Brake Problems

vee eight · Post by **vee eight** » Thu Jul 02, 2015 8:44 pm

Hi to all you brake experts, This is for a RHD 4.2 roadster 1967 S1. I have a problem with my brake system and wondered if anybody has had the same or a similar problem or can offer me some advice.

When the brakes are applied and then released, the two front callipers do not release fully and keep some pressure on the discs. Not enough to stop the car moving forward when letting the clutch out but enough to stop it rolling on a gradient. The front brake hoses and callipers (upgraded to Zeus) have been replaced in the last 18 months. Could it be the slave cylinder attached to the servo or the master cylinder or the reaction valve?

Thanks Phil

abowie · Post by **abowie** » Thu Jul 02, 2015 9:36 pm

Reaction valve would be my first port of call.

christopher storey · Post by **christopher storey** » Fri Jul 03, 2015 10:19 am

It may be the reaction valve, although these do not seem to me to be as troublesome as people think . The common fault these days with modern ( dot4 etc ) fluids is that they do not have the lubricity of old fluids, and the servo shuttle has a tendency to stick as a result. Before you go to the trouble of stripping the servo and its shuttle, get some red rubber grease ( a 1lb jar costs about ?9) dissolve a few ounces in some fresh brake fluid , and thoroughly flush the system with the new fluid to see if that helps . I now rebuild all hydraulic components with a mixture of red grease and fluid and it seems to eliminate these sticking problems

PeterCrespin · Post by **PeterCrespin** » Fri Jul 03, 2015 11:37 am

vee eight wrote:When the brakes are applied and then released, the two front callipers do not release fully and keep some pressure on the discs. Not enough to stop the car moving forward when letting the clutch out but enough to stop it rolling on a gradient. Could it be the slave cylinder attached to the servo or the master cylinder or the reaction valve?

Yes.

Assuming you want a better answer (and to a different question), we need more info.

How do you know only the fronts are sticking? Describe the tests you did.

Pete

vee eight · Post by **vee eight** » Fri Jul 03, 2015 8:15 pm

Hi Pete

When the binding brake problem started it was a hot day and it seemed to get worse the hotter the car was and the longer it was driven. When the car was jacked up at the front, the front discs and wheels were very hot (as you would expect) and the wheels were difficult to turn.
The rear wheels were cool and (like a wally) I forgot it was inboard brakes so thought it was only the fronts.

Looking at it this morning, when it had cooled down overnight, the brakes were working as normal and the wheels turned as they should. So I took it out for a run and it was fine until it got hot. When I got back home, it was the same as yesterday, the front wheels were binding. I jacked up the rear and the rear wheels did not seem to be binding as bad as the fronts but it was difficult to be sure.

With the engine running, when the brake pedal is pushed, there is a hiss type sound coming from the area where the reaction valve is located. Is this normal?

Any help would be great as I am not sure where to start with the problem.
It seems that the heat in the engine bay is a big factor as to why it starts off the brake binding.

Thanks Phil

christopher storey · Post by **christopher storey** » Fri Jul 03, 2015 9:32 pm

The hiss is normal. You should try this test : stop the engine, and press the brake pedal 7 or eight times . You should hear a hiss ( which is the release of vacuum ) on each occasion, gradually diminishing. You may also hear a knock from the left hand front footwell which is the sound of the servo shuttle and spring releasing as you release the pedal. As the vacuum is exhausted , the pedal should feel harder . Starting the engine, with your foot on the pedal, you should feel the pedal go softer. All this, if present, shows that the servo , the reaction valve, and the vacuum reservoir are working. What it does not show is whether the servo is sticking on, and this can most usually be detected by the brake lights staying on ( with the ignition on of course ) after the pedal is released, for a duration of between a few seconds and in one case on my FHC, up to 24 hours !

One thing about these test is that if the servo is sticking, then it is likely that all 4 brakes will bind more or less equally. If it is the fronts only, then another possibility is collapse of the internal bore of the flexible hoses to the front calipers, which then act as one way valves and trap some pressure in each front caliper. This is uncommon with new hoses, but quite common with old ones particularly if they have been maltreated by hanging the caliper from them, or twisting them

vee eight · Post by **vee eight** » Sat Jul 04, 2015 9:18 am

Thanks a lot Christopher, some good advice. I will try your test, as you explained.
I have a feeling in my water that it is the servo sticking as both the front hoses have been replaced very recently and the chances of 2 new hoses collapsing is very remote.

Thanks again Phil

PeterCrespin · Post by **PeterCrespin** » Sat Jul 04, 2015 10:25 am

Disconnect vac connection at manifold, plug manifold and drive car. If all is well (except harder than normal brakes) your problem is vacuum not hydraulic.

Have you got all heat shields in place including the large one between the frame rails that protects the servo?

vee eight · Post by **vee eight** » Sun Jul 05, 2015 8:56 pm

Thanks Peter,

Will try your suggestion, sound a good idea, to eliminate one or the other.
All heat shields are in place.

Phil :D

vee eight · Post by **vee eight** » Mon Jul 13, 2015 8:02 pm

Hi all,

An update on the brake problem.
I have concluded that the problem is hydraulic because when the engine compartment is hot after a 15 mile run and I am back home, without the engine running, the brakes are still binding when the brake pedal is pushed. They do free off a little when left for a few minutes but if the brakes are applied again, they bind. They becomes free when everything has cooled down.
Thinking that it was the slave cylinder or servo sticking I have changed the complete unit for a new Lockheed one but the problem is still the same.
After talking to a couple of E Type owners over the weekend the suggestion is that it could be the master cylinder sticking, with one owner saying that it is fairly common for the push rod to cause the sticking problem.
What do you think? Has anybody had a similar problem with the master cylinder?

