Drum Brakes Question

[David D.]

I'm going through the drum brakes on the ole girl ('64) and was going to simple take the drums out for a turning. After they come back I was planning on simply installing the new brake shoes, springs, etc.....

I recently was talking to a Vette guy and he suggested to me that it'd be a mistake to waste time turning the old drums and that I should just buy some new durms (~$25 ea) because if the current ones have been turned in the past, I could end up with drums not sized to the shoes?

Anyone have experience with this and is it something I should be concerned about? Especially being the car has original 50K and I doubt the brake drums have ever been turned, since I've owned for more than 27-28 years and I've never had it done.

How do I make sure the drums are turned to the shoes? Is taking them to a regular parts store for turning OK? Or simply take his advice and toss the old and buy the new?

David

[Timothy B.]

Re: Drum Brakes Question

David,

I know in a perfect world turning the drums is a good idea. You state the 64 only has 50000 miles and I say why turn the drums at all. Unless there is some problem with braking, keep your original parts and don't worry about it. Somewhere on the drum there is cast 11.090 which means they can be turned to .090 thousands max diameter and be OK. At 50000 miles there is probably nothing wrong with drums anyway.

[Stuart F.]

Re: Drum Brakes Question

David;

I have a 63 with a little over 44k on it. Mine had the sintered metallic linings, and I had to replace them as some of the pads had rusted loose and were floating in the drums. I chose the Matrix Ceramic linings to replace them with as their braking characteristics were similar to the metallics. I had been told that I should assume my drums were scrap as the metallic linings were known to chew them up pretty good. So, I went out and bought new replacements from Ecklers. After reassembly with the all new parts, I found I just could not get them to adjust right - it would pull one way or another, and the pedal would sink, etc. I had them pressure bled by "Just Brakes" and readjusted pretty tight. That helped but they still were not right. While at their shop, I had brought along my original drums and had them mike them. All four (4) were able to be cut and saved, well within tolerance. As I continued to experience poor braking and becoming more frustrated, I deceided my last move would be to put my old (recut) drums back on. In the process, I noticed there was some differences with the replacements vs. the old. Basically, it looked as though the relationship between the hub mounting surface and the braking surface was different as well as the position of the drum relative to the backing plate. Of course, it is deceptive as the replacements do not have anti-chatter grooves either so they look different. They are some type of generic 11.00" drums, and they do NOT work well on Vettes! Once I got my original drums back on, I still had to swap some of them out left to right until I had them back where they originally came from. They now work wonderfully. My big mistake was in listening to others tell me to assume my old drums were junk. In so doing, I never even marked them as to what position I removed them from. Also, there is a hole in them (along with the wheel stud holes) with a little tab which leaves an impression on the hub. Make certain they are replaced exactly as they came off; exact wheel position and exact position on the hub. Least wise, that's what I found necessary on mine to get my good brakes back.

Stu Fox

[Bill M.]

Re: Drum Brakes Question

I had a brake engineer tell me not to turn rotors or drums because it weakens them. His explanation was that the edge is the weak point; if you don't turn them, you don't thin the edge. He said that the pads/shoes would quickly wear to accomodate any mismatch to the old rotors/drums. You may get imperfect feel until they wear in. (I'm sure a professional doing customer cars would get immediate complaints about this, so they turn drums/rotors. The customer feels great brakes the first time he tries his new brakes.) However, I would not want my drums/rotors to ever get thinner than the dimensional spec. because of reduced heat capacity.

I've followed this advice except when my rotors had a high spot that created a vibration; they had to be turned or replaced. I've had no problems so far...but haven't done any front drums.

[Duke W.]

Re: Drum Brakes Question

The OE drums are not marked with the 11.090" maximum diameter. That was a FMVSS that went into effect circa 1968, so it's there on post-'68 replacement drums.

If the drums are not out of round, they don't need to be turned, and a decent brake shop should have a brake drum mic, or you might be able to rent one.

Metallic linings wore the drums more rapidly than the base linings, but either way with 50K miles your drums are likely okay. I've recommended to some low miles J-65 owners that they just rebuild or replace the wheel cylinders, clean everything up and put the system back together with the OE shoes and drums.

Even scoring, which is typical on J-65 drums is not a problem as long as the drum is round, however, scored drums require a gentle and somewhat lengthy (a few hundred miles) break-in of the new shoes.

Inspect, measure, and use as many of the OE parts as possible.

Duke

[Stuart F.]

