68 power drums - ERRATIC

[AnotherWs6]

Hey there, I have a 4 wheel power drum setup on my 68 burb from the factory. Previous owner installed a new master cylcinder and booster from a local auto parts store type place. They SAY they are correct but who knows.

The issue is this.... in low speed situatiosn, parking lots etc, the brakes are usually super touchy and will lockup if you look at them the wrong way. Once at speed the brakes require a lot of travel before they even begin to bite. They have a lot of stopping power once you get through the dead zone, but hit them hard and they occasionally make the truck darty and chirp/lock up/ The brakes themselves were all gone through. I installed a new check valve in the booster and it seemed to help a little. What do I have going on here? Wrong parts? Vacuum issue? It makes driving this thing a little scary@

[68Gold/white]

Have you tried adjusting the shoes?
I'm concerned that the M/cyl might be for front disc brakes, it would make it super touchy...

Picture of m/cyl might help...

[AnotherWs6]

I agree with the idea, the thing of it is is that at high speeds it has so much pedal travel before doing anything. Then it has light grip, then you get into it and it has medium grip....but get onto it hard and it wants to lock up so perhaps it might be.

I purchased the truck a coupe of months ago and it has basically sat since. Of course the day after I got home I ordered the correct master, booster and proportioning valve from classic industries. It was an impulse buy. I'd rather not spend all of the money and time if that's not the issue.

I can post some pics. It looks like standard GM issue for decades. Should it be smaller? - referring to the booster.

[68Gold/white]

Drum brake master cyl's have the same fluid volume compartments inside the m/cyl. Disc m/cyls have a much larger compartment for the front brakes 2-3 times as large.

If you have not checked the adjustment of your shoes, it's the first thing to do!

[mike16]

usually a disc brake master cylinder has a larger diameter piston, typically one inch rather than the 15/16th's diameter piston found in drum brake applications.

go to your auto parts store and determing what diameter piston/kit your truck calls for and compare it to what you have. too much volume and power assist will make for some fearsom stops.

the fact that it pulls erradically may be caused by poor break in procedure, poor adjustment, oil on shoes or drums not being resurfaced or too thin.

[AnotherWs6]

Saying it pulls is probably misleading. It doesn't pull 99% of the time, just when the brakes bite to hard at speed, and I think that is from the wheels locking up for a split second.

I have not tried adjusting the shoes. I am very very far from a novice, but I must admit that drum brakes puzzle me a bit. It's been so long since I have owned anything with them.... I don't know how to adjust them. I'm sure it will make sense when I get the drums off. Any tips here?

How would I know if the proportioning valve is installed correctly? Having it backwards would cause the rears to be awfully touchy and perhaps explain why there is such little initial bite at highway speeds. That touchy-ness might go away when the wheels are spinning at 60mph. And the fronts would be nearly worthless with all of that weight spinning. What do you guys think?



The site doesn't seem to like my pictures from photobucket. Do I not have enough posts or something?

[kwmech]

I think you need to pull the tires and drums and actually see what you are working with in regards to shoes, return springs, wheel cylinder possibly leaking/seeping, out of round drum etc.

[mild68]

The first step would be pulling the drums and check the shoes. I would suspect leaking wheel cylinder or perhaps rear axle seal.

[mike16]

its time to invest in service, repair overhual and parts manual.

pull your drums and take a look. anything looks bad or rusted, replace, if too much needs replacing just replace everything. new stuff is available and its everybit as good as any 40 + year old hardware.

do one side at a time so you can refer back when doing it all up. and burn lots of photographs. lots and lots.

I had erratic bakes for a while. one wheel kept locking up. because it kept locking up , and wheels arnt supposed to do that, I always thought it was the offending wheel and focused all my trouble shooting and pit side maintenance on it. wrong. the other side wheel cylinder was leaking. it was months of stoopit and a conversion to a dual mastercylinder set up for me to realise........ it was a leaking wheel cylinder.

so .......service the system, repair as needed and ruthlessly replace any offending brake parts.

