brown7373

Should have read Lousy 72 Cutlass BRAKES. I converted from Power Drum to Power Front Disks a while back. I got parts from a 72 Cutlass parts car, added new pads, hoses rebuild calipers, new rear wheel cylinders, new master cylinder and rebuilt booster by Steve Gregori. Master was bench bled and all 4 wheels bled fine. Bleed screw are up. I previously fixed a vacuum leak at the front where the booster seals to the master cylinder, and that improved but didn't fix the problem.


Normal driving, the brakes are fine. Smooth, straight stops, good pedal feel, does NOT go down if you keep pressure on the pedal. But if you have to panic stop, or greatly increase braking, it just seems like the calipers don't clamp enough. I don't normally want to lock up my brakes, but shouldn't I be able to?


Any ideas? If I don't need to do a panic stop, I would never suspect anything was wrong.

brown7373

I just tried something...I started the car, then shut it off. I could pump the brakes immediately after shutdown 3 times and it still had booster vacuum. I started it again, then shut it down and did nothing for a half minute. It had zero vacuum after 30 seconds. Should it hold vacuum longer than 30 seconds?

svnt442

Yes. It sounds like you have a vacuum leak somewhere.

gs72

Or a bad check valve

76olds

[QUOTE=brown7373;922222


Normal driving, the brakes are fine. Smooth, straight stops, good pedal feel, does NOT go down if you keep pressure on the pedal. But if you have to panic stop, or greatly increase braking, it just seems like the calipers don't clamp enough. I don't normally want to lock up my brakes, but shouldn't I be able to?


Any ideas? If I don't need to do a panic stop, I would never suspect anything was wrong.[/QUOTE]


I don't think your callipers would be a problem at this point. Have you tried turning them by hand them having someone press the brake and see if you can turn the rotor?
It should lock up the rear brakes if you slammed them on, I also would look for a slight vacuum leak, also try to set up the rear shoes just so that the turn freely by hand but no excessive play when removing the drums.
I hope this helps
Eric

AzMotorhead

Well The problem I'm reading is that you didnt install a new proportioning (combination)valve. You went from power drum to power front disc. There's a difference in the combination valve between those 2 setups.
Booster should hold enough vacuum to assist in 3 brake pedal applications once vac source is removed. Are you sure the vacuum check valve is ok?

To test the booster with engine off pump pedal several times to deplete vacuum. Now hold pedal down and start the car, the pedal should sink. if not booster is bad.

joe_padavano

The proportioning/combo valve doesn't change how the front brakes feel. It only modulates pressure to the rear drums. Leave the combo valve out and you still will be able to lock up the front brakes. The problem is elsewhere. Most likely is that there is still air in the system. Also verify that the rubber brake lines are in good condition and don't have deterioration of the inner liners.

brown7373

I installed a new combination valve I purchased from InLine Tube when I did the brake conversion. They did say NOT to hold the button in when bleeding the brakes. But the brakes bled fine, with no problem getting fluid to flow to both front and rear.


I started the car with the brake pedal pushed. The engine started and the brake pedal went down to normal applied height. I can put my left foot under the pedal with brakes applied, and it never goes down further, indicating there is not air in the system. After I shut it off, I waited 10 seconds and still had vacuum to pump the pedal 3 times.

joe_padavano

You're doing all the right things to troubleshoot this. How many miles are on the brake shoes and pads? One thing I've found is that until the pads bed-in, braking force is reduced. Also, if the arc of the rear shoes doesn't match the drum radius, additional pedal force will be used up deflecting the shoes instead of braking the car. This gets better as the linings wear in to the drums. Finally, what type of disc pads did you get? Metallic pads are notorious for reduced friction when cold - they work much better when hot.

joe_padavano

Also, are the calipers new, used, or rebuilt? Crud can build up between the piston and bore, limiting piston travel. Is the caliper mounting hardware new? Same potential problem.

brown7373

I did the conversion about 2 years ago. Calipers were rebuilt NAPA units. All 3 hoses were new. I don't remember the brand of pads, but they were not metallic or high performance, just OEM replacement quality. The rear shoes were arced to match the drums.


No changes were made to the rod, and the booster was correct for front disks. Could the length of the rod have any effect on this?


