Sticky Brakes

[Stephen Dow]

I have a 64 TR4 and the brakes have always been a bit "Sticky" that is the car on a flat surface (like my garage) does not freely roll in neutral with the brakes off like my other antique cars.  Recently this has gotten worse and the brakes have been sticking slightly on (all 4 wheels) so when I get home from a short ride they are smoking hot!  The brakes are slightly on all the time.  I have a new master cylinder and I bled the entire system with new DOT3 fluid.  The brake pedal is firm but occasionally soft. Any thoughts would be appreciated. 

Edited September 6, 2020 by Stephen Dow

[Geko]

Good question: 

 

[RogerH]

Hi Stephen,

as per the above link - if you have a valve fitted in the 4 way junction then simply remove the internal parts  - item 43  Here

Check/change any/all rubber pipes.

 

Roger

[ianc]

In addition to the above, check that the pistons in the disc callipers have not become stuck - it can happen, especially if the car is not getting much use!

If the pads are removed, the pistons can be pushed back (using levers) and forth (using foot brake - don't allow them to come too far out of the calliper).

Ian Cornish 

[stuart]

The fact that they are sticking on all four wheels points more to flexible brake hoses breaking down I would have said, when were they last replaced?

Stuart.

[Malbaby]

Have you checked that the master cylinder actuating rod has a small amount of freeplay at rest.

Could be that the rod is tightly fitted and is applying some residual pressure on the brake system.

[Nobbyc]

Do you have a brake booster in the system as the small piston that breaks the vacuum as you release the brake pedal can stick keeping pressure on the brakes.

[jerrytr5]

Not wishing to re-open the fluid debate: Has it ever had silicone fluid in the system? Mixing fluids could cause this issue.

Jerry

[Stephen Dow]

Thank You ALL!  I replaced the master cylinder, front brake calipers, rear brake cylinders and ALL the rubber hoses about 10 years ago when I bought the car.  I flushed out the system with DOT3 fluid back then and I most recently replaced the brake fluid about 3-4 years ago.  As suggested above I removed the  restrictor valve and removed the contents (Just a spring and adjusting screw).  I just got back from a spin and the front brakes spin better.  I think I probably should have removed the restrictor valve when I installed the new "premium" brake calipers.  So the rear brakes are still "Dragging"  At this point I am suspecting the parking brake system which I plan to completely dismantle and replace as needed since the parking brake is non operational and a problem anyway.  I also plan to do a full brake fluid replacement as the current fluid is dirty and over three years old.  I also live in a humid environment so there could be water in the brakes.  Another note, The brakes still ocassionally (not always) get soft and need some pumping.

[Charlie D]

On 9/8/2020 at 1:00 AM, Stephen Dow said:

...the current fluid is dirty...

Stephen,

I think the only reason the fluid can be “dirty” is because some rubber somewhere is breaking down. Not a good sign as it could eventually break down altogether and leave you with no brakes at all.

If it’s 10 years since you replaced the seals etc, maybe it’s time to do it again.

Charlie.

[stuart]

On 9/8/2020 at 1:00 AM, Stephen Dow said:

Thank You ALL!  I replaced the master cylinder, front brake calipers, rear brake cylinders and ALL the rubber hoses about 10 years ago when I bought the car.  I flushed out the system with DOT3 fluid back then and I most recently replaced the brake fluid about 3-4 years ago.  As suggested above I removed the  restrictor valve and removed the contents (Just a spring and adjusting screw).  I just got back from a spin and the front brakes spin better.  I think I probably should have removed the restrictor valve when I installed the new "premium" brake calipers.  So the rear brakes are still "Dragging"  At this point I am suspecting the parking brake system which I plan to completely dismantle and replace as needed since the parking brake is non operational and a problem anyway.  I also plan to do a full brake fluid replacement as the current fluid is dirty and over three years old.  I also live in a humid environment so there could be water in the brakes.  Another note, The brakes still ocassionally (not always) get soft and need some pumping.

If the rears are dragging check the back plates inside where the handbrake lever swivels in the rear of the brake cylinder, they can wear a groove in the back plate that stops the cylinder sliding properly in the back plate, this will give odd brake response on the rear, get the grooves welded up and ground back to original height and use plenty of copperslip when reassembling the cylinders.

Stuart.

[Andy Moltu]

On 9/6/2020 at 11:34 AM, stuart said:

The fact that they are sticking on all four wheels points more to flexible brake hoses breaking down I would have said, when were they last replaced?

Stuart.

One flexible pipe collapsing internally might explain one brake binding but to have all of them would be unlikely as it would require a similar fault to occur at the same time on all 4.  Could theoretically happen if all the flexi hoses had the same manufacturing fault but as they are 10 years old all four suffering the same failure at the same time?

 

If the car has stood for a while it could be the case that all of the seals had stuck so that both slaves and both calipers were seizes to an extent but again 4 separate faults are unlikely.

I would start with the things that would cause the pressure to be maintained even when the pedal isn't being pressed.  So Roger's sticking valve is one as is a faulty m/c or a restriction in the pipework prior to the point that the lines split into left, right, front and rear. My money would be on the maste cylinder