Brake Problem 10 Years, Never Solved! - Clevis Adjustment?

[davepl]

Short version: Has anyone had a brake issue created or resolved by adjusting the pedal angle via the clevis?


Not my blue truck, but I've had a brake problem for 10 years. No one has ever been able to solve it. Everything has been replaced and rebuilt and the problem remains... so where does it hide?

Here's the problem: you cannot panic brake. If you attempt to, the pedal responds but slowly. So about 1/2 second later you get full braking which is more than adequate.

So braking is powerful, but slow to respond. This started when I first added rear discs from a Master Power kit, but I'd also upgraded fronts and master at the same time. So the last time it responded well was drum brakes.

I have this same vehicle in a factory disc-drum setup and that's all I want, it to respond as well as the stock one I have!

Here's just a bit of what I've done:

I replaced the master.
I replaced the booster.
I tried a Hydraboost for more assist.
Various different pad materials for different grips.
I had the car fully restored, all new lines and distribution blocks, etc.

It still remained!

So since everything was now new and the problem remained, I threw in the towel and put a full four-wheel Wilwood disc brake setup on it. Everything from the booster to the rotors is Wilwood.

Same problem.

After 10 years of trying everything and 5 shops and no ideas, I just gave up and don't really drive it. But I'd still like to fix it.

Then this month I was reading a magazine tech article about a guy describing the same thing, who's done all the same things, and he's concluded then that since he's replaced everything, and describing the same slow-to-respond problem, that it can only be in the pedal adjustment because that's all that's left!

The magazine response wasn't helpful, but someone else had the same problem.

The brake pedal is adjusted to be about as high as the clutch pedal right now.

Before I try to change it though, here's my question:

Has anyone had a brake issue created or resolved by adjusting the pedal angle via the clevis?

That's really my question for today!

[Steeveedee]

Did it have power brakes before you made the upgrades? Manual versus power brakes mount the push rod on different locations on the brake pedal lever.

[davepl]

It was power before and after, thanks!

[Steeveedee]

Mine was power before I went to disc brakes. The pedal was as hard as a rock after I installed the disc brakes. In my case, the booster had been damaged in shipping. Is the other vehicle a truck?

[jocko]

On the brake pedal lever - in which hole is your pushrod clevis? (upper or lower)
I believe power should be the upper location - and, while you shouldn’t have to change it if you went from a power setup to a power setup, if it’s always been bad, then perhaps it’s always been in the wrong hole. Probably not the issue, but just a thought. I would have guessed it was the booster, but sure sounds like you’ve eliminated that as a possibility several times.

[JustLiveIt]

Very interested as I have this exact problem with the exact same symptoms. I have stock front disks from a 71-72, new corvette master and dual 9” booster, all new hard and flex lines, new rear disks/pads with parking brake, wilwood adjustable prop valve, new front bearings.

I’ve bled this thing many times using the pedal method, vacuum, and tried pressure bleeding as well.

[KQQL IT]

Residual pressure valves.

[7 Devils]

I'm wondering if it's a fluid volume issue with the master cylinder. The pistons on disc set ups usually have significantly more fluid vume requirements than drums.

Just a thought.

Dan

[Andy4639]

As far as I know there is only one hole in the brake pedal in my 71. I had factory front disc so the hole should be correct.
Adding the rear disc brakes gained me nothing as far as stopping power in normal driving. The only help I have seen on this problem for me was the pedal travel. I need to re adjust my pedal so it's not up against the rubber stopper on the dash bracket.
The pedal should have a 1/4" gap form the rubber. The rubber is for rebounding when you let off the brake pedal not where it should rest.
I hate getting under the dash so mine isn't set right as of right now.

[Andy4639]

This is what I need to do.

CCP

Check Pedal Assembly


Something that many people are not aware of when upgrading their system is the brake pedal adjustment. Improper pedal adjustment can do the following:
•Preload the booster causing brakes to drag and eventually lock up.
•Damage the booster's internal components by actuating at an improper angle.
•Allow slop in the pedal if adjusted too low.

