Hi All,

Hoping a brake system expert can help me out here because I've tried the brake shops in my area and they're booked solid for the next month and couldn't give an answer over the phone.

My 85 TransAm's brakes are pitiful and I'm trying to isolate the issue. They were pretty average to start with but upon throwing parts at them they're actually worse....

I put an Ls1 in the car and at the same time got a 97 Camaro 3.42 LSD rear end to put in there with disc brakes to replace the 2.77 open end with drums.

So far for the brake system I've put in:

New rear rotors and pads
New rubber line and T-fitting
new e-brake cables to suit
ran new 3/16ths line from rear to front
new 3/16th lines for front brakes
new wilwood adjustable proportioning valve
new 3rd gen master cylinder

The rear camaro brakes are the stock pbr single piston ones
The front's are the stock 85 TransAm ones

Brake booster holds 15" vacuum for more than 48hrs and I've checked while driving it has vacuum pressure. Also installed an auxiliary pump to get me in the 20-25" range but doesn't help

Master cylinder was bench bled properly with no bubbles coming out at all, capped and transferred straight into the car.

No fluid leaks anywhere, all checked and tested.

Pedal is hard to press straight away with no vacuum and no play.
On vacuum pressure pedal goes down about 1/4 on first press before resistance. After that has resistance but just no stopping power.

At 35mph and stomp the brakes the car will not lock up and comes to a stop not slowly but definitely not fast enough to stop hitting the car in front if they decide to surprise me.

Any ideas for further tests or where I should be looking with these symtpoms?

 

Proportioning valve might not be working correctly. Get some new semi metallic pads up front to make sure you aren't using store brand compressed llama dung garbage pads. New rotors are also recommended.

 

I thought about the proportioning valve, as I can't confirm if it's a proper Wilwood one or a knockoff, but I've wound it all the way to each side and confirmed it locks off front/back, and set it to exact middle for the time being while I diagnose the issue.

Could a restriction or fault in that stop pressure flowing through to the calipers?


Based on the 2nd half of your comment, you think the brake system is working but shitty pads could be the whole issue?

 

Try biasing towards the front a bit. I think if you have shitty pads, you have an issue. Whether or not that's your whole issue remains to be seen.

 

I'll give the biasing a go.
Do you have any part numbers for recommended brake pads and I'll see if they're available here in Australia, or a similar part.

 

So i did some more testing yesterday and found if I push hard enough I could get it to lock up, but from the feel of the braking I think it was just the rears.
I tried adjusting the bias a turn but didn't really make a difference.

There's no sponge to the pedal at all, it just feels like the brake booster isn't working, but it had 25" vacuum pressure when i tested the brake.
Is there any other fail mode for a booster other than torn/damage diaphragm? i.e. holds vacuum but doesn't distribute/focus it when applied?

 

Front brakes always get full pressure, you cannot increase front braking with a prop valve. A prop valve only decreases pressure to rear brakes unless you installed it wrong by accident.

 

So that means if I increase the pressure all the way I'll have 50/50 equal pressure to front and rear yes?
So to get a 60/40 front/rear I'd be looking at closer to 75% full or therarbouts, but definitely not 6.5 turns of the 13 total turns available on the dial?

 

Best to read this thread first. Even if you can't do the math, the concepts are still well described in posts #2 and #3, https://www.thirdgen.org/forums/brak...ng-torque.html

I started trying to explain things here for you but it was getting too complex and that thread does a better job of explaining.

 

Thanks for the link, I adjusted the proportioning valve almost all the way and was then able to lock up and confirm the rears were working well.
Now that I've isolated the issue to the fronts I'll get new hoses pads and see if there's a rebuild kit available in Australia for the calipers.

Thanks for the help