Brakes Sticking On

[kingzetts]

OK, I know this has come up before, so bear with me.

My car, although a 3.8, has a 4.2 brake setup - remote servo on the LHS bulkhead etc. During my restoration 4,000 miles/4 years ago the primary master cylinder/vacuum valve assembly, the vacuum hoses, and all the brake lines and hoses were renewed. I re-used the servo and secondary master cylinder but did split the servo and fit a new diaphragm.

I've always since my rebuild had a slight delay in the brakes releasing. It is worse when hot. So far, so standard. There IS a heat shield protecting the servo/secondary master cylinder from exhaust heat (standard manifolds).

The sticking is getting worse and this weekend on a trip to Wales and back made the car quite unpleasant, verging on dangerous, to drive.

I have fitted a pressure gauge in the line to the rear of the servo (the one which is vented to atmosphere/reconnected by vacuum by the valve on the nose of the primary master cylinder). This shows a normal reduction of vacuum in that hose as the pedal is pressed, reaching atmospheric pressure when the pedal is pressed hard, and shows an instant return to full vacuum in that hose when the brake pedal is released. So it seems to me the vacuum system may not be at fault.

With the engine off and a full vacuum reservoir (it still has the 3.8 reservoir plumbed in) I can hear what I think is the servo shuttle moving back after the pedal is released. There is an appreciable but brief delay between releasing the pedal and hearing the sound. Any thoughts on that - should the shuttle move instantly such that the apparent delay points to the servo being at fault?

Having read the various posts on here, I'm now trying to come up with a good sequence of diagnostic steps. How does this sound to you guys?

Step 1; get the car hot and make sure the problem is apparent.
Step 2; disconnect both vacuum hoses from the servo and drive - if the problem vanishes I have a vacuum problem. If not, I have a hydraulic/mechanical problem.
Step 3; Fit a 1500 psi pressure gauge in the line from the primary to secondary master cylinders. Apply and release brakes. If pressure drops instantly, primary master cylinder likely to be OK, if not suspect primary master cylinder.
Step 4; move pressure gauge to front brake circuit close to secondary master cylinder. Apply and release brakes. If pressure drops instantly, suspect problem with front hoses/calipers. If not, suspect secondary master or servo.

Thoughts?

[Heuer]

Even after fitting a heat shield I still get the same problem, although nowhere near as bad on my 4.2. I wonder whether it is the actual brake servo that is causing the problem given we both have reproduction, or at least new, ones. I was intending to take my car to Ian Nuttall Racing in Nottingham and get their opinion. They specialise in classic racing car preparation and usual have several E-Type's in there. However I will wait to see what you find John!

One thing you could check is the hoses are correct and not collapsing under vacuum.

[kingzetts]

It may take a while :(

Work is very busy right now (despite being officially semi-retired - my clients don't seem to realise this though!) then I'm committed to family stuff until the start of July :?

So serious investigations will probably have to wait until then.

[Heuer]

Off to INR then!

[kingzetts]

Do let us know what they suggest/find. Then I might get there quicker hen I do get started!

[PeterCrespin]

Step 1; get the car hot and make sure the problem is apparent.
Step 2; disconnect both vacuum hoses from the servo and drive - if the problem vanishes I have a vacuum problem. If not, I have a hydraulic/mechanical problem.
Step 3; Fit a 1500 psi pressure gauge in the line from the primary to secondary master cylinders. Apply and release brakes. If pressure drops instantly, primary master cylinder likely to be OK, if not suspect primary master cylinder.
Step 4; move pressure gauge to front brake circuit close to secondary master cylinder. Apply and release brakes. If pressure drops instantly, suspect problem with front hoses/calipers. If not, suspect secondary master or servo.

Thoughts?

Sounds logical, except for Step 2 where I'd disconnect the front side of the servo first and plug it. If the symptom disappears you know it's to do with the front side and vacuum. Then disconnect the back side which could make the brakes drag harder if the front is reconnected. My guess is the pin in the end of the slave cylinder binding which slows the reaction valve, or the reaction valve closing sluggishly due to a weak spring thus failing promptly to re-establish vacuum at the back of the diaphragm and pull the brakes off.