Many vehicles have a second hole on the pedal assembly that was originally intended for power brake applications. The required hole is generally 1" to 1-1/2" lower than the original manual brake hole. If there is no second hole, you may need to drill the hole in the pedal arm to properly align the push rod. The easiest way to determine the perfect location for this hole is to find the center of the push rod's vertical travel to ensure that its actuation is as inline with the booster as possible.
1.Gently lift the end of the pushrod until it stops and noting the location where the clevis on the pushrod locates on the pedal arm. You can mark this location.
2.Then gently push the pushrod down until it stops. Mark this location as well.
3.The proper hole location is in the middle between the two marks on the pedal arm. Mark and drill the new hole in the center of the pedal arm. Attach the pushrod to the pedal arm.




CPP
Check freeplay in the pedal by applying pressure to the pedal with your hand and noting how far the pedal travels before resistance is felt. It should be approximately 1/4". This freeplay allows the master cylinder piston to return to the "at-rest" position and prevents preloading the system. Too much freeplay will drop the pedal too far before applying brake pressure and may even hit the floor before applying full braking force to the system. Note freeplay is also dependent upon proper adjustment of the booster pushrod. See "Check the Booster Pushrod" below.)

[tdangle]

Very interesting conversation. I have a feeling my pedal is also not adjusted correctly. the bump stop is missing and the pedal is no where even close to where it should be per the pictures posted.

[Steeveedee]

Originally Posted by Andy4639

This is what I need to do.

CCP

Check Pedal Assembly


Something that many people are not aware of when upgrading their system is the brake pedal adjustment. Improper pedal adjustment can do the following:
•Preload the booster causing brakes to drag and eventually lock up.
•Damage the booster's internal components by actuating at an improper angle.
•Allow slop in the pedal if adjusted too low.

Many vehicles have a second hole on the pedal assembly that was originally intended for power brake applications. The required hole is generally 1" to 1-1/2" lower than the original manual brake hole. If there is no second hole, you may need to drill the hole in the pedal arm to properly align the push rod. The easiest way to determine the perfect location for this hole is to find the center of the push rod's vertical travel to ensure that its actuation is as inline with the booster as possible.
1.Gently lift the end of the pushrod until it stops and noting the location where the clevis on the pushrod locates on the pedal arm. You can mark this location.
2.Then gently push the pushrod down until it stops. Mark this location as well.
3.The proper hole location is in the middle between the two marks on the pedal arm. Mark and drill the new hole in the center of the pedal arm. Attach the pushrod to the pedal arm.




CPP
Check freeplay in the pedal by applying pressure to the pedal with your hand and noting how far the pedal travels before resistance is felt. It should be approximately 1/4". This freeplay allows the master cylinder piston to return to the "at-rest" position and prevents preloading the system. Too much freeplay will drop the pedal too far before applying brake pressure and may even hit the floor before applying full braking force to the system. Note freeplay is also dependent upon proper adjustment of the booster pushrod. See "Check the Booster Pushrod" below.)

That first part works for the case where the push rod for the brakes goes directly into the booster. If your truck has the bell crank on the firewall, it doesn't matter (within reason) where the push rod goes on the input end.

[54belair]

I have not had this particular issue on a GM product--But, I had an almost identical issue on a 66 mustang. I changed over to front discs and the problem came along. I researched everything I could think of and finally, just by chance I happened onto an old mechanic (yes, there are people older than me), after explaining my issue, without hesitation he told me it was the pedal adjustment that was the issue. In the end, I adjusted the pedal height (which adjusted the stroke as well) and the problem went away.

[CC69Rat]

Dave -- remember a post about the 4wdisc on my 68 ? ^^ This is what ultimately fixed it. Yes, The pedal, Clevis, preloading, etc. all of it. Angle is very important and as Andy mentioned put about 1/4" of 'slop' in the brake pedal so when it hits the top of the pulloff stroke before it hits that rubber pad.

