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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

405 front drum brake advice

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Old 03-09-21, 06:34 AM
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Default 405 front drum brake advice

Hi all, I'm new to this forum and I'm seeking help. I have a Werner Oswald Frazer Nash Le Mans replica copy and it has front drum brakes from a Bristol 405. These are Lockheed TLS 12". The car is new to me and the brakes were binding unacceptably. I stripped them down and addressed all the 'gunge', corrosion, cleaned and fitted new seals to the slave cylinders. Upon reassembly I find that they are still binding unacceptably with the drums up to 40-50 degees C after only a mile of running. The w/shop manual says to apply the brake pedal and the shoes should adjust themselves automatically and to check that the drums are 'comaratively free' when the pedal is released. The ratchet system, as far as I can tell, seems to be designed to keep the shoes in contact with the drums when the pressure is off!!! There seems to be not way they can back off enough to enble bind-free rotation of the drums. The springs also seem to be placed so as not to be able to pull the shoes off the drum as effectively as they could be, that is, they are placed near the fulcrum end, not near to the actuating/slave cylinder end.
Can anyone shed some light on how this set-up might enable bind-free rotation as I'm worried about warping the drums??

Last edited by GlennBurnage; 03-09-21 at 06:40 AM.
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Old 03-09-21, 09:13 AM
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Glen ,
I fitted 405 front brakes to my WOK#11.
Initially with the self adjusting links but I found it was difficult to get them both adjusting correctly and evenly . Your problem could be the tension of the bolt on the opposite end of the link to the serrated adjuster. This should have just enough tension to allow it to slide.

After fettling it for a while I decided to convert the wheel cylinders to the earlier 400 - 403 system where there is a cam adjustment with a screwdriver through a hole in the brake drum .
One end of each shoe had to be modified to fit the cam adjuster.
I never had any further problems, although I never covered high mileage in it before I sold it a few years ago high.

I'm pretty sure there are plenty of 405's out there that still have the self adjusting system working well , but will one of those owners reply to you post !!!
Geoff
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Old 03-09-21, 10:34 PM
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Glenn,
I have a 404 with the same front Lockheed 12 x 2-1/4 inch alloy drums.
If the brakes were OK before, but now BOTH front drums are dragging simultaneously, it could be a hydraulic problem - and logically there are only 3 reasons for this i.e. sticking slave cylinders, a faulty master cylinder, or blocked pipes.
(1) You have just serviced the slave wheel cylinders.
(2) If your m/c is single chamber (and not tandem/dual chamber) - one would expect the back drums to be affected as well, if it is faulty, if not.....
(3) it leaves only the front brake pipes - more likely in the rigid pipe section, unless BOTH flexible pipes are coincidentally blocked!!
I have never had the front brakes drag, and there is no provision for manual adjustment as you say.
vincent
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Old 03-09-21, 11:06 PM
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Vincents comments are interesting and they reminded me of trouble I had on two seperate occasions with my 365 GT4. The brakes would lock on and my mechanic at great cost had the cylinders reconditioned only to find it made no difference. The problem turned out to be the flexible rubber hoses swelling on the inside. This would allow the master cylinder to put the brakes on under pressure but would not allow the fluid to return . Problem solved. The car has Disc Brakes but drums have heavy return springs so blocked hoses may not create the problem you have. Has any one had this problem on a drum brake car, I havnt. Food for thought.
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Old 04-09-21, 01:08 AM
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Peter,
Once, I had a rear brake drum drag (on my 1968 Morgan).
Only one drum was affected - and the problem was its blocked flexible pipe.
Glenn did not say, but if the car was laid up, corrosion and gunk causing partial blockage in the hydraulics is possible.
vincent
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Old 04-09-21, 07:24 AM
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Firstly, many thanks for all the advice and pointers so far from all the repliers.
Yesterday I had all ratchet bars off and inspected again, reassembled and refitted. Prior to this I had everything off whilst awaiting new s/cyl seals. Bleeding, using an 'Easybleed' presurised system went smoothly with no apparent restriction in flow on the front brakes, or on the rears when they were bled.
Took it out for a test run accompanied by my trusty IR temerature gun. The readings taken were from the hottest part of the drum:-
NSF-28.0c OSF-45.0c NSR-35.0c OSR-35.0c
This showed that all were ok except the off-side front! During the short test drive, under braking, the car was noticably pulling to the right, the OSF doing more work than its partner. All this could suggest a hose 'swelling' problem, but the pipework is solid (copper?) up to where it passes through the body and braided s/s from there to the drum, so I don't think that the famous 'swelling pipe scenario' could be the cause, or a sticking master cylinder seal/piston.
Further investigation will take place over the weekend and I may have the M/cyl off for inspection as the rear brake temperatures (hotter that the NSF) could possibly mean there is a bit of stickiness there, we'll see.
Glenn.
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Old 06-09-21, 08:52 AM
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As I could find no problems with sticking master cylinder, lack of free play in the brake pedal, and all hoses/pipes fine. It came down to the springs that return the shoes were not best placed to do the job intented as they were exerting their force close to the fulcrum end of the shoe, not at the s/cylinder end where they would be most effective. I drilled the brake plate and repositioned the springs so that they now operate close to the m/cylinder end - NO MORE DRAGGING FRONT BRAKES!!!!!!
Thanks for all end helpful replies and advise - there will be more requests for same, no doubt.
Glenn
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