Supernaut72

My car is one of those late-'60s oddities with power-assisted drums. Just replaced my master cylinder and booster with units of like dimensions. The old pair was the last component of the brake system left untouched. The booster leaked vacuum with the pedal depressed, and while the car would stop on a dime, if sitting at a stoplight for over 30 seconds in hot weather the pedal would begin to creep to the floor and would need to be released and re-applied to keep the car stopped.

After bleeding down the new MC and all the lines, the pedal isn't spongy or anything. It's good and firm and the booster holds vacuum for three full pedal depressions after shutting the engine off. All brake linings, hoses, lines, and wheel cylinders are new and have 1,000-2,000 miles on them, and are in proper adjustment.

The car stops fine, it just seems like it takes about as much leg muscle to stop it as in one of my manual drum cars, but with considerably less pedal travel. Is that the idea? The only other car from the same era with power brakes that I can compare it with is a slightly newer Cadillac with a meaty dual-diaphragm booster and disc brakes, so it isn't really a direct comparison.

Oldsmaniac

The condition you described with the pedal slowly going to the floor at a light is a good indication of master cylinder failure. Power drum brakes were very common in 60's cars, not an oddity at all. The pedal effort should be next to none with power brakes. Harder linings (metallic) will require just a bit more effort.

Supernaut72

Yeah, I figured the pistons were starting to bleed pressure when the fluid was warmed up and thinned out a bit. The pedal drop never happened when everything was cold, like just starting out on a drive on a cold day. Thankfully, that doesn't happen anymore.

The brake linings are Wagner Thermoquiet, not sure what they're made of, maybe ceramic? I'll have to drive the car again and see what the pedal feels like now that I'm not at the tail-end of a 20 hour day, could take less pressure than I remember to get the brakes to actuate and I was just a little underwhelmed (at least when comparing them to my Cadillac's brakes).

Oldsmaniac

Also too with new linings and old drums the shoes do not make full contact with the drum because the drum is slightly worn. The shoes need to "wear in" so to speak...

Supernaut72

Thanks for the idea, that might be exactly it. All four drums have been cut. I expected a longer than usual wear-in period when I did the brake job, since nobody likes to arc shoes anymore, but wasn't sure how long it would actually take for full wear-in.

Last I checked, there was a good amount of wear at the top and bottom edges of each shoe but still none in the middle, and I haven't done all that much driving or braking in this car since then. Force of habit, I tend to coast a lot more than I brake. Maybe they still haven't fully worn in because of that.

Just got back in from some testing and the booster's definitely assisting, the pedal holds firm and then falls away just a little bit when the engine's started.

joe_padavano

Probably 75% of the cars built in the late 60s came with power drums. Hardly an "oddity".


What does that mean? Were they exact replacements or not? If the booster is not a correct Delco replacement, all bets are off on pedal feel and assist. Differences in diaphragm diameter, internal valving, etc all affect pedal force. Same with the M/C. What is the piston diameter? A larger M/C piston will increase pedal force and decrease travel. And did you connect the booster pushrod to the proper hole in the pedal arm? The upper hole is for manual brakes, the lower for power.

Finally, as noted, a pedal that drops over time is indicative of a master cylinder problem, not a booster problem.

Supernaut72

Ok, I stand corrected on the amount of cars equipped with power drums vs standard, I was going off of personal experience. Most cars this age that I've encountered do not have power assist unless they're early disc brake cars. Just the way I've experienced it, that's all. Can't argue with production numbers though, 75% is way more than I ever figured.

Never meant to imply that the pedal sinking problem was a booster issue, I said that the issue with the booster was that it leaked vacuum very audibly with the pedal depressed, both components were shot. If the MC was fine I wouldn't have messed with it, since in my experience that's a good way to break a good working system. The master cylinder and booster were sold to me as a matched pair specifically for 1967 and 1968 Olds 98s, Delmont and Delta 88s with 4-wheel drums only. The guy who rebuilt it could have been mistaken but he was very specific about only paying me for my core if it was out of one of the aforementioned cars.

