Front brakes seizing after a short drive.

[Castanley]

Hi guys, I was wondering if any of you knowledgeable folk could give me any insights on a braking problem I'm having?

After a month of hard work my newly acquired Series 2 (803cc) is now back on the road. In a previous little test drive I noticed that after driving a few miles the front brakes started to bind more and more up to the point where the poor engine struggles to pull the car. Returning home, the rear wheels are warm (as expected) but the fronts are too hot to touch. The previous owner had recently fitted new shoes & wheel cylinders, and also a new master cylinder. I took the fronts apart and everything looked good in there so I just copper-greased the contact points and reassembled them.

Fast forward to today, I took it out for a longer drive but the same thing happened after about 7.5 miles. Car became sluggish so I pulled over for a while to let the wheels cool a bit. After a few minutes they were seized solid (brake pedal was solid too) and I couldn't drive the car an inch resulting in a 2 mile walk home.
I returned to check on the car after an hour and the brake pedal had softened up again so I was able to drive home with no problems!

So, given that the shoes & wheel cylinders look fine and seem to operate correctly, could it be a master cylinder issue maybe? That's the only thing I haven't investigated yet. I'm only a rookie at this but I'm having immense fun learning!

Apologies for the long waffle but hopefully someone might know what the problem is.

Thanks,
Chris.

[Trickydicky]

First check is that the master cylinder is adjusted correctly, check the manual for the correct setting.
I think it should be 3/4" free play at the pedal.

[Castanley]

Thanks Richard.
I do have an original workshop manual so I'll have to take a look.

Chris.

[simmitc]

From your post, it looks like the brakes are of original drum style, but if by any chance they have been converted to discs then it is a common problem caused by failing to remove the top hat seal from the master cylinder; but I stress that this applies only if converted, and I don't think your are.

[Castanley]

No I've heard about that little mod needed for disc brakes too but mine are just the original drums.

Chris

[liammonty]

I would check what others have said - I’ve experienced a problem with a master cylinder that caused similar symptoms. First though, I would check the cheaper things - firstly, are the return springs present, correct and strong enough to return the brake shoes after you release the pedal? Secondly, how long is it since the flexi hoses were replaced? Quite often, they can collapse internally while looking ok on the outside. When you brake, the force of the fluid makes it through the swollen innards of the hose, but the resistance is too much for the return springs to overcome as they attempt to return the shoes and push the fluid back from the wheel cylinders through the flexi hoses en route to the master cylinder.

Good luck - you’ll get there!

[martin418]

over adjustment can cause this as the drums heat up they expand and stick on the brakes , i went through a similar issue which i found was caused by weak brake shoe return springs worth a try especially if the springs are fairly new and likely to be of poor quality

[Castanley]

Yes the springs are present and although they're not new, they seem to be in very good condition and like I said, the brakes seem to work perfectly for the first few miles before the front brakes start to bind more and more. The fact it only seems to happen on the front wheels makes me wonder if fluid is slowly leaking past the piston in the master cylinder that controls the front circuit.

As for the hoses, one side looks brand new and the other side looks old. Talk about skimping on the repair bill! I think it would be a good idea if I replaced the old hose in the near future.

Not sure about over adjustment but as all the brake shoes are brand new I backed off the adjusters all the way, just as a test, so there was definitely no brake binding before I started driving. It seems like the problem slowly builds up each time I press the brake pedal during my drive. Once they start to bind badly then I leave it about an hour and everything returns to normal!

Chris.

[philthehill]

I would suggest that the recuperation valve in the master cylinder is not allowing the brake line pressure to return to normal. There should be some line pressure (to keep the seals against the wheel cylinder walls) which is controlled by the recuperation valve.

It may be as simple as adjusting the master cylinder operating rod to allow the piston to return fully back against the circlip.

[Castanley]

Thanks Phil, yes that sounds like a very likely candidate based on what's happening. I'll definitely have to do a bit of research on that.

Chris.

[Castanley]

FIXED!

Thanks to philthehill who was pretty spot on with his suggestion. It was indeed that the piston in the master cylinder wasn't fully retracted when the brake pedal was released. Whoever fitted that new master cylinder (just before I bought the car) adjusted the operating rod for the correct amount of free play. Then they screwed the floor panel back into place. Now as you know, the floor panel does have a cut out for the brake and clutch pedals, however as you screw it down it does actually depresses both pedals by about half an inch. This effectively lost any free play in the MC and probably blocked off the recuperation valve even when the pedal was fully 'up'.
I have slackened off the floor panel screws around the pedals, allowing it to pop up enough to allow the brake pedal to come all the way up and surprise surprise, the car now drives fine with no brake issues.
All that remains is to adjust the MC for the correct clearance even with the floor panel screwed down. I'm going to get it all checked by a professional though because I'm only a novice spannerer and the brakes are fairly important!

Chris

[philthehill]

Glad to hear that it is now all working correctly.
To set the master cylinder operating rod correctly before fitting the floor panel - put a piece of flat bar across the chassis rail opening - just below where the pedal would normally come through the floor panel. Secure the flat bat with one or two floor panel screws screwed into the floor panel captive nuts. This replicates the situation as if the floor was in place. Adjust the piston rod so that the piston comes hard back against the master cylinder piston securing circlip plus a small amount of clearance between operating rod and piston. Remove flat bar after adjustment - then when fitting the floor panel it can be safely assumed that the master cylinder operating rod has been set correctly.
Make sure that the brake pedal return spring is effective and secured to the loop bracket in the bottom of the chassis leg.

[Castanley]

Thanks Phil, that's good advice. I like the idea of using a piece of flat bar to simulate the position of the floor panel!
I did check the condition of the pedal return spring and it looks to be fitted correctly.

Chris.