Dragging disc brakes

[Tom Brearley]

My front brakes are binding up and dragging , causing the discs to get very hot. And probably not doing much for the car's performance either. This seems to be the case on both sides, so may perhaps be due to lack of use during the lockdown. Could I have your advice on the best way to free them up please?

Tom

[Ian F]

Tom, I think it depends on how old those calipers are? If they have been on the car for a few years the pistons may be corroded and may be best replaced.
If the pistons are good then I would take the pads out on one side at a time and gently depress the brake pedal - just enough to get the pistons moving. You may need to do it one pad at a time. A helper is almost essential so that you don't pop the pistons right out! Be gentle!
I use some red brake grease around the piston to help keep it moving. If you manage to get some movement in them all then they should retract enough not to bind.

Ian F

[Peter Cresswell]

Ian - I fitted new ones from MGBHive to my roadster. One word of caution though with new ones - the rubber dust seal seems to be too strong and they retract the piston back into the caliper, resulting in no brakes when you first push on the pedal! The do improve with miles (about 2000+) and you do get used to braking with two pushes. A bit of brake grease on piston does improve things for a while but the effect doesn't last long!

[Bumpa]

What age is the MGB? What kind of brake light switch does it have, the hydraulic one plugged into the four-way union, or the mechanical one operated by the pedal? If the latter type, it is not unknown for the switch to be holding the pedal from reaching its rest. Try unscrewing the switch and see if the binding goes away.

[Tom Brearley]

Many thanks for all the suggestions.

Well, some progress...

I have a hydraulic brake switch so I tried exercising the pistons with a smear of red rubber grease, they being a newish pair. But there was no improvement. It then occurred to me that I'd recently fitted new metal shims to the back of the pads. Could they be the problem? Re-fitting the old shims was no improvement but oddly re-fitting an old set of pads without any shims showed the problem was indeed the thickness of the pads.

Why they have started being a problem now, when I've been running shims for 100s of miles is a mystery.

Anyway I like the pads, which are Mintex V8 size, so taking some friction material off them might be the way round this. Unsatisfactory as it is.

[Ian F]

Sounds like the non standard pads might be too thick?

Ian F

[Tom Brearley]

Well, the pads are the same thickness as standard ones. It's the shims needed to stop them squealing that add an extra mm or two. Investigations will continue!

[Ian F]

Tom, perhaps if the pads are a different shape to the ones you have been using, could they be not seating properly on the disc? I'm thinking of the raised edge around the disc caused by corrosion. This often adds a little thickness to the disc (all that oxygen combined with the iron I guess).

Ian F

[Peter Cresswell]

The V8 pads use the same backing plate as the normal B, it is just the material is a bit longer but not if I remember correctly wider. I don't fit the anti squeal shims but just coat the back of the pad plate with a smear of Copperslip in the area where the caliper piston will touch it. Also I have in the past had to rub down some MGA pads using a piece of glass as a flat plate and some very rough (I can't now remember the grit grade) emery cloth because of a similar problem, but the reason was the piston wouldn't retract enough because of rust!

[Tom Brearley]

I've experimented with taking the backings off the pads and that does stop them binding. So it would appear to be the thickness rather than the shape that's the issue.

The pistons can be retracted right back with a rewind tool. But in actual use they always have a mm or two protruding from the calliper.