[AnotherWs6]

^^^^I suppose popping things open first is the way to go. For what it's worth I have receipts from the previous owner for new everything. There are no old parts left in the braking system and they have almost no miles on them. Not that this means nothing is wrong or mis-adjusted but it does make me think that maybe the wrong booster or master or prop valve was installed. Especially since they came from an auto parts store. I know I would never trust my auto parts store to get me the correct parts for such an old vehicle.

[67 chevelle]

recently acquired a 59 Apache , everything new on it also , 4 wheel Manuel drums , buuuttttt , guy put the shoes on backwards on the right rear , big pad forward , fixing that helped but , drums will never stop like discs

[68Gold/white]

Some good hopeful things about taking a look at your shoes, etc, with new drums you won't have a ridge on the inner edge of the drums, the drums should slide right off, easy.
The front drums also will not be riveted to the front hubs like the originals were.
I get the feeling that the adjustment is on the loose side, which should without doubt allow easiest removal of the drums...
If you are in doubt about what's going on, you could post some pictures here, allow experts to help out!!!

[AnotherWs6]

I'd love to. But how come I can't post pics?

[GASoline71]

Originally Posted by mild68

The first step would be pulling the drums and check the shoes. I would suspect leaking wheel cylinder or perhaps rear axle seal.

This is my thought as well.

Originally Posted by AnotherWs6

I'd love to. But how come I can't post pics?

You have to upload them one at a time. You can upload multiple pics in the same post. You just have to do them one at a time.

Gary

[AnotherWs6]

I pulled the brakes off a couple of weekends ago. Nothing was leaking, everything looked great. I adjusted them and they felt much better, but not great. Still a bit too easy to lock up, but they could be modulated better. Then I backed the truck into my driveway and I guess they auto adjusted and got partially stuck. I had to actually apply throttle to go back down my downhill driveway. I took it around a couple of blocks since they they freed up at but it felt grabby again. What a complete pain in the ass. The next Monday I ordered a 4 wheel disc kit. I can't be effing around with these things and wondering what's gonna happen every time I need to stop. Or lock wheels on the highway at 70mph when some a-hole inevitably cuts me off.

[snipescastle2]

Does your booster have the adjustable pushrod? You may have to adjust the travel of that pushrod before you make any real changes. Reason being, you said they are real touchy, if the pushrod has no free play or slack,the master cylinder is already partially depressed, or, you could simply have the wrong application of master cylinder.
Both,
Ben

[AnotherWs6]

I'm not sure. How would I know?

[mike16]

like alot of others have said above, you ought to pull the drums and inspect and service everything. look to see if the drums have been cut too often. check all four of them. look for leaky wheel cylinders and bad hoses. also make sure the wheel cylindersd are the correct diameter and that the master cylinder is correct and functional.

I've hade many trucks and cars with drums and they work fine when services correctly. discs are nice but drums have always worked very well too.

It seems to me that disc brakes are over rated and most people would rather just slap on some disc brakes rather than sort out a drum set up. too bad because drums work very well and remember that they can very easily stop the truck with a full load in it too, and many a time My truck has been over loaded too and it stops very well.

[AnotherWs6]

I DID pull all of the drums. Everything is in excellent condition. At the end of the day something just isn't right. And if I'm going to start thinking about changing masters and boosters and quite possibly spend time and money and not fix the problem........ I'm just putting a complete disc setup. I'll change everything, do it ONCE and not have to worry about adjusting brakes periodically. And be less concerned with brake fade while towing a trailer.

[mike16]

change everything.... do it once.......and not have to worry about adjusting brakes..... periodically....less concern about brake fade ....while towing a trailer.....

good luck there. and dont forget the cost, the down time, and the proprietary brake hardware and trying to adjust the front to rear balance.

Like I said, Ive had drums on many a vehicle in the past with no problems, adjusting and servicing them is not a problem to me. I like any excuse to check up on them every so often. they are a very important part of the ride experience. I dont do fix em and forget em too well when it comes to brakes.

[AnotherWs6]

I know the cost, I already bought the kit.

Don't care about down time, it's my fourth vehicle.

Uses readily available pads, rotors and calipers.

Comes with a non-adjustable proportioning valve already calibrated for the vehicle and setup.

I have ZERO interest with playing with the brakes, driving is the experience I enjoy.