Brake issue

[Michael Oritt]

During a drive today I noticed that the brake pedal is higher and harder than normal and as I come to a stop it definitely feels as though the brakes are dragging, plus there seemed to be a lot of heat coming from the front brakes.

BTW a few months back I adjusted the brake pushrod to raise the pedal's point of engagement to provide for better toe-heeling. Perhaps I did not tighten the nut enough and things have gone out of adjustment?

In any case I suspect a problem with the master cylinder's activation but would appreciate any suggestions as to what the issue and fix might be.

 

[HealeyRick]

Higher and harder pedal sounds like less fluid is getting through the system. Wonder if it could be an issue with brake hoses collapsing internally? That would also explain them failing to release and dragging the brakes.

 

[Michael Oritt]

Rick--

I'll probably be able to get under the car tomorrow.
Short of R & R'-ing the present line(s) how would I check for/diagnose a collapsed brake line?

 

[HealeyRick]

Only way I would know of is remove them and inspect. Age is a pretty good indicator of condition. How long has it been since they've been replaced? Steve G and I have had good luck with Techna-Fit stainless hoses: http://www.techna-fit.com/brakekits.html

 

[red57]

I don't know just how recently/how many miles ago you adjusted the master cylinder push rod but I'm wondering if your adjustment could have been just a touch too tight and be preventing the foot valve from opening and releasing the pressure in the lines to the wheel cylinders? Might be able to feel with your hand if there is still some free pedal before the piston moves. Otherwise I agree with the possibility of a blocked rubber hose.

Dave

 

[Deleted member 8987]

before you do all that, I have never heard of someone adjusting the master cylinder pushrod to set a different pedal height. You move the pedal up, you may just have set the piston up to not fully release.
Indications are, hard, high pedal and dragging brakes.

FIRST thing you check.

 

[Michael Oritt]

NEWSFLASH:

After letting the car sit for a few hours I just checked the pedal and it has gone back to normal with an inch or two of motion, same as it was before i started out this morning's drive.

At the same time i adjusted the pushrod length a few months back I also removed some exhaust heat-shielding and have not yet gotten around to replacing it. Given the high ambient temperatures I wonder if heat is getting to the MC, causing the brakes to somehow stay partially or fully activated?

 

[HealeyRick]

I'm still voting for brake hoses. The fluid that gets caught in the brake cylinders by the restriction in the inner hose which causes the brakes not to release will slowly move back to the master cylinder giving you good brakes for a couple of applications, then you'll have the same problem again

 

[Michael Oritt]

Rick--

I'm going for a short ride in a little while to a destination nearby and I will carefully observe if the pedal gets high and hard and if the brakes drag, etc.
If there is a collapsed line the condition should appear relatively quickly don't you think? OTOH if it does not appear before the car heats up that might be significant.
I am sometimes a sucker for easy solutions....

 

[Michael Oritt]

During this evening's rides to and from a nearby destination the brakes felt fine and pedal travel was normal--naturally! I hope to get under the car tomorrow.

 

[Michael Oritt]

This morning I got under the car and shortened the brake actuating rod's length by spinning the nut two full turns. Though this probably does not amount to much more than 1/16" I think that is all it will take, assuming the issue was that the fluid return hole was being partially or fully blocked by the seal/piston when things heated up and tolerances tightened down. We'll see--unfortunately I will not be able to take the car for an extended drive until tomorrow ore Sunday.

Thanks to all for their input.

 

[steveg]

I recall there was an article in one of the national club mags, prolly in the oughts, where it was described in detail a fix for this problem on the 100 master cylinders.

 

[Deleted member 8987]

High hard pedal and dragging brakes.....unless all three hoses failed in the same manner simultaneously.....probably not hoses.
On vehicles you can look into the reservoir and see the port, have one person slowly step on brake peal while you look into reservoir (with rag around it just in case), and not when it squirts back a bit into the reservoir. Yell out, have assistant note position of pedal...that is where the m/cyl unloads. If it doesn't....either too tight a pushod adjustment, crud buildup on pushrod end of cylinder, internal failings in master. Remote reservoirs, no dice.

 

[Michael Oritt]

I finally got to take the car out yesterday evening and while all at first seemed good after five or so miles of driving the brakes began to harden up and became so bad that they almost brought the car to a stop even under throttle. I pulled over and after about 30 minutes the brakes released and I crept back home.

At this point I am assuming nothing. Other than perhaps by feel I don't know how one can inspect a brake hose for internal collapse but I will go over each component and probably rebuild or replace the MC on general principle. I am also going to replace the heat wrap that went around the manifold which I removed when I first adjusted the brake actuating rod as perhaps it was preventing the MC from overheating, etc.

