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View Full Version : Brake shuddering - HELP!



Scott
08-29-2007, 10:28 AM
I'm sure that with enough money and hours my mechanics could figure out the cause, but maybe someone here has a clue. Here's the situation: my 1962 Hawk's brakes -apparently the fronts - are grabbing and not releasing all the time. It used to be a bit of a pain, but now the car shudders at highway speed and sometimes slower. The brakes were readjusted yesterday because the fronts were found to be too tight. Now it's worse and sometimes when warm the shuddering is almost violent when slowing down from 55 mph. ALL the brake hoses have been replaced. The fronts were done in 2006, which is probably less than 200 miles ago.
The hydrovac is rebuilt and the hoses for that have been replaced. Its performance seems to be sporadic. Sometimes the pedal feels normal and then hard a rock (that's when the brakes are dragging usually). I don't think the unit is bad, but something else is hanging up.

The front wheel cylinders are leaking and the brake shoes show uneven wear.

The brakes have always tended to drag, but the shuddering has only happened since the installation of the new (2nd time) master cylinder. It seems the problem is in the front only. Could it be sticking wheel cylinders? I'm planning on replacing them as soon as possible, as well as shoes AND return springs if I can get them. Can return springs look ok, but be weak and allow a sticky cylinder to keep the shoes more or less engaged? I'm pretty sure that in the multiple times (as in more than 8 times this car has been in for brake work) the car has been worked on the steel brake lines have been inspected. This car has been bled more than an obsessive blood donor!

I'm sticking with the stock setup because I don't have the money to get a Turner system and I want to keep it stock.

blackhawk
08-29-2007, 10:47 AM
Scott,

I suggest systematically eliminating or isolating parts of the brake system to try to pin point the problem. For instance, try bypassing the hydrovac since you say it is problematic. You could also back the shoe adjustment off more than you normally do when adjusting them so you know there is no way that the shoes are hitting the drums, getting hot and grabbing. Then, if it starts shuddering, you know for sure the pressure is not releasing after you brake. You say the front wheel cylinders are leaking. Have you checked inside to see if there is brake fluid on the shoes?

Dale

Chucks Stude
08-29-2007, 11:03 AM
The wrong master cylinder will cause the binding. Ask me how I know (the piston is slightly longer on some than on others, and does not uncover the bleedback hole in the master cylinder). Loose tie rod ends might also contribute to the shuddering.

dictator27
08-29-2007, 11:09 AM
Scott

Have the brake shoe return springs ever been changed? If they are weak, they can cause this problem.

Terry

41 Frank
08-29-2007, 12:00 PM
If the wheel cylinders are leaking as you indicate, fluid could be getting on the brake shoes and causing the shudder, ask me how I know. The first order of business would be to repair or replace the wheel cylinders, everything else comes after that. Not enough freeplay at the master cylinder rod could cause the front brakes to drag which could get the drums so hot they are now warped. From what I gather that has been done sounds like you need to find a different repair shop.[:I] Any of the things suggested here could cause the brakes to drag. Hydrovac, hoses to hydrovac, front brake hoses swollen inside, not enough push rod clearance, seizing wheel cylinders. The return springs would be the last thing to check.

Frank van Doorn
1962 GT Hawk 4 speed
1963 Daytona Conv
1941 Champion R-2 Rod

Dick Steinkamp
08-29-2007, 12:23 PM
I looked at the brakes real briefly while I was at Scott's just before the SB meet.

The brakes definitely drag. Initially, I thought the MC pushrod must be adjusted too long, but I adjusted it so that it had plenty of slack and the brakes still dragged. Probably not the MC or pushrod. I'd also say that the return springs would have to be almost non existent in order for them not to be able to retract the wheel cylinders.

I'd suggest weak flex hoses that let fluid past under pressure, but won't allow fluid to return when the pedal is released, but Scott has had these replaced. (have all five (5) hoses been replaced?...including the 2 at the booster?)

The front brakes found to be too tight is probably not a result of a bad adjustment, but rather "something" keeping the shoes away from their retracted position.

The wheel cylinders shouldn't be leaking after just 1 year. I'm wondering if they were new or maybe poorly rebuilt?

Brake fluid on the shoes will cause pulling and sometimes shuddering...but definitely pulling.

I'd suggest either the front brakes have been assembled incorrectly and/or with wrong or bad parts, OR the hydrovac is bad.

I'd definitely replace the leaking wheel cylinders (check the rear also, replace the shoes if soaked with brake fluid, and insure things are assembled correctly...per the shop manual. They are simple brakes but even a little thing like putting the anchor block on backwards will cause problems.

If there is still a problem, I'd either bypass the hydrovac OR maybe just disconnect and plug the vacuum hose to the manifold as a test.



http://thenobot.org/images/s2d/s2d_01.jpg

Scott
08-29-2007, 12:28 PM
Thanks for the ideas, guys. I'm going to replace the return springs just in case, but I'll see if the mechanics can try your other suggestions. I don't think the shoes have gotten wet, but I could be wrong. The weird thing is that the shuddering happens a lot, but not always.