I'll check on the hole I installed the securing pin through, I didn't notice any second hole (at least, not anywhere near the one the pin came out of when I removed the original booster). I was aware from reading around here that that's a common mistake, so I tried to avoid messing that up.

Supernaut72

Update: I'll have to find time to pull the wheels to verify, but I'm increasingly sure that the mismatched arcs of the new brake linings are the culprits here. Just replaced the stretched-out, kinked front parking brake cable to match my earlier replaced middle cable, and while actuating and releasing the parking brake I can hear the rear drum brake return springs expanding and contracting a great deal... But it won't hold the car at all, despite the pedal travel having felt perfectly normal ever since I installed and adjusted the shoes.

Guess I'd been attributing the extra pedal effort to the worn out MC/leaky booster, and I'm only noticing it more now that those components are new. Normal pedal travel means nothing if the actual lining contact area is super small.

Supernaut72

Well, I've been attempting to really bed the brakes in and I've noticed that an old problem I'd forgotten about is still there. When the brakes get hot during 65 to 20 MPH braking runs, they tend to pull to the right, a little at first and then progressively worse and worse until they sit and cool. The springs are the originals as far as I can tell, so I'm going to go out and order new springs for all four wheels.

I'm not usually a parts-replacer since I can't afford to be, but at this point I can't think of anything else that would be causing this, as there are no fluid leaks and the system has just been bled in the correct order several times. All four drums' auto adjusters have been tested and work, and each wheel auto-adjusts to have a light drag. Naturally the fronts get hotter than the rears, but the drums seem to get evenly hot from left to right.

oldcutlass

The parking brake has nothing to do with the master cylinder leaking, its 100% mechanical. Make sure your cables are adjusted properly.

Drum brakes usually pull because one of the wheel cylinders is sticking. You need to remove and inspect all of them to make sure the inner cups move in and out easily. You can either buy rebuild kits and a small hone or new wheel cylinders. If the insides are pitted they will not hone out.

Supernaut72

Oh I know. I'm saying, the brake linings not being worn in is likely why the parking brake won't hold at any tension (too little friction material making contact, which would also make for harder stopping in general).

The wheel cylinders are all new, and do not leak or stick as far as I've observed. I was aware that on occasion people have gotten bad cylinders out of the box, so I've made sure mine were good. The problem goes back a ways, it isn't anything new. I'm just generally very easy on my brakes and so I hadn't noticed the hot pull again until I made another effort at really seating these new linings.

oldcutlass

Granted I drive an A body, just did mine about 2 weeks ago and they settled in quick. Another thing that will cause a car to pull is worn front end components.

Supernaut72

Hmm... Not sure if it being a B-body has a part in it, but like I noted earlier, without thinking I tend to coast down and use the brakes very gradually and lightly. Often times when rolling up to a red light I don't even wind up having to use the brakes. Just how I was taught to drive, hard habit to break. The four drums auto-adjusting to always have a bit of drag also helps the car slow down "automatically" as well, so the brakes don't really get used to their full potential unless one of our famous Grant Road jaywalkers steps out in front of the car. That's happened in this car a couple of times now.

Worn front end parts would make sense, though I've done all the CSM checks for front end play while I was diagnosing my steering and front tire wear issues and everything checks out fine. That all came down to rotted control arm bushings, busted steering link, and then a tie-rod end the shop damaged while removing the control arms. All of those have been replaced. No pulling or veering while driving or while braking when everything is within regular temperatures.

Reason I'm going for new springs is that I thought I'd remembered hearing that fatigued return springs can get reluctant to pull the shoes back in, particularly when it gets hot inside the drums. IIRC I was a little harsh on a spring that didn't want to cooperate on the right rear drum, though whether that killed an old spring's ability to function or not, I'm not sure. At any rate it's kind of a MAW, they have front drum spring kits for $0.55 on RockAuto currently (Bendix closeout).

