brakes getting stucked

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brakes getting stucked

Post by jvasabra » Thu Jun 21, 2018 9:15 am

Hello,
I have a problem at the brakes, and I need the wisdom....
After winter stop , already in 2017, I had on the first trip the brakes beginning to foul the drums/disks and getting warm till it was impossible to move the car. Once cooled everything was back to normal and all Summer was ok.
This year I have the same problem , but now it stays. So I need a solution. I willl explain exactly what happens and what I already did.
When cold no problem. Pedal is as always, some play, then good pedal feel and good braking.
I checked the movements of rear and front brakes all ok, brake shoes move to the drums and release as they should. No leaks at all. Handbrake works ok too.

After driving (mostly city traffic) for 8 miles the brakes start to get stuck. The pedal then feels very different, there is no play at all and it is very stiff, and you cannot control the brake force. Brakes are less efficient for sure. After another say 5 miles they are so stuck that when stopped the engine has difficulties to get the car moving. Rear drums get very hot of course. The brake lights are ON, even when one does not push the pedal.
Once cooled, 15 minutes, everything is back to normal , brake lights off too. And the whole process starts over when driving...

I bleeded all brakes , although the brake liquid was clear , it has been in for 3 years. After bleeding, no air came out, I removed the rest of the lquid of the main brake cylinders' reservoir and filled it with new DOT 4 ( as was always used).
I retried , but the same as explained above. I got the car on a hoist, so now I know also the front brakes are stuck, once cooled front and rear are free again and move on/off as they should.

I now think that it is something at the main brake cylinder, but I thought that when this one gets stuck the pedal stays low ( towards the bottom) and in my case it immediately tries to brake when the "thing" happens.

Before I remove the main cylinder and change the rubbers I would appreciate your ideas.
Thanks, Jacques
PS I need the car in top condition because we have our annual Sabre/Sabra meeting in September in Belgium.



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brakes getting stucked

Post by philhoward » Thu Jun 21, 2018 9:37 am

It does sound like the master cylinder isn’t releasing the fluid back into the reservoir, hence why you get trapped pressure (keeping the brake switch on).

I’d say a rebuild of the master cylinder is in order?


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brakes getting stucked

Post by scimjim » Thu Jun 21, 2018 9:38 am

I presume there’s no servo?


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brakes getting stucked

Post by philhoward » Thu Jun 21, 2018 9:44 am

scimjim wrote:
Thu Jun 21, 2018 9:38 am
I presume there’s no servo?
I assumed there isn’t.


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brakes getting stucked

Post by chrisgallacher » Thu Jun 21, 2018 9:47 am

I've had exactly this in my Sabre Six Jacques, way back on the Classic Marathon in 2003.

Presumably you have a hydraulic brake light switch? Since the brake lights stay on without the pedal being pressed when this happens, that means the fluid is under enough pressure to operate the switch - as well operating the braking components. In other words, you don't have some sort of purely mechanical binding with one or more calipers/wheel cylinders or whatever.

I discovered on mine that where the brake-pipe junction & hydraulic switch is, on the left front chassis member, there was also what looked like a short (50mm?) in-line length of hexagonal bar - just brake pipe in, brake pipe out, nothing more. IIRC it screwed directly into the brake pipe union. I was never entirely sure what it was supposed to do, but I recall Adrian Stapley suggesting it was some form of anti pad knock-back device. Early Sabres can suffer from this - mine certainly did (badly) until I changed the stub axles.

My symptoms were that brakes were all fine on the open road until I applied them - when they would stay slightly binding with the brake lights on until after a while the hydraulic pressure reduced and all was normal again. Clearly this was worse in town with the brakes being applied frequently.

I was stumped by this, until I removed the anti knock-back device (if that's what it was) and the problem disappeared never to return. I can only assume it had become sticky internally, keeping the brake fluid under some pressure after the pedal was released.

Hope this helps.


