The Stovebolt Site Forums The Shop Area Engine Shop discs in rear & drums in front

I am planning on swapping out my rear axle on my 38 3/4 ton to a more modern one. If I find one with disc brakes, can I hook it up? I will still be using the drums up front, I'm assuming I will have to use a proportioning valve to balance everyting out. but will the rear still have too much braking power? I understand that the front should have more power than the rear.

how hard is it to put discs on the front? does anyone make a kit?

I replaced my orginal master cyl with a new one. and then I found a NOS forklift master cly that has a much larger bore. I think I can swap this in.

How many lugs on your 3/4-ton? The later 3/4-ton trucks have 8-lug hubs and there do not seem to be any conversion kits.

I believe some of the pre-Advance Design 3/4-ton trucks used 6-lug hubs, and if that is correct you might investigate using a disk brake kit for an Advance Design 1/2-ton on the '38. May not work, but might be worth checking out...

Another possibility to investigate is swapping a 1/2-ton axle under the truck to support the commonly available disk kits.

Read up on brake system hydraulics before swapping to a master with different bore. The relationship between master and wheel cylinder bores has a lot to do with pedal pressure and braking power. You'll want to make sure you have those issues under control.

I don't think I'd put disks on the rear with drums on the front. But if properly balanced I don't know that it would not work. But your brakes are too important to take chances.

thanks steve!

yeah, I didn't think discs on the rear only was a good idea, but you raised another question, if the wheel cylinders are different- bigger in the rear, will that change my braking? will I still need a proportioning valve?

MAC 38,

There is a thread in the General Truck Talk forum titled "brake hose replacement". TCLEDERMAN enclosed a link to a site that has, among other things, info on proportioning valves, when and why they are used...just for your info.

Stuart

Also remember that the lion's share of the stopping is done with the front brakes. I thought about changing mine, but I didn't want to loose my 1 ton rating and went with kevlar brakes from www.praisedynobrake.com - they work very well.

Seems to me 3/4 tons and larger already have larger rear brakes than front;adding disc brakes will increase the stopping power on the rear proportionally. It would probably be possible to make this set up work,but you'd have to consider how much line pressure you'd need to make rear discs work,how much pressure the drum rear brakes required,and how the difference would relate to the front brakes,then would your master cylinder provide enough pressure and volume to handle the change. You'd likely have to use a proportioning valve and I'd bet you'd have to replace the master cylinder. You might be able to connect and use the disc rear brakes directly VERY temporarily if you plan on converting the front to discs too but that would be very marginal and I wouldn't expect them to work right. Converting the front to discs might not be too hard;you'd need to build caliper brackets,make some rotors fit your hubs,and I'd SERIOUSLY consider whatever work it took to convert to tapered roller wheel bearings.
there's also caliper to wheel clearance to consider.You could very well end up changing to newer wheels or using spacers and longer wheel studs to clear the calipers.
OldSub is right-read everything you can about brakes before you start;brakes really are too important to just wing it.
Speed

thanks everyone... you all confirmed my thoughts that it wasn't a good idea. yeah, my stock rear brakes are huge, I MUST use the factory 17" wheel to clear the drums.
I think when I go looking for a rear axle, I will look for one w/ large drums.

What is the deal with the stock wheel bearings?

An interesting article on TV recently about the big manufacturers having trouble with rear disc brakes in snowbelt areas. Seems a lot of slush and such is throw up against them from the front wheels and causing rust and brake caliper seizing. Many have gone back to the drums on the rear. An interesting topic which most of us have never thought about.

yeah, I have a 2004 2500HD and I have that problem, just when you are about to stop, under 3mph, the brakes completely let go. to say it is nerve racking is an understatement. Im about to pull the fuse on the ABS.

the problem is with the sensor that monitors wheel speed. they get rusted and mis-read; they think the wheel is locked-up and skidding.

Chevy dealer "fixed" the problem 3 monthes ago