Brakes: What is diameter of rear wheel cylinder?

[studefan]

I have a 64 HT with front disc brakes. Can someone please verify the diameter of the "rear" wheel cylinders?

To simply things I asked my parts store to look up the Avanti rear brake cylinder repair kit and he said they show 7/8 inch diameter in their books. Is the 64 HT the same rear cylinder as the Avanti and would mine be 7/8 inch also.

[Gunslinger]

Be very careful when dealing with local parts stores...no reflection on them but their books are wrong. Their books show the rear wheel cylinders interchange with older Jeeps...7/8" diameter as you said. While they physically look the same and fit the same, what is needed is a wheel cylinder with a 3/4" diameter bore. I found that out the hard way...when the 7/8" wheel cylinders were installed the rear brakes immediately locked up due to more fluid in the cylinder. When I paid the price for correct 3/4" wheel cylinders the brakes worked properly.

What I believe happened is parts suppliers have consolidated parts numbers for older vehicles to cut down the number of parts to be inventoried for slower moving stock. The 7/8" wheel cylinders fit Jeeps and Studebakers...it's easy to think they're each the correct application but they're not. I've seen the same thing happening with fan belts...part numbers being consolidated and the parts may well fit, but won't be correct. Imagine if all Stude vendors consolidated water pump numbers for V8 engines into one number to stock...the standard duty water pump being stocked instead of the HD version for "R" engines. The water pumps would fit but wouldn't be correct...and "R" engine drivers would be constantly replacing water pumps.

Do yourself a favor...spend the extra and buy the correct wheel cylinder or rebuild kit from one of the Stude vendors.

[52 Ragtop]

Rears are 3/4" most of the Studebaker Vendors have them.

Jim

[Mangusta1969]

Be very careful when dealing with local parts stores...no reflection on them but their books are wrong. Their books show the rear wheel cylinders interchange with older Jeeps...7/8" diameter as you said. While they physically look the same and fit the same, what is needed is a wheel cylinder with a 3/4" diameter bore. I found that out the hard way...when the 7/8" wheel cylinders were installed the rear brakes immediately locked up due to more fluid in the cylinder. When I paid the price for correct 3/4" wheel cylinders the brakes worked properly.

What I believe happened is parts suppliers have consolidated parts numbers for older vehicles to cut down the number of parts to be inventoried for slower moving stock. The 7/8" wheel cylinders fit Jeeps and Studebakers...it's easy to think they're each the correct application but they're not. I've seen the same thing happening with fan belts...part numbers being consolidated and the parts may well fit, but won't be correct. Imagine if all Stude vendors consolidated water pump numbers for V8 engines into one number to stock...the standard duty water pump being stocked instead of the HD version for "R" engines. The water pumps would fit but wouldn't be correct...and "R" engine drivers would be constantly replacing water pumps.

Do yourself a favor...spend the extra and buy the correct wheel cylinder or rebuild kit from one of the Stude vendors.

I just checked with a local NAPA store and with NAPAOnline.com (including their Chat line) and can confirm they still have not corrected their invalid part listing for the rear wheels on 1963/64 Avantis. NAPA is still listing the UP19238 replacement cylinder with the wrong 7/8" bore size. They must not get many purchases or returns from this misinformation.

Has anyone been able to correct the performance of the too large UP19238 wheel cylinder or other rear brake problems by using Summit Racing's brake proportioning valve (see http://www.summitracing.com/parts/sum-g3905/overview/)? My 63 Avanti is becoming a little twitchy on hard stops and sometimes locks up one of my rear wheels before the front wheels really grab. Perhaps a former owner didn't do the right thing when replacing some wheel cylinders...

I powerbled my brake system a year ago with pretty decent quality fluid still in evidence, so I may give the Summit Racing brake proportioning valve a try rather than pulling off the rear drums when I upgrade the whole system to a dual master cylinder setup. There is some good information on the setup and use of this proportioning valve on Bob Johnstone's excellent Resource Page that is located at the studebaker-info.org web site.