Older Jeep disc brake conversion

Hello - does anyone know how to convert drum to disc brakes in a 1950 Willys 4x4 station wagon? Does any company make a conversion kit? Thanks.  

Is it 2WD or 4x4?  

It's a 4x4. Thanks.  

It's actually pretty simple. You can get GM Dana 44 caliper brackets and calipers (73-79), and Ford F150 Dana 44 rotors (5 on 5.5 - 79-85).

Press out the wheel studs, mount the rotor behind the hub, and press the studs through the rotor and back into the hub. You'll also need 1" longer fine thread bolts that held the backing plate onto the knuckle to mount the caliper bracket.

Fitting the caliper requires just a little grinding on both the knuckle and the caliper so that the caliper can slide on the caliper bolt without touching the knuckle.

Get the caliper bracket, caliper (core), rubber brake lines, and banjo bolt from the junk yard, reman calipers from the parts store ($20ea + core), new rotors ($35ea), and new caliper bolts ($10). You'll also need a metering block to split out the hard line from the master, and some bendable steel lines from the parts store routed down to the frame rails on both sides.  

Thanks for the info - I gather you described the conversion for the front Dana 25 axle? Is it worthwhile to even attempt to convert the rear drums to discs; and will it be the same parts and procedure? I think it has the old Dana 44 2-piece rear axle.  

Yes, that's for the old Dana 25 closed knuckle axle.

I don't know your uses, but I would strongly suggest swapping both the front and rear axles if you actually use it as a trail rig.

An axle swap is pretty straight forward, and you would get better brakes at the same time as better strength. Neither of your axles is very strong. What would work very well is axles from a SJ Wagoneer ('74-'79) with Quadratrac. The Quadratrac is a fulltime transfer case that requires the rear differential to be offset to the passenger's side, just like your Dana 18 setup.

The Quadratrac Wagoneers are not highly sought after because of the offset diff and can be picked up for very cheap. They run Dana 44s front and rear. The rear drums are much bigger and the front discs are the same as used on the GM 4x4s. Your axles are about 58" wide and the Wagoneer axles are about 59 1/2" wide.

About rear disc. I don't think they are ever worth converting to unless you are having problems stopping because of mud and water contamination. Drums are inferior to Discs for a lot of reasons, more complex, need adjusted, and performance is affected by road contamination. But, not so much just pure braking performance on the rear.

Rear drum braking force is reduced as you apply more pedal pressure. This is controlled by the proportioning valve. As you brake harder, more and more of the vehicle's weight transfers to the front axle. As much as 70-80 percent of the braking is done by the front axle during hard braking. If the rear brake pressure was not reduced during hard braking, the rear would just lock up because of the weight transfer off the rear axle.

Drum brakes will lock up easily on the rear if you don't use a proportioning valve. And locking the rear wheels is an indication that there is enough braking force. So, do you really need the greater forces from disc brakes and then have to just proportion them back to keep them from locking up?

Most people don't improve their overall braking performance when they convert to rear disc. In fact, most people reduce the performance because they get such an imbalance between braking components. The master cylinder and booster need to be sized correctly for the fluid volume of the calipers and/or the wheel cylinders. And that doesn't just mean a large master cylinder. It needs to be the right master cylinder.

When thinking about changing brake components, always remember this formula:

Pressure * Volume = Force

All three are related and can't be separated. If you change the volume, then it will take more force to build the same pressure. That usually means you need a bigger booster to apply the greater force.

Anyway, there's a lot to it and I could go on and on. 99% of guys who start messing with their brakes don't learn enough before they start. Then, they are forced to learn after their brakes don't work very well and that's usually a longer learning curve and a more expensive project.  

I think you are right. I will take your advice and try to swap the axles with the Wagoneer's and keep the rear drums. I think I may also need to switch to dual circuit master cylinder; and perhaps hanging pedals though that may be a bigger job. What do you think?

Thanks again..........George  

Yup, the pedal, which has a certain amount of leverage, also plays a part in applying force. And then there is the push rod and the bolt pattern compatibilities of the master and booster combination. And then there is the size/space thing. It is often very difficult to fit a booster on the firewall of early Jeep vehicles.

