(Note that these numbers can change a bit in different "books" used. I have older rear listed as 45 then "updated" to 48mm on one page in my cave because of catalog data. Some cat's are just errors, others round up to whole numbers. If you follow rounding rules, both are 48mm but isn't for people designing or working on them.)

May seem to work and Yes, Seems very small dif but 88 shell w/ 84-87 piston can have seal leaks etc because of total size diff.
GM et al make the main piston seal to fit a specified bore AND the piston in that bore. Tiny piston size change makes the seal compress more or less. Less here old piston w/ 88 seal. Tight/loose seal can effect piston self adjust etc.
Plus will make rear brakes weaker because of hydraulic rules but you might not tell for normal driving.

Lower Performance? How bad? See my Cave, Brake Upgrade DL excel sheet and adjust to used 88 MC size and both pistons.
Unprotect the sheet then just enter diam and sheet should do the rest.
I get...
code:
Setup             	MC mm	MC area	Cal mm	Cal area 	Ratio	Change vs Stock
Rear
OE MC & caliper 24 452.389 47.75 1790.757 3.958 0.000
OE MC & Old piston 24 452.389 47.57 1777.281 3.929 -0.030

At the very minimum... If you run older piston you need to run them on both sides on rear axle or likely have brake steering problems, one wheel locking more/easier, etc.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)


The Ogre's Fiero Cave

[This message has been edited by theogre (edited 11-18-2019).]

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theogre
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Report this Post11-18-2019 04:41 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

theogre

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Member since Mar 99
 
quote
Originally posted by FX:
Cam-a Lot. Calipers are very easy to rebuild. The kit consists of a new O-ring seal, and a new boot. Just pop the piston out with compressed air, hone the bore, clean the piston up really good, install the new O-ring using brake fluid for lubrication to slide the piston back in, install new dust boot, and reassemble.
Never hone the aluminum caliper shells. Just remove whenever crap being careful around the seal metal. Bores don't touch the pistons.

DIY Front rebuilding is easy but DIY rebuilt the rears often have problems. The rear piston is why and leaking hidden inner seal isn't only issue there.
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Report this Post11-18-2019 06:00 PM Click Here to See the Profile for FXSend a Private Message to FXEdit/Delete MessageReply w/QuoteDirect Link to This Post
Thanks Ogre, I stand corrected I've always had good results lightly honing my trucks, cars, and bike calipers by hand with light emery. is this proprietary with the Fiero's ?
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theogre
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Report this Post11-18-2019 11:35 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 FX:
Thanks Ogre, I stand corrected I've always had good results lightly honing my trucks, cars, and bike calipers by hand with light emery. is this proprietary with the Fiero's ?
Not really. Any "Sand paper" to remove crap from any aluminum calipers, MC and others can remove a thin layer of anodizing that manufacturers use to fight corrosion.
Even w/o that removes normal oxide layer protecting Al parts. Worse, the part may have uneven surfaces and leftover "sand" when done and in the case of MC etc can make the seals to fail fast.
Unlike Caliper main seal moves a few mm over years of use on the pistons, MC, Drum and Clutch slaves will eat the piston seals fast w/ uneven surfaces and crap in those bores.

I just pick off big crap and ignore staining etc. for calipers.
I just replace MC and others w/ wear/crap problems because DIY honing is impossible including done by most "Pro" repair shops. Yes they make "rebuild" kits but most shouldn't bother rebuilding them unless getting rid of a car very soon.

The only part that matters is the "lip" holding the "o-ring" seal in the caliper bore. Clean carefully because scratches you make doing this can haunt you now or down the road.

For this and E-brake screw hole try soft Scotch-Brite to wash dishes etc. w/ brake fluid or brake clean.
Harder Scotch-Brite can "eat" aluminum etc same as most "sand paper" things.
Many are familiar w/ 3M Roloc but many of them are too abrasive for aluminum parts too.
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Report this Post11-19-2019 10:16 AM Click Here to See the Profile for FXSend a Private Message to FXEdit/Delete MessageReply w/QuoteDirect Link to This Post
...Thanks again Ogre, you've just altered my MO...I never knew this...
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