Colt

I have the 1LE brakes on my car, but as far back as I can remember the brake pedal engagement has been very close to the floor. That is, the first 75% of the pedal travel does nothing. I'm trying to figure out why this is and I’m thinking it’s something to do with the design of the 3rd gen brake booster or MC. I know it’s not air in the lines or a bad master cylinder - all of those have been replaced and bleed many times.

I heard someone talking about how the original fbody calipers didn’t retract the pads, and they designed the master cylinder to do this task. But that sounds like BS and someone is going to have to prove this to me. They just don’t design calipers that way. Plus, the person who said this sounded like he had no idea what they were talking about.

I have thought about putting in a LS1 booster and master cylinder, but I don’t want to go experimenting. Has anyone done the conversion and noticed any difference with the feel and specifically the engagement point of the brakes?

Thanks

Painrace

I have the same problem I think. With the engine not running I have a good brake peddle. However, when I start the engine the brake peddle goes way down and stays down? Master and booster were changed by the previous owner. What do we do?

Jim

Tibo

iTrader: (15)

I have LS1 master cylinder and brake booster, wilwood prop valve and LS1 front and rear brakes. Going from a non 1LE fbody brake setup to this is a difference in engagement and performance but not a difference in pedal travel. It is sort of correct in that with floating calipers the first 100 pounds or so is said to go to taking up the looseness in the floating caliper design. Whereas with a fixed caliper you have immediate and better pedal feel. If you know the system is functionally flawless I would try a good set of pads such as Wilwood, porterfield, stillen metal matrix and properly seat them. If you still aren't happy you can look into a fixed caliper system.

IROCmenace

iTrader: (1)

OP and 2nd P. Did you guys ever fix this? I have a similar issue

New LS1 master
Earls braided lines
used LT1 booster
gutted prop valve for rear circuit
LS1 front brakes, new ceramic pads, new drilled and slotted rotors
PBR's in the back, new Drilled and slotted rotors
Rear axle hard line is new

Brake pedal is rock hard with car off.

I have buddy bled, gravity, and power bled with the Motive bleeder. Numerous times. New fresh fluid. No air in the lines. Bench bled the master off and on the car. Last attempt I spent an entire Saturday afternoon bleeding with 3 large bottles of brake fluid, Dot 4. I did get better pedal but still nothing before 2/3rds pedal travel.

Used the factory manual guide for bleeding lines at the master

Fronts will lock, rears will not. About 2/3rds of the pedal travel before I feel any significant braking force. From there to the floor it stops fine. But the low pedal is un-nerving.

Tibo

iTrader: (15)

Do you have proper vacuum? is the master cylinder fully seated to the brake booster which in turn is fully seated to the firewall? The caliper guide pins are freely allowing movement?

IROCmenace

iTrader: (1)

Yes, yes and yes.... unfortunately

IROCmenace

iTrader: (1)

Actually, the fronts are LS1 brakes so the are not guide pins per second.

IROCmenace

iTrader: (1)

"Per se" ....... spell correct got me

Colt

I think the pedal travel is, sadly, a part of the design with these cars.

I believe the problem lies in the booster. I feel i know quite a bit about cars, but the booster has always been a black box for me. From what I understand, when you step on the brake pedal, you are actually operating a valve in the booster that then actuates the master cylinder pushrod.

I believe this valving in the booster has a very long amount of travel, and that's why our brakes engage so low to the floor. This is why bleeding, SS lines and whatever dont help.

The thing to do would be to open the booster and see how far that valve has to be pushed before it starts applying force to the MC. Maybe we could shorten that distance somehow.

Tibo

iTrader: (15)

When I had the LS1 brakes with the Thirdgen booster I never had to press 3/4 before having any real braking. You can easily switch to the LS booster easily enough if you think the booster is to blame. Without a doubt the setup I have now with the LS master and booster and Wilwood four piston FSL front and LS rear caliper has a short and firm pedal with no slack or take up.

Jeffs82TA

iTrader: (1)

did 3rd gen have an adjustable booster rod like vettes did?

I have 3 4th gen and neither does what you describe most the pedal moves down is about 3"-5"

scoflaw

iTrader: (2)

3rd gen booster does not have an adjustable rod, but there might be an adjustment at the brake pedal linkage, under the dash, haven't looked yet

IROCmenace

iTrader: (1)

There is not one on my 88.

Colt

You have to be careful if you are going to preload that valve. If you do, it may create a condition where the brakes start to drag when the engine pulls high vacuum.

scoflaw

iTrader: (2)

You don't want it preloaded, but you don't want freeplay either.
If a stronger PV spring makes the rears work better I would think no spring would do the opposite
A simple test to find out where all the play is would be to start at the beginning of the system and work your way back.
Go to your local autoparts store and get 2 plugs to block off both master cylinder ports. I believe they are a M12x1.0 and a M11x1.5
You should have a high hard pedal if your master and booster are working properly
If that checks out you can connect the fronts and the rears individually to see which 1 is giving you all that travel.

