Power Drum Brake Questions

[goodemj]

Work picked up and the garage progress is suffering, I bought a new drum/drum MC for a 69' one ton and a new dual diaphragm brake booster for a 72' one ton. I had to make a longer push rod since drum/drum was no longer an option in 72' but before installing I questioned myself again.

Does anyone know why the front and rear axle ports are opposite on a one ton MC than on a 1/2 ton MC? I was initially going to make new MC-to-proportioning valve lines that would cross and correct this but then questioned why they were switched in the first place. Is there different fluid proportioning within the MC since one ton trucks were hauling heavy loads over the rear end?

I could just return the drum/drum one ton MC and get a 1/2 ton MC but then I would still wonder why they switched font/rear ports on the one ton MC.

[dutchmanz]

Originally Posted by goodemj

Work picked up and the garage progress is suffering, I bought a new drum/drum MC for a 69' one ton and a new dual diaphragm brake booster for a 72' one ton. I had to make a longer push rod since drum/drum was no longer an option in 72' but before installing I questioned myself again.

Does anyone know why the front and rear axle ports are opposite on a one ton MC than on a 1/2 ton MC? I was initially going to make new MC-to-proportioning valve lines that would cross and correct this but then questioned why they were switched in the first place. Is there different fluid proportioning within the MC since one ton trucks were hauling heavy loads over the rear end?

I could just return the drum/drum one ton MC and get a 1/2 ton MC but then I would still wonder why they switched font/rear ports on the one ton MC.

I realize this thread is over a year old at this point but did you finish the project? I may have a future project doing the same thing.

[goodemj]

Originally Posted by dutchmanz

I realize this thread is over a year old at this point but did you finish the project? I may have a future project doing the same thing.

Yes I did finish this particular project but the list is never ending.... Since the proportioning valve and lines were setup for the 1/2 ton MC I returned the one ton MC which had reversed ports since this seemed to be the easiest option to reuse my current setup and I couldn't find any info on why they they were switched or any benefits over the 1/2 ton MC. I did use the one ton brake booster for 72' model because imo it looks better than the stubby one on the 69' model trucks, but if you choose this path you will have to fabricate a longer plunger since the recess in the one ton booster is deeper than the 1/2 ton booster. The depths in both MCs was identical. I can't seem to find my pictures of the plunger or side by side comparison of the boosters but I did find one of the two MCs and a picture of the setup currently in my truck. Good luck and let me know how yours turns out or if you have any more questions.

[goodemj]

I found the pictures I was looking for last night. The three push rods pictured are: (left) 72' 1/2 ton blazer MC with disc/drum with single diaphragm booster, (middle) fabricated rod for my application 69' 1/2 ton pickup MC drum/drum with 72' one ton pickup dual diaphragm booster, (right) factory rod for 72' one ton pickup MC disc/drum with dual diaphragm booster. The 72' one ton booster requires a deeper push rod if being used with a drum/drum MC since they only came with disc/drum MCs which have a shallower depth for the pushrod to enter. I still have a brand new 72' one ton MC disc/drum in the box collecting dust because I bought them as an assembly if anyone is interested?