Brake Effectiveness?

[BillCA63R1]

The drum brakes on my '64 R1 were all to quick to 'lock up' the rear wheels, but the disk brakes were not able to stop the front wheels from rotating, even as the car was coming to a full stop. My mechanic installed a proportioning valve to tame the rear brakes and checked that the brake booster is holding pressure, but I am still unable to apply enough brake force to cause the front tires to skid.

I feel that my overall stopping distance is greater than it should be due to this lack of 'authority' of the disk brakes in front. Is this normal?

[mfg]

The rear wheels shouldn't be quick to lock up. There could possibly be something wrong with the linings.(contaminated)...... Installing the proportioning valve to control rear brake action was probably the wrong approach to this problem......if everything is 'right', there's no need for one, and Studebaker didn't use one in this system.

Check for a collapsed vacuum hose from the manifold to the booster.....Lack of authoritive front disc brakes on Studes has been traced to this hose before!

[Gunslinger]

First...make sure the car is using too much distance to stop. It could just be normal for your car but you know how your car drives and brakes better than anyone else so we have to take that at face value.

It could be a couple of possibilities. First...if your brake pads have been replaced at any time, the composition of the pad material is not likely to be what was originally installed. You may well have pads of much harder material than stock as it's mostly what's available today for obsolete applications. The hardness of the pads will wear long but not as "grabby" as the originals. There are more modern technology pads available today but they're generally expensive and have to be ordered plus they have a much shorter lifespan. My feeling is that the best brakes are barely good enough.

You could have a rear brake cylinder leaking onto the shoe linings which can make the rear brakes grabby. The rear brakes are not self-adjusting and have to be manually adjusted from time-to-time. Maybe they're adjusted wrong.

There could be a restriction in the front brake lines reducing brake pressure to the front. Completely flushing the brake system might not be a bad idea.

How did the mechanic check the brake booster is holding pressure? The best way is to push down on the brake pedal with the engine off. While holding the pedal down start the car. the pedal should go down further as vacuum builds up. If the pedal doesn't go down, the booster is bad.

Between those possibilities, I would think the brake pad composition would be my first thing to look at. The booster the second. The other are less likely but still possibilities.

All that being said, you really don't want the front brakes locking up as it creates a loss of control. I'm guessing you want them to lock up to give you a feeling of security that they can.

[mfg]

Once again,.......Check out the engine vacuum hose............

[Rob Dudley]

My '64 Cruiser had this problem and it turned out the front calipers were so dirty they were nearly seized. The pads were good and it had new lines but upon further investigation the calipers just weren't functioning well. It may have been due to a lack of use as the car sat a lot.

Rob

[BillCA63R1]

Thanks for all of these responses and I will pass them on to my mechanic.

As to my underlying concern about braking, I have always understood that any braking system should have enough 'authority' to fully brake (stop) a turning wheel (at low speeds at least). Am I wrong?

Bill

[PackardV8]

Thanks for all of these responses and I will pass them on to my mechanic.

As to my underlying concern about braking, I have always understood that any braking system should have enough 'authority' to fully brake (stop) a turning wheel (at low speeds at least). Am I wrong?

Bill

You are correct. In a conventional system, you should be able to have the brakes lock the wheels with a maximum application of force. If they won't, especially with a light car and skinny tires, such as our Avanti, something is wrong.

jack vines

[billsr2]

Someone may have simply installed the wrong wheel cylinders.

They are special for disk brake cars.

[Gunslinger]

That's a possibility. Vendors like NAPA have new wheel cylinders their application book says will fit...which it does. It's the same fit for some older Jeeps but the problem is it has a 7/8" bore but the Avanti uses a wheel cylinder with a 3/4" bore. With the larger bore too much fluid is introduced and causes the rear brakes to lock faster. The only fixes are to either install the correct wheel cylinders for an Avanti or an adjustable proportioning valve and play with the adjustments until you find the correct proportion.

It seems the suppliers have consolidated parts numbers to reduce inventory requirements for older applications. Just because the Jeep wheel cylinder is a visual and fitment match for a Studebaker doesn't make it the right part. There's a lot more older Jeeps out there to service than Avantis so guess one is the one they keep the correct part for?

I've experienced the same thing with fan belts for older cars so it must be happening pretty much across the board.

[PackardV8]

As mentioned earlier, the problem is often in the relationship of front pad and rear shoe friction materials. If a too-hard pad is installed on the fronts, along with regular linings on the rear, the rears will lock too soon.

