Disc brakes and Hydrovac.

[johnesmonde]

Still working on the '62 Hawk brakes. With Turner disc kit and new dual M/C with no Hydrovac (I found out the hard way)brakes are there but not great. I then hooked up the Hydrovac to the front discs and bled it out. What a difference! Something approaching excellent braking. There is a problem, however. The calipers seem to stick on and heat up. With wheels raised, wheel is stiff to turn. After a while pressure seems to subside and wheel turns freely( with motor off). Pumping brake(with motor off) returns it to stiff until pressure subsides again.Any ideas on what is wrong?

I feel the solution to my braking woes is to return to the old single M/C with boost on all four wheels. I hooked the boost up on fronts only to test how it worked with the discs and came accross this problem.

'62 Hawk
'30 Chev Coach

[Dan White]

I would recommend scrapping the dual MC and put it back the way it was designed to work. As you may note in my post to the "Truck Disk Brake" list the Hydrovac/updated disk brake setup works great and I have had zero problems. Running with boost to only front or back is asking for big trouble since you will most likely be unable to balance the pressure with that type of setup. Your lockup problem is most likely due to a sticking relief valve on the Hydrovac, or the dual MC relief valve is incompatible with the Hydrovac. I assume you are using a Hydrovac for a disk brake setup, it is slightly different than the all drum Hydrovac.

Dan White
64 R1 GT
64 R2 GT

[johnesmonde]

Thanks Dan. I am using the power brake unit that was in the car for the drum brakes. Is this the problem? Originally I was going to use Jim Turner's disc kit using the original single M/C and power brake unit.I changed to a dual M/C with the Turner bracket after reading something in this forum that said it would be safer. My shop manual refers to the booster in my Hawk as a 'power brake unit' and also has pictures of another unit that it calls a 'hydrovac-Hawk w/disc brakes' that is a bit different. Several people told me not to worry about losing the booster because the disc with standard braking would still be very good. I found this not to be the case. I know that it is inadvisable not to run a booster on the front only but did it as a test and was impressed with the better breaking. Do you think that going back to a single M/C would cure the pressure balancing you mention. I assume you mean balancing front to back. I wondered if opening up the proportioning valve on the rear and installing a 1/4inch rear line would help balance. As instructed, I have a #2 residual check valve in line between the M/C and the booster. I'm not sure what you mean by incompatibility between M/C relief valve and the hydrovac. Any ideas on how to address a sticking relief valve on the hydrovac? I can't find a relief valve in the diagram. Should I try removing the front #2 RCV?

Regards, John ( struggling novice )

'62 Hawk
'30 Chev Coach

[Dan White]

John:

I am not an expert on all of this but I know what I have tried and what worked for me and what did not. I would suggest that you get a NOS or rebuilt Stude MC for a disk/drum setup if yours did not come with it. This has the proper valving for the disk/drum Hydrovac and is different from the all drum MC. The disk/drum brake Hydrovac is definitely different from the all drum unit, the balance front to back is probably different. You might want to put up a post here or on the Stude Newgroup forum for a disk/drum Hydrovac to see if any one has one for sale or rebuild, OR you can use your Hydrovac and see what happens, if you get premature lockup on the front or back you could try putting propostioning valves in line to regulate the presssure (this would probably be the cheapest way to go since you already have the various parts to try this.) I will say that the disk/drum Hydrovac is more difficult to bleed than the all drum unit due to the omission of the bleeder on the end of the snout.

I would try removing the #2 check valve, it is probably holding the disk brakes in the braked position too long and not releasing pressue as it should. As I said before, I have not heard of any problems with the single MC on Studebakers and moving to the dual MC just creates a lot of problems where none existed before. If you do have a problem you have an emergency brake!

Dan White
64 R1 GT
64 R2 GT

[MikeW]

John, did you also change out the rubber lines? They can deteriorate internally and you get a flap of rubber that acts as a one way valve. I don't know if you can use the original lines on a disk setup. Also, has the Hydrovac been rebuilt? The newer rebuilds seem to have a problem breaking in the relief valve. This results in the brakes hanging up for awhile before releasing. I have three of the units that have been rebuilt by various rebuilders and all three do the same thing on two different cars. With use I have found that the units finally begin to "break in" and the brakes release as they should. I would NOT recommend that you try breaking them in by driving it that way. Break it in while sitting still.

Mike

https://www.packardhawk.com

[johnesmonde]

Thanks Mike! The booster was rebuilt before I got the car but that was 3 years ago. As Dan suggested, I removed the #2 residual check valve but I don't think it made a difference. I'm afraid to drive it for fear of warping the rotors. Jim Turner suggested the symptoms match the brake pedal linkage being too tight. I have it backed off so there is a significant amount of free play. How would you 'break it in' while sitting still?

'62 Hawk
'30 Chev Coach

[jcstude]

We are running on parallel paths here regarding the dual m/c with Hydrovac subject. I think you did the right thing with regard to removing the 2lb valve since S-P did not use one in the first place there must be something in the valving of the Hyrovac that accounts for the m/c being below the floorboards. The only other thing I can think of is that the dual m/c has a built in residual check valve that should be removed. I understand that it is either inside the body of the m/c or at the outlet where the brake lines connect. If your brand X dual m/c was used with a combination valve then it should not have residual check valves as the combination valve serves that function. The later Stude service manuals show how to remove the valves in the outlets that were part of the firewall mounted stock dual m/c.