Brake issues

[MyFirstRV]

I have a 1994 Holiday Rambler Endeavor LE, diesel pusher. I am in the process of replacing the master cylinder and noticed something odd. On cars and trucks with a front engines the master cylinder is set up with a proportioning valve that restricts flow to the rear brakes and allows the front brakes to grab first. This is because the majority of the weight is over the front axle. I had assumed the brakes on a diesel pusher would work in the reverse, back braking first and then the front. However, the old and new replacement master cylinders, with an internal proportioning valve, is set up like a front engine vehicle. Is this correct or did someone install the wrong master cylinder in my RV at some point? The part number for the master cylinder I found was a 10-8039 which was the same number, also not the original, on the old part.
Any help would be greatly appreciated.

[n2zon]

Originally Posted by MyFirstRV

I have a 1994 Holiday Rambler Endeavor LE, diesel pusher. I am in the process of replacing the master cylinder and noticed something odd. On cars and trucks with a front engines the master cylinder is set up with a proportioning valve that restricts flow to the rear brakes and allows the front brakes to grab first. This is because the majority of the weight is over the front axle. I had assumed the brakes on a diesel pusher would work in the reverse, back braking first and then the front. However, the old and new replacement master cylinders, with an internal proportioning valve, is set up like a front engine vehicle. Is this correct or did someone install the wrong master cylinder in my RV at some point? The part number for the master cylinder I found was a 10-8039 which was the same number, also not the original, on the old part.
Any help would be greatly appreciated.

As the weight at the rear axle is close to double the weight on the front axle, it seems quite possible that a proportioning valve would be used to provide higher pressure to the rear brakes, not the front brakes. But you'd have to find out from the chassis manufacturer what's supposed to be there and compare it to what you have.

[twinboat]

You can proportion brakes by different rotor / drum diameters or different size caliper / wheel cylinder bores.

[n2zon]

Originally Posted by twinboat

You can proportion brakes by different rotor / drum diameters or different size caliper / wheel cylinder bores.

You sure can! Many or most cars and trucks are built this way. On our Winnie, though all the calipers and rotors were the identical (other than the L/R location of the bleed screws).

The rear brakes wore noticeably faster than the fronts, which makes me think that there was probably a rear-biased proportioning valve in there somewhere. But since I traded it in with all the manuals, I can't check any more.

[MyFirstRV]

Originally Posted by n2zon

As the weight at the rear axle is close to double the weight on the front axle, it seems quite possible that a proportioning valve would be used to provide higher pressure to the rear brakes, not the front brakes. But you'd have to find out from the chassis manufacturer what's supposed to be there and compare it to what you have.

Thanks all!

[MyFirstRV]

Originally Posted by twinboat

You can proportion brakes by different rotor / drum diameters or different size caliper / wheel cylinder bores.

On this model all rotor and Calipers are identical. Thanks

[j.m.jackson]

You'll still want the front brakes to come on first like a traditional vehicle. When you apply your brakes, the weight shifts to the front axle as you apply them. That's what causes the nose to dive down.

I have a 1993 southwind DP on an oshkosh chassis, most likely the same as yours.