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brakes getting stucked

Post by jvasabra » Thu Jun 21, 2018 9:54 am

Hello,
Quick reply.
There is no servo, everything as per Original set up.

There is no extra device at the brake lights hydraulic switch on the left front chassis member.

I wait for some more info , then attack the master cylinder.



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brakes getting stucked

Post by scimjim » Thu Jun 21, 2018 10:06 am

I can’t imagine how something inline could be an anti-knock back device, without continually keeping pressure in the system?

Was it inline with the front or rear brakes?

Sounds like a proportioning valve to me - limiting pressure to the rear brakes with a simple spring?


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brakes getting stucked

Post by philhoward » Thu Jun 21, 2018 10:12 am

Could be a delay-return valve, but you can also get residual pressure valves which keep a little pressure in the system (which could help with pad knock-back)?

Back to the original issue - don't forget to inspect the cylinder bore as if it's corroded in any way, the new seals won't last very long at all.


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brakes getting stucked

Post by chrisgallacher » Thu Jun 21, 2018 10:20 am

scimjim wrote:
Thu Jun 21, 2018 10:06 am
I can’t imagine how something inline could be an anti-knock back device, without continually keeping pressure in the system?
Yep, I've been musing over exactly that point Jim. It was many years ago!

This is the thing, dug out from my man-cupboard:
IMGP4267.JPG
IMGP4267.JPG (123.26 KiB) Viewed 802 times
TBH I can't recall if it was inline with the front or rear brakes, but could check. It's not simply a spacer - if you unscrew the union there is some springy witchery inside the hex bar. I never knew whether it was original fitment or an after-market add-on.

All I know is that removing it coincided with the problem disappearing never to return, and I've never missed whatever benefit it was supposed to bring either. At the risk of hijacking Jacques' thread, anyone know for sure?


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brakes getting stucked

Post by philynnbob » Thu Jun 21, 2018 10:23 am

Have similar arrangement on straight 6
Front brakes only
6EDB93BF-9A28-42A8-8736-CA2BD40FF6AA.jpeg
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brakes getting stucked

Post by chrisgallacher » Thu Jun 21, 2018 10:32 am

Maybe you have one too Jacques, but like in the pics above it's not located at the brake switch union where mine was. Looks like it was original fitment though.

I'm pretty sure removing mine cured the problem I had, not just coincidence.

Edit: having said that, if it's inline with the front brakes only it's difficult to see how a faulty one could keep the whole system pressurised and operate the brake light switch too.


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brakes getting stucked

Post by scimjim » Thu Jun 21, 2018 11:12 am

Maybe take it for a drive and confirm if all 4 brakes are getting hit or just front/back?


Jim King

Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), Sabre/MX5 auto (The Flying Broomstick),
1300 SS1 (Number One) & Sarah's coupe.
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brakes getting stucked

Post by jvasabra » Thu Jun 21, 2018 12:39 pm

Hello,
I can confirm that alll brakes are stuck ( front and rear).

Rechecked on the car and there is no such device installed.
Jacques



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brakes getting stucked

Post by b.c.flat hat » Thu Jun 21, 2018 12:44 pm

I'd start at the pedal, is it returning to the brakes off position freely?
Next would be the master cylinder piston, is it moving in the cylinder freely and not sticking so as to prevent pressure release fully?
As both drums/ discs are mentioned in the first post, that about covers things that affect all brakes at the same time?



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brakes getting stucked

Post by jvasabra » Mon Jun 25, 2018 8:42 pm

Problem solved.

I got the master cylinder out and it was a bit rusty/dirty were the plunger begins, so the part where the push rod pushes. I cleaned and checked and no damages inside the master cylinder's body.
I changed the seals, etc and evrything works and after a test drive with a lot of braking, no sticking brakes any more. The pedal goes lower that I was used to, but I will adjust the rear brakes and that will sort it , I am quite sure.

Thanks for the input all.
Jacques



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