Vehicle Braking

dlfrisch

dlfrisch

Senior Member
I just read "29 cabriolet" thread - Braking shoe centering ( today at 5:08 PM).
I don't seem to understand the technical answers or follow the applications.
If, I understood I may be able to solve my braking problem.

When stopping and I apply my brakes the car jumps, as if I am applying the brakes on and off. The transmission lever bounces back and forth and the whole drive train seems to bounce or move until I have stopped.

I do have the Les Andrews brake peddle wood tool and I have followed the procedure in his book, plus some Youtub videos depicting brake adjustments. I still get the vehicle bounce when try to stop. As I have just bought the car and the brake shoes look like new.....maybe it's an adjustment I'm not aware of or maybe it is some sort of centering the shoes.

Any ideas would be appreciated.

Dave
 
I agree that you may have a damaged drum. Jack up each wheel and spin it to see if if has a tight spot from being bent.

It might also be loose chassis parts, like the wishbone or front axle, that can rock back and forth due to loose or worn parts. You'll have to check it over.
 
Y-Blockhead, it sure feels like a drum or two may be out of round. As far as I know, they and the brake shoes are new, but who knows they my have been mfg.ed and bought from - you know where. Kind of seems like the rear brakes, as to my professional driving feeling. How would I measure or calculate a a drum being out of round ?
Dave
 
Hi Tom, Yes, adjusting the brakes. both rear wheels have a real tight spot while turning and adjusting for proper brake shoe drag.
 
Sounds like you may need some help from your local model a club. I vaguely remember a post a while ago that had a brake pulse related to something flexing or loose. Maybe someone else remembers it.

Suggestion for a couple of things to check. Can you tell if the engine is lugging when braking with the clutch depressed? If it does it may be something in the clutch/pressure plate/throw out bearing area not fully releasing. Take a look at the brakes. Check the rods and make sure service and emergency brake rods are straight and correctly installed and routed. Remove the drums and verify that the service & emergency brakes are assembled properly and function correctly. Check the cross shaft to make sure it is not afloat and also check that your wishbone and rear radius rods are secure. Check springs and shackles to make sure nothing is broken allowing the front or rear axle to move. If brakes are correctly installed and everything tight possible U-joint or rear end. Good luck!!
 
I also agree that you've got out of round drums. If the drums are cast iron, a brake shop may can turn them and true them up. Otherwise you may have to find better drums.
 
I forgot to mention, check the tightness of the rear axle nuts. I had a loose one and after re-torquing to ~100 ft/lps the brake pulsation went away.
 
youll need to find a place that can jig up the rear drums. i had to buy a special arbor and cone kit to mount them on my aamco machine.
the front are no problem being they have normal size bearing cups / races
 
I may be dancing in the dark. I do agree the logical explanation are the steel drums. I warped one of my rears coming down from the Pikes Peak Meet a few years ago. I then went to all cast iron, since the steel drums were borderline anyway. But, once, some time ago, while reassembling the front units one of the "pills" on the brake operating pin fell to the side and resulted in all kinds of jerking and inability to adjust.
 
Cast iron drums can also be out of round or have been installed incorrectly. Cast iron drums need to be turned to true them up after installation. If there are tight spots when the wheels are turned that is an indication of out of round brake drums . It could be a combination of a front end shimmy problem. Sometimes the shimmy will show up when the brakes are applied or after hitting a bump in the road.
 
We have been buying "cast iron" drums from Bratons recently because those purchased from other sources required more lathe work. When we fit new drums to hubs we do the following:
Chuck up the hub (front or rear) in the lathe and clean up the mating surfaces. They get burrs or other problems from either the first installation or when being removed from the drum. They sometime require a skim cut to clean them and true them up.
After swedging they are again chucked up and the braking surface trued up round. Usually .010 is all that is necessary. The ebrake surface is also checked for proper diameter and a cut is made if needed.
 
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