47-55.1 Firewall mounted Master Cyclinder/booster/pedal assembly differences

[Artie Sellars]

I’ve spent an hour looking through here ( and longer than that off this site) and can’t find what I’m looking for. What’s the difference in the booster, master cylinder and brake pedal assembly from 47-53 and 54-55.1? Why will a combo kit for a 47-53 NOT work on a 54-55.1?

[mr48chev]

The only difference would be how the end of the bracket bolts to the dash.

Personally I won't stick that much ugliness under the hood of my 48 again even though they work great because I don't want it hiding the engine that I have spent so much money dressing up to look great on. That and it won't clear my manifold and carb as far as I can figure.

OOPS I came close to making one of those "assume" mistakes but caught it, whew. Western Chassis shows a 54/55 unit with hydroboost rather than a vacuum can but it is a bit spendy. https://westernchassis.com/1954-55-C...CwKk43EqFiTRoU

More editing: POL shows several firewall mount units for 54-55.1 and the images for 47-53 and images for 54-55.1 do show the difference and it is a big one. https://www.performanceonline.com/Po...5-chevy-truck/ Choices include plain or black powder coated from Wildwood or Plain or Chrome units from POL. https://www.performanceonline.com/Po...5-chevy-truck/

[mr48chev]

Here are the difference in 54 / 55.1 brackets and 47 / 53 Brackets.

[Artie Sellars]

Thank you. I can see the differences in the two, I was curious as to what was different on the trucks that warranted having two different styles. I have a 55.1 that I bought in 100 pieces and I’m at the point of needing brakes. The previous owner had already drilled holes in the firewall for a firewall mounted setup so that’s why I’m going that route. This is the first one of these trucks I’ve ever put together and I’m not familiar with all the model year differences. I ordered a setup from POL but after being jerked around by them for several weeks I cancelled the ordered so now I’m on the hunt again.

[mr48chev]

I like the way that a firewall mounted master cylinder works on these trucks and did have one on mine when I had the Turbo 400 in it. What I don't like is that they clutter up the engine compartment and block the view of the engine from that side. In my case I have over 400 tied up in polished finned aluminum and another 400 in an aluminum intake and another 250 in Cast iron headers on my 292 straight six. When the hood is open at a rod trot that is what I want folks to see, not a booster and master cylinder under the hood Entirely personal choice.

Doing that search last night was more than a bit educational for me too. Folks will tell you that I know a lo1t about these old trucks having had mine since 1973 but in truth a lot of it is because I actually love to do the research and learning.

[caseyjones]

Originally Posted by Artie Sellars

Thank you. I can see the differences in the two, I was curious as to what was different on the trucks that warranted having two different styles. I have a 55.1 that I bought in 100 pieces and I’m at the point of needing brakes. The previous owner had already drilled holes in the firewall for a firewall mounted setup so that’s why I’m going that route. This is the first one of these trucks I’ve ever put together and I’m not familiar with all the model year differences. I ordered a setup from POL but after being jerked around by them for several weeks I cancelled the ordered so now I’m on the hunt again.

The distance from firewall to dash is different. I have a 54 and bought the brace for the earlier trucks and modified it to fit my truck. I think it’s better to have the bracket tied into the dash to minimize the flex of the firewall.

[Artie Sellars]

Originally Posted by caseyjones

The distance from firewall to dash is different. I have a 54 and bought the brace for the earlier trucks and modified it to fit my truck. I think it’s better to have the bracket tied into the dash to minimize the flex of the firewall.

I agree, and I guess I’ll do the same and modify an earlier style bracket to fit my needs.

[JDarby]

I believe they ( Chevrolet / GMC ) did a frame tweak on the 54-55.1 model year trucks.

It's important knowing what year truck you have so as not to return to many parts to the vendors.

You have found the right place here though, Lots of knowledgable folk here
to answer your questions!

Welcome