But yes, your sequence is fine.,

[christopher storey]

I had this persistent problem, and if you have detected that the servo shuttle is moving after you release the pedal then i suspect that your problem is the same as mine. I only cured it in the end by reassembling the servo shuttle ( again ) but this time using copious quantities of red rubber grease on all the moving parts, after which the problem never recurred. Those greybeards amongst us will remember Girling crimson brake fluid ; I have a feeling that this had red rubber grease dissolved in it, hence the crimson . Modern fluids, even older ones such as dot 3 which is my preference, definitely do not have the same lubricity as early fluids.

My lifetime's supply of red grease ( A 1 lb jamjar ! ) came from the Morris Minor centre in Sussex

[kingzetts]

Well, it seems that I have resolved this problem, by fitting a new servo/secondary cylinder assembly. Since fitting I have done a few long runs and today went out for 3 hours spirited driving around rural Worcestershire and Herefordshire. There is now no sign of the brakes sticking on even momentarily whereas previously even if acceptable there was nevertheless always some occasions on which brief binding could be detected.

So fingers crossed the problem is solved, for me at least.

Incidentally, to minimise bleeding I was careful to cap off all the hydraulic lines as I detached them from the servo. After reassembly and filling the reservoir instead of jumping straight in and bleeding the system I tried gently squeezing the flexi hose from the reservoir to the servo cylinder and was rewarded with a substantial stream of bubbles out into the reservoir. I found that once no more bubbles were forthcoming, if the system was left alone for a few minutes more bubbles could be coaxed out, so I left the car standing for several hours, squeezing the hose every so often, and in total the reservoir level fell by about a third. So nearly all the air in the new cylinder must have been expelled that way. When we then bled the system a firm pedal was accomplished very easily.

Worth trying as otherwise all that air would have had to come out via the bleed nipples somewhere.

[Peter Harrison]

Hi All, this is clearly a common problem. It is happening to me (series 2 OTS) and looking at many previous entries on the forum, I have checked the reaction valve release spring on the end of the master cylinder. I was disappointed to find the assembly clean and as it should be. If it is indeed the servo - I'll shift my attention. David, can you detect a consensus on this? Regards, Peter H

[Heuer]

My problem was caused by an intermittent leak in the vacuum hose connection together with some air in the front brake circuit and at the moment the problem seems to have gone away. I do know CMC fit a stronger reaction valve release spring (mine has one) which is supposed to fix the problem. So I suggest you:

a) carefully check the condition and connection of the vacuum hoses as any minute leak can cause weird effects. SNG sell the correct braided hose - ?15 for 3' which should be enough for both hoses

b) fit a stronger reaction valve release spring. CMC can sell you the correct one

c) fit the servo heat shield if you have a 4.2 (they were missing on the early cars)

d) be very careful to ensure the brakes are bled properly so don't be miserly with the fluid - buy a 1 litre pack even though the car only requires half of that

e) try replacing the servo/cylinders if all else fails

[christopher storey]

Have a splendid holiday, David

[PhilBell]

My rear brakes stuck on so heavily that they caused a strong smell of friction material, brought the car to a halt as if I had my foot on the pedal and had a little smoke coming out of the wheelarches when I pulled into a layby.
By the time the recovery truck had delivered me back home two hours later and things had cooled off the rear brakes were free. With the car jacked up I could rotate the rear wheels easily with just a light audible drag.
All this was just two days after a 300-mile round trip to the Revival with no obvious problems.
I checked the handbrake and that works and releases properly, but when I ask my wife to operate the footbrake it applies the brakes fully but leaves them binding slightly.
This is with the engine switched off. Many of you have traced binding rear brakes to a sticking servo, but that would require the engine to be running. I guess I'm looking for another cause then.
My 1962 car has the original Kelsey Hayes servo, Coopercraft front brakes and I fitted Zeus rear callipers earlier this year - 2000 miles ago. Until now I've been happy with the brake performance and pedal feel.
Thoughts?

[christopher storey]

So far as I know, there are no sticking problems which are common with the Kelsey Hayes servo, although a brake bias problem does seem to be a hazard of these mechanical servos ( but one would hardly expect that to be intermittent ). Since it is affecting the rears only, a first suspect may be the flexible hose between body and rear suspension . Internal collapse is quite common in these hoses as they age. After that, a master cylinder defect would be next on the list, but it is perhaps a little odd that it is affecting rears only

[PhilBell]

After a jacking the car off the ground I can confirm that the front brakes apply and release instantly with no binding at all, so it looks like I can rule out servo or pedal mechanism related problems.
That just leaves the (rear brake) master cylinder, flexi hose (8 years old) and Zeus rear calipers (2000 miles/3 months) old.
Tried extracting the rear pads but they won't budge. Next test is to bleed out some brake fluid to see if residual pressure in the rear brake circuit is holding the slave cylinders on. If not it must be seized slave cylinder pistons.