Re: Drum Brakes Question

The main problem with that is finding OE linings for the J-65. I searched for several years w/o success. I knew my old ones were failing as I checked them on my last tire change circa 2004. My drums were scored, slightly out-of-round and tapered. Not enough to scrap them, as they all cleaned up between .032 and .045. Do I feel they have been weakened? NO!

I now have close to 600 miles on the new Matrix Ceramic linings w/cut drums and I am very happy with them relative to their cold and hot performance. My cold braking is improved greatly, and my hot braking seems to improve with heat w/o any noticeable fade - but then, I'm not racing them. I should mention I installed a correctly dated sleeved master cylinder at the same time to replace an incorrect 64 put on by the shop that stole my original 63. If I were to try to improve anything it would be with the master, but I wanted it to be correct so I'll live with it.

With disc brakes, I have had two sets of rotors now on my 2000, each having been cut once. It is true that cutting the rotors seems to weaken them, because the first real hard stop thereafter you'll probably get pulsing as they seem to warp real quickly once cut. So has been my experience with a number of other cars too.

Stu Fox

[David D.]

Re: Drum Brakes Question

Thanks to all for your replies....I really appreciate all your suggestions, experiences, etc.

I was thinking of new drums or turning current, just because.....but that is what is so great about having a forum with such knowledable folks. I now have a different approach for attacking this. I am going to clean and mic the originals, replace/repair wheel cylinders, check/replace hosing, check master, replace springs etc......and just replace shoes.

Thanks again,
David

[Duke W.]

Re: Drum Brakes Question

Most shops want to turn drums/rotors with every brake job because they don't want to take the time to measure everything, and the pads/shoes will break in quickly.

Restoration work is a different ball game and you should reuse original parts whenever possible even if you spent more money to recondition them than new parts may cost, especially when the "new parts" may not be the equal of original.

The front rotors on my Cosworth Vega have about 40K miles on them, which includes about 5000 miles hot lapping race tracks. They are on their sixth set of OE semi-metallic pads, are scored silly, and have numerous short radial cracks, but they have no runnout and only about .020" wear. They will last forever! The rear drums and shoes are original and will likely never need anything done to them. Given my low current mileage accumulation and the fact that I have pretty much retired from racing, I doubt if they will ever need work.

I rebuilt my original J-65 system on the SWC in the seventies at 115K miles, which included several hundred miles on racetracks. The drums were worn about .060" and the shoe material was well worn, but not worn out.

I decided to buy new shoes, drums, springs from GM (and I kept all the original parts), which were still available at the time, along with new m/c and wheel cylinders, so the system was essentially brought back to new, but the drums are later part numbers with the max diameter in the casting.

Being as how everything was new, I flushed the brake lines, including the new hoses with denatured alcohol, disassembled the m/c and wheel cylinders, cleaned them with alcohol, then assembled everything with silicone fluid and filled the system with silicone fluid.

Duke

[Gary B.]

Re: Drum Brakes Question

First, you do not really have to turn drums unless they are out of round or the shoes wore off and you have grooved the drum. I am only referring to standard shoes. We were the local brake drum and shoe experts in the 50's and 60's. My '62 has over a 140 thousand miles and I did turn the drums once. If you turned a drum, or have considerable miles and brake action on the drum, then the diameter has been enlarged slightly and the standard replacement shoes will not make 100% contact as the diameter of the standard shoe is slightly less, therefore only the center contacts the drum and the shoe must bend slightly to get full contact. The way this problem was solved was to use oversize shoes and sand the correct diameter on the replacement shoe. By doing this the customer felt a solid braking upon leaving the shop and that is what he paid for. When using a standard shoe on either a worn drum or cut drum, the brakes will feel slightly spongy as the new shoes must wear and bend to fit the slightly larger diameter requiring slightly more muscle action on the brake pedal for a short while. Personally, I always put a new set of standard shoes on my drum cars when the shoes were worn down.

Adjusting the shoes in the drum is key. The trick to adjusting is to tighten the shoe snug, meaning you can't rotate the wheel anymore. Then pump the brake pedal a few times to center the shoes in the drum, then back off till you can rotate the wheel by hand, but still feel a little drag. Then the shoes will wear in to the drum on use. I have tried to describe a feel that I learned from lots of experience.

Brake shops are not allowed to turn a drum beyond the tolerance diameter, but we never saw a failed drum in the sense that the brakes gave out. In the days of the riveted shoes, we would find drums that had parted in that we had a series of unattached circles, but these always constrained the shoe so the cylinder did not fail.