One other thing it could be: When the left rear wheel cylinder kicked the bucket, it got some fluid on the primary shoe's lining. Of course this was while I was tinkering with the brake system so I almost immediately hit the lining and the drum with scalding hot water, and scrubbed the lining with a scotchbrite, as someone on the HAMB had suggested. It seemed to do the trick, the brakes dried to their original appearance and didn't give me any problems whatsoever in the weeks that followed. But then, anything's possible.

oldcutlass

In most cases if the shoes get soaked in brake fluid, it may brake the lining down and eventually lead to failure especially with bonded shoes. No amount of cleaning may get all of the fluid out.

MDchanic

I've always just used some lacquer thinner when I've gotten brake fluid on a shoe or a pad, and never had a problem, but if a shoe has become saturated with brake fluid over time while in use, it needs to be replaced.

- Eric

Supernaut72

Yeah I imagine brake fluid isn't great for the material or the bond, fortunately when the wheel cylinder puked it didn't really soak the linings through. Just splashed a bit of fluid on the primary shoe. Don't remember the details of it, think it might have blown out while pressure testing after a system bleed or something like that. Most of what I recall is that the car hadn't been driven anywhere since the system repair prior to that incident. I saw you had a bonded shoe spontaneously delaminate recently, seems like that could have some unpleasant consequences.

Lacquer thinner would be a bit easier than boiling up water, and probably more effective. I'll have to keep that in mind.

oldcutlass

Yeah, I don't know what caused mine to come apart, I had some weird pedal feel. I had just changed my shoes about 6 months prior.

Supernaut72

Spooky. Good thing it was in the rear, rather than some sort of front failure. Thinking about it, I'm fairly certain mine are riveted, I'll have to go look at the box I chucked the old ones in though. Either way I think I'll be swapping the shoes left for right when I receive the springs, just to see if the problem follows the linings, assuming new springs don't fix it.

oldcutlass

I don't change springs unless there is a visible defect. Be curious what you find.

Supernaut72

Yeah, on most of my other cars that have needed drum brake work in the past I've just replaced linings, checked drums, and away I went. Honestly, as I recall it the springs looked reasonable, minus all the coloring being long gone. It's just that one spring in the right-rear drum that worries me a bit. Think my spring tools were on loan to someone at the time, so had to lever the springs off and on with a long screwdriver, which I recall went well on every spring except one. It gave a bunch of trouble and the screwdriver shaft stretched it a fair bit further and played hell on one hooked end of the spring more than the proper tool would have. I know they're tough stuff, but I admit that was a fair bit of abuse that one endured during both removal and installation.

I'd leave the fronts alone unless it became apparent that they're causing the issue, but the front springs were the ones that I found the closeout deal on. Plus the el cheapo replacement inner wheel bearings stick tight on the spindle and require some serious prying to remove them whenever the drum needs to come off, which I've always been uncomfortable with. Got some Nationals en route with the spring kits, so MAW get that junk off of my car while I'm inspecting the brake system.


Edit: D'OH! Think I might have figured out at least part of the problem. Silly me, I filled the master cylinder reservoir to the top anticipating another round of bleeding, and left it that way when the pedal felt good and firm instead of bleeding it down the 1/4" or so that it should be from the top in regular operation. Hot, expanding fluid + brake application = at least one cyl sticking, I would imagine. Now, whether it causes a pull to the right due to line dimensions or in conjunction with a compromised return spring that makes the passenger's side more prone to dragging, I don't know. Guess I'll drop that fluid level first, and worry about the rest when the parts get here.

Supernaut72

Almost forgot to update this, amid other projects. I did the rear springs, noting that the springs on one side were almost entirely discolored while the other set still had much of their color under the layer of brake dust. Don't think that's necessarily an indication of anything, though it's possible. The new springs won't need attention anytime soon so I'm glad I swapped them, but I think the rub spots on the backing plate had more to do with the pulling than the springs.