If there were still air in the system, would I still get a steady pedal? I always though (maybe incorrectly) that if there was air in the lines, the pedal would slowly go to the floor. It doesn't. As I said previously the brakes seem to work perfectly for normal stopping. But I was driving through one of the STUPID circles the other day, and a car didn't yield, and darted out in front of me. I had to increase the pedal pressure to keep from hitting her broadside. That was white knuckle, as the car just doesn't really lock them down. There just isn't any more braking available.

droldsmorland

Air in the system. Ive had this problem countless times. Repeated bleeds using a power bleeder usually does the trick. Love to see how the factory does initial bleeds. Love to know how Foose and the other resto shows get it right the first time....Ill tell you how. Its called CUT...re-bleed the brakes....ACTION.
Nobody mentioned proper placement of the drum (primary and secondary) shoes being reversed? Not sure what effect that would have? They could either lock up or do what your experiencing? Havent had the pleasure of dealing with that screw up.
Dont rule out a bad master cylinder right out of the box?

Fun71

I had this problem after my car sat for an extended period of time. I removed a caliper from its mount, pushed the brake pedal to extend the piston, pushed it back in manually, and repeated numerous times until the piston moved freely in the bore. Put that one back on and did the same thing to the other side.

Then a while later I discovered that remanufactured calipers were $16 each so I replaced both of them.

76olds

Alot of things can change in 2 years, I like what Kenneth just mentioned about checking for a sticky calliper. I would start a that point seeing as it has been 2 years. Also set up the rear shoes if need be .

brown7373

Wouldn't a sticking caliper pull one way or the other? Car brakes straight as an arrow. If you drove the car under normal conditions, you'd say the brakes were great. Even in a panic stop, which requires a LOT more pedal pressure, the car brakes straight. I'm beginning to think it may be air, or not sufficient vacuum to really lock them up. There is sufficient vacuum for normal braking, just not enough to really apply them in a panic stop.

76olds

My term sticky is wrong yes, a sticking calliper will generally pull. The piston travel would be putting it correct.
As I mentioned in my previous post have someone press the brake while you try to turn the rotor.
Use a screwdriver to push the piston back as far as it will go while on the car then press the brake until the pads contact the rotor.
I don't think it would be air in the system simply because you didn't mention brake fade when braking.
I figure its the set up myself, could be the slider pins binding a bit
Eric

RetroRanger

How do the shoes fit in the caliper? How are they wearing? I had a truck once that one of the shoes was slighltly oversized only allowing it to fit slightly cockeyed the result was reduced braking performance.

Fun71

This didn't work for me - I had to remove the caliper and let the piston move beyond the point where it would typically stop with everything installed. The oxidation on the inside of the caliper bore (or whatever the issue was) had to be cleared further than the point where the piston compressed the pads so that full travel could be achieved without running into the "sticky" part.

brown7373

Any possibility that the rod is not the right length? I did NOT change the length when I did the conversion. before the conversion, I was less than impressed with the drum brakes. They didn't seem to have enough power either, but then I radiused the shoes and the stopping power seemed fine.


The Service Manual says to depress the button on the combo valve when bleeding the brakes. But InLine (their combo valve) said NOT to push it. Might that have any connection?

76olds

As for the rod at the booster,
Where does the brake pedal land when full braking ? Is the brake pedal at the same height as the gas pedal? Is it lower? It should be a little higher than the gas pedal with new pads and shoes I would say 1/2 inch above +/- . Did you have to adjust the brake light position at the brake pedal.
I've never heard of anyone having to radius the shoes, perhaps your drums need to be replaced or turned this is new to me.
Joe will have to chime in on the newer combo valves when bleeding, I've never switched from drum to disk in the past.
Eric

brown7373

Pedal height is fine, as you described. There is space under it when braking and it does not ever go down too far.


New brake shoes frequently are a larger diameter than the drum, so the ends of the shoes hit the drum first. As you apply the drum brakes, the wider ends now are pushing on the sides of the drum and prevent the middle of the shoe from contacting the drum with sufficient force. The shoe diameter needs to be the same or maybe even slightly smaller than the diameter of the drum, so the middle of the shoe can fully contact the drum. The bulk of the stopping power comes from the middle of the shoe.

Fun71

Do you mean the width instead of the diameter?

I have never experienced that in the 36 years I have worked on my Oldsmobiles, nor did I ever hear of it when I worked in the auto parts business. Is this a recent thing?

