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Drum Brake Adjustment

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clevitt
Posts: 64
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Drum Brake Adjustment

Post by clevitt » Thu Oct 18, 2018 6:25 pm

The standard recommendation for adjusting drum brakes is to lock the drum and then back off the square adjuster by two clicks, but I have always found that 3/4 clicks is necessary to obtain a freely rotating wheel. I have recently relined my DB18 (GIrling 2 Leading shoe hydraulic) front brakes and now need to back off by 8/9 clicks, and can still hear it catching at one or two places when rotating the wheel. Is this normal for new linings that need time to bed in, because the result is an increase in brake pedal slack, with the pedal now getting close to the floor .
I also notice that when applying and releasing the brakes, there is an increase in friction for several minutes as if the return springs are worn. It is also recommended to replace springs when fitting new linings, but is there a new source for these springs?
Thanks in advance for any advice .
Chris

Stan Thomas
Posts: 446
Joined: Sat Feb 13, 2016 2:14 pm
Location: Penkridge. Staffs.

Re: Drum Brake Adjustment

Post by Stan Thomas » Fri Oct 19, 2018 6:50 am

You will find the amount you need to "back-off" the adjusters will deminish as the linings bed in and any high spots wear down.

Were your brake shoes relined by rivetting or bonded (bonding is best)? If the former, the surface accuracy of the linings is usually less accurate - hence your high spots if that be the case.

Also, as new linings have a sharp radial edge that will need to mate into any wear ridge in the drums- also giving rise to the symptoms you have, including slight drag upon release.

Its good practice when fitting new linings to file a small chamfer around the edge of the new linings and on both leading and trailing edges each end of the linings to eliminate this tendency. Again, a sharp leading edge can give rise to the brakes not releasing immediately.

So I doubt if the return springs have become weak - but if you are concerned, remove the drums and observe the return action after someone depresesses the brake pedal a SMALL amount (Dont give the pedal a full stroke or the pistons will pop out and your missus will go barmy at the hydraulic fluid leak on the floor)!!

clevitt
Posts: 64
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Re: Drum Brake Adjustment

Post by clevitt » Fri Oct 19, 2018 9:07 pm

Thanks Stan, I think that you have hit the nail on the head as I didn't put any chamfers on the new linings which were riveted rather than bonded. It won't be for a few weeks, but it's on the list of jobs for the next time the car out of storage ( kind neighbour's unused garage)
Chris

clevitt
Posts: 64
Joined: Wed May 18, 2016 1:02 pm
Location: West Hertfordshire

Re: Drum Brake Adjustment

Post by clevitt » Wed Dec 05, 2018 9:45 pm

Finally solved my brake problem thanks to the GIrling technical info on the DB18 website (thanks Graham) .
My schoolboy error was not to have the shoes locked up to the drum when adjusting the steady posts. As a result the linings were not sitting parallel to the inner face of the drum. The drum now rotates almost free of any friction after backing off by 3 clicks, and I expect any residual high spots will soon wear away.
Chris

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