I’m fairly new to the third GEN game as I only purchased my 1987 formula about six months ago (although I had a beloved 91 formula some 20+ years ago when I was in college).


I’ve been doing track days for more than 10 years, I instruct, and I do some amateur endurance racing (I consider myself a gentleman racer ie I pay for my seat).

Although my 87 has disc brakes all around I would characterize them as terrible. I ran one time attack event in the car and it was clear that the brakes were the Achilles’ heel. The petal is not only unacceptably soft but there is absolutely zero feel as to what the tires are doing. My joke is that the brakes are really just suggestions. You’re just kind of asking it to stop and it just kind of does what it wants.


And keep in mind I was running Motul RB 660 brake fluid.


After searching around on this form for solutions it seems most include swapping out the calipers and upgrading to factory performance options. However, the lack of brake pedal feel points to flex in the system that merely changing the calipers won’t fix. And a major source of that flex is our master cylinder.


Actually, flex seems like a common theme for our third GEN’s. And although there’s an endless supply of subframe connectors for our cars, surprisingly no one makes a master cylinder brace.


So I decided to take it on myself to see if I can fabricate something. I did do a search and found that one member on this forum attempted a design using his strut tower brace. The piece was beautifully tig welded and really looked good. However, it was kind of a failure because the master cylinder was actually flexing the strut tower bar.






With this in mind I set out to build a really stout piece. In fact, I decided I would go for overkill rather than realize I didn’t make it strong enough. I used quarter inch welded angle iron and a hacked up Harbor freight C clamp.


Here is my finished product. I know my welds are really ugly but they’re functional. There’s no way that this thing is going to flex, right?


Wrong!






Wrong!

So I added another quarter inch steel brace bolted to the shock top mount and welded to the original piece. Now that’s a full half-inch of steel.


The improvement in braking is night and day. It’s like it’s a different car.

Sent from my iPhone

 

I made a master cylinder brace recently. I loved how much flex it removed under stomping conditions, but I removed it for a very good reason. I hit a bump on my driver side wheel, and the brace was fastened to the strut tower. I immediately felt the brake pedal get shoved back since I was braking significantly at the time. It made it very unpredictable whenever braking heavily on a bumpy surface. There really aren't many good places to mount a brace like this except for the strut tower. Your brace is nicer because it can translate along the back edge of the master cylinder when the strut tower moves; mine was bolted to the booster mount.

I didn't really notice a significant difference in pedal feel. In your case, with the stock POS disc brakes, you probably have to stomp on them to get any considerable braking action. I run LS1 front brakes, LT1 rears, adjustable prop valve, vacuum canister, and vacuum pump that kicks on to keep the vacuum supply from dropping below 14 in/hg. I don't have to give it the beans to get it to launch me out the windshield. I autocross this car too, and it does pretty well.

If you think a simple brace made a night and day difference, you'll be blown away if you upgrade to a decent brake setup.

 

I can't believe how much flex there is even with your first revision, and even with the second revision! It does look much better. I may have to consider making one for myself

Looking at your design again, you may want to consider boxing the added brace part, that may reduce the flex even more.

 

Nice work ResIpsa. Have you tried it out on the road yet?

 

If I was going to do a v 2.0 I would design the original brace a little different by adding a gusset. However, because I already welded everything on the car it was easier to just add the second bracket.

I did not initially add a gusset to the second bracket because I needed some flex to get it flush with the origional brace (the second angle iron was not square and I had to use vise grips to get it flush).

 

I have about 200 street miles so far with the brace and I love it.

I have not experienced anything like RJ IROC described yet. But I appreciate his post and I will be keeping a special eye out for any similar behavior.

 

So what's actually flexing, the firewall?

 

Yes the firewall flexes big time on our cars with the hood open you can see the master move close to 1/4" when you got the brakes.
It will seeing in a arc with the front raising up towards the hood.

 

The flimsiness of the firewall has been an issue that GM has known about since production. That's why for manual thirdgens there is a doubler plate on the firewall for the master. The Thirdgen clutch pedal also has to use a beefier support rod, fourthgen doesn't because on the Fourthgen the firewall is stronger. I used 16 gauge steel to plate my firewall with in the hopes that it makes a difference. Stock firewall metal was something like single sheet 20 gauge.

 

I like your bracket and the member's bracket that you posted. I think I will try his design when I build my 3 point strut tower bar. I'm wondering if he used a 2 or three point brace and what size tubing he used and what the wall on it was. It looks like 1" OD tubing. I thought that I had seen a member on here that had a STB made from 1"x2" aluminum tubing and I've been thinking of doing that for a 3 point.

EDIT:
I found where it was posted about: here and here
The member used 0.75" OD tubing with a 1/8" wall. Not very strong tubing.

 

I finally saw your post on my computer at work and could see your signature and the picture of your engine bay. If you’re strut tower brace is anything like the one in your picture it should make a really good foundation for the master cylinder brace.

you’ll have plenty of options for reinforcing in both compression and tension. Just remember to post your progress in this thread or a new one if you want to start it. I love fabrication and I love improving on designs. I’d like to see what you come up with.

and if you could come up with something that’s not so much as an eyesore like my design I bet the community would appreciate it.

 

I would like to see pictures of the 16 ga doubler plate installation. Do you think we could get the stock GM doubler plate for the firewall? Has anybody installed a GM doubler plate?

 

Very interesting topic, had no idea this flex was going on. What causes the flex? Is it the braking action, or just flexing because the car is in motion? What part of the firewall is flexing? Entire firewall or just some section?

 

This what I did to make my doubler for the firewall. But the master still moves. Not a much but it still moves. Planning on making a brace for the front this Winter sometime...

My plate I made

 

Thanks for the picture and the comment that the doubling did not help that much. I did spend the last hour going through the GM Parts and Illustration catalog/May 1989 revision and could not find a stock doubler plate.

I think I will fabricate a support bracket this winter also.

 

The flexing comes from the firewall. The firewall is probably 20 gauge and holds the brake booster/master cylinder assembly by four bolts through that 20 gauge steel. The pedals don't help too much with their brackets. You can see the master cylinder moving if you've ever used the two person brake bleeding procedure.

 

It's going to be on my project list for 2020 but I probably won't get to ti till summer.

 

Interesting info here. This is all news to me but seems to make sense. I may have to explore a master cylinder brace myself at some point. Thank you everyone here.