Handbrake not holding

[peters3103]

I have just had the rear suspension out of my 61 for a diff rebuild and I refurbished the the unit at the same time including new rear brake pads and calliper seals. I didn't replace the handbrake pads as they looked almost new, nor did I (stupidly) check the automatic adjustment or pad clearance. Upon reassembly and handbrake cable adjustment (it was always marginal at best) I note that the cable needs to be fully adjusted to the point of the clevis coming into hard contact with the threaded block to get the wheels to lock but it's insufficient to hold the car on a slope (ie my driveway, hence the need for a working handbrake). Is it possible to adjust the pads at the calliper with the suspension unit in place? I have removed the inspection plate inside the car but it looks tight. With the handbrake released the 4 pads sit close to the discs although I probably need to disconnect the cable from the compensator and recheck the clearance? I would prefer to retain my original setup but an alternative is SNG's compensator upgrade with the cable arrangement. It seems this gives more "pull" than the original. Any feedback on this item?

Regards
Pete

[kingzetts]

Peter,
My comments pre-suppose that you know you have the correct handbrake cable, and not one of the types which are known to have incorrect-length clevis forks which cause premature binding. Search on this forum for threads in which the issue with the cable is well-covered, and if in doubt source a correct new cable.

If this is eliminated as an issue, then first off you need to be sure if you have the automatic adjustment type handbrake calipers or if, as yours is a very early model, you may have the non-automatic type.

The non-automatic type are designed to be adjusted on the car. The factory manual describes the procedure - remove the cover as you have done, put a 4 thou feeler gauge between one pad and the disc, screw in the adjustment bolt (which runs through the centre of the pad) until it nips the feeler gauge, withdraw and repeat for the other side.

As you can see, with only 4 thou clearance, if you can see a visible gap then your pads are probably not tight enough.

If you have the later automatic adjusters, then adjustment should be automatic! As the pads wear, the pad/disc clearance will gradually increase until the movement in the caliper internal mechanism as the lever is pulled is enough to allow the adjustment pawl to advance one notch and tighten the clearance up again. It is possible if the internal adjustment mechanism is worn for the amount of travel needed to turn the pawls over to be greater than the handbrake cable can provide and this is when problems occur (or at least this seems to be the problem I had).

In this case your options are either to strip and overhaul the handbrake caliper adjustment mechanisms (realistically an IRS-out job although some people have said they can remove the handbrake calipers with the IRS in place) or find a means of increasing handbrake cable/lever travel to allow for the increased pad/disc clearances. The latter is what the SNGB compensator does - it gives half the lever/cable travel for a given amount of reduction in pad/disc clearance as the standard design, hence it can cope with twice as much pad/disc clearance before running out of cable/lever travel.

I was involved in the development of SNGBs item so am perhaps biased - so take my comments accordingly.

Good luck.

[peters3103]

Hi John and thanks for your comprehensive reply. It seems my car has been retro-fitted with the later handbrake callipers of the auto adjusting type. Possibly not working as it should. Looking at the pad clearance with the cable disconnected it is perhaps .5mm. I have screwed the bolt on the end of the cable out nearly to the end of its thread (not ideal) and this will get just enough bite to hold the car on a slope. This of course means the clevis is pulled up tight against the block so no more adjustment left. Do you happen to have the measurement of the cable with the shorter clevis so I can see if this might help? I have received details of an easy mod from Dave K which he said has worked for him so maybe worth a try before changing over to the SNGB compensator.

Cheers
Pete

[kingzetts]

Pete,

0.5mm is about 20 thou, but I don't offhand know what clearance is the point at which the auto-adjuster should click over another notch (although I think I vaguely recall from somewhere that you need about an inch of travel of the two caliper lever ends towards each other to trigger the adjusters).

I don't have measurements relating to the clevis lengths but you may find this thread helpful as it includes a comparison photo of the correct and incorrect cables.

http://www.etypeuk.com/forum/viewtopic. ... e&start=20

It would also be worth checking your threaded block in the compensator is the right way round - also described in the above thread. If its the wrong way round you will run out of clevis/block clearance too soon.

Another way to check is to compare the cable travel with the compensator travel. To explain - the compensator mechanism is a scissor linkage. If you disconnect it totally from both the handbrake cable and the caliper levers, you should find that there is an absolute limit to how close together the anchor point for the outer cable (ie the threaded block) and that for the inner cable can be at the point when the linkage itself binds.