The other option is to use a hydro setup from the '70s and '80s GM diesel vehicles. They require a power steering pump to supply the fluid pressure, but the p/s pump may be easier to package than a vacuum booster.  

Using a power steering pump to supply the fluid pressure to the brake system is a new concept to me. How does one set that up? Thanks.  

Instead of a vacuum assist booster, it's a hydraulic assist booster. The p/s pump supplies pressure to the booster. You still have a master cylinder supplying the brake fluid pressure.

Diesels don't produce vacuum, so they use hydro assist brake boosters.

Hydro boost systems can deliver an incredible amount of power assist and makes it possible to use a big volume master cylinder without a big footprint on the firewall.

Click Here for some info from a company that sells complete kits. But you could also scrounge the parts from the junk yard.  

Thank you for sharing a wealth of information. I am sure I'll run into hurdles during the course of this project and may need more help later.  

Hey, I have an old 72 Jeep J2000 with the closed knuckle 44 front end.  It was my dad's.  I Just use it around town and lock the hubs at the deer camp on occasion.  I want to keep my old axle, but want to improve braking on the road.  I have seen this conversion posted several places.  I was trying to determine if the old manual master cylinder was adequate?  Will I need a proportional valve?  Will simply "bolting" on the recommended parts give me the fix I want?  I'm OK with the old master if it will do the job and put a few extra seconds between me and the kid in the Honda at the stop sign that is scared to be behind my old truck.  I looked at robbing a booster, vacuum can and proportional valve from a newer late 70's early 80's Wagoneer or truck, but this will add a lot of extra effort on this conversion if it really isn't needed.  Any advice would be great.  

Very important. Keep this in mind when thinking about brakes...

Volume * Pressure = Force

You can't change one of the paramters without affecting the other two.

Wheel cylinders require less fluid volume than calipers. So if you swap over to calipers, the stroke of the piston in the master cylinder will have to travel a greater distance to supply a greater volume of fluid to the new caliper and still provide the same pressure at the caliper.

If the master cylinder can't provide the needed volume before the pedal hits the floor then you need a larger volume master cylinder. A larger master requires more force to build the same pressure. So, if you change the master and then can't apply enough pressure with your foot to build the pressure, then you need either more leverage (longer pedal) or a bigger booster.

Now to answer your question. The closer that the individual components of the brake system are matched, the better the brakes will work. People have differnt levels of tolerance. You may be a bigger guy with a longer, stronger leg that would get use to the need to apply a lot of pedal pressure. But, if the pedal goes to the floor after the system is properly bled, then obviously you'll need a larger volume master.

A larger volume master will make the pedal feel firmer, higher in its travel and require more foot pressure. A smaller master will lower the pedal feel, not as firm higher in its travel, and require less foot pressure.  

That answers the booster and master cylinder question, but what about the proportional valve?  Is it necessary?  It seems like from what I've read that it just helps prevent the rear drums from locking up before any real braking or slowing down takes place.  I would assume what seems to be the proportional valve in my existing system is set for the drums and not adjustable.  Should it be changed for one like in the new truck mentioned before or will the old one do?  I have seen adjustable valves in JC Whitney and the like, but it would be easier and cheaper to get one from a donor truck if it is needed.  I'm trying to be reasonably sure about what my changes will create before I down the truck for a month doing trial and error (I expect some)to get this right and safe.  

What you don't want is locked-up rear wheels. That's almost the same as no brakes and can cause the back-end to come around. It would be better to have average rear braking performance than rear brakes that locked up before the fronts.

Weight obviously plays a big role. The more weight in the bed, the greater the braking pressure can be in the rear.

The proportioning valve is very specific to the vehicle weight as well as the braking system and can be hard to dial-in perfectly without trial and error. Try it with and without. If the rear doesn't lock-up without, then go with it. Just remember most of your braking during hard braking comes from the front, so you might not even notice lazy rear brakes if you're not carrying a load. It's when you load it up that better rear brakes will have a greater effect.