Coupe brakes binding

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Brucky
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Coupe brakes binding

Post by Brucky » Sun Sep 23, 2018 8:48 am

Hi all,

After some advice please. My 67 Coupe has binding breaks. I’ve just replaced the calipers with fully refurbished ones (brand new) from GW but they are still binding. The problem is intermittent some times you can hear them dragging and feel the resistance when driving other times she will free wheel with no problem. There’s no difference in pedal feel either. Yesterday after coming out of very heavy slow moving traffic I hit the duel carridgeway got about 10 yards and had to pull over due to the binding. I had an infra red temp guage and put it on the front disks they were at 280c. I cursed a bit, had a row with a cyclists, waited 5 min then drove back home no problems, front disk temp was 80c when I got home. Any suggestions would be greatly appreciate. Thanks John.



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Coupe brakes binding

Post by halfpenny » Sun Sep 23, 2018 8:54 am

Trapped pressure in the calipers. Both front brakes, or one? Could be collapsed hose internals acting as one-way valve. Could be master cylinder (or servo) restricting fluid return.



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Coupe brakes binding

Post by peter freeman » Sun Sep 23, 2018 9:14 am

What servo do you have fitted - if Lockheed then there is a known problem with it having two seals in the piston - -note below.

The problem lies with the piston seals in that part of the hydraulic
circuit controlling the air valve (the white disc on top of the servo
brake cylinder). In order to prevent the possibility of of brake
fluid (very rarely) seeping around the piston - a second 'O' ring had
been fitted to it as a precaution. This can lead to the sort of
problems I experienced when counter pressures in the system are not
enough to overcome the pistons' 'inertia' and return it back to its
start position.

Here is the corrective procedure.

1. Swap the lids from the brake and clutch reservoirs (providing your
car isn't an Auto) - this will enable you to trap a piece of
polythene sheet under the brake reservoir lid (screw it down
tightly), which will reduce fluid loss.

2. Remove 5 screws to separate the valve body. Inside you will find a
rubber membrane - worth checking for holes.

3. Remove 3 countersink screw holding the valve body to the the servo
master cylinder.

4. You will need help here - someone will need to gently depress the
brake pedal while you hold a clean cloth over the exposed face of the
cylinder. The piston (it's only about 8 - 10mm dia.) should partially
pop out.

5. Inspect the piston and note that there are 2 'O' rings. I removed
the one furthest from the 'pointy' end. Clean the piston surfaces
with Meths. and re-insert.

6. Re-assemble as above, remove the polythene sheet, swap the
reservoir lids back and top up the fluid if necessary. Mine didn't
lose much fluid and didn't require bleeding.



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Coupe brakes binding

Post by b.c.flat hat » Sun Sep 23, 2018 9:17 am

Hi John, had the same on my newly-bought coupe. It was a sticking servo, keeping the brakes rubbing sometimes enough to severely impede progress. I found by accident that tapping the brake pedal released the servo fully. However, 'twas only a "get home fix" and annoyed the heck out of the drivers following me what with my brake lights flashing!

I removed one of the two small "o ring" seals on the vacuum piston (underneath the white plastic thingy) but it only lessened the stickiness, I bought a replacement eventually.

I checked the brake pedal and its return spring, the master cylinder and calipers for defects before I found the servo. Best o' luck, Brian.



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Coupe brakes binding

Post by Coupe Racing » Sun Sep 23, 2018 11:11 am

The orientation of the servo can also have an impact on this problem
There is a thread somewhere if you do a search


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Coupe brakes binding

Post by Roger Pennington » Sun Sep 23, 2018 11:55 am

This old thread in the members' technical archive may be the one you're thinking of?


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Coupe brakes binding

Post by Coupe Racing » Sun Sep 23, 2018 2:31 pm

thats the one - thanks


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Coupe brakes binding

Post by Brucky » Fri Oct 12, 2018 8:44 am

Thanks for the input gents, my brake woes still continue and the problem persists. I've put on new calipers, new servo, new master cylinder and I am still having the same problem. Its an intermittent problem that seems to be when the car has been driven for around 30 min, with a good bit of stopping & starting (this may have nothing to do with it). I've been checking the disk temperatures on various runs. Yesterday I could hear the pads dragging. I stopped at the lights pulled off got 10 yards then both front disks locked on solid. I gently tried rocking the car forward with the engine, then all of a sudden the freed up. Any suggestions would be greatly appreciated as I am starting to loose the will to live. :cry:



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Coupe brakes binding

Post by roymck » Fri Oct 12, 2018 8:50 am

Have you got free play on the brake pedal , unless the master cylinder returns all the way back pressure will stay in the brake system . The pushrod should be adjustable ? I have found cars with the wrong pushrods before now .
The effect would be like driving along with your foot on the brake all the time .



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Coupe brakes binding

Post by Brucky » Fri Oct 12, 2018 9:19 am

Hi Roy,
We thought that at the beginning but there is no free play in the pedal. My mechanic says there is no adjustment/pushrod fitted, its a single line system on the car not duel. The servo was supplied by QRG & a new Lucas girling master cylinder has been fitted and the problem is still occurring. I've sent my mechanic this link so I am open to any suggestions at this stage, otherwise its going on the bonfire at Halloween.



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Coupe brakes binding

Post by rebel alliance » Fri Oct 12, 2018 9:40 am

Disconnect the servo pipe and blank the inlet ..then carefully drive it around and see what happens..



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Coupe brakes binding

Post by roymck » Fri Oct 12, 2018 1:45 pm

You say no free playbut there has to be free play at the pedal . A new master cylinder makes me think it’s been fitted with the pushrod as supplied , when I done it the last time I had to change the pushrod from the old master cylinder to the new. And yes this applies to single circuit and dual circuit .
Has this happened since you fitted the new master cylinder?



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Coupe brakes binding

Post by Brucky » Fri Oct 12, 2018 2:42 pm

Hi Roy & rebel alliance,
Thanks for your info. Yes theirs some free play in the pedal, the pedal doesn't drag when it is depressed and returns back to its normal position. Last week we fitted new front calipers, new servo, & new master cylinder to try and fix the problem of the front breaks dragging, and then locking on. However, this hasn't worked and the same fault as before still persists. Today my mechanic advise blanking off the servo to see what happens. I don't think its sh1te in the lines as they have been flushed through. Its going in again tomorrow so all observations are welcome.



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Coupe brakes binding

Post by Coupe Racing » Fri Oct 12, 2018 5:48 pm

Still sounds like the valve on the servo to me

Or the orientation of the servo

There must be free play in the pedal via the actuating rod otherwise the heat transfer from the engine bay will take away any slack if any


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Coupe brakes binding

Post by Brucky » Thu Nov 08, 2018 2:52 pm

The brake problem is now resolve. After changing everything it turns out the car had the wrong pedal & pedal alignment on it from when the previous owner rebuilt her. She now free wheels in neutral which is a novelty for me. The original steel wheels are now refitted & and new recon rad fitted with an extra core, and its driving like a dream thanks for all the advice from forum members.



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