Was installing a Tick master cylinder the other day and was actuating the clutch by hand to adjust it, when I realized that I have quite a bit of flex in the firewall, even with the thirdgen pedals/ braces and an additional piece of sheet metal sandwiched in between the support rods and firewall.

Video:
https://youtu.be/BCtp6NVOFMo

Pic of my support plate, with the right/ lower support rod removed:


Granted, my car is an A4>t56 car. The m/c holes I drilled aren't the prettiest, but were rounded and smoothed, and I've seen some as bad or worse on the web. It seems as though most of the flex is near the lower hole and where the wiring harness comes through.

The holes:



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Are all third gens this bad? Anyone come up with a good brace for this? Odds of this actually causing a major issue (cracking/blowing through) in the near-ish future? I know the brake master has some flex in these cars without known issue, still doesn't give me a warm fuzzy about this though.

 

Yeah that area is weak. Thats why GM welded in a doubler plate and used the support rods.

 

You can make a plate to re enforce the area and bolt or weld it in. I made sure to do this when I converted my cars.

 

Thanks for the photo, Drew. The plate I made is similar, but a good bit smaller. Maybe just too small to distribute the load well? Edited the photo to make mine stand out more, not sure if you guys saw it. 86T/A, do you have any photos of it or rough dimensions?




Also, I used roughly the same thickness as the firewall sheet metal, maybe slightly thicker. Is the factory stamping or the 86T/A special significantly thicker?

 

Iirc I started with a 6x6 pc of 14ga, trimmed and bent it to fit the contures of the car. Don't have any pictures handy.

 

I've made a couple different reinforcement plates, will test them today. Some google-fu revealed that firewall cracking has proven to be an issue on fourth gens and gto's, guess the Tick M/C requires enough force to actuate that flexing the firewall is a common ordeal. I'd be curious the difference in deflection from moving to a stock third or fourth gen system, and to the supposedly even lighter Fbody mc/ Cavalier slave combo. I don't remember any flex when I installed the modified fourth gen hydraulics, but I probably wasn't looking for it. (Side note, there is a hollow spot in those rods that is a weak point. I didn't get the die nut on 100% straight and the rod snapped after ~100 miles of driving, leading to the Tick and this ordeal)

If the plates don't work, I've got an idea to make a plate with a gusseted upright and a long carriage bolt to be bolted to the frame rail and press on the m/c block from the engine side, similar to the STB based brake master cylinder brace mentioned in another thread on here. I'll keep things updated and provide dimensions for whatever the final fix ends up being in case anyone else has issues with this or wants to take preventive measures.

 

You got those measurements by chance? I've got the same issue, could save me the headache!

 

spread the load and increase the capability more... ie wider and thicker... you can see what i did starting at post 177 in the link below

https://www.thirdgen.org/forums/engi...al-88-a-4.html

 

Here is the one I made from my auto to manual swap.

 

So add me to the WTF happened to my clutch story.

went to start the car a few weeks ago so I could wash it. Car was in neutral so I just started it. After the car was warmed up I went to put it in gear and the clutch went to the floor. Felt like a seal popped somewhere.


since the car was still in the garage I shut it down and looked for fluid and checked the master, found it to be slightly low. Chalked it up to the master or slave going bad.


on a whim, decided to check the mounting tonight when I got home. Took about 10 seconds to move the wiring loom so I could see the bolts.

unstead I saw that the firewall had completely cracked, both bolt holes gave up and the master was completely hanging freely.


I don’t have a welder, nor the immediate skill.

so I think for now I’m going to get a sheet of either 12g or 14g sheet metal and cut/hammer it into thr right shape, then glue or rivet it into place. Rivets would be easier to deal with when I eventually have the plat I’ll make welded in. Glue would be messy to remove before welding.

There is no real rust except where the exposed metal of the cracks are. So the existing metal is still good, I’ll have to clean, seal, paint it.


I guess this might explain why I’ve been having difficulty with high RPM (7k+) shifts at speed. I thought it was just the t56 synchros hating me, but it might have been flex in the mount the whole time.

 

Did you have a doubler plate or just the basic firewall ?

 

My car was a t56 conversion. So no plate. Gonna need one now though.

 

yes the plate is a must... combine it with the big tick / hawks type master and it is much more solid

 

I used a machined piece 1/8 steel and also used the 2 rods that go to the brake/clutch pedal bolts. The master cylinder I have is also steel. I don't get why GM made plastic master cylinders. These cars need all the rigidity they can get in this area. My car is an 82 and was a mechanical clutch initially so I'd had nothing there for support.

 

Mine is also an '82 with a T56 conversion. After going through a few crappy master cylinders and having shops install them, I finally decided to do it myself. Got this master cylinder: https://www.ebay.com/itm/121275126805
I had to shorten the push rod, but it otherwise fit.
My car's firewall there is completely cracked and messed up, so I JB welded cookie tin metal on both sides and used large washers on the bolts. Works perfectly. Function over form is what I say when it comes to hidden mechanical stuff.

 

That's pretty sweet looking. I used the American powertrain setup w a hydra release bearing and their modified master setup. It all bolted in and works really well. I was aggressive w the firewall bracing before there were any issues. I've seen too many issues there w other cars.