Handbrake/rear calliper - How to refurbish(temp).

11 years 1 month ago - 3 years 4 months ago #176 by David Aiketgate
I recently replaced the rear calipers on the MGF, which solved the handbrake problem. Incidentally it also improved the overall efficiency of the braking system.

Being an inquisitive type, I decided to strip the old callipers down, to try to discover the problem with the handbrake mechanism.

Let me say right away:- For me, this was an exercise of curiosity only.
I do not know how long this method will keep the handbrake working properly.
A WARNING
Don't mess with your brakes unless you know what you are doing.

Having said all that, this is what I did.

The caliper showing the handbrake mechanism.




PART A. STRIPPING, FREEING AND REBUILDING.

1/. Firstly, I disengaged the spring using a pair of long-nosed pliers. The spring can now be removed and at this point, attempt to rotate the mechanism. The lever should move freely against the pressure of an internal spring.



Ha! The mechanism was actually stiff, almost to the point of seizure!

[imghttp://www.the-t-bar.com/photos/david/stuff/_DSC0003a.jpg[/img]

Nb.
Please note that any movement of the lever will move the caliper piston out from the cylinder. Using the long-nosed pliers, screw the piston back in (clockwise).



(in this picture the piston boot has been removed)

2/. Remove the 17mm nut and spring washer, and you will see that the lever has a rectangular locating hole that fits onto the shaft.


This is merely a push-fit, honestly! Some Plusgas and a small persuader enabled me to loosen and remove the lever.



3/. Now you can see the shaft seal, beneath which should be some high temperature grease to lubricate the shaft, allowing easy rotation.


This grease degrades over time and usage, and causes the seizing problems. By carefully easing the centre of the seal aside, I was able to insert the feed tube of a can of Plusgas, and used it to flush the solid remnants of the old grease out.



4/. Now I temporarily refitted the lever, and repeatedly manipulated it until the mechanism became free.



Again, you need to remember to screw the piston back in as you rotate the lever back and forth.

5/. The lever should now rotate easily.
The internal spring should return the lever from this position(a)




to this position(b).



6/. I then refilled under the seal with Red grease, which is a special grease for brakes, and rotated the lever to spread the grease further into the problem joint.

7/. I then rebuilt the mechanism by reversing the steps 1 and 2.


I REPEAT:-Don't mess with your brakes unless you know what you are doing. However, if you want to refit the caliper and use it, it's up to you. If so, follow part B.

Part B - REFITTING AND HANDBRAKE ADJUSTMENT


1/. Remove the sliding mechanism(in the concertina sleeves) on the carrier. Clean and re-grease with high temperature grease. Refit to carrier.

2/. To refit the caliper to the car, first refit the carrier to the hub(2x17mm bolts). This enables you to refit the brake pads onto the disc.

3/. Trial fit the caliper unit over the disc and pads, if necessary screw the piston in(clockwise) or out(anti-clockwise) until the caliper is a close fit(1-2mm clearance total.)

4/. You can then re-bolt the caliper to the carrier(2x12mm bolts), and re-connect the brake pipe. Now re-bolt the handbrake arm to the caliper(2x12mm bolts).

5/. Repeat 1-4 for the other caliper.

6/. Make sure that the handbrake cables are free and adjust them (under the centre console) until you can attach both back to the calliper handbrake levers. WITHOUT MOVING THE HANDBRAKE LEVERS. In other words, pull the cable to the lever, do not pull the lever to the cable.

7/. Adjust the cables again until the handbrake levers just begin to move. Your handbrake is now adjusted.

8/. Bleed the brake system. Test the brakes and handbrake are operating properly before road testing.

David
:shrug:
The following user(s) said Thank You: Bob, martin_bmth, graham1

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8 years 8 months ago #43006 by chchezzy
Thanks for the excellent guide on handbrake mechanism stripdown and rebuild with really clear pix. I'll give that a try when I next have a few hours to spare. Looks sooo much easier than changing cables! (which as you say may not sort the problem). I'll report back as and when.

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8 years 8 months ago #43009 by MGF MARK
just a note iv been told by variouse garages

never move the hand brake arm when not on the car with no pads due to the back pressure helps keep the linkage in the correct place
other wise will fail at any time

mad about cars and bikes :)
if it aint broke dont fix it :)
The following user(s) said Thank You: bryan young

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8 years 4 months ago #58726 by chchezzy
Almost given up on summer but in meantime decided to change rear pads. Whilst doing this I removed the sticking caliper from the car as per Dave's guide. The handbrake actuator shaft was very stiff and not returning properly so I tried the WD40 tube down the side of the seal with little success. So I decided to remove the seal (as I think is shown in pic 9 of Dave's guide) and found a mass of crud behind it. This was excavated with small screwdriver and much WD40 applied and hey presto - it came free! Re-packed the cavity with grease but getting the seal back was very difficult - I think it may have got a bit 'chewed' in the process. Anyway, it couldn,t have been very effective before else it would have kept out the crud. Brakes bled and cables adjusted it's all fine again now.
Also fitted a new rear screen (got it from Maidstone trimming, good sevice, looks great) but they go into chapter and verse about never drop the top without unzipping the rear window. Sorry but to hell with that; I just make sure the plastic is flat as it's being lowered down and so far no probs. What does everyone else do?

Bye for now, just off to view the weather forecast..........

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8 years 4 months ago #58856 by squire2710
Never unzipped my rear screen, I always ensure it does not crease when lowering the hood. No problems yet in over two years. Pete

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3 years 8 months ago #176328 by Trikingrider
Any more info on this comment please I'm not sure I follow. Sorry.
The following user(s) said Thank You: COMMANDER

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3 years 5 months ago #178733 by COMMANDER
A great "how to". One question. What level of force would you expect to use when winding the piston
into the cylinder?
Chris.

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3 years 5 months ago #178737 by cairnsys
Difficult to quantify but as I recall and bearing mind that you're holding the caliper in one hand while turning the rewind tool with the other, it's not that excessive. Reasonably stiff but not major.

Robin ;)

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