Sticky Brakes

[80 XKE]

As I approach a roundabout in my 1962 'flat-floor' "E" Type at a normal to slow speed, I apply the brakes and they do not "come off" after taking my foot off the pedal.
I would appreciate any advice as to what the problem/s may be.
Many thanks,
Geoff.

[ChrisC]

This could be one of two things in my humble opinion. A partly collapsed flexible brake hose acting as a one way valve or a sticky piston in the brake calliper.

A collapsed hose is more common than you would think. The rubber breaks down internally over time and you cant see it so you think its fine. I have had one car lock the brakes on because of this.

A sticky piston is easier to check for because if you can move it to remove the pads it may well be fine but I am not a mechanic just an enthusiast

[00series]

I had the same issue on my S2, which now seems to have now been simply cured as i just fitted new goodridge brake hoses (SNG are currently doing a deal on them) to the front calipers & as i bled the brake loads of black stuff shot out of the NS Front bleed hole - which must have been causing the NS caliper to stick on, the off side caliper fluid was perfectly clean.

The brakes now work better than ever - but I will soon be rebuilding the calipers & properly flushing the system as a safety measure.
i'm not saying that a simple brake bleed will fix your problem - but you never know it might be worth a try.
Good luck, Bert.

[1954Etype]

Which braking system do you have on the car? Is it the standard bellows system with the dunlop pistons?

[38E]

Have you had one of the Dunlop master cylinders rebuilt recently? Because there seems to be a problem with aftermarket seals sticking and causing this problem.

I had this same problem (on the fronts only) after I had installed a new seal kit in one of my re-sleeved Dunlop cylinders. I cured it by substituting a used original seal I had that was still serviceable.

There is another sticking problem you can get with these early cars and it concerns incorrect set-up of the boost assist. There is a cam on the assist linkage which needs to be set correctly (together with a vacuum gauge at idle RPM, IIRC) and this is explained in the manual.

As mentioned above, it could also be caused by an old deteriorated hose.

[80 XKE]

Firstly, my thanks to Chris C, Bert, our Moderator and Clive for their kind suggestions.
This response is a little late, but it has taken a few days to track down the details of the car's current braking system. It transpires that in 2002, during a total re-build, the car was fitted with a complete Coopercraft High Performance Braking System which included a new servo, pedal box and all the ancilliaries which apparently brought the spec up to 4.2 standards. The car has covered only 5.500 miles since the restoration.
Any further comments will be much appreciated,
Thanks again,
Geoff.

[christopher storey]

If this is now a 4.2 system, the servo will be the remote one attached to the left side toeboard. If it is not a problem with the reaction valve which controls the vacuum - this is the white plastic device on the front of the pedal master - then the problem you describe is very characteristic of the shuttle sticking in the servo master cylinder ( others call this a slave to differentiate it from the pedal master cylinder) . There is no sure test to establish this, but it tends to be less of a problem if the vacuum side of the system is disabled , so the first test I would make would be to exhaust the vacuum by several pedal applications with the engine off , and then see whether the brakes are still sticking on . In particular, get a helper, or a mirror, and see if the brake lights stay on . If they do, then it is a strong pointer to this being the problem rather than a collapsed hose acting as a one way valve . The only sure way of curing this is to dismantle the servo master cylinder and, if the parts are in good condition, lubricate the seals thoroughly with red rubber grease and reassemble .

The only good bit of news is that if the car has suffered from disuse, sometimes, and I mean sometimes, it may cure itself with plenty of brake applications , but frankly I am not very hopeful of this

[GSR 54D]

Over the last 3-4 trips in my 4.2 I've started to notice my brakes staying on a second or 2 after releasing the pedal more so if I've applied pedal pressure gently over a longer period. I have tried the test that Christopher suggests in the above post (engine off) and the brakes are fine and not staying on. I changed the master cylinder seals 18 months ago and re-bled the brakes again 8 months ago. The vacuum does not appear to be leaking because even after a week, with no engine run, when I fiddled with the reaction valve a lot of vacuum was released.
Problem has only started to occur in last month and was wondering what you experts think?

