Anybody a drum brake expert? I have a 66 buick Skylark with power drum brakes.

To date I have replaced front wheel cylinders, front shoes, bled system, replaced power booster and still have a rock hard pedal and cannot get the car to stop without using both feet on the pedal.

Plus, you cannot hold the car against the engine "brake torque" as it will literally drive away.

This is probably a simple fix, but I can't seem to find the answer.

Thank you for your hrlp.

Not an expert but there was an earlier thread on replacement shoes that performed so bad they would hardly stop the car. New shoes all the way around. They replaced the shoes again and the car stopped fine. If your pedal is solid and there is very little travel, I'd say the new shoes may be your problem. Sounds wild but its true.

You might also check to make sure that the vacuum line is supplying vacuum. I ran into a situation where the vacuum line was plugged.

My first idea was brake power booster vacuum supply. Since every car is somewhat different, refer to the shop manual for your car. Proper adjustment out of the front brake shoes is critical as well, but you have probably checked that already. Make sure the back shoes are helping the fronts.

I have had similar issues with a 66 Oldsmobile Toronado I used to own, that was caused by vacuum issues because of a modified camshaft and too high of an idle. It was intermittent as well.

Double check your vacuum source.

Well, I've just about given up on this project and the car!

As soon as I can locate a brake shop that will work on it, I'm turning it over to professionals?
So far I have: 1. replaced power booster
2. confirmed vaccum at the booster is 13" per the factory manual
3. Checked out the master cylinder
4. Replaced one leaking wheel cylinder
5. Installed new front shoes with new springs and hardware (I removed the self adjusters)
6. Bled the system with a vaccum pump
7. also replaced brake fluid
8. adjusted both front and back brakes per the factory manual
9. Car stops better, but will not lock up the wheels in gravel and will no hold the car against the engine torque.

Time to find a new hobby??

I know your frustration well, just one question, if you took out the self adjusters on the fronts, how are the shoes set to factory specs? Or did I read this wrong.

The self adjusters do not impact the initial operation of the brakes. Thier only function is to keep the brakes in adjustment as time wears on.

I'm not interested in keeping the system original, and will put the adjusters back on once I've gotten some whoa established.

Just a thought here...

Did you replace the flex hoses to the front wheels and the rear axle? If these are worn out, they can fail internally and block pressure to (weak/no brake) or from (locked wheel brake) the wheel cylinders under braking pressure, but still flow under low/no/vacuum situations.

JMC

Not an expert and really not trying to irritate ya...but. If the self adjusters are out the brakes on the front have to travel to max if they are even making contact. The way I was taught to install shoes and adjust was to assemble and move adjusters till the wheel dragged a bit. Do this on all four. Your car has the single cyl master which means all the travel is happening in the fronts if there are no adjusters. You could simply have the master maxed out. I'd put the adjusters back in and adjust till there was a little drag on all four. At this point what have ya got to lose? A pro would charge ya to put in the adjusters anyway. Hope this helps.

Sound like the problem I had ( Link ).
If your replacement shoes were made by Raybetos that may also be the problem.
Willie

Yes - you can not differentiater AT ALL from the factory settings which include self adjusters to keep the shoes at the minimum possible distance to the drums. The return springs are taking the shoes in to the minimum setting each time. the self adjusting is much more then what it sounds like.

Let me put this another way -

With disc brakes the second you take your foot off the brake, the physics involved take the pad off but just barely. The caliper piston is extended as far as it can be. Now imagine if each time you took your foot off a disc brake car the caliper piston retracted all the way into the piston and then had to travel all the way back out. You would smash into the car in front of you.

Please try returning the system to the exact way it was.

I also did something stupid with my Toronado. I put new brakes all the way around on it (4 wheel drum) and when I couldn't figure out why my brakes were bad I took it to my mechanic (this was during my auto tech days when I wasn't as expereinced) I had put the shoes/kit on in reverse on at least two wheels, so the duo servo action wouldn't work. The main brake shoe was not contacting enough to throw the other shoe against the drum.

Just some ideas. Keep trying.

Well, you're the second person who has advised replacing the hoses, so guess what's next?

I'm ordering both front hoses and the rear one.

