Hitchcocks Forum

So, i have a 1994 bullet with diesel engine.. double leading front brake, made the connector arm adaptation, This brake was Always a hassle to adjust(as with my jawa, also has a twin leading front brake, adjusting is 2 min. work and works good!)
I had the brake keys(those levers which push the shoes against the drum, what are they called in English?) machined down to 20,0mm so both were equal and more pressure against the drum, new linings, made to diameter of the drum, i thought after adjusting braking was reasonable and would improve, but it got worse over time, also more spongy..

Maybe the distance from the 2 axles to centre is not equal? Also it seems the brake plate is not in a right angle on the axle.. it tens to tilt a bit..

Anyway, a drum brake this size and this lining material should be able to work well..
is the 'improved'2002 brake plate & stuff better?
-yes i know how to adjust a double leading drum brake, but when tightening the lever makes the wheel turn more freely, something else goes wrong..
am thankfull for any tip!

Assuming the brake drum isn't oval (it can be skimmed back to true by someone with a big enough lathe), one tried and tested way is to have the brake shoes relined with over-sized linings which are then turned down to fit the drum. A.

I wrote i did that??? and these set up worked but gets worse over time! you cannot let one side touche the drum and then do the same to the other, without the wheel first running more freely when tigthening the upper lver.. very strange...

My apologies, I should have read your post more carefully. If the alloy backplate has been incorrectly machined see our hosts about a new one, they will be able to check that all the holes are where they are supposed to be and pointing both spindles parallel to the front wheel axle. I would also check the condition of the drum to make sure it is still properly round and not worn unusually. The only other thing I can think of is that the adjustment keeps slipping even though you take the trouble to set the linkage correctly, having a left-hand adjuster thread at one end of the rod and a right hand thread at the other doesn't help, perhaps. I assume you have already read the following in our hosts' technical notes:



"The reason for a poor front brake can often be traced to
glazed linings and poor adjustment. Both shoes must
contact the drum together but this can be difficult to do
with the standard linkage with its left and right hand
threaded link rod. You can improve this situation by
simply ensuring that the left hand threaded end of the
rod is at the bottom, drill out the top trunnion's
right-hand thread so that the threaded part of the rod
passes through freely. Refit the trunnion and nut with
an added 5mm lock nut. This then allows adjustment of
each shoe independently. Hold the handlebar brake
lever on firmly, to do this wrap a bungee round the
lever or temporarily over-adjust the cable. Then with
the link rod locked in the bottom arm trunnion, adjust
the top nut down until this shoe is hard against the
drum and then tighten the extra locknut.



Check the brake is functioning correctly before taking
to the road.



Not everyone agrees with this!



Hopefully you will not need to replace the whole lot - if all else fails, there is always the disk brake conversion (/runs and gets beer).



A.

What is wrong with the method of 2LS brake shoe adjustment described on many web sites which resorts to 'adjusting' the link-rod?
Most everything, as you have discovered...


It is a misinformed method of brake adjustment that has been on the Net in a multitude of place for many years, and was written by some well intended person who has a complete lack of understanding of the functionality of mechanical drum brakes.
The degree of accuracy required to accurately set a Twin leading shoe brake is more exacting than that needed when setting ignition timing!


To which end, in the case of racing applications, we are talking about .002” or less in accuracy of measurement!


The mechanical twin leading shoe brake functions on a very simple mechanical principal: Leverage.
The moment the levers no longer function as a true parallelogram, ie one lever is set at a greater or lesser angle than the other; you will have less pressure (leverage) being applied to one brake shoe.


For a Twin leading shoe mechanical drum brake to function with its full potential, BOTH levers MUST be set so that they operate in perfect harmony; balanced leverage. Otherwise over a very short period of time you end up with only one brake shoe actually making contact with the drum; thus one shoe wears faster than the other, as its partner is not having the same leverage applied to it. A spongy brake.


The ideal situation to adjust the brake to is that BOTH levers are set ‘square’ to each other, with both levers being pulled up to 90 degrees, AND that the brake cable to Primary-lever also coming up to 90 degree. A cable with the absolute minimum of compressive flex (lost motion) and the hand lever and the top nipple also approaching the 90 degree angle.


The optimum point to exert maximum leverage is as the lever moves up to 90 degrees; at which juncture you will get full braking potential.




If you contact me off list I can send you a Word doc detailing the procedure for setting the levers CORRECTLY...


royalenfield AT clear DOT net DOT nz




What ever you do, DONT drill out the trunion!!! It is THE WORST possible thing you can ever do the brake!

The ONLY way that one should 'true' a brake drum is by Grinding. NEVER Turn a brake drum!


The RE front axle is 5/8", to correctly 'true' a pair of Enfield Brake shoes, you will in all probability need an old modified brake-plate which has had the axle center hole machined slightly larger to accept the common Mandrel size that most Brake shops use: +17mm - 19mm ...


It pays to get the shoes/linings trued...

The thing that pushes the shoe is called a cam, useful diagram - http://www.hitchcocksmotorcycles.com/pa ... ront_Brake



As Tim NZ says, they must operate together. Ideally the shoes should both make contact with the drum with their Operating Levers at 90° normal to the cam pivot, in other words at right angles to the diameter at that point so the lever can apply maximum pressure for braking; this may mean moving the levers on their splines



There is a bit of a black art to setting up a 2LS because you have to allow for the mechanism to take up slack and play. Mainly it's practice fiddling with the thing until it works properly. Understanding how it is supposed to work is half the problem solved. The diagram helps but look at the thing apart in your hands.

Take the Link Rod out and apply the levers by hand so they make contact, the levers should be parallel; if not then adjust on their splines so they are as parallel as possible and will apply maximum leverage, or moving towards max leverage rather than away from that point. Now refit the link and adjust so both shoes hit at the same time when pulled by the cable.

Now when you pull the cable you should feel the shoes make solid contact with the drum, together, at the same time. The Operating Levers should not be able to move perceptibly from this point, only apply more force as you squeeze the brake. Watch the levers as you pull the brake, if the Operating Levers stay put but the brake lever keeps coming back then you probably have a stretchy cable, usually the outer sheath compressing.



One cause of sponginess is a spongy brake cable. If the cable outer is shot it is little better than a coil spring.

Don't be in too much of a rush to true up the brake drum unless it is badly out of shape or scored up. It is a skilled job and there are pitfalls; you may have to unlace the wheel, the drum/hub can be distorted afterwards by spoke tension, so it should be done with wheel and even tyre on, just like the do with truck wheels. In any case the shoes are abrasive and will to a large extent true up a drum by themselves, if all is working properly. Best done on a big brake drum lathe by an expert service. They use a lathe cutting tool, you can watch online videos.

I writhe watching diy YouTube bodgers using sandpaper and rotary tools, eek.

Jefrs, some years I chambered the inside of some 9mm rifle barrel stock, to take the ammunition, using wet and dry sandpaper and a bit of rod split at one end. All of the barrels had to pass official testing to get certification. The did that with no problem. It is who is using the sandpaper that matters, not the use of sandpaper.

To true a scored drum DONT ever strip the wheel! Relacing the wheel, or even the action of fitting a new tire to a recently re-laced rim WILL cause the 'truth' to change and even the drum to distort.


ALWAYS true a drum with a the rim and spokes fitted, and preferable AFTER a few road miles have been covered so that the assembly has settled into its final running shape.


IF the drum needs Grinding, simply remove the axle and take the COMPLETE wheel assembly to the machinist. If they do not have the capability to handle the job, you are at the wrong shop...