Thanks

John H.

[christopher storey]

John : I should try to determine whether all 4 wheels are sticking on, or whether it is only some of them . If it is one front only, or both rears only, then it is a pointer to a collapsed hose operating as a one way valve. If,however, all 4 are sticking on, then it is likely to be a master cylinder or servo problem. If the servo is functioning , you should be able to hear a knock from the left hand toe board on each pedal application ( until the vacuum is exhausted). If there is no knock, then I would suspect a sticking servo shuttle

[GSR 54D]

Christopher

Thanks for info. plenty of knocking coming from the servo. Tested servo and reaction valve using vacuum gauge today using guidance details from a previous "Brake problem" post copied here.

The servo is controlled by the reaction valve, on the front of the
master cylinder. To test the servo, disconnect and plug the hose
going to the backside of the servo. With the engine running, that
should have the brakes fully applied without you having to touch
the pedal. If that works, then replace the reaction valve, and
you'll probably be OK.
You can test the reaction valve by putting a vacuum gauge in that
same hose. With the engine running, and your foot off the pedal,
you should see full manifold vacuum in that hose. As you depress
the brake pedal, you should see the pressure rise. With the pedal
applied firmly, the hose should be at atmospheric pressure. The
other hose going to the servo should have full manifold vacuum at
all times. If it doesn't, then you may have a collapsed hose
between the manifold and reservoir, or between the reservoir and
reaction valve, or a failed check valve on the reservoir.

Have stretched the spring slightly in front of r.v. which may have helped or might be a coincidence since all ok on test drive today.
If this reoccurs it will be attempting to check each wheel independently at a convenient time!

Cheers

John H.

[Neil1624]

Hi all,

I've had a similar problem in my '66 RHD series 1 OTS, the brakes sometimes stick on and require a 'double tap' on the brake pedal to get them to come off.
This was noticeably worse during a trip to the Le Mans classic last year after the car had been in slow moving traffic for an extended period, I don't know if on that basis heat soak was an exacerbating factor. All components in the braking system have been overhauled and/or replaced over the last 2-3 years.
Goodrich hoses have replaced any rubber based flexible items.
An annoying spasmodic fault !

Best

Neil

[PeterCrespin]

Have you got the lower heat shields, especially the one between the upper and lower frame rails to protect your servo?

[1954Etype]

Neil,

Petes post could be spot on. Can you confirm that you have the shield, if not, strongly suggest you fit one. If you don't have one and fit one, can you report back on your findings? I know of one guy this happened to but it was a couple of years ago. He fitted a temporary shield and the problem went away. Be good to know if it fixes your problem as it adds more credibility to the solution.

[Neil1624]

Hi all.

The quick answer is no heat shield fitted, on that basis and following what would appear to be sound advice I'll get one fitted and report back.
I'm planning on attending the Classic at Silverstone in a couple of weeks so should have some feedback reasonably quickly.

Best

Neil

[Heuer]

Sage advice indeed! My wife navigated us into the centre of Blois yesterday to see some sort of Chateau and the resultant heat soak started to affect the brakes much as described - 'sticky' and spongy in my case. As soon as we cleared town and I could get my foot down and with lots of air moving through the car the brakes returned to normal. Good luck with finding the shield/brackets though. Angus pointed out my car lacked one so I started looking for one. Dave Kerr makes the shield but was waiting for stock and does not have a pattern for the brackets. SNG did not have a clue what I was talking about despite giving them the part numbers (they are in another recent post on the Forum if you do a search) and promised to ring me back but never did so I had to wing it without one.

If anyone has a spare bracket please can you send it to Dave so he can make some up as it seems he is going to be the sole source of these parts apart from XK's Unlimited in the US. As for us we will be staying out of towns and making sure the car gets lots of air

[1954Etype]

David, it is probably my fault for pointing it out in the first place as you've never had this problem before?!

Good luck with the rest of the tour and try and keep the MPG reasonable.