Grand Am/Blazer brakes almost feels like ABS under heavy braking?? (Page 1/3)
Additivewalnut OCT 07, 09:23 AM
86 3800 4spd. Recently put on Grand Am brakes on all 4 corners, paired with a 93 S10 Blazer 4.3 master cylinder, and braided steel lines. The brakes are really quite nice and are a huge upgrade over stock, but for some reason when going over ~30 the pedal hits a wall about halfway down, after I slow down under 30 it'll go down the rest of the way and lock the front tires.... it almost feels like ABS which would be impossible so clearly something is wrong. Did I get the wrong master? Prop valve acting up? Both?

Keep in mind this is a dedicated track car at this point, so if I need to get an adjustable valve or something, I'm fine with that.

EDIT: Forgot to mention, but the brake warning light comes on the dash after the wall goes away and I can lock the tires. Turns off when I let off the pedal and doesn't come back until I brake heavy again. Fluid is full and new in the reservoir.

[This message has been edited by Additivewalnut (edited 10-07-2024).]

olejoedad OCT 07, 10:11 AM
The M/C should be from a 2 wheel drive, not a 4 wheel drive.
Additivewalnut OCT 07, 10:46 AM

quote
Originally posted by olejoedad:

The M/C should be from a 2 wheel drive, not a 4 wheel drive.



I got it off rockauto from a 93 S10 Blazer 4.3, I didn't see any mention of 4wd or 2wd in the options.... did I mess up and choose a year that was 4x4 only or something?
olejoedad OCT 07, 02:55 PM
When I did the GA brakes on my 86 years ago, I used one from a 1991 S10 Blazer 2WD.
But, I only buy my parts locally, from knowledgeable countermen who have been doing their jobs for a long time.
My experience with Rock Auto was not worth the hassle of wrong parts and returns, let alone the wait.
Dennis LaGrua OCT 07, 08:20 PM
The Master cylinder was changed therefore if not matched correctly to the wheel cylinder capacities the braking may feel strange. I just keep My stock Fiero system in good shape and it seems to work OK, Never had a problem stopping even from 90-100 MPH.

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

olejoedad OCT 07, 08:56 PM
The GA upgrade works much better than the stock Fiero brakes.

Fieroguy did a test some years ago, comparing pedal pressure vs caliper pressure.

Maybe he will chime in with a link.

It's the system Pontiac should have used on the Fiero....
Additivewalnut OCT 08, 12:03 AM

quote
Originally posted by Dennis LaGrua:

The Master cylinder was changed therefore if not matched correctly to the wheel cylinder capacities the braking may feel strange. I just keep My stock Fiero system in good shape and it seems to work OK, Never had a problem stopping even from 90-100 MPH.




I'd agree that changing the master may have messed something up if it weren't a tried and true upgrade on this car. Im just not sure what, if anything, I did wrong to cause the pedal to act like this.
cartercarbaficionado OCT 08, 03:48 AM

quote
Originally posted by Additivewalnut:


I'd agree that changing the master may have messed something up if it weren't a tried and true upgrade on this car. Im just not sure what, if anything, I did wrong to cause the pedal to act like this.


nope not you. ran into this on a white gt a few days ago. actually threw out the stock master since it was leaking and had the same thing going on. so a big bore (fiero store but it's just an s10 one) went in for the LeBaron brake upgrade kits needed fluid volume but the issue is almost like the reservoirs are swapped. it hits the fronts first then the rears which might be correct but tends to have that dead wall and act funny sometimes. the brake light is triggering due to the proportioning valve recentering since it feels like it's having a leak in the fronts due to the massive fluid volume needed for the brake pad clearance. I bet if you look you can wiggle the fronts a bit and they won't be touching the rotor
Additivewalnut OCT 08, 10:28 AM

quote
Originally posted by cartercarbaficionado:

nope not you. ran into this on a white gt a few days ago. actually threw out the stock master since it was leaking and had the same thing going on. so a big bore (fiero store but it's just an s10 one) went in for the LeBaron brake upgrade kits needed fluid volume but the issue is almost like the reservoirs are swapped. it hits the fronts first then the rears which might be correct but tends to have that dead wall and act funny sometimes. the brake light is triggering due to the proportioning valve recentering since it feels like it's having a leak in the fronts due to the massive fluid volume needed for the brake pad clearance. I bet if you look you can wiggle the fronts a bit and they won't be touching the rotor



yeah that sounds about right. So I guess go get an adjustable proportioning valve and see if that takes the wall away?
olejoedad OCT 08, 10:35 AM
I've done several of the GA upgrades my with the proper M/C.

Never had an issue.

Be sure you actually have the correct M/C before trying to reinvent the wheel.

Don't trust an online vendor because you like the price.
Buy local.