The hard pedal might not be related to the shuddering, too. Someone suggested I have the hydrovac bled again and also check and/or replace the vacuum line from the engine.

Scott
08-29-2007, 12:56 PM
I'm glad you got to see it, Dick. The rear brakes were inspected yesterday and everything is in good order back there. I'm not sure if I ever replaced the front cylinders. These could be very old.

Yes, all the flex hoses have been replaced within the last few years including the hydrovac flex hoses just a few months ago.

I just looked under the car at the drums and I don't see any wet spots at all. I also checked the vacuum line from the engine and it looks good, but I noticed it is actually fuel hose and I am able to squeeze it a fair amount between my thumb and fingers. Is this not the right hose to use for vacuum?

I also found out the system has not been power bled. This shop does everything manually (2 people).

41 Frank
08-29-2007, 01:17 PM
Scott you need to get a piece of regular vacuum hose in 3/8 or 1/2 inch whatever it is. Fuel hose is not rigid enough for vacuum use and could collapse inside causing a hard pedal.

fmarshall
08-29-2007, 05:32 PM
"all the flex hoses have been replaced within the last few years" concerns me a little. A good mechanic won't rely on a statement like that. Rather, he/she would make certain that the lines are clear. I would disconnect them and inspect them to ensure that they were not collapsing internally. A few years? How many 2, 7, 10? And does the car get driven regularly, say weekly??

The brake system on our old cars is pretty simple. A simple hydraulic system, if clear, clean, unobstructed and properly serviced will work. The other parts are just linkage and leverage. Without measuring the drums, looking at the brake shoe assemblies, and inspection, it will be hard to tell.

Another thing that could cause shuttering, may be a loose/worn wheel bearing. And it may be possible to not otherwise notice it while driving.

John Kirchhoff
08-29-2007, 09:21 PM
Mashed or crushed steel brake lines will cause problems but at least for me it was delayed application. I'd give the hoses a good going over because the symptoms remind me of when I've had old lines swell inside. If it's only one side dragging, I'd give that brake cylinder a good going over but if both front, I'd suspect the line from the master cylinder to the junction. If you get on gravel or grass, you might get the culprit to skid if it's only one side. There could be rust floating around in the brake lines or hoses and a good flushing might help.

gordr
08-29-2007, 10:51 PM
If, as Dick says, the master cylinder pushrod is properly adjusted, and you are still getting a hard pedal, there could be some trash blocking the relief port in the master cylinder.

As to the brakes dragging or pulsating, look for an out-of-round brake drum up front. When I first got my '63 GT Hawk, it had a problem with the left front brake locking up. Stayed locked, even if I opened the bleed screw. Turned out the drum was egg-shaped, which caused the automatic adjustor to over-tighten. Replacing the drum fixed it permanently. You might be able to machine an eccentric drum, if it's not too far worn, or too far out of round.

Gord Richmond, within Weasel range of the Alberta Badlands

Scott
08-30-2007, 09:09 AM
The front hoses were replaced in July, 2006. The hydrovac and rear hoses were replaced this year. An out of round drum sounds like a possibility, and the worst side is the front left. The right side also seems to be having trouble, too. We don't think the steel lines are the problem, since it bleeds fine.

As for the master cylinder, who knows? It is new, too.

nels
09-02-2007, 08:54 PM
Sort of sounds like a cracked brake drum. Especially the violent part.

JoeHall
09-03-2007, 09:09 AM
If the shoes have even the slightest bit of brake fluid on them they will grab, shutter, pull to one side, etc. I would begin by replacing the leaking wheel cylinders. A leaking wheel cylinder on a car with a single reservoir is a serious safety issue anyway; if it lets go completely you lose all brakes.
Along with new wheel cylinders, I would also replace the brake shoes. The brake fluid soaks into them, and they will continue to 'sweat' the fluid to the surface every time they are heated up (applied).
Joe H

jackb
09-03-2007, 09:41 AM
Sometimes that shudder can be caused by someone having struggled to remove a rear drum/hub assy. then coating lithium or some lube on the axle shaft for easy removal next time...result is that the hub runs up the axle and splits itself...always reinstall the hub/drum dry to torque.

JoeHall
09-03-2007, 11:47 AM
The weird characteristics I was referring to were on the front brakes; when the rears get wet they just lock up prematurely.
The rears are not hard to get wet either; it happened to me a few times when visiting a family member who lived on a hillside. Every time I visited a few hours while parked sideways (so that one wheel was much lower than the other), oil from the rear end would seep past the felt seal and make its way to the insides of the drums. Took a while to figure out, but I never park sideways on a hill anymore, no matter who I am visiting :)

Joe H