76olds

Are the drums aluminium ? Buggered up? I've seen aluminium drums but not on anything much older than 1979.
If not, I would say take your drums to a machine shop or brake shop and have them turned or scrapped, simply because most brake shoes are usually returned for relining not re stamped and relined.
I think you found your problem, ditch the rear drum and shoes.

brown7373

Width and diameter are the same. A couple articles on the subject. http://www.autoandindustrial.co.uk/i...adius-grinding http://www.jalopyjournal.com/forum/t...-shoes.317327/


Since the front brakes do most of the work, and most cars since the late 60s had front disks, this is something that isn't done much anymore. So 36 years in business, 1980, most of the machines had been scrapped.


I drew a picture that is exaggerated, but illustrates what happens. If the pressure is on the ends of the shoes and not spread equally around the whole shoe, then the drums won't work very well. One of the articles talks about using a marker on the shoe, driving the car and seeing where it doesn't touch the drum. Once the ends of the shoe are tight against the drum, the middle of the shoe can not be pushed closer to contact the drum.


Even if my rears didn't work at all, if the front disks are working correctly, I should be able to apply sufficient force to lock them up. Might not stop in a straight line though.

76olds

That's interesting, I never heard of arcing brake shoes. I think the casting process on drums have come a long way since. Also the relining process has also come a long way to eliminate rivets with bonded shoes. That's why its important to bed the pads and shoes and check for uniform braking everytime a brake job is done.
I would go to a local parts place have a look at new drums with shoes and eyeball them up or use some feeler gauges and check before purchasing a new set.
I would want my rear brakes to lock up and slow the car down before my front brakes locked up.
I hope you get the issue worked out .

Eric

brown7373

The arcing was a lot more important with 4 wheel drums. With disk/drum, the rear drums are only doing 10-20% of the braking and the disks can overcome a lot. But a front drum shoe, if not properly contacting the drum can result in very poor braking.


The one article talked about how shoes were made a little larger to allow for arcing. Also, everything changes when the drums are turned down.


Anyway, I am suspecting a vacuum issue with mine, which only shows up when more pressure than normal is needed.

Fun71

Not what I was thinking. The shoes are typically ~2" wide and the diameter is ~11". Your picture cleared up what you were saying for me.

Have you tried driving in reverse and pressing the brake pedal hard to see if the fronts will lock up? This transfers a lot of weight off the front so you can more easily tell if the discs are clamping, and if one is grabbing harder than the other. I do this a lot to check my brake operation.

joe_padavano

Cutlass drum brakes are 2.5" x 9.5" diameter for the front (and rear on a VC) and 2" x 9.5" on the rear. Full size cars and the 73-77 A-body cars got 11" drums.

Rocketbrian

I've been reading this thread with great interest as I have lousy brakes on both my 71 factory equipped disc brake equipped Cutlass and my recently completed 442. The 442 with almost everything new, has especially poor braking action. It has one of those inline tube repro boosters. I don't want to hijack your thread but in my case in both cars there is no way you can lock the front wheels. In fact when you push fast and hard on the pedals, there is an immediate resistance before the pedal goes down to actuate the brakes. You get the feeling the pedal is bottoming out before full pressure is achieved to clamp the pads well enough to lock them up. The pedal feels dead, and compared to any other car I've driven the braking action does not match the force you are applying to the pedal. The cars stop, but there is the feeling of delay in response without the expected braking results.
I would be very interested to hear if any other 71/72 Cutlass drivers can lock their front wheels if necessary. 71 was the first year for the combination valve and I'm wondering if that had any affect on the braking action.

Fun71

My '70 Supreme that I drove through high school, college, and my first real job had factory front power discs and it would lock the brakes easily. The current '71 convertible originally had power drums that I swapped to front discs and until my booster started acting up operated the same as the '70.

So yes, if everything is working properly you should be able to easily lock the brakes.

brown7373

RocketBrian, yours sounds just like mine. When I transition from normal braking to a panic stop, it feels like I am driving a power disk car without a functioning booster. It takes enormous pedal pressure to get sufficient increased braking, but still with no lock up.


My booster was rebuilt and replated by Steve Gregori. I have never had a problem with his rebuilds, but I may send it back to him to have him check it out if I can't find a solution.

Rocketbrian

Any updates? FWIW, years ago, I sent away a booster to Steve Gregori from a friend's 70 Cutlass for replating and when we got it back and installed, the pedal was much harder than it had been before. We never addressed it with him and the car was sold. So perhaps it is possible to have boosters rebuilt that only partially work as intended.