Under-Cab Power Brakes and Dual Master

[Tom Petroff]

Very Nice Greg!
Well thought out.
TGP

[CSCameron]

Looks awesome! Have you thought about a skid plate for it?

[Bruce]

Good Idea

Looks awesome! Have you thought about a skid plate for it?

I had not thought about that, went back and checked, it wouldn't be over kill, in my opinion. Is the reservoir accessed from the cabin floor?

[Greg Coffin]

Skid plate

I thought about a skip plate early in the design process, but I decided to put the bracket high under the cross member to keep it out of harms way. The bottom of the bracket is higher than the bottom of the transfer case, and only 1 3/4" below the bottom of the frame rail. It's also much higher than the bottom of the front axle. It's possible that something could hit the bracket, but I think the transfer case will get hit at the same time, which will either take the brunt of the inpact, and/or take the truck out of commission.

Reservoir access: At this point I'm not sure where the reservoir sits in relation to the floor board and seat base. I think, give the booster I'm using (single diaphragm 7"), that the center of the reservoir cap will be near the rear of the floor board opening. I'm planning to access the cap from under the truck, but pulling the floor board may be easier. Either way, it will be easier than in the stock position. With a double diaphragm booster, the reservoir will be near the center of the floorboard. I'll do some measuring tonight and post the results.

[W_A_Watson_II]

Looking good, but be ware not all obstacles are flat/symmetric, so it's still prone.

[Greg Coffin]

Yes, there is a chance the bracket could be hit. The issue is that I don't know how to transfer the stresses of a hit through to the chassis without making the booster, master and linkages inaccessible. So for now I don't have a skid plate.

[CSCameron]

Greg, it's still awesome! Thanks for taking on this project and showing us the progress.

[Jalopytech]

Just curios regarding your thoughts on the belcrank leverage / arm throw issue, would you of preferred it to of been like 1:1.5 instead of 1:1 or ?

[Greg Coffin]

I measured as much as I could the best I could during the design phase. Now that it's all together I should have made the master cylinder arm 12% longer than the pedal arm to get full motion out of the master cylinder. The next version of the bracket will take this into account.

[Jalopytech]

Thank you for this valuable info. Your time and expertise is much apreciated..

[Greg Coffin]

Correction to my last post: I should have made the master cylinder arm 25% longer than the pedal arm (not 12%). Both arms are 2" long right now, and I plan to make the master cylinder arm 2 1/2" long on the next version. I've also figured out how to fit a bellows over the booster push rod, to help keep dirt and moisture out of the air intake. I'll run a remote air intake into the cab, behind the seat. I drove an old Ford cabover that had a setup like it. I just have to find a shock absorber bellows that I can make fit.

Here are the booster and master cylinder numbers for people who may be interested in that info:

7" Brake Booster: Tuff Stuff 2221NB
Master Cylinder: Dorman M101266, 1-1/4" bore

The booster and master cylinder fit together perfectly, much to my surprise and relief!

[CSCameron]

Very good! Keep the updates coming...

[Jalopytech]

Thanks for the update / clarification, we appreciate the time involved and information you have supplied.

[Greg Coffin]

I made some changes to the bracket today. I moved the lever pivot 1-1/2" to the rear to make room for the bellows. I also extended the booster arm length to 2-1/4" to see how it will perform. This bracket isn't set up to allow the needed 2-1/2" arm length, so 2-1/4" will have to do.

The bellows fits and works great. It's a rack boot for a Ford Exploder. I was fortunate to find a counter man who had a creative bone in his body. He found it on the first try.

[Desoto61]

That's a quality piece of work! Thanks for sharing.