74 CJ5 front drum conversion to disk

A few questions:
Will the disk brake parts from an 80 CJ (axle flange out) bolt in place of the 74 drum parts?
Will I need to change the proportioning valve?
Can I use the 74 drum master cylinder? If not, what later model year will still bolt in place of it?

Thanks for your help.
KSA

 

You need the axle nuckles and everything from the ball joints out. It will bolt in place of the knuckle from the 74.

There is a residual vavle in the drum master cylinder that could cause the brakes to drag and possibley lock up as they fluid temp increases. Its best to either remove that valve or replace the master cylinder with one designed for disk brakes.

 

I believe you will also need to change the proportioning valve. When I swapped the '73 axles into my '83 I used an 11" disc set-up off from a '79 and used everything from the knuckles out. I retained the non power '83 mastercylinder until it finally failed a year and a half later and then replaced it with a remanned unit for a '79 as I thought it might be better matched to the 11" brakes. I believe the '80 brakes are 10" . With a search on here I think you can find how to retain your '74 6 bolt hubs if the '80 has the 5 bolt units.

 

Only the postals used 10" brakes after 1972, AFAIK. The rear CJ brakes are 11"x2" drums but different because they go with the AMC 20 axle, not the Dana 44. Compare the wheel cylinder size between the D44 and M20 rear brakes for an idea of how compatible the components will be.

 

Where is the residual valve in the master cylinder?

 

Tim, there were quite a few CJ's with the AMC 20 rear that ran 10" brakes, and some that ran 11" brakes. I think it was the later models that ran 10" ers. Never made any sense to me except maybe to save weight in an effort to meet the more stringent fuel economy requirements.

 

The residual valve is inside the master cylinder where the line goes out to the porportioning valve. Find the line for the front brakes, (think its the rear line) pull it off of the master cylinder and you should see a little cone shaped cap inside with a hole in the center, pull that out and behind it is a little one way plastic valve, that would be the residual valve. I Machined the back of my spindles (1975) down to match the back of the newer disk brakes style (from a 1977). This allowed me to put rotors onto my original spindles and keep my 6 bolt hubs. I then used the disk brake knuckles and capilers on my original axel. I'm still using my original proportioning valve and master cylinder with now problems so far.

 

Great, I'm going to try removing the residual valve first since I can do that without having to pull the master cylinder.

Another question now:

It might have been answered above but bear with me.

My 74 spindles use the same hub bearings inside and out (I believe). The spindles I have from the 80 have a smaller outer bearing. Can I retain my existing spindles, hubs and bearings for the swap?

The reason I ask is that the bearings are almost new and I only have one hub for the tapered type spindle.

Guys as always thanks for all the good info.

 

I'm guessing you mean you machined the bearing hub down? The spindles don't need any machining. The bearing hub is the part the wheel bolts to, the locking hub bolts to, and the disc brake rotor is held onto with the wheel studs. The spindle bolts to the knuckle and the bearings are a slip fit onto. The outer axle shaft protrudes through the middle of the spindle. Just trying to clarify for anyone reading this.

 

Yep, bearing hub. Thought they were spindles, but I'm a technical lingo dunce.R)

 

as nickmil states above, you probably mean the bearing hub, rather than the spindle.

if you wish to use the original 6-bolt hub that came with the drum brakes on your '74, you'll need to machine the back side of the hub (only the front face came machined from the factory) in order for it to cleanly mate with the discs, which mount on the inside surface of the hub, rather than the outside surface that the drums mounted to.

some people have done that, while others have just swapped in a 6-bolt later-year hub. the later hub will have the smaller outer bearing, unlike yours which has the same bearing inside and outside.