Turns out, there was a groove in the lowest rub point of the primary shoe on the right rear which the shoe wanted to really settle into. Took an old sturdy metal file and carefully filed it down so the shoes would slide smoothly, removed the very slight lip that had formed on the other two primary shoe rub spots, cleaned and greased everything. Left rear had some grooving as well on both lower rub spots, but those came out without too much trouble. Not sure how I missed this when I did the linings since I did grease all the points, but they're pretty well taken care of now.

Still planning to get out there and do front brake springs so I can check the front backing plates and replace those troublesome inner bearings, but so far the brakes feel great. Nice straight stops. Will have to warm them up a little and try them on a level road after I get the fronts done, but even on crowned roads it feels much better. Used a higher temperature grease in the auto-adjusters this time, too, so those should spin easier. Brake linings look bedded in nicely, so the fronts should look the same.

joe_padavano

That is an excellent observation. I had the same problem with the rear drum brakes on my truck, and it required the same solution. I now check the backing plates and file these rub pads as needed when doing brakes. I have always used a small dab of grease at the rub points when installing new shoes.

MDchanic

I've never seen that failure mode. I will be sure to look for it every time I do brakes in the future.

Thanks!

- Eric

Junkman

How old are the rubber brake hoses? If you don't know the answer to this question, then it is time to change them. They deteriorate from the inside, and can cause brake drag, because the fluid can't return to the master cylinder when you release your foot from the brake pedal.
If you haven't rebuilt or replaced all the wheel cylinders, you are living dangerously, because they do wear out, and can fail at any time.
The last point that I will make, is if you purchased a "off the shelf" rebuilt power brake booster, it might be good, or it could be bad. My experience with store bought rebuilt power brake boosters, has been mediocre to say the least. Now, I send the originals to Booster Dewey, and they come back working perfectly. It costs a little more, but it is worth the cost to know that my braking system is working perfectly.
Keep in mind, that bad brakes or steering can kill or maim you for life, but a bad engine or transmission will just leave you on the side of the road waiting for a tow truck. I would rather wait for a tow truck than to take a ride in an ambulance, or something worse, like a hearse.
Almost forgot to mention the correct way to know if a brake spring is defective. You drop the spring on the cement walkway, and if it lands with a dull thud, it is good. if it lands with a "bong" type of sound, like you think a spring should sound like, it is definitely bad.

Supernaut72

I wonder how long these grooves had taken to form, on both our vehicles. Rub pad lubrication hadn't been something I'd ever really thought about about prior to seeing that canyon carved in the RR plate. I did the fronts today and had to remove shallower but larger grooves on the lower rub spots on those wheels as well. Had other plans after the job and didn't get to test drive the car today, but that should do it for the brakes.


Junkman, way ahead of you on that. All new lines, cylinders, hoses, linings, front hub grease seals, master cylinder, booster. No leaks, pedal's firm and after eliminating that pulling issue, the car is capable of stopping in an incredibly quick and controlled manner for a non-ABS car of this weight. The frail master cylinder wasn't much of an issue when the car was rarely started, let alone driven around in actual traffic, but I'm hoping this is the year that that changes. I won't easily forget the first time I lost my brakes, going downhill at 50 or so in a Galaxie when the pedal went to the floorboard. Split LF hydraulic hose did that job. Limped her into my parents' garage with just the rear brakes before figuring out what had happened. Not sure how I got out of that one, looking back, and not eager to repeat anything of the sort.

I have over two months left to warranty replace the booster if I somehow confirm that it's bad, but at the same time the car brakes better and better with each adjustment I make so I don't want to jump the gun on tearing it back out, since it's technically passing all of the functionality tests. I'll have to keep Booster Dewey in mind, though, thanks for the lead.