Egg on my face....

 

[steveg]

Egg on my face....

Nah, just the way it goes.

 

[CraigC]

Michael, go back to the brake pushrod adjustment as the likely culprit IN SPITE of the fact you backed the adjustment off a random 2 turns. If you have a brake hose problem it would result in a pull to one side if it were in a front hose and both rears dragging if it were the rear hose.

Let's properly inspect the pushrod adjustment first. You will be pushing on the brake pedal with two fingers of your right hand while kneeling next to car with driver's door open. There will be 3 distinct levels of resistance to pedal movement when the pushrod is properly adjusted. FIRST, you should have approx 1/8"-1/4" movement with very little resistance. At this stage you are feeling only the resistance of pedal return spring. This is also the clearance you need for the piston to fully retract in the master cylinder. SECOND, as you continue to push on pedal you will feel a substantial increase in pressure. This is where you are moving hydraulic fluid and causing wheel cylinders/calipers to move shoes/pads up to the drums/rotors. THIRD is where the pedal stops moving as all brake travel has reach its limit.

You need to focus on the first stage. If there is insufficient/no easy freeplay, you are likely holding pressure in system as a result of not allowing the piston in master to reach its rest position.

 

[Michael Oritt]

In yesterday's fiasco after a few miles of driving the brakes went to full lock with no play whatsoever in the pedal, an d I had to pull off the road and wait about 30 minutes until the pressure let off enough so that I could make it back to the shop. The consensus opinion, both on this forum and on the Healey autox email list, is that there was not enough free play in the master cylinder pushrod, thus preventing the MC piston to go past the return hole and relieve pressure.

Earlier this afternoon, with everything cool, I put the car up on jack stands and while under the car I actuated the brake while spinning the left front wheel. Whatever free play I had--or thought I had--last put into the pedal linkage had disappeared and with no free play the slightest bit of pedal movement brought about brake activation. So after loosening the lock nut I rotat the shaft about 1/4"-3/8" until there seemed to be the appropriate amount of free movement and, again using moving the pedal from under the car and spiing the left front wheel, there seemed to be some gradual brake actuation. So I locked the shaft down and went out for the proverbial test ride. At first all seemed good but as the engine warmed up and after using the brakes several times with different degrees of pressure, etc. I could again feel the brakes begin to drag and by the time I got back to the garage the pedal height had changed with all free play having disappeared.

I can't help but feel this phenom is--at least partially--related to heat transfer into the MC. It is very warm here in MD and, with the same pedal shaft adjustment as yesterday, prior to temperatures going up there did not seem to be any issue. Then again maybe there has been some deterioration within the MC and/or debris within the cylinder itself.

Anyway, I will make another attempt at adjustment tomorrow morning and report back. In the meantime thanks for the many helpful suggestions. Craig C's in particular was very presceient and as it turns out this was the procedure I followed and reading his post was most encouraging. However it appears that more work needs to be done.

 

[Michael Oritt]

I got serious with the car this morning and after loosening the locking nut I shortened the rod's effective length by about 1/2", then locked everything down and went out for another test drive. I drove about 15-20 miles using the brakes from normally to hard, including several just-short-of-emergency stops from about 60 mph to 0. Despite all this, and with the engine at 180-190 on another pretty hot day the brake pedal is staying where it should and everything seems fine.

There is now about 3/4"-1" of free travel after which the brakes gradually engage and the pedal is about where it was before I first adjusted things a few months back. Why my shortening of the pedal's travel did not present a problem at the time I did it is a bit baffling and I can only think that lower ambient temperatures must have played a role. In any case things seem back to normal, though I do plan to replace the heat-shield that i removed when I first fiddled with things.

Thanks everyone for their patience and suggestions.

 

[Deleted member 8987]

3/4 to one inch is about normal.

What was happening is the brake fluid was being heated by transfer from wheel cylinders and/or calipers, could not vent, expanded, locked the brakes.

The real quick fix when this happens and you're stuck at the side of the road is a rag and a wrench.
Wrench on an easily accessible bleeder, rag over the top to catch anything that might damage paint, crack the bleeder...AFTER you either A) kill the engine and place transmission in reverse, or B) set emergency brake hard...because when you pop the pressure, the car will ROLL.
Usually enough to allow you to get off the road and figure out the pushrod.

Old habit from decades of repair....I always check brake free play and clutch free play when getting into a car.

 

[Michael Oritt]

TOC--

On pages M/1 and M/4 of the Shop Manual 1/8" is specified as the correct free movement of the brake pedal which is what I followed in my initial fiddle. I'm not sure how to crate enough room in the system for heat expansion with that setting but in any case I am back to where I used to be, minus perhaps some brake material.