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Brakes grabbing?

Afternoon all
I have a question to check my logic please.

On the way home from a trip there was a real thumping from the front under our feet as i applied the brakes (1933 box).
Checks showed nothing loose or obviously wrong.
Brakes still worked if you were brave enough to push through the noise.

Having spoken to some learned owners it wa ssuggested that ovality of the brake drums could be causing hem to grab as the pressure was light when initially applying brakes, made worse by having been on a run with hot brakes and then applying the hand brake before then leaving with cold brakes, resulting in distortion of the drums.

I have taken the drums off and the pivot pind, drums etc etc all move properly although I did think that he brakes were in need of some adjustment to take up some slack in the cable (not done before the noise started).

I cleaned everything, greased the loop where the cable runs through the handbrake point in case it was catching and pulling between the 2 wheels but nothing obvious here either.

free wheeling the wheels and pulling on the cable applies and releases the brakes no problem.

Out on a run again and initially fine. on way home again thumping from under feet.

My next thought is to swap the brake drums front to rear to see if there is some ovality that might be worse on front loading. Is there any reason why I shouldn't do this?

thanks
Andy


Location: Norf Essex

Re: Brakes grabbing?

I take it that neither of the brake pivot pins was even slightly loose?
Regards,
Stuart

Re: Brakes grabbing?

Hi Stuart
No they were nice and tight and rotated evenly and smoothly with the cable pull.

Andy

Location: Norf Essex

Re: Brakes grabbing?

Andy,I deduce from your reply that you are referring to the shafts of the brake cams while I am referring to the (hopefully) fixed pivot pins diametrically opposite. Forgive me if I have misunderstood. Unless, of course, you have Girling brakes in which case you should ignore me!
Regards,
Stuart

Re: Brakes grabbing?

Has something came adrift at the radius arm anchorage? Should not be able to lift the connected arms, and if diff placed on a trolley jack, brakes applied, car pushed and pulled, radius arms should not move at anchorage.Or can adjust front brakes for a huge lead so the back do not operate.
Under very effective braking the early pre girling radius arms can cause judder

Location: Auckland, NZ

Re: Brakes grabbing?

Thanks both.
Will have a good look today and report back
Andy

Location: Norf Essex

Re: Brakes grabbing?

Andy B
..... I cleaned everything, greased the loop where the cable runs through the handbrake point in case it was catching and pulling between the 2 wheels but nothing obvious here either.

You mean the cable can actual move - is meant to move - along the curved loop, either way, under the handbrake pivot?

Location: West Cornwall

Re: Brakes grabbing?

thanks all
quick message as am running around.

Sandy: I always assumed that the cable moved a little through the central pivot section as the steering went from lock to lock and was wondering if it was catching and dragging by just a few mm in the groove and causing the noise.

anyway I seem to have solved problem.
I spent much time resetting the front brakes, making sure pins were tight etc (they were all was OK). I also took up a little slack in the front cable. I added a little more chamfer to the leading edge of the pads.

I went for a drive and better but it still made some thumping, just not as much.

went back to basics and checked all wheels. I felt that the nearside rear was hotter than the rest after 5 mile run with some deliberate heavy braking to make the thumping noise, but appeared to be moving freely and working with the brake cable when up on axle stands whilst still hot straight after run.

Anyway, I slackened the cable just a hint and went on a 30 mile club run and not a single thump or bang. Part way round I checked and the wheel was warm but not hot to the touch as it had been before.

SO, it must have been rear rather than front, or perhaps a bit of a combination. The engineer in me doesn't like things that partly 'solve themselves' as they have a habit of coming back. I can't quite work out why, if perhaps it was rubbing just a little and so warming up the hub and then grabbing when I applied brakes after a few miles. Perhaps it is as simple as that.
Anyway thanks as always for the help

Andy B

Location: Norf Essex