84 1LE

iTrader: (9)

My guess is the MC.
Third gen MCs have a quick take up valve, because of the "low drag" feature used to help with EPA ratings.The qtv allows fluid to flow into the primary chamber first.Its suppose to keep excess pedal travel to a minimum, but travel is more than disired.

ramicio

iTrader: (-1)

From what I read in the factory manual, this low-drag concept applied to drums only. This information's correctness doesn't change the fact that people are using LS1 masters and boosters, and an adjustable proportioning valve, and still having issues. I am chasing down the same problem. Braided teflon lines are going to be the last straw with this car.

Colt

I fixed and found the problem, but you're probably not going to like the solution.
When I was experiencing this, I was running the 1LE PBR calipers. So it turns out, those calipers, and the stock ones, simply have too much piston area (thus fluid volume) to have good pedal feel and the proper amount of travel with these master cylinders. I am now running Wilwood forged superlite 4 piston calipers that have significantly less piston area.

But anyway, I now couldn't ask for better brakes. The pedal is firm and starts almost immediately. It is as good or better than most modern cars. I track this car on road courses and have over 400hp. I have yet to experience any fade with my current setup.

Here is a chart showing all the different piston volumes for different calipers.
http://farm9.staticflickr.com/8046/8...6d0949fe_h.jpg

Attached a picture of my setup. The front brakes are ducted with 3" tube. I do not run the ducts on the street since they limit steering angle and will get crushed in parking lot maneuvering.

Bullydawg

iTrader: (7)

So I’m basically having the same symptoms as everyone else and I’ve swapped the master, booster, front lines and calipers.

I am running a 4g master, 4g booster, 4g front brakes, and stock rears. I’ve bled multiple times with a motive power bleeder, bench bled master. And I have low pedal engagement. If I clamp the front lines, pedal feel is awesome, same with car off. Once the car is running and the booster is on, the pedal damn near goes all the way down.

Now I know there are people running 4g front brakes without issues. Has anyone figured this out? If I clamp the front hoses the brake pedal feels perfect with the car running... so it definitely seems like the fronts aren’t pushing enough fluid.

Any advice? Yes, I know it’s an old thread, but it is relevant.

Colt

I know that the 3rd gen calipers retracted the pistons a lot father than normal calipers since they have a "low drag" design. What's probably happening is that the rears are consuming most of the fluid in the 'take-up' which is making your pedal feel like mush. Dual circuit master cylinders like ours, even though they have 2 pistons in them, are hooked up in a series so they are not totally independent. If there was a complete loss of one of the circuits, the second active circuit only works when the piston for the dead circuit bottoms out. So, if your rear calipers need to take up a lot of space, its going to effect the pedal like you are seeing.
The stock 3rd gen master cylinder has some provisions to prevent this, but now you are running a 4g master so you don't have that anymore.

Bullydawg

iTrader: (7)

Ill swap the stock 3g master cylinder on and see if it helps. Thanks

edit: swapped the masters back to stock 3g that I bench bled. I swapped it quick and didn’t even bleed the brakes and the pedal already feels WAY better.

Tibo

iTrader: (15)

I read this and I can't help but wonder if we are complaining about the effectiveness of our 30 year old breaking system that actually is running perfect, for how it was designed and with the components it was made with but we are just unhappy with them because of how much better today's average cars breaking system is. I know I might be. I've found that I've become used to daily driving newer cars with a modern, performance leaning break system and then I drive my Camaro and I all the sudden think it has an issue I need to fix it.

Bullydawg

iTrader: (7)

I see where you are coming from. I do however have three thirdgens, all modified and love them. This one definitely wasn’t right. Even bled perfectly if I pushed hard enough I could bottom out the pedal.

Colt was dead on. It was definitely something to do with the rear brakes and the 4g master not being compatible. I have been working on the brakes off/on for a month now and it has been the only thing stopping me from driving the car. I bought it as a basket case in a million pieces and ditched most of it and swapped in an Ls1/4l60e.

I think on these cars anything past halfway on the brake pedal push needs attention.

Colt

The funny thing is that modern cars use all of the same tech as our cars do, but the execution is just better. I always wonder why so many people lust after old muscle cars, then get behind the wheel for the first time and realize that it drives like a turd. I guess they say "never meet your heros". But part of the fun is making it drive as good as it looks.

I don't think people understand how old cars drove. In the world of classic muscle, our third gens are considered really fantastic handling cars. I can only imagine what something like a '68 Chevelle is like.

Colt

You might want to look into putting in a manual proportioning valve. Just replace the factory one with it. The 3g master cylinder has 2 different bore sizes, I'm sure that's going to be throwing off your brake bias with your setup.