I was wondering what if any folks were using instead of the 88 specific brake master cylinder?

I realize that the 84 to 87 masters have different bores and that S10 master will change the pedal feel (not sure if its better on not)

I have been looking on line to purchase the 88 master cylinder on line and locally and it seems that they are not in stock or not available at this time. I went looking at the master cylinder rebuild kit on gm parts on line it shows that the rebuild kit will work on a bunch of other master cylinders. rebuild kit

Just wondering if anyone has swapped one out for a different one.


marc-alan

The 88 master cylinder is not like any other......but the rebuild kit works.

[This message has been edited by Gall757 (edited 03-07-2022).]

quote Originally posted by Gall757: The 88 master cylinder not like any other......but the rebuild kit works.

Curious how that works.
I would think they might be the same, since the proportioning valves are different.
Edit - Rockauto says they're different. So...

[This message has been edited by Raydar (edited 03-07-2022).]

88 calipers have the same piston bore front and rear.

Pre 88 has different diameter front to rear.

Hence the different bias valve.

Does anyone know the master cylinder bore for the 88?

Although, I support improving performance though modifications, I am always cautious when those mods are for the braking system. It is a system that must be carefully designed, matched and balanced to work well. You change the calipers or MC and that could affect performance and require another change. For instance if you change to Corvette calipers and even if use the Corvette MC, the braking balance of a Fiero is not the same as that of a Corvette. Has anyone figured out the exact formula for an efficient brake upgrade?

------------------
" 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 "

I picked up a master from RockAuto for my sons 88 about a year ago. Took a while but they eventually got new ones back in stock.
While we were waiting I went ahead and just did a rebuild.

I ordered a rebuild kit, really want to purchase a new one or an alternative that would work.

There is No "Alternate" MC for 84-87 or 88.
88 MC is Mostly Same as early ones but Main Bore that does all the braking is different diameter.

Rest of 88 brake system parts are different is some ways and same in others.
Ignore pads and rotors...
Caliper pistons are different diam but P-brake works exact same and have same problems.
Prop valve of Combi valve is different because 88 has no "Natural" Brake Bias that 84-87 Fiero and 99+% of everything else has. "Natural" Brake Bias means systems that have Front/Rear Bias without the Prop valve and may never activate the P-valve for Many Years.

See my Cave, Brake Service and rest of section.
Nearly all applies to 88 but lube points and some others may need to change for 88.
Example: Can even press in a rear piston but need a different "clamp" w/o taking off iron part. (Which you should avoid that in most cases...)

Rebuilding MC is iffy at best. May work If the bores aren't "rusted" or have other problems.
If someone tells you to "hone the bore," ignore them. That will wreck the bore if not already bad from "rust" etc.

So Rebuild if have to but keep eye out for a new one.

Note: You "hear" there's an alt MC for 84-87 because TFS and others "claim" an "upgrade" to 84-87 Fiero to add GA and Blazer parts but is 100% . Is only "luck" that someone hasn't been hurt or killed by most Fiero Brake "upgrade."

------------------
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 03-09-2022).]

I'm bringing this topic back up because I may have an answer for the OP's original question.

I might have found an 'alternative' master cylinder for '88 Fieros.

I was rebuilding the entire brake system in my '88 GT about when this subject came up. I replaced the everything except the combination valve, rear calipers, the hard lines and the SS lines to the wheels. I am using some major components not listed for the '88 Fiero. They are:

Booster - Cardone #54-71215, listed for '84-'87 Fiero (Cardone lists #54-71216 for '88)
Master Cylinder - Cardone #13-2921, listed for '02-'04 Bravada, '02-'05 Trailblazer, others)
3/16" NiCopp brake line (MC to prop valve)

I chose these components because I couldn't find new or rebuilt parts for '88 Fieros. (I know I can have these parts rebuilt. I still plan to rebuild the original MC but was having issues getting the rebuild kit. I couldn't find many specifications for these parts, so I still don't know the difference between the boosters by year (The diameter of the diaphragm on both is the same. The booster pin from my original '88 booster is 0.040" longer than the one that came in the new one, so I used it instead, but I doubt that's the difference). To be perfectly honest, I sort of guessed on the MC. I wanted the newer style reservoir, and beyond that I looked for one with the same specified bore diameter, ports on the left, and I figured it a good idea to go with a part from a vehicle with a front/rear weight distribution and brake sizes that were equal (or at least close). But in the end, it was a guess.

