Disc conversion for Dana 41 rear and Dana 25 front axles
Parts required (per axle):
2 - Pre 87 Chevy 1/2 ton backing plates for 6 bolt axles (Junkyard)
2 - Pre 87 Chevy 1/2 ton calipers (cores from Junkyard, then exchange)
1 - Set Chevy Brake Pads
4 - Chevy 1/2 ton Caliper sliding Pins
2 - Chevy Front Brake Hoses (same year as calipers)
2 - 78 Jeep CJ disc for 6 bolt mount Mopar# J5356183
10 - 78 Jeep CJ Wheel studs Mopar# J5357196
A couple folks have tried this
conversion and had problems.
1) This conversion may not work
with your rims! I have been told that the stock Willys rims don't fit over
the calipers, and that some other rims don't clear. I am using AR-767 rims
which work fine.
2) This is a major modification
to your braking system. You may need to do some things that are not
described in this article due to differences between your vehicle and mine.
3) Modifying your brakes can be
dangerous to your health. If you are not sure if you are qualified to do
this, don't - go spend $300 on a kit with directions and a warranty.
OK - now on to the directions
Remove the old brakes
and backing plates from the axles. Separate the old hubs from the drums by pressing
out the wheel studs.
It has been
recommended to at this time replace the knuckle bolts with studs. Apparently the
spindles can cause the threads to pull out of the knuckle. To do this you need to drill out the bolt holes with a
3/8" bit, the studs to use are Mopar knuckle studs #J8124847 (dana 30). The
knuckle will have to be removed. Some of the stud heads will need to be ground
to insure proper turning. If you have very early knuckles (some 46 and before) with
a raised area around each hole on the inside of the knuckle you will have to leave the
bolts in the 3 and 9 o'clock positions and stud the other 4 holes.
Before you put it all
back together check bearings, seals, and get everything cleaned up, it's all apart anyway!
Install the backing
plates. Early backing plates are side non-specific, grinding needed on left backing
plate to make newer calipers fit.
backing plates are preferable if you want to run dust shields, they have a 1 piece design
which is about 3/16" thick. Some later backing plates have a heavy caliper mount and
a cheesy sheetmetal dust shield, which can be removed if desired.
Correct mounting position for
backing plates is with opening facing directly rearward.
- Some amount of grinding is necessary on the
front knuckles to ensure full travel of the calipers on the pins should the brakes wear
unevenly. Replacing the oil fill plug with a recessed head pipe plug will also be
necessary (these can be found in the electrical department of a hardware store - used for
sealing out door electrical boxes.
- Now you have a choice, in order to get
enough clearance for the brake pads on the inside of the disc you need to do 1 of 3 things
(this only applies to the front brakes)
- Have the back of the hub machined to remove
the raised portions (in a star pattern around the bolt holes) this will allow the disc to
seat 1/8" closer to the hub.
- Add a 1/8" bearing spacer to the
spindle before installing the hub.
- Use a belt sander on the inside brake pad to
reduce it's thickness by 1/8"
- Rotors attach to rear face of hubs as
opposed to the front for drums. Press or pull studs through the back of the
disc and into the hubs.
My parts sources:
Discs and Studs www.wilsons4x4.com
Brake hoses Big Wheel Rossi
Thanks to Jack Starcher for the knuckle
photo's, and a lot of the information required to do my swap. Some of this
information was taken from an article by Rick LeBlanc. Original article can be seen
here http://personal.nbnet.nb.ca/leblanrr/cj-2a/Home.htm at his website.