Hints and Tips - Grabbing Brakes Again...

From: OLIVER TOMLIN
Sent: 15 July 2002
To: british-cars-pre-war
Subject: HWM brakes

Hi all,

I must again start off with apologies for not talking about Pre-War cars, but I'm totally stumped by a problem with my grandfather's special (built 1954 for hillclimbing, 5.7 chevrolet). As there's only one Chapman Mercury 3, the e-mail list would consist of me!!! And I can't find a list talking about HWM brakes!!!

My grandfather used loads of different bits, American Engine, MG TD front suspension, Willy's Jeep rear (!!!) and I think HWM brakes. They are Wellworthy Aluminium finned drums with twin leading shoes. The shoes also float. My problem is that I cannot stop the front left snatching and locking up. I thought the problem was intially the front right not working properly, but thats not the case, as sometimes it pulls dead straight and then on the next application will suddenly lock the front left. I was competing in it at Prescott a couple of weeks back and had no idea where it was going to go next!!!! I also checked the corner weights but they are within a couple of kilos of each other. Yesterday, I smoothed the edges of the shoes where they float in the slave cylinders as I thought they might be catching - but no difference. I can get new linings fitted for £ 20 a shoe, which will probably be the last resort, but I can't get them done before VSCC Prescott - and I want to take it there.

Does anyone have any ideas?? (apart from oiling the left shoes to calm them down a bit!!!!) I've rebuilt all the slave cylinders with new seals, silicon brake fluid and lubricated the steel pistons with copper slip to stop them welding themselves to the ali. cylinders over the winter. Is there any filing on the leading edge of the shoes that would help?

Thanks in advance.

Oliver


From: Dr G W Owen
Sent: 15 July 2002
To: OLIVER TOMLIN
cc: british-cars-pre-war (E-mail)
Subject: Re: HWM brakes

First dont use Silicon brake fluid! So I was told by a brake system expert, certainly not on a racing car anyway

I have an idea for your grabing brakes. Take off the drums and shoes, and check the drums are the same diameter as the shoes (or more strictly, the radius of the outside of the shoe is the same as the drum) by putting the show in the drum and seeing where it touches. If you have had too thicker lining put on (say 1/4 instead of 3/16) then the shoe only touches at the ends with a gap in the middle. That is until you have it on the car and apply the brakes then when you press a little harder and the shoe deform and grabs along its whole length, and the flex of the shoe pushes the outer ends into the drum really hard and locks the whole thing up.

Fixing it is easy, either have them relined with the right thickness lining. Easily done before Prescott (there is a place in Bristol that will do them in 24 hours for about 40 quid). Or more sensibly, machine the linings until they are the right radius (backplate in a lathe? or I do it on the car with suitable protection from the asbestos and a good rasp). If you are rasping the linings down, use tippex correction fluid over the surface of the lining and put on the drum, spin the wheel and apply the brakes, the tippex nicely marks where the high spot is

Geraint

__________________________________________________

Dr Geraint Owen


From: OLIVER TOMLIN
Sent: 15 July 2002
To: 'Dr G W Owen'
cc: british-cars-pre-war (E-mail)
Subject: RE: HWM brakes

Geraint,

cheers for the advice. As for Silicon fluid, you are quite correct that it is unwise to use it in a race car, I think mainly because of its lower boiling point than standard fluid (I think its something like 300C, whereas standard stuff is about 450C). But, the car only gets used on hillclimbs so I don't term it a "race-car" and I like the fact that its not hydroscopic so corrosion is minimised. I've not had any problems yet - touch wood!

I'll check the relative diameters of the linings and drum and employ my rasp if necessary - cheers for the tippex tip. Interesting that you say the shoes will deform, its very easy to think that they are rigid. JEM in Hinckley (10 mins away) have quoted me £ 20 per shoe for bonded linings.

