Brakes: Possible wrong rear wheel cylinders on my 63 Hawk GT

[phwold]

I found in my receipts from my previous '63 GT Hawk owner (now deceased) an order for two rear wheel cylinders - 535586. Since the car has front discs, it calls for rear cylinders - 1557668. What is the bore size of the 535586? Would it even work and what are the consequences? I'm not sure whats in the car. It has worked fine for a few years. My mechanic put on a Turner set up, with proportioning valve, that I had to adjust at first. If I pull the axles, is there an easy way to tell what wheel cylinders are on there by a visible part number or some other method? Perhaps the previous owner bought the 535586 for another vehicle. What to do? I'd rather not change them out, if not needed, especially since the specified ones are much more expensive, at some $85.00 dollars each.

[jostanton1]

I had the same problem on my 64 GT with disc brakes. Unfortunately, you will have to bite the bullit and pay the $85 to get the correct cylinders as no auto parts dealer has a replacement. I bought mine from Russ at studebakerparts.com in AZ. They fit and work great.

[studegary]

For piece of mind, inspect what is installed in your Hawk. Use a hub puller. You can determine if you have the correct wheel cylinders by measuring their bore (while installed).

[tim333]

Don’t mess with safety, bite the bullet and buy the correct cylinders.

[swvalcon]

If it has worked for a few years with no problems and is still working today I wouldn't worry about it. DON"T FIX WHAT ISN'T BROKEN.

[thunderations]

You say it has been retrofitted with a Turner disc brake kit with a proportioning valve. Please contact Jim Turner and give him the info you have given the forum. Jim will let you know if your setup is correct or not and what to do the correct any problems.

[StudeRich]

I found in my receipts from my previous '63 GT Hawk owner (now deceased) an order for two rear wheel cylinders - 535586. Since the car has front discs, it calls for rear cylinders - 1557668. What is the bore size of the 535586? Would it even work and what are the consequences? I'm not sure whats in the car. It has worked fine for a few years. My mechanic put on a Turner set up, with proportioning valve, that I had to adjust at first. If I pull the axles, is there an easy way to tell what wheel cylinders are on there by a visible part number or some other method? Perhaps the previous owner bought the 535586 for another vehicle. What to do? I'd rather not change them out, if not needed, especially since the specified ones are much more expensive, at some $85.00 dollars each.

You have Rear Wheel Cylinders for a '54 to '66 Studebaker V8 with DRUM Brakes. They are 7/8" bore and a totally different shape, so NO you can't make them work.

You need 3/4" Cylinders. Using that rear brake setup you can throw the proportioning Valve away, it is definitely NOT needed, your Mechanic should have been given the '59-'64 Studebaker Parts Catalog to figure this out FIRST before throwing unneeded parts at it.

If Jim T. were TOLD that this is NOT a Drum Brake Car, he would not have supplied the Valve.

You can check for a Rear Brake setup used with Front Disc. Brakes, by looking for the Front and Rear Shoe adjuster eccentric's with a stud and deep Lock Nut at the front and rear of the backing plate.

They also have NO 1 inch open slot at the bottom for a Brake Spoon to adjust the starwheel adjusters used on Drum Brakes.

You do not "Pull the Axles", if you needed to go inside of the rear brakes, you would use a HUB puller to pull the Hub and Drum assemblies.

Looks like you found this site WAY too late, these kind of questions that you did not ask, are asked and answered about every 2 weeks here.

[swvalcon]

I think everyone goes too far on what can be changed and what can't on a brake system. Just because not as Factory doesn't mean it wont work. Case in point. 2800 lb vega drag car tube chassis, Mustang 2 front disc brakes, mid 70' corvette master, came stock with front and rear disc mounted under the floor. 12 bolt chev 1/2 ton rear end with 11" drum brakes on rear. Now none of this was stock or made to work together. Would stop straight as a arrow from 130 mph on any track we ran it on and some had shut downs way too short and you where one shot from locking up the wheels. so modified does work.

[Jerry Forrester]

If it ain't broke, don't fix it it.

[JoeHall]

I think everyone goes too far on what can be changed and what can't on a brake system. Just because not as Factory doesn't mean it wont work. Case in point. 2800 lb vega drag car tube chassis, Mustang 2 front disc brakes, mid 70' corvette master, came stock with front and rear disc mounted under the floor. 12 bolt chev 1/2 ton rear end with 11" drum brakes on rear. Now none of this was stock or made to work together. Would stop straight as a arrow from 130 mph on any track we ran it on and some had shut downs way too short and you where one shot from locking up the wheels. so modified does work.

Agree, 100 percent, especially with the OEM rear brakes on front DB equipped Studes. Almost any change you can make is an improvement over the stock setup. In stock form, about 90 percent of the stopping power comes from the front discs, and 10 percent from the rears. If you are safety conscious and installed a tandem MC, and ever lose the front brakes for whatever reason, you still have the rears, but might as well try to use the hand brake to stop (ask me how I know). With standard rear 10", self-actuating drums, it is more like 70/30. I have driven both, extensively, and will take the 70/30 setup any day of the week.
For sure, Rich is right about no need for a proportioning valve for the rear on stock setup, DB equipped Studes (with or without Turners up front). If anything, could use a pressure multiplying valve (if there was such a thing) for the rears. The stock 11" rear drums are not self-actuating, and work on the same principle as the front discs. That principle works well for discs, but shoulda been discontinued with the Model 'T' on the rear. Nowadays ABS is state of the art, but prior integrated braked vehicles used 70/30. Nothing I am aware of ever used a 90/10 combo, except Stude, and it sucks.

So to the OP, if those larger rear wheel cylinders will fit, I'd give them a try. The larger bores will apply more PSI to those rear drums, and maybe improve the distribution to 89/11, if you are lucky. LOL

[62champ]

So to the OP, if those larger rear wheel cylinders will fit, I'd give them a try. The larger bores will apply more PSI to those rear drums, and maybe improve the distribution to 89/11, if you are lucky. LOL

The rear brakes for DB cars are the same used on 1/2 ton trucks from 1956-62. I have a pair of rear cylinders that I believe are 1 1/8 inch bore. Need to be rebuilt, but they are yours (or anyone else) for the shipping if you want to try them out. PM me if interested.

[phwold]

Thanks for everyone's helpful suggestions and for StudeRich's inclusion of the bore sizes of the two wheel cylinders in question. I used a hub puller today in the 96 degree heat of Iowa. I was pleased to find that my '63 GT has the proper rear wheel cylinders for a front disc car. The previous owner must have used the other wheel cylinders on another vehicle and somehow the receipt for them was given to me by mistake. Examination of the wheel cylinder installed in my car has the correct FD8374 stamped on it. Looking the number up on the web led me to an article on Bob's Resource Website that I hadn't seen previously. It covers a rear brake rebuild for Hawks and Avantis with great pictures. My 1984 purchase from Turner brake included a proportioning valve in the inclusive kit, even though it was ordered for a front disc GT. I did need to use it get the proper front/rear balance. My GT has a Mitsubishi master cylinder with about a half inch trimmed off the Studebaker push rod, as I remember. That effects things too, I'm sure, but don't know quite how. Thanks again for everyone's helpful input.