[davischevy]

When I put rear discs on my 55 Chevy 210 I could not get pedal.

I pulled the pedal, and drilled a hole one inch down from the original, lowered the clevis and now I love the brakes.

Lowering the clevis gives the piston a longer throw and pushes more fluid to the calipers.

[Andy4639]

Originally Posted by davischevy

When I put rear discs on my 55 Chevy 210 I could not get pedal.

I pulled the pedal, and drilled a hole one inch down from the original, lowered the clevis and now I love the brakes.

Lowering the clevis gives the piston a longer throw and pushes more fluid to the calipers.

This maybe is what I need for the truck since I added the rear disc's!

[Leonard1]

Originally Posted by Andy4639

... I need to re adjust my pedal so it's not up against the rubber stopper on the dash bracket.
The pedal should have a 1/4" gap form the rubber. The rubber is for rebounding when you let off the brake pedal not where it should rest.
I hate getting under the dash so mine isn't set right as of right now.

My pedal is pulled back all the way to the rubber stopper by the spring. Is it supposed to be adjusted without the spring? Otherwise, how can it not touch the stopper?

[davepl]

Thanks guys! I'm going to digest Andy's post and then take a look at my pedal angle. Sure hope this hunch plays out, it's reassuring to hear that others have solved actual problems in the same arena!

[Richard2112]

I am going to fix this same problem on my brothers car. He has been swapping part for a long time and no results. I looked at it a couple days ago and pedal geometry is certainly part of the problem, if not the whole problem.

I am going to adjust the booster/firewall geometry and check/adjust booster/MC relationship. My thoughts are that if you have an air-tight system and properly matched components, geometry is very likely the culprit.

[Andy4639]

Originally Posted by Leonard1

My pedal is pulled back all the way to the rubber stopper by the spring. Is it supposed to be adjusted without the spring? Otherwise, how can it not touch the stopper?

The adjustment will stop it where ever you adjust it to.

PICKMUP
Take a look at the pedal location on an original pb truck...the pedal hangs down an inch or so. That is how it is designed. It doesn't need any cutting/welding/adjusting. You just need to make sure you don't extend it so far that it is pre-loading the mc. There should be a little free play so brakes release completely.
Remember, the travel of the pedal into a booster is a lot less than the travel of the pedal directly into a mc.

[Boog]

Adjusting the pedal just off the rubber stop makes the rubber stop useless doesn’t it? I think of it as a rattle preventative.

[Andy4639]

Originally Posted by Boog

Adjusting the pedal just off the rubber stop makes the rubber stop useless doesn’t it? I think of it as a rattle preventative.

Not really it keeps the pedal from hitting metal to metal when you let off the brake pedal. That's all it is intended for I think. The spring pulls it back up so it has a purpose.

[davepl]

On cars (like the Impala) only cars with manual brakes or cruise control got a return spring. Otherwise it's up to the booster. My car is missing its bumper as well, which I found out when I was restoring my next one and went back to look as a reference. So it could be even further out of whack.

I just went out and looked at it, it's not that bad in terms of angle, but it is "highly adjusted", meaning the brake pedal switch is thread in the maximum amount to reach it, for example. And about 1" of rod comes through the clevis. So I'm going to back it off a bunch and see if it changes anything for better or worse.

At this point I don't see any "aha!" issues, but am still hopeful.

[Leonard1]

Originally Posted by Andy4639

The adjustment will stop it where ever you adjust it to.

So at rest, the return spring holds tension on the pushrod, and the pushrod is what keeps the pedal from touching the rubber stop?

Sorry davepl, I wasn't meaning to hijack your thread.

[Steeveedee]

There should be free pedal such that the brakes do not have any pressure on the hydraulics. I know that all my vehicles have bumpers on the brake pedal lever. I'm surprised that your Impala does not. It may help to check with anyone having an Impala to see if there is a return spring inside their car for the brake pedal. I think it should have one. Is there a hole or slot somewhere that the pedal arm could contact when the brakes are not applied?