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8 & 10 cyl Bristol cars From Type 407 onwards

410 Handbrake

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Old 10-08-18, 11:07 AM
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Default 410 Handbrake

My 410 has "always" been somewhat on the edge when it comes to achieving the stopping power required of the handbrake for the MOT test (for those outside the UK that is the official name for the annual fit-for-purpose test), relying on a sympathetic tester with a very strong left arm to get a pass.

I had been wondering about this situation when the same sympathetic tester suggested it might be cheaper to get the handbrake pads relined rather than buy new. This wasn't actually the case but it did allow me to specify a "soft" material for the pads, reckoning that I needn't worry about brake fade but it would be nice to have a handbrake that might stop the car in an emergency.

My word it's made a difference. I know we in the UK no longer have to worry about an MOT pass on cars over 40 years old, but the fit for purpose requirement still stands and the handbrake is now fully fit for purpose.

But here is another problem.

Whilst inspecting the newish soft handbrake pads the other day with the same sympathetic tester we noticed that, whilst the callipers open and close with ease and the return springs work perfectly, the callipers themselves are slightly unbalanced. This unbalance causes the inside pad to just touch the disc, on the heel of the pad, whilst the calliper is open. The pressure is infinitesimal, but this contact would explain why one pad wears asymmetrically, which I attempt to show in the attached photo (which is of a "hard" pad material)

This wear pattern means that the effective surface area of one pad on each caliper is significantly reduced over time, making it harder to both meet the MOT requirements and to stop the car in an emergency.

We have tried to balance up the imbalance with the aid of a very light spring, but I doubt that this will provide a long term solution.

I would be very glad to hear from anybody who has experience of this latter issue and has come up with a long term solution.

Roger Morrall
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Old 10-08-18, 06:08 PM
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I'm not familiar with the design on the 410 handbrake caliper mounting, but isn't there a provision for shimming between the caliper and the mounting to even the clearance between the pads?
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Old 10-08-18, 10:52 PM
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Default Same problem

My 411 mk 2 does exactly the same thing . All cables and levers are free to float and properly lubricated yet I get that uneven wear . Any thoughts much appreciated.
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Old 12-08-18, 12:57 PM
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Thanks both,

No, John, the pad mounting and centralising with the handbrake applied is not the problem. The problem is that with the handbrake off the handbrake calliper itself is out of balance on its mounting, which causes the inside pad to lightly touch the disc, albeit very lightly.

Peter, to explain what we have done. We have added a very light spring, in tension, between the handbrake calliper and the bracket that holds the brake cable outer. There is a convenient mounting point for it on the calliper and it's just secured at the other end with a cable tie. This might provide a solution, but time will tell. The tension we applied was pure guesswork, just enough we hope, but not too much.

Having thought about this over the last couple of days I looked up the excellent Australian RR site as I know contemporary Rolls's also used Girling brakes. I found a far more detailed parts list on this which includes a mystery item, a "centralising strap". Just a rod with a mounting hole at one end. But it isn't clear where or how it's fitted.

I took myself off under the 410 this morning and scratched my head for a long time, but I still can't imagine where such a thing might go so am no wiser. Perhaps a RR/Bently owner might be able to enlighten us.

I am now wondering whether this tendency for the inside pad to touch might be behind the very slight whirr that I have always had when slowing down after a good run. This is clearly at wheel rpm but I'm assured the bearings are fine. If they weren't they wouldn't have lasted the 18 years I've had the car.

Any other thoughts anyone?

Roger
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Old 12-08-18, 04:14 PM
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There are some quite good exploded drawings of the rear brakes for the Silver Shadow on the Introcar website which might help you identify where it goes.
Geoff.
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Old 13-08-18, 10:07 AM
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Thanks Geoff, however your reference brings up the same drawings as I found on the Australian RR site, so I'm no wiser. Further head scratching suggests that the RR callipers might have had an extra lug on the bottom, not present on the 410, perhaps it was attached to that?

However I think that light is finally beginning to dawn. It appears, although none of the books spell it out, that the handbrake cables on the 410 were intended to to be set up to hold the imbalanced calliper(s) off the disc(s) with the handbrake in the off position. I paraphrase the handbook. "In the 'unlikely' event of the handbrake cables stretching (due, perhaps, to desperate attempts to get far too hard pads to bite hard enough to pass the MOT) dive under the carpet under the transmission tunnel and adjust to take up any slack in the cables". What the handbook fails to spell out is the consequence of this 'unlikely' event.

Perhaps thiat will do the trick, I'm not all that confident as there is only one adjuster in front of a balance bar, but it might work if both cables are the same length and there is little friction anywhere, but I will report back, eventually.

Peter, perhaps you might like to try checking touch, balance and adjustment as above, if the 411's handbrake set up is similar

Roger
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Old 13-08-18, 04:46 PM
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Roger,
Knowing that we are shortly going to have to overhaul the rear callipers on my old Diesel Silver Shadow I did a search about rebuilding them and came across the first two out of three technical videos uploaded for the Rolls Royce Owners Club of Southern California the subject being Corniche rear brake caliper overhaul.
At the start of the first video the presenter doing the work mentions a missing part which he describes as a small 10/32 bolt with two tabs the function of which is to keep the handbrake mechanism centralised, he then shows were these should be positioned. The remains of the scrap 603 don't give any clue as the handbrake mechanism is a mass of rust, as far as I was aware the Rolls Royce and Bristol callipers were the same but I might be wrong.
This "missing part" referred to in the video does not sound like the strap you mention and a quick look on the Introcar and Flying Spares site indicates this is available, part number CD5731 which you probably got off the Australian site. The drawings on the Flying Spares site don't show were this strap goes either and I don't ever recall seeing anything like that when we have being working on the brakes of my cars, then again might be that I was not paying sufficient attention.

Geoff.

Last edited by Geoff Kingston; 13-08-18 at 05:35 PM.
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