As to the shoes, they came from AutoZone, so there is no way to track the heritage of where they came from.

The adjuster I removed was for the automatic adjustment, not the "star" wheel adjuster. It will go back to original once it starts acting less like a runaway train.

Once again I thank all of you for the advice. I take constructive comments as a path to improvement, so speak your mind!

Misunderstood adjuster, you are correct the star wheel is what makes it. Looked up AutoZone and your shoes are either Duralast or Valucraft. I wish like hell I could remember where I got my shoes for my 65 Skylark which has manual brakes.

Just curious, how did the manual say to adjust the brakes? I certainly agree with the slight drag recommendation. The thing is I would back off the star and return the self adjuster lever. That is because I have also gone the route of counting the clicks from the star wheel running across the self adjuster, untill the first wheel's pads just scrape the drum. Then I would adjust each wheel the same number of clicks, then apply the brakes once and let them off then adjust again till you get the scraping of shoes on the drum.

BTW, were the drums turned? and then installed clean? By this I mean it's not a case where the drums were turned and then oiled to prevent rust on the brakeing surface, is it?

JD

Got an idea. But do not attempt if your emergency cables are froze, don't force em. But if they are operable maybe we can narrow the point of the problem. Had my system fail in Bo Fo Egypt once. I literaly drove the car home on emergancy brakes only. It was a white knuckle drive. They don't stop very good, but they do stop. If your car stops with emergancy brakes and is about as responsive as the system, at least we can isolate if its a problem in the wheels or if its a master/booster thing. I'll keep thinking but this is the best I can come up with for now.

Whether the car stops or not would have no bearing upon the self-adj mechanism (i.e., cable) being in place. On some cars, the "hd" or "police" brakes were not self-adjusting, but the normal brakes were . . . same parts other than the self-adj items. The self-adj items are there to keep things adjusted all of the time (whether from a reverse stop or forward stop to make it work), not to make it stop better per se, but to keep the pedal travel more the same over the life of the brake linings.

On what 3Jakes mentioned about disc brakes . . . the earlier disc brakes did have more drag on the rotors when the brakes were not applied. That was the nature of the system, back then. When fuel economy became more of an issue in the early 1980s, the disc brake calipers were changed to let the disc brake pad retract more into the caliper, reducing drag on the rotor. To make that system work, with no delay in their application, a "quick take-up" master cylinder was developed. It had some different master cylinder bore arrangements that put a lot of fluid to the caliper first, to get the pads against the rotor and then a normal bore area that functioned as the prior system did (once the initial pedal travel was initiated). That way, they got the same fuel economy advantage as drum brakes but with the expected performance of disc brakes. Seems like one of the first applications for this type of system was the 1981 Chevrolet Citation (and other fwd X-body kin)?

As for the drum brake adjustment . . . there is a brake adjustment caliper that you can buy to do the initial adjustment of the new brake linings with. Much easier and quicker than doing it under the car . . . plus you don't need an overhead lift. It has one side that takes the drum's internal diameter and then the other side matches that to the brake linings "diameter", which is adjustable when the brakes are not applied. I believe it's calibrated to have the desired clearance between the brake linings and the inside of the drum, as it's supposed to be.

I remember seeing mechanics do the drum brake lining adjustments. As I recall, they went until they got a slight drag (seen AND heard) and then backed off the star wheel enough clicks (consistently) until the noise and drag just went away. I suspect that even with a very slight drag of the brake lining against the drum, enough heat would be generated to partially fade the brakes as you drove down the road. So, adjusting them up until you hear the drag and then backing off a slight amount until you don't hear anything anymore, but not "massively" backed-off, would be the best way to do the adjustment (other than with the brake lining/drum caliper). KEY thing is to make sure they ALL are adjusted the same, especially the ones on each "axle".

Another issue, if the drums were turned, is just how much of the brake lining is actually contacting the drum's inner surface? Wear pattern??? Considering that most replacement linings are pretty tolerant of this situation (being a little "oversize" in diameter themselves), I don't recall ever having or seeing any real issues in this area, but it might be worth checking into.

