Hub/drum specs

cmperry4 · #1 16-01-06, 03:45

I'm planning to take all my brake stuff to a shop for new linings and drum turning/de-rusting.

I talked to the guy and he asked me if I knew the specs. I said I had all the specs for the linings, but I haven't so far been able to find any numbers for the limits of turning the drums in the C8A manual. (Including the parking brake) Any enlightenment?

cmperry4 · #2 23-09-06, 04:51

OK, no one has yet enlightened me on the brake drums, but I could still use the info.
I finally took them to the brake shoppe today, along with the shoes and the master cylinder. The guy who seems to know his stuff was immediately skeptical about how much meat was still usable on the rear drums. He put a very Cronenburg-esque diameter gauge on each of them and made comments about the being 90, 90 or near 100, which means no machining possible - I'm not sure if he was measuring millimetres, percentages or picas. Said he would consult with one of his shop experts on how much if anything they could do more me. He said the front drums looked OK.

I am having him switch LH studs from a cracked drum to a front drum that currently has RH studs in it, though he seemed a but unsure at first about how the studs are mounted in the drums. But, as I said, he seems to know his stuff, and I had had this place recommended to me by another experienced restorer.

The brake guy also seemed to think refurbishing the master cylinder wouldn't be a big problem, depending on the bore condition, which was nice to hear.

So, I gave him the lining specs from the manual, but said I had not found any specs for drum wear limits in any of my manuals.

Anyone know these?

RHClarke · #3 24-09-06, 02:55

Mark,

Just how bad are your drums? I can't imagine that your drums are so worn down that they can't be turned. Those drums are massive. Even my very abused 45 HUP's drums seem substantial, particularly when I compare them to the 43 HUP drums I have laying about...If you like, I'll measure my drums the next time they are off and send the info to you.

I would be inclined just to tell the chap to turn the drums and leave it at that. If he balks, then ask him for the specs. If he finds them, then great, we all win! If not and he refuses, find another shop.

cmperry4 · #4 24-09-06, 03:14

I agree Rob, the drums don't seem to be that worn out - they have a little scoring and a coating of rust, but not what I though was a whole lot of wear. They guy thought they might be just within limits, and I did suggest that all I really needed was a little dressing, remove the rust, but not much more.

He was pretty harried with a lot of stuff happening on a Friday afternoon, and as noted, he said he would have another guy take more time to look at them.

I'll talk to him again Mon. or Tues, but I did promise him I'd try to find out some specs in the meantime.

If he does refuse to do them, I guess, I'll just take them back, do a little home-honing and use them. Of course, if I try to licence the thing, and need to pass some sort of safety inspection, I'll be screwed.

RHClarke · #5 24-09-06, 03:30

Quote:

Originally posted by cmperry4
Of course, if I try to licence the thing, and need to pass some sort of safety inspection, I'll be screwed.

Mark,

Safety first! I agree wholeheartedly. I trust that your brake linings are up to par? If you get the drums turned, and have good linings, new brake lines, wheel cylinders, then you should be good to go.

If during the inspection your drums get pulled, what data are the inspectors going to use to determine the thickness specifications? If they are not turned (but cleaned up) - what would be the concern?

Anyone out there with the design records?? Experience with inspectors?

RHC

Paul Singleton · #6 24-09-06, 05:29

If I remember correctly drums up to 13"diameter can be machined up to .060" larger than the original size. Drums over 13" can be machined up to .090". For safety inspection purposes drums will pass up to .090" for up to 13" and up to .120" for over 13" diameter. This is to allow up to .030" for wear after the maximum machine diameter. This is provided if manufacturer's specs are not available and you know the original drum diameter.

cmperry4 · #7 24-09-06, 06:51

Paul: Thanks for that - I'll run that by the brake guy when I talk with him. It seems to jibe with what he was talking about when he had his gauge on the drums. Fronts and rears are both 14" on C8A.

cmperry4 · #8 27-09-06, 21:45

Well, here's an update: the brake shop called this a.m., early for me, so my wits were not all about me. The brake maven said he had turned all the drums (yay), refurbished the master cylinder (hooray), and relined all the shoes, including parking brake (good-oh) - BUT, he was "washing his hands" of doing a RH to LH swap of studs because he couldn't figure how to get the locating cones off. He said he had spent a half-hour turning one and it still hadn't come all the way off, and he didn't want to spend (or charge me) that sort of time.

I said OK, I'd pick everything up, and think of something else.

In the meantime, I checked the manuals, and the cones are not handed, as are the studs and nuts, so I'm guessing they must just press on with the studs, and thus could come off with a puller of some kind or when the studs are pressed out?

Anyone have experience with this?

RHClarke · #9 27-09-06, 22:34

Mark,

I removed some of my "cones" using nothing more than a pair of vice grips. I would recommend using a piece of leather to wrap about the "clean and dry" cone to mitigate the bite marks (although they do grind off).

I don't know of a special tool...good luck.

Gunner · #10 28-09-06, 00:01

An old RCEME type showed me this trick when I was removing my carrier axles years ago:

Try a sacrificial nut screwed almost flush with the head of the stud and give it a whack with a ball pean hammer. The jarring force usually unseats the cones and then you can slide them off by hand. Just be careful not to damage the stud. Hitting too hard could bend the stud or disrupt the threads.

Mike

cmperry4 · #11 29-09-06, 05:23

Paul: As it turned (pun intended) out, .090 is exactly what he machined them out to, which he confirmed he had found out was the limit for those drums (but he wrote them up for a potential safety cert if I need it down the road)

Four drums turned, eight shoes plus parking brake relined, master cylinder refurbished, many $$$ later, but, he did not get the cones off the studs tow switch them over. He turned the RH-thread drum that I wanted the studs out of. While I was there, he took another shot at pressing out a stud from the cracked LH drum, and the drum just cracked some more. He says, why not just get six RH lugnuts and stick the whole megillah on the LH side, since who's going to know.

We'll see. At least I have the cracked drum to play around with, but what are the odds I'd crack the good RH drum, too. Thanks for the tips, guys.

Plan B is to try to find a whole other LH drum ass'y.

Paul Singleton · #12 30-09-06, 16:42

When pushing the stud did you have a receiver for the stud supporting the drum? All you would need is a piece of pipe just large enough that the head of the stud will pass through. When pressing the stud the pipe would support the brake drum and take the force of the press. Cast iron does not like to be stressed and can crack easily. The cones could be very tight. By design the cones tend to clamp to the stud especially if the wheels have been over tightened, it may take some heat on the cones to break them loose.
Paul