Thanks again,

Oliver


From: Richard Brown
Sent: 16 July 2002
To: british-cars-pre-war
Subject: Grabbing brakes

I had the same problem with the brakes on my Mk VI Bentley. They were normally fine, but on odd occasions and for no apparent reason the left front (better than the right I suppose!) would bind up and refuse to go off without reversing a short distance. They were a somewhat different arrangement, being leading and trailing shoe with the two connected by jointed and pivoted push rods presumably intended to make them both work the same amount. However, the cure (as suggested on the service sheets sent out by the factory from time to time) may be applicable. This involved the 'backing off' with a coarse file of the leading 3" of the leading shoe, and the leading 4" of the trailing shoe. My recollection is that my heart quailed at the idea of reducing the apparent braking surface to such an extent and that I did rather less, but it did cure the problem and the brakes still seemed as effective as ever.

Richard Brown


From: OLIVER TOMLIN
Sent: 17 July 2002
To: british-cars-pre-war
Subject: RE: Grabbing brakes

Richard,

That sounds like almost exactly the same problem - and you had the same thought as me, "I'm glad its not the right hand one doing it"!!!!!

I can feel it staying on briefly after I release the pedal, but there's no significant heat in the drum to indicate that its binding continuously. I'm going to employ Geraint's suggestion about checking relative diameter's and if that's OK (which I think it might be 'cos the shoes have been on the car for about 20 years!!) then I'll get filing.

I also have a 1932 3-wheeler Morgan that I restored and haven't used for a couple of years because the brakes were so awful. I fitted Hillman Imp twin leading drums to the front as the original Moggy ones were useless. This used to steer all over the place under braking and beacuse the rear wheel has a tendency to lean to one side, it results in the car wandering wildly. I never found the problem, but I think these solutions are applicable to the Moggy aswell.

Looks like there's lots of shoe filing to be done!!!

Oliver


From: Stuart
Sent: 15 July 2002
To: OLIVER TOMLIN
cc: british-cars-pre-war (E-mail)
Subject: Re: HWM brakes

Oliver, You don't have a weak brake return spring on the snatching side? Just an idea.

Regards, Stuart


From: OLIVER TOMLIN
Sent: 15 July 2002
To: Stuart
cc: british-cars-pre-war (E-mail)
Subject: RE: HWM brakes

Stuart,

thanks for the idea. When putting it all back together I haven't noticed one shoe being easier than the other, and it wouldn't explain why it brakes fine one moment and not the next. I'll check the lengths and strengths when I next take it apart (AGAIN!).

Oliver


From: Johno
Sent: 15 July 2002
To: OLIVER TOMLIN; stuart_ulph
cc: british-cars-pre-war
Subject: HWM brakes - well, actually Alvis

Seeing all this brake correspondence prompts me to ask advice for my 1925 Alvis 12/50. Brakes work well and pull up sharply, balanced and straight. Front right, however, make a horrendous screeching sound like metal on metal. Taken apart several times and cleaned, champfered edges of shoes, all appears OK, and reassembled. No squeaking for about 10-15 solid brake applications, then it starts again. Somebody suggested skimming the drum a minimal amount which I haven't done. Any thoughts?

John Layzell
Miami, Florida
1925 Alvis SC 12/50 (with original FWB) - oldest Alvis in North America


From: Dr G W Owen
Sent: 16 July 2002
To: Johno
cc: OLIVER TOMLIN; stuart_ulph; british-cars-pre-war
Subject: Re: HWM brakes - well, actually Alvis

Some cars (including early Nashes) fit a band around the outside of the drum. I have seen them made of flat Dexcion Stip (big Meccano!), pulled around the drum with a bolt through the two turned up ends.

The secret is apparently to fit it really tight, then slacken it off a little at a time until the noise goes away. Or is it fit it loose and tighten it up?!?!?!

One or the other

The alternative is apparently to oil the brakes!!!!!

Geraint

__________________________________________________

Dr Geraint Owen


From: Johno
Sent: 17 July 2002
To: Alan Fairless ; Geraint Owen
cc: OLIVER TOMLIN; stuart ulph; british-cars-pre-war
Subject: Re: HWM brakes - well, actually Alvis

Would a giant Jubilee clip (hose clamp for those in US), assuming such a size is available, work as a substitute?

John


From: Tony Souza
Sent: 17 July 2002
To: British-Cars-Pre-War
Subject: Re: HWM brakes - well, actually Alvis

Johno wrote:
>
> Would a giant Jubilee clip (hose clamp for those in US), assuming such a size is available, work as a substitute? John

Better yet, maybe two head to tail, for symmetry and balance.

Tony Souza


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