Just some thoughts,
NTX5467

Thanks Willis. I'm eager to find out what it is. This drum brake issue pops up from time to time. I see less posts regarding disc brakes systems. As a mechanic starting in 1997, modern braking is all I've ever worked on. other thenmy 66 Toronado. Now I have 3 projects all with drum brakes, so I am interested to find out what it is.

3Jakes, drum brakes are still "modern" brakes, still being used on GM and other brands of light duty trucks. Not to mention smaller versions as the parking brake parts of rear disc brakes. Until recently, if disc brakes were on the front, drum brakes were on the rear, in most everything on the road.

What has changed? Still the same basic setup as they used to have, but with a few changes to the way the shoes are separated (some with a big omega-shaped wire spring or with the smaller coil springs that take the special tool to remove and re-install). Used to be that the parking brake cables both went in from the front of the backing plate, but somebody figured out that you could use the same left hand backing plate on the right side if you ran the cable for that wheel behind the rear axle and entered the backing plate from the backside of the vehicle. The backing plate stampings are usually the same, right to left, on the rear, just where they punched the hole for the cable to enter is different.

The other thing that changed, back in the later 1960s or early 1970s, was the lining composition to comply with federal specs for max pedal pressure for a certain rate of deceleration when stopping. This kind of standardized the lining composition with this "min spec" approach, but there were still some linings that were better than others (especially for heavy-duty applications). I remember some brake lining tests in the earlier 1960s (using a 1960 Ford Galaxie for the test vehicle). You'd be totally surprised how much difference there was, even in the more major brands, not to mention the less expensive brands (at a time before widespread use of auto supply "house brands")--they had pictures, too. Sure, typically all people generally worry about is that first stop, but when you're in the mountains or pulling a trailer (or similar), fade resistance and such can become very important (as the article and pictures demonstrated).

One other thing to consider . . . in the world of brake linings amd pads, there is an "industry number" that each lining set or pad set has assigned to it, like a manufacturer's part number. In some cases, this number is the selling manufacturer's part number, in some other cases, it's not (but on the box for reference). So . . . if two different brands might have the same "industry number" for their part number, it does not necesssarily mean both sets of linings came from the same source OR are the same exact part in different boxes. These common numbers greatly simplify things at the consumer point-of-sale location, meaning that the supplying jobber for the auto supply can change brands and the auto supply counter persons can still go by the industry number (as the manufacturer's part number) regardless of brand (or have that reference on the box). Makes things easier for them.

As has been recently pointed out, "brand" can be important now as it was in the middle 1960s.

Enjoy!
NTX5467

This was also done to reduce heat build up, reducing rotor warping. If for some reason the discs at rest are applied too heavily against the rotor the heat build up can be tremendous. Bad lines or dirty booster check valves have been known to boil brake fluid with catastrophic consequences. (I had a serious problem with a Celebrity that did this.)

Another idea is to take the car to a VERY open place (empty parking lot) which is nearly level. Be sure (as Bruce says) that your emergency brake works and can stop the car inside the available distance if the car fails this test! Going up a slight grade at very slow speed, try applying the brakes with vacuum to the booster disconnected. (It will be necessary to plug the vacuum source to get the car to run properly.) Compare that to the distance it takes before the disconnect. It will be necessary to stop the car with the emergency brake afterward, so go slow and give yourself lots of room.

If there's no difference you know its the booster (even though it's new/replaced), the check valve to it (if external), or the vacuum line itself. (Did you test vacuum at the booster or at the beginning of the booster line? Vacuum hoses are even more prone to failure than brake hoses.) If a difference is noted (i.e. no brakes at all!), then it's likely a hose or line problem. My 1960's brake lines (not the hoses, although they're more likely to go bad with age) were corroded almost shut when I got the car. One brake locked up on the first trip I took when the line finally collapsed while I was applying the brake, trapping pressure behind it. You may have one or more collapsed lines or hoses with no pressure behind them.

Good luck (and be careful!!!!!) <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

Well, the great brake problem is solved! <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

I put on an old used brake booster that came with a bunch of parts I bought off e-bay and now I have brakes.

Previously I had put on a rebuilt Cardone unit from Advance Auto Parts that turned out to be the problem. Car now stops very well and acts like it should.

Thanks to all of you for your help and input. I guess I'll think twice before putting "will fit" stuff on this old girl.