Hi all I apologize if there is a similar thread but I could not find one.

I had a 5.3L LS swapped into my '86 camaro. Now i have virtually no brakes at a low RPM, a problem that I did not have prior to the engine swap. Related to the engine swap i also upgraded the rear end and the brakes. Originally, I had drum brakes in the rear which are now disc brakes. I also upgraded the front brakes to the 4th gen SS brakes.

If I try to launch the vehicle, the brakes will only hold the car at about 1,000RPM and then the car will start to creep forward. If i put the car into neutral and rev it with my foot on the brake pedal i can feel the pedal begin to sink and then the brakes will hold more RPM for launch. This makes me believe the problem is independent from the engine swap because typically you should have more vacuum at idle.

Does changing the brake system require upgrading of the master cylinder or booster? Hoping you guys can provide me help because this problem is killing me and I hate wasting money.

Has anyone else had a similar problem???

 

Are you still running the stock proportioning valve? A lot of times when working on the rear brakes the valve gets air in it and moves over limiting flow to the rear brakes. I had this happen when doing wheel cylinders on my trans am. The pedal would feel stiff, almost like it was hitting a wall. It also wouldn't lock up the rear brakes, even with the wheels in the air. I’m assuming the 5.3 is relatively stock? Does it have a cam?

 

Thank you for the response!

it has a moderately aggressive BTR cam and supporting mods. I dont think the cam is aggressive enough to require a vacuum pump or anything like that. I am running the stock prop valve, master cylinder and booster.

I can definitely relate to the hitting a brick wall feeling in the pedal. At a low RPM I have that problem but like I said if i rev it while keeping my foot on the brake pedal I can feel the pedal begin to go down and the brakes do bite more.

I wonder if the additional and bigger caliper pistons make a difference?

 

Did you swap the brakes before or after the engine swap? If you kept them the same and swapped in the cammed 5.3, my money would have to be on the cam unless there’s a vacuum leak at the booster or something.

Also does your booster make a lot of noise when pressing the brakes? If there’s an air noise or some kind of excessive whoosh when pressing the brakes then the booster is possibly bad, especially if its original. It could be that it was bad to begin with, but with the cammed motor there just isn’t enough vacuum to make up for the leaking booster.

 

86 I-Roc, do you understand what LsxMatt is talking about here? This is a very important thing that must be right. If the brake warning light is lit up then this is 100% the problem.

Really just need to get back to the basics and confirm the components in the braking system are functioning proper. Your engine makes adequate vacuum. Your master cylinder is probably fine.

Lift the car off the ground and observe if all the brakes grab at all. Let the rear wheels spin while idling in gear and test the brakes. You'll need to spin up the front wheels by hand. If you really want to do this right then you would need a tool to measure line pressure at each brake. I don't think it's necessary yet though.

Make sure the brake calipers aren't mounted upside down (I'm totally serious). The bleed valve must be located at the highest point of the caliper hydraulics or else the air won't bleed out.

Make sure you have quality brake hoses. Old rubber hoses could be disintegrating inside and causing blockage.

Go through the procedure to re-center the balance piston in the prop valve. Even if it turns out okay, that will eliminate that issue and you can confidently move forward knowing that's okay.

.Next bleed the brakes again. Put a little pressure on the pedal and crack the master cylinder nuts just enough to let some fluid leak out. I'll bet anything you get air bubbles. That will help with air trapped at the master cylinder because you'll probably not get it out via normal bleeding.

Move on to the brakes. First slip a few feet of clear tube over the bleed screw. Make sure it's a tight fit. Loop the tube UP and then DOWN into a little bucket. The purpose of the loop is so that there is always brake fluid (no air) on the bleed screw when you close it during bleeding. And you'll be able to witness air bubbles.

Start the bleed by putting a little pressure on the pedal, and then crack the bleed screw. ALWAYS have pressure on the pedal when the bleed screw is open, and NEVER run out of pedal travel while you're bleeding. Use a steady, moderately slow strokes. DO NOT move fast and DO NOT pump the pedal. Fast movements just emulsify the air in the brake fluid and you'll not get it out. (Large air bubbles are good and easy to bleed. Teeny tiny bubbles are your nightmare.)

If you think there is air emulsified in the fluid then you have no choice but to just walk away for a few hours and let the bubbles settle at high points and reform into larger bubbles.

Keep the lid on the master cylinder, and the lid on your bottle of brake fluid the whole time you're doing this. Brake fluid absorbs water from the air ridiculously fast.

If after all this the brakes are still bad, then come back and we'll bat around new ideas.

 

By the way, what rear brakes did you install?

 

Thank you both for the responses and help. I do recall hearing a whoosh and having the pedal return slowly when pressed, and it also being hard to get the pedal all the way to the floor. I am in the process of getting the brake booster off and will probably end up replacing it. I also got the prop valve and MC correct for 4 wheel disc brake, maybe it isn't necessary but id rather not take it all apart again and i want to rule out these components. I do recall on a couple of occasions the brake light came on after compressing the brake pedal, but it went off shortly after. For these reasons i have decided to start with inspecting the booster. Right now i'm having a good time getting the four nuts off behind the firewall

 

Any advice on how to detach the brake pedal?

 

i was able to get it all disassembled, but im not entirely sure what to look for.

 

You just needed to get the hydraulics set up properly first and then decide if there is a different problem to solve. But since you already have the booster out you might as well replace it because it's not a job you want to do twice (as you already know! ). I've never been able to find a rebuild kit for the diaphragm. If you do find one then please let me know!

As far as prop valve, give this thread a browse and you'll see how to identify which prop valve you have, how it varies by year, and a little tutorial about the "spring" mod to make the rear brakes bite more aggressively.

https://www.thirdgen.org/forums/brak...ng-torque.html

 

Thank you for pointing me to that thread! I plan to run vacuum to the booster and manually push the rod and see how it operates, then remove the check valve to ensure its holding vacuum. I think that isolating the booster from the MC was the best way to do this. I will probably end up replacing it anyways since it appears to be original and like you said its not a fun job, but i'm really hoping the rod doesn't operate as its supposed to so I can sleep better tonight Im currently charging my batter as the winter killed it, just another thing to replace lol. I will update after the results from the test

 

I tested the vacuum, it was at 12psi at idle and oddly enough it actually increased when i revved the engine (the engine has a crap tune). I would think 12 psi would be enough to give me at least some brakes at idle so i tested the booster isolated from the MC by attaching the vacuum line to it and pressing in the push rod. I could push it in but it was pretty stiff, it wasn't that much easier than it was without the vacuum line. The rod also returned to neutral pretty slow as well.

I also came across another problem this morning when I tried shutting the car down, it wouldn't shut off. I had never had this problem before. I was able to take the key completely out of the ignition and it kept running. I had to disconnect power from the alternator to get the engine to shut off. Ugh, one problem at a time with this demon car.

 

Sounds like it might be 12 psi absolute pressure, and not 12 psi gauge vacuum. If so, then that would mean you have very little vacuum at idle.