Great advice regarding the springs, that replacement job is now done but I think I'm going to test the old springs out of curiosity.


Last order of business before testing my latest work is to fix the auto-adjuster on the front-left wheel, which I'll have to troubleshoot. The adjusting/locking arm doesn't contact the star wheel, so I'll have to figure out why. Possibly a dulled star wheel, but it's a pretty big clearance despite everything being installed and seated the same way as the RF brake. I recall it was working fine a little while back, and had no reason to suspect it before disassembling it so I'm not sure if it was locking against the star wheel right before disassembly or not. Other three work great.

oldcutlass

The adjuster arm may not be seated properly or the bottom spring is installed wrong and interfering with the arm.

joe_padavano

There are two rather obscure drum brake failure modes that have caused me problems in the last few years. The first is this wear problem on the backing plate where the shoe rides on the plate. As we drive these vehicles more, the edge of the shoe wears a groove in the backing plate that can restrict shoe movement, as noted above. Keep in mind that these cars were never intended to be driven for half a century.

The second is even less obvious. On several occasions I've installed brand new Chinesium drums after a brake job. The brakes would over-adjust as I drove over the course of a few days or weeks, to where they were dragging and obviously heating up. I had to physically back off on the adjuster. This one had me puzzled for awhile, until I realized that an out-of-round drum will cause the whole shoe-adjuster-spring assembly to move back and forth on the backing plate. This would then actuate the self-adjuster, causing the brakes to over adjust. Having the brand new drums turned solved the problem. Yes, I was pizzed about that, especially considering that I had paid a premium for NAPA's top grade drums for my truck, which were STILL Chinesium!

Supernaut72

Good suggestions, thanks. Turns out it was neither of those, though. Disassembled the adjuster assembly and compared the star wheel and the adjusting arm against the LR wheel's, turns out it was bent away from the star wheel just enough to stop working. Don't know when or how that happened, as I've never man-handled that component. Bent it back little by little until it held the star wheel correctly, now I'll just have to keep an eye on it.

Also finally got the idea to borrow my Roadmaster's scissor jack. It's rated for this car's weight, it's lighter than the hydraulic jack I'd been keeping in the trunk, and it doesn't dig into the dirt. Pretty good upgrade.

I've had this same thing happen on my Chevy, though I didn't go for the most expensive drums. The out-of-round was bad enough to cause severe pedal pulsation. Pathetic that a more expensive drum would still be out of round. If these manufacturers are dedicated to producing borderline unusable crap, it seems like they should at least slap a "must turn before installation" label on new drums.

Even giving them the benefit of the doubt and assuming it's a storage issue instead of a manufacturing problem, it's still on them to clearly print their boxes so it's apparent to even the thickest dullard in the warehouse which way they're supposed to be stored.

joe_padavano

I've grabbed several of those in wrecking yards. The late-80s H-body cars (FWD D88, Bonneville, etc) have this jack in a plastic storage case. Very nice for older cars.

oldcutlass

Glad you got it fixed, brakes can be challenging at times

Junkman

Don't feel bad about having to turn the drums. Back in the 1960's I always had the machine shop take a "trueing" cut on new drums, and they almost always were out of round, right out of the box. Back then, we would measure the drum size with a brake micrometer, and the auto parts store would custom grind the shoes to the contour of the drum.

Supernaut72

We have a fair amount of those cars in our local yards still so I'll have to keep my eyes peeled next time I stroll through one. Could use a dedicated one for each car, bonus if it still has the plastic case.

Definitely, glad the remaining items I'd been putting off are finally done. It was about time. Thanks to you and everyone else who offered tips and suggestions here.

Ha, good to know, gives a little perspective. Guess I should start factoring the cost of an initial cut into the price of new drums as a given. I think I'd just figured that with how "superior" modern manufacturing is alleged to be, that that wouldn't be necessary, but at least that particular issue isn't any worse than it was back then.