At this position you measure the distance from the hole for the cable clevis pin to the near edge of the threaded block, then compare that to the distance from the clevis pin hole in the cable clevis fork to the front end of the clevis fork. If the fork length is the same as or shorter than the gap available in the linkage, then the cable should not be the root of your problem. If it is noticeably longer, then a shorter clevis fork would give you move linkage movement before binding occurs. I believe the correct-length clevis fork will be almost exactly the same length as the gap in the linkage.

You don't have to fit a new cable if your clevis fork is too long - you can either redrill the clevis fork to shorten it, or fit another, shorter fork to the cable - but don't do this unless you know what you're doing.

I've no personal experience of DKs mod but I do know several folk who have found it improves the situation, so again if you're happy with the work involved its a simple and cheap first thing to try if you're sure you have the correct cable clevis length.

Finally, if you like taking measurements, here's something to try; With the compensator disconnected from the caliper levers, measure the distance between the pin holes in the two levers. Then using a cord or strap or something, pull the levers towards each other until you have the handbrake pads as hard against the discs as you can and re-measure. The difference is the amount of travel needed to apply the pads.

The scissor linkage is an equal-length-arms device so that figure is also the amount by which the cable end of the compensator must move, and therefore also the amount by which the inner cable must travel. With the compensator connected up to the calipers and the cable and appropriately adjusted, if you measure the reduction in length of the inner cable between "off" and "fully on" it needs to be at least this same amount and it must not be binding at that point - you need the cable travel available to be longer than the required travel or you have no mechanism to put the cable into meaningful tension to generate some braking force. If you can't get to a point where the handbrake is applied with available cable travel remaining you'll never get much braking effectiveness.

This is all much harder to describe than to see in pictures so I hope it is helpful.

Good luck again!

[christopher storey]

The auto adjustment of the handbrake is wholly dependent upon the screw-in adjuster bolts being engaged with the split pin through the slot of the screw. It is amazing just how many of these setups are missing the splitpin, without which there is no automatic adjustment . It works by the pawl rotating a threaded adjuster along the screw. If the split pin is missing or not engaged, all that happens is that the threaded adjuster rotates the screw with it , and thus does not travel along it so as to effect adjustment of clearance between pad and disc. You can short circuit the whole procedure by screrwing in the scrrew until you have minimal i.e. a few thou clearance between pad and disc, and then inserting the splitpin so as to prevent further rotation of the screw

[peters3103]

Thanks again for the responses. John the adjuster block is correctly positioned and the clevis is "stepped" at the end where the hole is, so a bit tricky to shorten by re-drilling. Christopher the split pins are in place and securing the screws so no issue there. I will continue to fiddle.

Pete

[peters3103]

Thanks for all advice. I seem to have had success. Slackened off the cable and removed the 2 clevis pins from compensator at hand brake levers. I pushed these levers towards each other and got 2 more clicks from each. Re-installed clevis pins and adjusted the cable. I now have a handbrake that will hold firm on a slope at 4 clicks at the lever and in the off position the rear wheels rotate easily by hand with clearance between pads and disc. Doing as it should I guess! I may replace the cable in the future as I think it may be slightly stretched/too long - still needs to be screwed out 3/4 of the way out of the block. Perhaps the JEC replacement. Can this be done with the centre console removed (I need to do this to fit the missing rubber around the handbrake lever) or does the exhaust have to come off?

Cheers
Pete

[kingzetts]

Well done - that's the result you need.

The handbrake cable can readily be changed without removing the exhaust, but yes you do need to remove the centre console (or at least lift it up to provide access to the business end of the lever).

But I wouldn't bother replacing the cable if you can still screw 1/4 of it into the threaded block and the handbrake is working well. Let sleeping dogs lie!

[peters3103]

Yes I think you're right - as long as its working well...

Cheers

[pmansson]

I seem to recall reading about a fairly recent product that operates the handbrake calipers in a different way to the original ones. Perhaps in the Jaguar World Magazine. Before I start going though the pile, does anyone else know about such an upgrade....?

[1954Etype]

Upgrade available from SNG. Alternatively you can mod it by cutting the mounting rod on the compensator and replacing it by welding on a tube. Dave Kerr has further details if required.

[Heuer]

Here:
viewtopic.php?t=6170
and here:
viewtopic.php?t=6072