VCCA Home Forums TECHNICAL - 1945 AND NEWER 1946-1948 Brake booster under cab

Hello,
I want to modify the single line brake system on my ’48 3100 Thriftmaster to a dual line. It has a manual transmission.
To keep it as original as possible I ”˜am looking for a power brake booster for drum/drum brakes.
What I see there are two option: under the cab or onto the firewall. I prefer the first one.
From what I read, it won’t work with a manual transmission. Why?
Does someone has experience with or can advise me what to do?
Thanks.

I expect that there is an issue with enough room for the diameter of the brake booster due to the adjacent clutch linkage. Plus the center-line of the master cylinder might need to be lowered so the booster will not hit the bottom of the floor. That might make it tricky to maintain the same brake and clutch pivot point center-line.

The brake and clutch share a rod that they both pivot on. When you go to a different Master brake setup, you lose the pivot rod support on one side for the clutch.

The Filling station or Chevs of the 40's may have a bracket for your year that allows support for the clutch and brake pivot arm when doing a change like this.

One member that pops in occasionally has converted an earlier truck master to a dual - 4 drum system using an early 70's Jeep Master cylinder. He has a very well done writeup on it. I would suggest sending a Private Message (PM) to BRINO and he can furnish you with his writeup. I may have a copy somewhere but he deserves the credit for it and can answer questions for you.

I agree with Tim that you should try to contact Brino. It can be done with some finesse and fabrication work. The key is finding enough space under the floor for the booster while maintaining the position of the pivot rod for the clutch and brake pedals.

The adapter brackets from Chev of the 40's are for non-boosted dual circuit master cylinders. They do provide the proper support for the pivot rod for the clutch and brake pedals.

"I would suggest sending a Private Message (PM) to BRINO and he can furnish you with his writeup."

Good morning Tim and Rusty.

He did contact me and I can share what I learned doing my own tandem MC conversion. He has lots of options, including a remote booster that some vehicles used in the past.

It's fun participating in these "outside the box" projects.

Ray W

Brino

I was thinking of using a remote booster for my 48 Fleetmaster as Some European cars used it with Good results.
Is there in the present market a booster that should work? ( the ones from older European cars were made for smaller brake cylinders so they should not have enough volume for the bigger Chevrolet ones) !
Thank you again.

Jianis

I found a 7" brake booster with a dual MC with should fit under my cab. It makes a difference if you have a steer or floor shift. This setup won’t work with a steer shift due to the levers. Additionally you need a modified transmission crossmember. I ordered this set at performanceonline.com. For convenience also a remote filling set.

I also found a 1:4 remote booster suitable for my 3100 truck from a Dutch supplier, Only this is a single line booster and my goal was a dual line system.

Thanks for all your help, especially Brino, who send me a very detailed description.

@ Jianis, send me a private mail if you want the address from the Dutch supplier.

Thank you message send!