Symptom: Hitchy Brakes

[Whiskey Whistle]

Hello,

I have my suspicion on what needs replacing, but would like y'all's input before I spend more time and money barking up the wrong tree.

While pressing the brakes, resistance against the leg's press is smooth until it hits a wall about 1-2" into the press. Pressing past the wall of increased resistance results in a sudden and powerful brake actuation, visibly pitching the car forward as it slows - and pulling a bit to the right. If the leg continues the press, braking continues to increase. If the leg lifts off and the pedal returns to its original position, then the leg returns to the pedal to press, it immediately meets the wall of resistance again.

I've pressure bled a whole gallon of brake fluid through, trying to force anything out causing a flapper valve. Didn't fix it. I found a small leak in a drum break piston and replaced it, but this didn't fix it either. Then I noticed that this wall of resistance isn't felt when the engine isn't running. Of course, the servo, the vacuum brake booster, I thought. I don't understand enough to realize exactly how it would cause this symptom, but it's my best lead at the moment.

So before I go buying a replacement, is there anything else I should check, or any easy fixes I should try first?

Thanks,
Whiskey

 

[Scotty]

Are you running a brake booster?

 

[Whiskey Whistle]

Are you running a brake booster?

Yes is has a "servo" or vacuum brake booster as it's otherwise called.

 

[Scotty]

Yes is has a "servo" or vacuum brake booster as it's otherwise called.

Well, ok then.

 

[sunalp]

It could be the booster, but could also be the master cylinder leaking past the seals.
You could bypass the booster ( reroute your lines) and see if that makes any difference.
At least that way you could rule out the booster . How old is your master?

 

[Whiskey Whistle]

It could be the booster, but could also be the master cylinder leaking past the seals.
You could bypass the booster ( reroute your lines) and see if that makes any difference.
At least that way you could rule out the booster . How old is your master?

I don't know, since I bought it two years ago. I considered the master cylinder, but wouldn't the affect be felt even with the engine off if the problem were the master cylinder? Since I only feel it with the engine running, that points me to the servo, since it's the only thing that relies on the engine running to work. I have no idea what within the servo it could be, though, since I have no experience with servos. Do i need to replace the whole thing? or can it be disassembled and a common problem easily be fixed somehow?

 

[husky drvr]

WW,

Pictures might help.

Did this issue begin with the rear wheel cylinder replacement?

Is your servo a Girling unit or one of the Lockheed units which have been fitted as replacements?

Do you have any idea of the master cylinder bore size - original or replacement?

Do you have ANY braking action in that first bit of travel - or just a minute amount?

Have you tried disconnecting the vacuum line to the servo and then test driving? It doesn't sound like there's a real issue with the booster. Your description sounds like it's working, just not timed well in its application.

Do you have self adjusting rear brakes or the manual adjustment style?

I'm not positive and someone will correct me if I'm mistaken, but I think the servo does not start boost application until there is some pressure developed in the brake lines to drive the control valve open. That first bit of pedal travel is just volume moving without any pressure development using the master cylinder's output to move all six brake pistons to cause contact against at the friction surfaces. The step up in braking is the servo beginning to supply boosted pressure. With that said, it's possible your rear brakes need to be adjusted a bit tighter - might also be a possible reason for pulling off line. If the rear brakes are loose, then adjusting them tighter will shorten the delay before boost actuation.

If you try adjusting the rear brakes, when you think you've got them tight enough then step on the brake pedal hard a couple of times and recheck the adjustments. That ensures the wheel cylinder is centralized. Both rear wheel cylinders need a bit of "slide ability". If they don't, that's an issue. The rear brakes are a leading and trailing shoe design. Part of the rear brakes force is developed by having the leading shoe's rotational force push through the wheel cylinder to cause the trailing shoe better engagement with the drum.

Sorry for being a bit long winded, but I hope this helps and gives you some ideas.

 

[spmdr]

Sounds like a Booster issue.

Years ago (lots) I had the same problem with a NON-Girling booster kit.

The control piston would not move freely enough.

The fix at the time was to Re-use the original seals on the control piston.

There was no other option, at the time.

The booster worked fine, as the original failure was the seal

of the main piston rod.

Original Girling Boosters, NOT My favorite things!

DW

 

[Acollin]

can a compromised servo cause the “pulling to the right”?

I think husky drvr is approaching the issue properly. When my servo went belly up, my brake fluid reservoir required constant topping off. While I know that there are causes aplenty, the grabbing sounds more mechanical in nature.

 

[todd reid]

The booster should not be a cause of pulling, although it might make the pulling more noticeable do to greater force being applied. Pulling usually attributed to uneven application of force from calipers and/or shoes. If you had a leaking wheel cylinder, did the brake lining get contaminated with brake fluid?

I run a Lockheed servo. I had a problem with the brakes sticking on and found others on the internet who had the same problem. The recommended fix was a stronger return spring (this was in the hydraulic part, not the vacuum chamber). I picked up a couple springs at the local hardware store and found one that worked. If you are running a Lockheed, is it possible someone has substituted a spring that is too strong? Your initial push is overcoming the spring, then the booster is kicking in. This is undoubtedly a longshot, but might be worth a look if nothing else turns up.

 

[Barry]

can a compromised servo cause the “pulling to the right”?

I think husky drvr is approaching the issue properly. When my servo went belly up, my brake fluid reservoir required constant topping off. While I know that there are causes aplenty, the grabbing sounds more mechanical in nature.

Don't see how. A factory Series Alpine booster setup has a single hydraulic outlet and the pressure should be the same everywhere "downstream" of the booster. A "collapsed" brake hose on one side might cause a transient pressure imbalance, but that is not a booster issue.

 

[Whiskey Whistle]

Thanks for all the input so far everyone. Here are pictures as requested. The servo seems to have been replaced. An older one (I assume the original) came in a box with the car. I don't know how old the master cylinder is. The brake hard lines might be orriginal. The hoses to the disc brakes are new.

Issue has existed since i bought it a couple years ago. Just getting around to it now. Brakes are self adjusting. There is some braking power before the hitch. I think bore size is 5/8, or at least it is on the servo.

I think it's likely more than one issue, with the pulling to the right being mechanical, and the hitch aspect being hydraulic. I just adjusted the drum brakes a couple weeks ago, but I can give another try to get them closer.

 

[sunalp]

Those are both Girling boosters, which can be rebuilt. They are expensive though. The reservoir that you show
being 1/2 full is an indication that the booster is sucking fluid into it ( and most likely your engine). A sure way
to tell is to take it off and shake it. I'll be you'll find the missing fluid there.

The lockheed replacements work really well and are much more affordable than rebuilding the Girling unit.
As far as I know, the larger one is available through Moss Motors ( somewhere around $300) and can be
fitted in the stock location.

The old one was removed for a reason, so I wouldn't use it unless you get it rebuilt. The seals inside wear out
and that causes the fluid being sucked into the can.

Keep us posted!

 

[hartmandm]

Agree with your thoughts that you have multiple issues in play.

The booster that is installed looks like the right booster for a series V. I'm thinking the spare booster you have is a smaller booster than what is currently installed. Are they different sizes?

I haven't seen this item before on a booster:


That is where the filter goes. Here is a picture of my booster after rebuild (yes the banjo connector is facing the wrong direction...) :



Mike