[Stuart F.]

Re: Drum Brakes Question

Gary;

I recall what you are talking about here as what they used to call "fitting the shoes to the drums". When I was in discussion with the Tech person at the brake mfg. where I bought my Matrix Ceramic shoes and kits, he told me they do not do that anymore. Now, I don't know if he meant that for just their product or in general. What I do know is my drums were cut, each to a slightly different size, and I did not have the shoes "fit to the drums". I did, however, adjust them as you described as at least I remembered how to do that from my past experiences. Again, after about 600 miles run in, they are working up to and beyond my expectations. I had a little sponginess in the peddle to begin with, but that seems to have abated.

Stu Fox

[James W.]

Re: Drum Brakes Question

I have a question... Do any of you with drum brake equipped C2's have a problem with the rear brakes locking up before the front brakes do? I have done some testing and the rear brakes always lock up before the front brakes do. I have new NOS drums with new standard lined shoes, new wheel cylinders and new brake hardware kits on all four corners. The car seems to stop great but when doing any type of testing, i.e. panic stopping or backing the car up in reverse to adjust the brakes, the rear wheels will skid but the fronts never do. I have also replaced all the rubber brake lines. I am wondering if I have some blockage in the front brake lines?

Any comments?

Also, here is the GM instructions for heavy duty brakes dated June of 1961.

Regards,

James West

[Stuart F.]

Re: Drum Brakes Question

James;

I never had any lock up with the previous metallic linings, that I can recall. The few times I made a panic stop, I was all too concerned about the passenger seat flying forward and anything in the back coming forward into the foot well! I was once in a road tour and, as is common when someone stops quickly up front, there is a whiplash effect further back. I stopped so fast from about 60 mph that all my cassette tapes from the back came flying forward, and a 93 Vette went sliding by me on the left on the concrete median. He told me later he'd never seen a C-2 stop so fast.

My current Matrix ceramic linings seem to be comparible with the metallics in stopping power w/o lockup.

Stu Fox

[Bill M.]

Re: Drum Brakes Question

I have a question... Do any of you with drum brake equipped C2's have a problem with the rear brakes locking up before the front brakes do? I have done some testing and the rear brakes always lock up before the front brakes do. I have new NOS drums with new standard lined shoes, new wheel cylinders and new brake hardware kits on all four corners. The car seems to stop great but when doing any type of testing, i.e. panic stopping or backing the car up in reverse to adjust the brakes, the rear wheels will skid but the fronts never do. I have also replaced all the rubber brake lines. I am wondering if I have some blockage in the front brake lines?

Any comments?

Also, here is the GM instructions for heavy duty brakes dated June of 1961.

Regards,

James West

This is not a safe condition.

I would check wheel cylinder diameter first. (I'm assuming you have a stock car, no 427 up front!) A sticky tire may contibute to rear lock-up. A car sitting too high may contribute to rear lock-up. A higher friction rear shoe (or lower front) would also do this, but I don't know how to check for this.

There are aftermarket adjustable proportioning valves you can use to limit rear lock-up, but I would use these as a last resort. Passenger cars are designed to lock front tires first...I think something is wrong.

[Gary B.]

Re: Drum Brakes Question

I have to ask the simple questions first. Have you thoroughly bled the front brakes and did you have any problem with the bleeding process, if not then there shouldn't be any blockage. Secondly, have you adjusted the front and rears correctly, see my earlier discussion on adjusting. If the back brakes are adjusted tight and the front loose, you could get an initial locking, although I might expect you to get a front pull in that situation. When you push the pedal down, is it solid, spongy or leak down? With car up on stands, can you spin the front wheels with the brake pushed down? Spongy usually means air in the lines, leak down means a check valve problem in the master cylinder. Also, do you have the correct free play, half inch or more in the brake pedal before you feel back pressure? Insufficient free play can cause the master cylinder to backup and start to apply pressure. I am not as familiar with dual MC but a section could be loading up over the other if you do not have sufficient free play.

[David D.]

Re: Drum Brakes Question

Follow on question - based on Dukes comment

I flushed the brake lines, including the new hoses with denatured alcohol, disassembled the m/c and wheel cylinders, cleaned them with alcohol, then assembled everything with silicone fluid and filled the system with silicone fluid.

What is best recommended brake fluid to use for driver? (No racing) DOT 3, 4, 5 ???

Any special precautions to be aware of?

Again, THANKS....
David