[christopher storey]

Phil : undo the bleed screws for a moment or two and then see if you can get the pads out. If pressure is trapped in the cylinders, then the pads will not come out, so it need not necessarily be seized pistons ( which in my experience is unusual on a car which is in use )

[christopher storey]

Phil : undo the bleed screws for a moment or two and then see if you can get the pads out. If pressure is trapped in the cylinders, then the pads will not come out, so it need not necessarily be seized pistons ( which in my experience is unusual on a car which is in use - and equally unusual for them to seize and then spontaneously release a few hours later )

[PhilBell]

Thanks Christopher.
So, tonight's entertainment: opened each rear caliper bleed screw and tried to extract pads - still stuck. Using a combination of mole grips, small blocks of wood as pivots and a screw driver as a lever I managed to extract the pads, which required the edges filing before they'd slip back in easily. Using a small strip of hardwood it was relatively easy to lever the pistons back into their calipers far enough to allow the pads to slip back in. So it doesn't look like they are the culprits. Maybe it was just the pads binding. So, experiment 1: jack each wheel enough to rotate by hand. No drag, as expected. Press brake pedal a few times, release then try to rotate wheels again - drag returns and pads are held too firmly by the pistons to allow extraction.
So I think I can rule out sticking slave cylinders or pads now, which leaves the not very old flexi hose and master cylinder retaining pressure. At least they're easier to change than the rear calipers. I think another axle out job would take away what's left of my sanity.

[PhilBell]

Popped the rear brake master cylinder off last night and found light corrosion on the cylinder bore up to where the piston seal runs (all cleany and shiny where the seals sweeps the bore), and a cocktail of corrosion and sticky gunk on the piston on the non-fluid side of the main seal. Although none of it looks heavy and cleaned up quite easily, I have a zero tolerance approach to cylinder and seal condition so a new master cylinder is on its way.
To prevent water ingress via the pushrod dust cover ruining another master cylinder I will pack the cover with plenty of red rubber grease.
With a new master cylinder and rear flexi hose there's nothing else than can be causing the rear brake binding – I've already verified that the rear pistons and pads are moving freely.
Watch this space.

[PhilBell]

Fixed!

After fitting a new master cylinder and rear flexi hose the rear brakes no longer bind, thoroughly tested the next day by setting off on a 450-mile round trip to take part in the Cromer-Maldon leg of the Coastal Drive. Superb fun.

The problem was clearly caused by water ingress into the master cylinder via the dust seal, so I packed the outer end of the new cylinder/piston with red rubber grease to try to stop it happening again. The front master cylinder beneath it looked nice and clean beneath its dust seal, but I applied a good dose of rubber grease to that one as well. I'll add checking and relubricating this area to my service schedule.

[abowie]

I have had the sticky brake problem in my S1 4.2 coupe.

I replaced the master and booster with new units from SNGB 2 years ago when I bought the car.

When on an incline, if I take my foot off the brake pedal there is a second or two hesitation before the car starts to roll. During this time the pedal is rock hard. When I pulled the cap off the reaction valve there was an obvious hiss of air escaping.

This happens whether the car is hot or cold.

I disconnected the vacuum system and plugged the manifold and drove the car. The brakes no longer stuck. Interestingly the car is pretty driveable without the booster. Heavy braking does require a lot more pedal force but light braking is little different from normal.

I removed the reaction valve plastic cover, and the metal plate bolted to the front of the master cylinder. These are easily accessed after removing the air filter can.

The small reaction valve actuator piston was noticeably stiff to push and I couldn't remove it without using pedal pressure. With gentle pressure I popped it out. The end of the piston outside of the o ring was obviously rusty. It was good to actually find the corrosion.

I wire wheeled it and coated it liberally with rubber grease both on the seals and the reaction valve end. I then put it back and further packed the hole in the master with more rubber grease. On reassembly the car now brakes well.