Thanks Phil

ralphr1780 · Post by **ralphr1780** » Mon Jul 13, 2015 10:09 pm

Phil,
I had a similar issue on my S2 few years back: though it was the servo, then the MC, but finally it simply was the pads that had developed some rust on the edges so they would not slide any more properly back to position when hot. Cleaned the brake guides and put in new pads applying some copper grease and the problem got solved completely. As simple as that.
Hope to have been of help here!

christopher storey · Post by **christopher storey** » Tue Jul 14, 2015 8:17 am

Phil : did you change the fluid and use dissolved red rubber grease as I suggested in my first post ? It is still worth trying this as if you have dragging m/c seals it may cure it

vee eight · Post by **vee eight** » Tue Jul 14, 2015 9:36 am

Hi Christopher,

I have flushed the old fluid out of the system with new fluid but I admit that I did not add the red grease. This was because I had convinced myself it was the servo unit that was at fault and as you know this was not the problem. I was also concerned that if it freed up with the brake fluid, red grease mixture, it might be ok for a while but happen again in the future.
I did not rebuild the servo unit but replaced it with a brand new one and I am thinking of now doing the same with the master cylinder.
If I do this do you know if you need to bench bleed the master cyl before installing it?
Your advice is much appreciated by myself. Can you think of anything else worth trying to solve the problem.
I tried your HISS test and it all seemed ok except the hissing stopped after about 3 or 4 presses of the brake pedal.

Thanks Phil

Ralphr,
Thanks for your suggestion. I will have a look at the pads and calipers in case this is causing the problem
Phil

vee eight · Post by **vee eight** » Sun Aug 09, 2015 10:23 pm

Hi All,

An update on my brake problem.
It turned out to be the master cyl that was causing the trouble. When it was removed from the car, pressing the piston in by hand took a lot of effort and was very stiff. It would not release smoothly and stuck in several places. Took a fair bit of time to find the reason but now it has a new cylinder the brakes are working better than ever before.
Thanks to all you guys that helped with advice.
Phil

Alty Ian · Post by **Alty Ian** » Sun Sep 20, 2015 11:50 am

On my S1 4.2 in which everything is brand new,.... the rear brakes keep locking on, only the back brakes, not the front. The reaction valve is part of the problem as it isnt releasing, (when I fiddled with it the vacuum released and we were able to drive it home) then dismantled and red rubber greased it but still happens.

Now with no hydraulic pressure apparent the rear pads are still solid as the car was driven a few hundred yards with them partly on and I cannot seem to free them off.

The pedal is rock solid, has been all along and the brakes did work when driven but wouldnt release.

I have checked and double checked everything is fitted right but still I cannot see why this is happening when the reaction valve appears loose, I am beginning to wonder if the servo unit is an issue as well if, as it seems brake pressure only seems to be going to the back brakes.

Completely baffled at this moment and in need of some ideas? Anyone got any thoughts what to look for next?

Post by **mgcjag** » Sun Sep 20, 2015 3:43 pm

Hi Ian....If you release the white plastic cover on the reaction valve does the pressure release if so look at the tiny piston in the end of the master cylinder that operates it is it getting stuck.....on mine it was and caused by the metal operating flap inside the master, it looks like a stamped out piece of metal, rounded edges one side square on the other....I turned mine around and all was ok. ...can't remember what way around it should be....hope this helps... Steve

christopher storey · Post by **christopher storey** » Sun Sep 20, 2015 5:41 pm

Ian : the common problem is that the servo shuttle binds sufficiently to prevent the large spring inside the vacuum unit from returning the operating rod to its proper starting position . This is where the red rubber grease is so useful - it lubricates the seal to bore interface and prevents this binding . It is a pain to have to dismantle the servo cylinder and the vacuum cylinder, but is worth doing in the long run . Another possibility worth checking is that the flex hose to the rear suspension has not suffered internal bore collapse

andrewh · Post by **andrewh** » Sun Sep 20, 2015 8:29 pm

Ian, are you using Green stuff pads? On my 3.8 they were binding in the calipers and sticking on and getting hot, expanding the hydraulic fluid and adding to the problem. I had to buy some new pads as the ones I had in there had glazed, but I filed them down a bit on the sides and cured the problem.

vee eight · Post by **vee eight** » Sun Sep 20, 2015 10:17 pm

I agree with Christopher, have a good look at the rear brake hose. If this has collapsed it would be causing exactly the problem you are having.
It could also be the piston in the slave cylinder (the one for the rear brakes) which is sticking in the opperated position and applying presure to the fluid to the rear brakes.
If you unscrew the bleed nipples on the rear brakes and let some fluid out, do they release? If they do then the calipers are more than likely ok and it could point to the hose or slave cylinder.
Good luck. Phil

Alty Ian · Post by **Alty Ian** » Mon Sep 21, 2015 10:05 am

I am certain its the servo sticking, I can bleed the rear brakes no problem, but the front brake pedal stays rock hard with BOTH front bleed nipples open! ALL the brake pressure is going to the rear and then to compound the problem, the reaction valve also sticks which locks up the rear brakes. If I remove the cap and fiddle with it it hisses and releases the pressure enough to move the car again, but as soon as I press the brake pedal it locks up again.

There is nothing wrong with the pipes or hoses, the only other issue I now have is that the rear brakes got so hot the pads (not green stuff ones) are stuck on (I have previously removed the pads twice and filed them so I know they fit OK).

I have checked and double checked the piping etc and its all correct.

To be faced with dismantling both the master cylinder AND the servo both of which are brand new is really annoying.

I am sure Chris is right about pistons sticking as when I orginally bled the brakes I was able to get all air out and brakes worked, but since I added the vacuum pressure its all gone haywire.

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