Clearly the original lines from the original MC weren't going to fit here. I chose to make the new ones out of nickel/copper line. I was going to use steel, but then I found out about nickel copper alloys. It is much easier to work with and I was convinced of its safety after reading articles like this one:

NiCopp Brake Line

I used 3/16" line because it appears to be no smaller than the ports in the MC. By the way, RockAuto lists the sizes of the ports incorrectly as Primary - 9/16 x 18, secondary - 1/2 x 20. In fact, both are 1/2 x 20. I looped the lined upward before going to the combination valve to allow enough flex to get to the booster without having to disconnect them. I may change to larger lines but right now the system is performing well without that. Still, I may at change to larger lines and fittings that do not require adapters. The adapters don't hurt anything, but I'd prefer fewer connections and chances for leaks.

Here's what my installation looks like:


I like the braking and feel very well. I've been driving this setup for about a month, maybe 200 miles so far. I don't know whether this MC has any 'natural' bias, but with the stock combination valve it seems to work well. I do want to test in some low-traction conditions to see that the rears lock first (on dry pavement it's very difficult to lock the brakes, but no different than before). I can still go to a bigger booster if I want, but right now I don't feel like I need it.

I'm not going to swear that this MC is a perfect replacement for the original since YMMV, but I'm real happy with it and will keep it this way until I find reason to change it.

quote Originally posted by theogre: Rebuilding MC is iffy at best.

Agreed, I wouldn't do it or recommend it.

Nearly All MC Do Not setup Brake Bias. That's by others things including pistons sizes for well over 90% of vehicles world wide.
88 Fiero Has No "Natural" Bias at all. Only Bias is in the Prop Valve in the Combi valve and likely because made GM Bean Counters happy. The rest of the world hates this setup because prop valves are known failure issue and when happens the rear can spin out very easy and labeled as "Unsafe at Any Speed" (R. Nader. Wiki Page)

The 2 bores in many GM MC are for added Volume of Fluid. When brakes are at Working Pressure, the Big Rear Bore stops working.
See my Cave, Quick Take-up notes

Very likely you run out of Volume for front, rear or both w/ this "Alternate."
More so if any caliper has problems and getting too much pad clearance.
While Rears have P-brake problems causing that there are other things that do the same like wheel bearings w/ too much play, slider that doesn't work right, etc.

MC Pistons have Hard Limits so the springs never crush beyond normal range. Once you hit either or worse both then whatever Pressure for a circuit is all there is.
Max Working Pressure often is 1200+ PSI put your MC may only putout 700 - 900 PSi Max when hit the hard limit(s). Might be ok at a stop sign/light w/ plenty of room to stop but not when you panic stop because a kid ran in front of you. If that happens... Can have Civil and Criminal Problems because you hack the brakes.

QT MC could allow the OE Fronts w/ problems use up the Volume and hit the hard limit but QT section will try to makeup the extra Volume w/ Rear that have problems often showing up as "Low Pedal" when really bad.

[This message has been edited by theogre (edited 04-05-2022).]

When I decided to post about my new brake setup, I was quite aware that I would get response(s) like this. A couple of additional notes regarding the use of this MC:

I was aware of the quick take up issue. While I was unable to find any information as to whether or not the Trailblazer MC is in fact a QT design, I figured as likely as not that it is, because I can't see any reason that ALL newer brake systems (GM, at least) would not have calipers that draw the pads back slightly and need a QT MC to compensate, given CAFE standards, etc. Admittedly, this was part of the guess I made when I selected it. It does appear to have a check valve where a QT type MC needs one. That's one of the reasons I tested a lot before driving anywhere.

quote Very likely you run out of Volume for front, rear or both w/ this "Alternate."

I'm quite sure I do not come anywhere close to running out of volume here. This MC has a listed piston bore diameter of 1.000", same as what I found for 84-87. The only MC bore diameter listing I could find for '88 is 0.937". As for travel, I lock the brakes long before end of travel. I know this because The first time I bled the brakes i got a massive amount of air in the system and found out just how far the pedal - and the MC pistons - would move. The brakes now apply when the pedal is a bit higher than before I did any work or made any changes.

quote Can have Civil and Criminal Problems because you hack the brakes.

Of course, ANY modification can have safety and legal implications if not performed responsibly. That's why any sensible car owner exercises loads of caution, good sense, and testing when making any safety-related change. The only other alternative would be not to make any changes at all, ever, and have all service done to stock specifications by an OEM. Even then, you can be liable because you contracted the service center. This applies to every safety-related system in the vehicle, from brakes to steering to suspension to headlights and on and on. We all undertake these projects at our own risk. That's why I put my own"YMMV" disclaimer in my previous post.

Ya pays yer money and ya makes yer choice...

Thanks for posting the alternative master cylinder.

To close the loop on my side, I used the rebuild kit for the master cylinder and also rebuilt all the calipers. I went from brakes barely working to a car that stops nicely.

Thanks for the replies

Marc-Alan