Conversely, if a too-hard rear lining is used, they won't contribute much to the stopping effort and may not even hold well as parking brakes.

How old are the front flex hoses? I've run into problems over the years where the hoses have deteriorated internally and were blocking the pressure to the calipers.

jack vines

[StudeNorm]

I have the same problem on my '63 Lark V8 with a brand new Turner brake system.

I have all new pads, S10 calipers, Mustang rotors and a new booster. The residual check valve in the dual M/C has been removed. The vacuum hose is new. The booster check valve is new. The car stops but I had a near panic stop one afternoon and the rear end decided it didn't want to play nice with the rest of the car as the rear brakes locked up early and I ended up a bit sideways in my lane.

The rear brake shoes are new and the rear calipers are new. Not NOS. They are the 7/8 calipers for the original V8 drum/drum system.

All lines have been bled many times from back to front starting with the longest line.

I was considering a prop valve but this forum seems to think that isn't the way to go. Mind you Gunslingers reply no. 9 above might be the fix I need.

This car could get squirrelly come winter...

[warren55]

I have the same problem on my '63 Lark V8 with a brand new Turner brake system.

I have all new pads, S10 calipers, Mustang rotors and a new booster. The residual check valve in the dual M/C has been removed. The vacuum hose is new. The booster check valve is new. The car stops but I had a near panic stop one afternoon and the rear end decided it didn't want to play nice with the rest of the car as the rear brakes locked up early and I ended up a bit sideways in my lane.

The rear brake shoes are new and the rear calipers are new. Not NOS. They are the 7/8 calipers for the original V8 drum/drum system.

All lines have been bled many times from back to front starting with the longest line.

I was considering a prop valve but this forum seems to think that isn't the way to go. Mind you Gunslingers reply no. 9 above might be the fix I need.

This car could get squirrelly come winter...

I had almost the same symptoms with my 73 a couple years ago, and I'm not sure I can offer a solution, but here's my experience. First of all, I have the stock Bendix disc brakes and my rears are also stock, but still not the same as yours.

My brakes would work pretty well under normal circumstances, but under anything approaching an emergency the rears would lock up and the car became almost uncontrollable. I had already changed all the brake hoses just because.

(As I side note, I have been a truck driver for about 40 years and I've had plenty of experience with dealing with brake lock up.;-))

My first instinct was to replace the brake distribution block, which has a proportioning valve built into it, but a replacement wasn't easy to find so I decided to check the rear wheel cylinders since I had heard of problems there.

My rear brakes looked almost new in every way, but I knew it had been several years since they had been serviced. I went ahead and replaced the rear cylinders since they are reasonably cheap. No change.

I next looked at the rear backing plate and springs, just in case there were any grooves that the brake shoes could hang up in. I replaced the springs and ground the backing plates smooth, but no joy again. Here is where I jumped ahead of myself and installed an adjustable proportioning valve. I happened to have one, but it was a bit of a plumbing nightmare to get it installed. Even turned down all the way I had rear brake lockup!

I finally turned to the only other thing I could possibly change (other than the entire system) and replaced the rear brake shoes. The old ones looked perfect, and I had washed them down with brake cleaner along with scrubbing them with 150 grit sandpaper in case they were glazed. Bingo. End of problem. I later removed the useless proportioning valve and now my brakes work as well as any car I have, except they haven't got ABS.

[StudeNorm]

Knowing that everything else about the brakes is new I think I might try Warren55's sugestion and replace the shoes. I expect a harder liner would do the trick here. I am hoping I have a set but I may have given them away with a car I sold a couple of years ago. Oh well. I will post my results after I get a chance to make the change.

[BillCA63R1]

"How did the mechanic check the brake booster is holding pressure? The best way is to push down on the brake pedal with the engine off. While holding the pedal down start the car. the pedal should go down further as vacuum builds up. If the pedal doesn't go down, the booster is bad"

The above test, suggested by 'Gunslinger', is an excellent technique when starting most any car, especially on the first start of the day when booster vacuum has normally bled off. Plus, it means your foot is already on the brake pedal should the transmission want to 'launch' the car!

As to my problem with the front brakes, it turns out that the caliper had reached its mechanical limit', despite the appearance of plenty of pad being left. New pads and rotors seems to have cured the problem. My thanks to 'Silverstude' for steering my mechanic to the correct diagnosis.

[Gunslinger]

Glad to hear you diagnosed it and cured the problem.