Front drum brake Upgrade

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Below is a Norton front drum brake upgrade available from Old Britts, as described on their website. I see the logic if you are going to arc your shoes as well. Has anyone done this, did it make a difference, can they recommend this?

Stephen Hill


Spindle Bushing Upgrade:
The stock spindle bore in the backing plate is around .705" and the spindle is around .6673" or .002" under the 17mm (.6693") wheel bearing I.D. The .002" bearing to spindle clearance is what you want to achieve for the backing plate spindle bore. What I am told is that the factory increased the spindle clearance to allow for the brake shoes to self align themselves to the drum, but if the brake shoes are arced to the drum, this extra clearance is not required, and in fact lets the backing plate wobble in the drum, decreasing the efficiency of the brake.

What we do is take some .750" round 6061-T6 aluminum and bore it out to 17mm to make the spindle bushing. We then bore the backing plate spindle bore to around .748 and press the bushing into the backing plate. We then re-bore the bushing to 17mm.
 
For the Front drum brake the stiffening kit is the one to go for, on the rear you open out the spindle hole to allow the brake plate to move to its best position with the brake applied just as the nut is tightened, how much wobble is there on the front once it all done up, on the rear there is no wobble as the plate is sandwiched between the nut and the flat on the stub axle.
 
I chose to do all the other things first before the stiffening plate and wasn't disappointed, I never did get the stiffening plate, but I did arc the new RGM shoes, adjusted the lever so both shoes contact at the same time and centered the axle while tightening.
 
DogT said:
I chose to do all the other things first before the stiffening plate and wasn't disappointed, I never did get the stiffening plate, but I did arc the new RGM shoes, adjusted the lever so both shoes contact at the same time and centered the axle while tightening.
It is possible to get a drum brake working very well, however it depends on how you are going to use the bike. If you are going to race your mates on twisty roads on a Sunday, you have some of the conditions which exist when racing - i.e. brake fade and the situation where the leading edge of the shoes can heat up and become sticky causing the brake to lock. It pays to make sure that the shoes fit to the drum very closely because if the cams are rotated too much the leverage and self-servo effect can alter. I would also cut the leading edge of each lining tapered well back to get heat distribution. A single disc is a much better way to go.
 
The factory "loose fit" mod is for the single leading shoe brake. It allows the back plate and shoes to be centred and then centred again when the shoes wear. Arcing the linings is good, but the leading shoe still wears faster than the trailing one, so the centring still has to be done.

Did Norton keep the loose fit for the twin leading shoe brake? That's strange.

The stiffening plate is for the twin leader.
 
Nobody have any experience bushing the backplate?
Yes, the oversize hole occurs in the double leading shoe backplate. About .035 oversize.
Makes me wonder why you would accurately arc brake shoes then have the back plate flopping around inside the drum.

Stephen Hill
 
Stephen Hill said:
Nobody have any experience bushing the backplate?
Yes, the oversize hole occurs in the double leading shoe backplate. About .035 oversize.
Makes me wonder why you would accurately arc brake shoes then have the back plate flopping around inside the drum.

Stephen Hill

The backplate doesn't flop around on my single leader with opened out hole. It is gripped when the spindle nut is tightened.
 
Stephen Hill said:
I suspect the backplate floats under braking pressure.

Would be no bad thing, but I find I have to re-centralise to take up wear.

Maybe I shouldn't tighten the spindle nut so tight.
 
Triumph made their brake shoes fully floating from mid sixties onward, no need to bore out holes to allow for wear adjustment, this carried over to the TLS where you also adjust the length of the rod to get the point where the leading edge touches.
 
I followed the advice from the Old Britts website (quoted above) and bushed the spindle hole in the backplate to a slide fit on the spindle. I then used the spindle as a mandrel to centre the backplate on the lathe. The oversized brake shoes were mounted on the backplate and turned until concentric and they slid into the drum with minimum clearance (.012").

I see the advantage of the oversize spindle: when you are adjusting the shoes, the backplate will move allowing the shoes to self centre (within limits).

I can also see a point to bushing the backplate: on the initial install after arcing the shoes, everything will be on centre. However, because the backplate no longer self centres, later on when you need to compensate for wear you have to be very careful to ensure each shoe is doing equal work.

Stephen Hill
 
I have a susuki 750 GT 4 leader for a project, bought from the USA ,there's a few out there. Bead blast and silver two pack?
 
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