Has anyone with a 1500 rear drums up sized the master and wheel cylinders from the 6400lb GVW to the 7000lb GVW?

I have handled them and the bores are a little larger, looking at the parts lisings they seem to interchange according to being up to an extended cab and then going up to 7000lb GVW for the crew cabs and such.

 

If the bore ratio of master cylinder to wheel cylinder remains the same, they are bigger only to move more fluid. If the new ratio makes the master cylinder smaller compared to the wheel cylinder, that will increase the pressure but need more pedal travel. If the new ratio makes the master cylinder larger than the old ratio compared to the wheel cylinder, that will reduce pressure and need less pedal travel.

 

OK, so no real benefit then. We did go with the 7klb gbw master & wheel cylinders, and not noticing much if anything better, nothing less either.
The 7k over the 64k where more readily available locally.

Thanks

 

A little update, I started getting a rear drum shudder. Not like a pedal up and down out of round drum. High frequency low amplitude.
So I put her in the air with tires off and see hot blued drum. Pull it off and see a shoe holding tab on the new wheel cylinder is broken off and the shoe leaning out ward a little.
OK, I figure I found the shudder but since shes in the air I look and find the other side the same!
I didn't do it. I have the special t-handle spring tool, it all went well as the second time with new wheel cylinders. China AC Delco?

 

Probably not; more likely, a ham-fisted "mechanic" visited it before you.

 

Thank you, this works as you say. I have been chasing a gremlin and have swapped Master Cylinders' back and forth from 6400# gvw to 7000# gvw on 6400# wheel cylinders and the pedal is noticeably better with 7000# master on 6400# wheel cylinders. The brakes respond sooner after touching the pedal with a little less effort required. I like it. Not night and day, just noticeably.

The gremlin I believe is the ABS module applying brakes randomly. Long story but it happens. In the process of getting it rebuilt.

 

That's not what I meant, but it doesn't matter now. I meant that the pedal will move less, but there will be less pressure at the wheel cylinder. Less mechanical advantage.

 

Heh! A Placebo! Thanks