brake cylinder diameter

[dazavant]

I see the brake cylinders on the rear of my 63 Avanti are 3/4" in diameter and the offerings at the local auto parts store are 1.375 in diameter, what gives?

[Gunslinger]

What I found out some years back is that parts manufacturers have consolidated parts numbers rather than stock specific parts for specific cars.  Just because a parts fits physically doesn't mean it's correct.  I found that out on the '70 Avanti and '69 Corvette I owned.  Parts books showed the rear wheel cylinders for the Avanti were the same as the front cylinders for certain Jeeps...wrong!  While the Jeep wheel cylinder looked and fit the same they had a bigger bore diameter and the rear brakes locked up immediately from the added fluid pressure.  

You have two options...get an adjustable brake proportioning valve and experiment to find the right front/rear pressure or go to Myers Studebaker or Dan Booth at Nostalgic Motors and order correct wheel cylinders.  That will be a bit more expensive but it will also fix your problem without experimentation.  

[dazavant]

Thanks, that is what I suspected but was hoping to save a couple bucks.

[64studeavanti]

avantiparts.biz is showing a new pair for $157.50.

Bob Ziff is a good guy to deal with.

[Dwight FitzSimons]

IIRC, there are also 7/8" rear wheel cylinders that fit the 11" rear drum brakes on an Avanti.  Perhaps they were used on a Studebaker truck???

Someone else would have to address the question of whether it is a good idea to use them on an Avanti.

Perhaps the 7/8" rear cylinders would work with the larger Sumitomo front cylinders???

--Dwight

[Zedman]

Hi Dazavant- You haven't declared the cylinders are defective/pitted/leaking so I'm assuming they are. You might consider getting the originals sleeved in Stainless steel or brass and re-kitted. I would caution using larger diameter cyls because it will alter the amount of fluid needing to be pushed into 'em (longer pedal stroke) and alter the braking characteristics.  Of course this will run into a bit of money but... Brakes.. Mate ! 😉

[Dunkin]

I have run into this issue, I wonder where the Vendors get theirs, the mark up is horrible. I was looking into getting a proportion valve and figuring it out. The large valves are all over the place. 

[Zedman]

On 12/20/2024 at 5:20 AM, Dunkin said:

I have run into this issue, I wonder where the Vendors get theirs, the mark up is horrible. I was looking into getting a proportion valve and figuring it out. The large valves are all over the place. 

I have had to replace my 1981 Avanti II's rear brake cylinders with genuine new ones-  these are 13/16" bore units very inexpensively from a Mustang parts supplier for 1967-69 models. They are a Dorman product.  I started a thread on the AOAI site addressing this a few months ago.  Sleeving to original bore is of merit, but do consider costs involved (it's reached poisonous prices here in Oz!)   Appropos the Proportioning valve- good idea.  I decided to replace the obscure Kelsey-Hayes unit in my '82 with a GM style 'PV2' all Brass unit meant for Disc-Drum brake combination. you can mount this high up next to your booster or down low on the Frame Rail. I have various Pics-  if you want these PM me please.

Edited December 26, 2024 by Zedman