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MG MGF Technical - Handbrake sticking - rear calipers to blame?

My handbrake light stays on unless I push it down. Searching the archive tells me that this is not uncommon but I can'tseem to find a cure.
Can Anyone help? Will Munns name kept coming up in the archive.

Also, if I decide to replace the caliper, can I use a Rover 800 if there is no MGF in the scrap yard?
Russell Parslow

Hi Russell,

The most likely cause, as I think you've spotted already, is the handbrake mechanism inside the caliper having corroded and partially seized. This means that the return spring is no longer able to pull the cable tight, so the handbrake lever has slack, so it doesn't press against the switch properly.

As to whether a R800 caliper would fit, can't say for sure. I'd say there's a strong likelihood that any caliper that old may not be any less corroded than your existing one. Try www.brakesint.co.uk for a 'new' caliper, AFAIK they are the cheapest source. They don't however supply new crush washers for the banjo bolt, so you may want to track some down - recycling the old ones usually works, but not always...

If your pads are particularly low, you may be able to delay replacing the caliper by fitting new pads, but only maybe!
Mike Hankin

Forget any problem with the calipers or pads. The common cause is the cable adjustment at the handbrake lever.
Geoff F.
G. Farthing

Easy enough to diagnose accurately - chock the front wheels, raise the back of the car, and release the handbrake. Using a screwdriver or some other lever, check whether the arm the cable connects to is returning easily just under the tension of the return spring, or whether it is possible to manually lever the arm back an extra few mm or so.

I agree with Geoff in that the light coming on is due to maladjustment of the cable, but logically something has caused the cable to become slack, and that invariably in my experience has been a partial seizure at the caliper end. The cables are pretty sturdy, so unless you're in the habit of applying the handbrake in Herculean fashion they shouldn't have stretched much.

The point about the pads is that as the pads wear, the adjuster mechanisms inside the caliper move down the ratchet to sections that haven't 'seen action' before, and are consequently the most likely to be corroded, creating too much resistance for the return spring to work fully. Renewing the pads and the consequent winding back in of the piston returns the mechanism to its original start point, which shouldn't have as much corrosion/resistance.

There are overhaul kits available for the calipers which involve renewing the piston & seals - this would I believe give you access to the adjusting mechanisms, and whilst they're not serviceable as such you may find that you're able to clean off the corrosion enough to remove the extra resistance.

You may resolve the immediate issue with some adjustment of the cable, but bear in mind you're probably only treating the symptoms not the underlying cause. Others have sometimes had a degree of success with working lubricant down the lever shaft into the caliper body, but Lucas designed the shaft entry point to be reasonably weatherproof so it's neither easy nor particularly effective.
Mike Hankin

Hmm I have the same issue. Handbrake light stays on unless pressed down. So I've had a look under the cubby bin and the bottom cable (orange) is not moving back, the top on (purple) is moving fine.

So I have subsequently checked the handbrake assembly at the rear wheels and guess what?

Yep the LH assembly is solid - no movement at all. I can easily move the RH assembly by hand and get it to pivot on the spring.

The piston is self is fine and the foot pedal works both sides well.

So is the only solution a whole new calliper?
Steve Ratledge

Not having much luck are you Steve..? You could be the guinea-pig of whether removing the old piston gives enough access to un-seize the mechanisms, but IMHO you will have much less hassle fitting a reconditioned caliper with brand new internals - they're not particularly expensive.
Mike Hankin

I don't have a garage so this time of year it's catch up time on all those jobs that I've put off during the winter. But even the hand brake thing is not the end of the world. I can still use the car and to be honest even with one side it still works very well.

I just need to get it sorted before the next MOT in the autumn.
Steve Ratledge

I'm afraid, Geoff, that its never as simple as that. The cable adjustment at the handbrake just fixes the symptom, in my case, not the cause.
I should have given more detail in my first post but I've already seen at the handbrake adjustment that one cable moves easier than the other and further investigation revealed that it was the left-hand caliper that had a stiff movent of the handbrake return spring.
For those that havent seen behind the cubby box tray, right and left rear brakes each have a cable that goes all the way to handbrake before joining to the lever. You can wiggle both and see which is more free.

Anyway, had the wheel off at the weekend and disassembled as much of the mechanism as I could at the caliper. There was enough corrosion of coponents to make it a bit tricky. There was a very secure rubber seal that I couldn't budge but tried to squirt some WD40 down it and will see if that helps.

Pads are new-ish and good.
Russell Parslow

This thread was discussed between 05/05/2006 and 08/05/2006

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