Smaller brake cylinders

[Mikel]

Hello,
I put a Chevy Dana 60 in a friend's M715 and kept the rear D70. Braking is very biased towards the rear, even with a proportioning valve.

Does anyone know of a vehicle that uses rear brake cylinders that will fit, with a significantly smaller bore?
Thanks.
Mikel

[Don Cavey]

Hello,
I put a Chevy Dana 60 in a friend's M715 and kept the rear D70. Braking is very biased towards the rear, even with a proportioning valve.

Does anyone know of a vehicle that uses rear brake cylinders that will fit, with a significantly smaller bore?
Thanks.
Mikel

Mike,

I would be more inclined to make the brakes bigger in the front. It may be that the proportioning valve is not doing its job (not defective, maybe should have different specs. I assume we are talking disc front and original drum back?

[Mikel]

Mike,

I would be more inclined to make the brakes bigger in the front. It may be that the proportioning valve is not doing its job (not defective, maybe should have different specs. I assume we are talking disc front and original drum back?

Hello Don,
The pistons in a "modern" Chevy dana 60 are gigantic and I think it would be quite a chore to make them bigger. I think the problem is that the M715 system was meant to be a low pressure unassisted system with large wheel cylinders, while the "modern" axle was never offered without a booster so it is designed to operate at higher pressures.
Thanks,
Mikel

[Don Cavey]

Hello Don,
The pistons in a "modern" Chevy dana 60 are gigantic and I think it would be quite a chore to make them bigger. I think the problem is that the M715 system was meant to be a low pressure unassisted system with large wheel cylinders, while the "modern" axle was never offered without a booster so it is designed to operate at higher pressures.
Thanks,
Mikel

Hi Mikel,

(Sorry for the misspell of your name) You could be certainly be correct. I don't know if there are smaller wheel cylinders for the back. While some Ford truck wheel cylinders seem to be able to be adapted to the backing plate. I recall that the front and rear wheel cylinders on the M715 are the same size, 1 1/16" which is large! and usually the rear is quite smaller with commercial vehicles. Maybe tomorrow more people will be watching the Zone and will have an answer. Good luck, please keep us posted...

[brute4c]

Did you think of trying an adjustable proportioning valve in the rear brake line? You could dial the braking down back there to get it where you want and adjust for heavier loads/towing in the future.

[Mikel]

Did you think of trying an adjustable proportioning valve in the rear brake line? You could dial the braking down back there to get it where you want and adjust for heavier loads/towing in the future.

Yes, but it only adjusts down to 55% of full pressure, and it's not enough.

[brute4c]

Gotcha!