Rear Disc Conversion options

[53HiHood]

I would like to lose my drum brakes. Who has converted their rear 44 to disc brakes and what parts did you use?

[Moses Ludel]

53HiHood...I did this on the '55 CJ-5 Jeep in my book.  The great thing about Spicer/Dana axles is the common housing end flange pattern for the front and rear axles.  I used a kit that was available from Warn at the time, using GM S-truck calipers with Jeep rotors as part of a rear full-floating hub conversion.  The kit provided caliper mounting brackets, OE replacement calipers, bearings, hubs, rotors and the axle shafts cut and splined for the application.  This provided free-wheeling hubs front and rear, popular for flat towing if you don't have an early Ross cam-and-lever steering gear....Frankly, I don't flat tow vehicles, especially short wheelbase Jeep 4x4s, for a variety of reasons.

A full-floating rear axle conversion does involve axle shafts splined for your axle's differential side gears and the wheel hubs.  Which axle are you using at the rear?  An original Spicer 44 with offset differential?  If so, the axle shaft part gets tricky.  Warn custom built my axle shafts, and they no longer do any of these conversions nor supply any parts.

If stock parts are your plan, you can use late '70s to early 'eighties Jeep CJ disc front wheel hubs, rotors and calipers for simplicity if you do go the full-floating route.  You'll need to deal with the axle shaft length issue and caliper mounting brackets.  I have seen conversions that simply used the front brake assemblies from the '77-'82 CJ front ends.  (The Dana 30 front axle has the same flange pattern as your 44 rear axle).  Again, this creates a rear full-floater similar to the Dana 30 front axle. 

The key here is a caliper mounting bracket that is safe and has the proper offset to center up the calipers.  If you go this route with free-wheeling hubs, make sure that you use wheel hubs with the six-bolt free-wheeling hub flange and premium free-wheeling hubs.  There is a lot of torque to the wheel hubs in 2WD mode...The axle shaft end float is also a concern, you want to minimize the axle shaft spline end float at the free-wheeling hubs.  Some use a solid drive flange instead of free-wheeling hubs.  (This would be similar to the front drive flanges used by Willys/Jeep when customers did not retrofit free-wheeling front wheel hubs.)    Another angle would be one-piece axle shafts with a solid flange that bolts to the wheel hub.  One-piece flanged axle shafts would eliminate the end float issue.  Perhaps Moser and others could custom build axle shafts with the right length, side gear splines and end flange pattern for this purpose.  We can discuss your findings and parts options...

Here is a currently available rear disc conversion for '70-'75 Dana 44 Jeep axles:  https://www.quadratec.com/products/32700_001X_PG.htm.  You would need to have custom axle shafts made that would accommodate your Spicer 44 axle housing.  This is a semi-floating axle arrangement, the axle shaft bearing fit/sizing would need to be compared to your early axle's tapered axle shaft housing and bearing design.  One question would be fitting the axle shaft bearings into the early axle bearing bores.  Will your rear axle work with a semi-floating bearing and seal arrangement like this?  The axle shafts would require custom building for your axle's width and differential offset if you're using the '53 axle and Spicer 18 transfer case.

Another approach that I believe is perfectly acceptable and much simpler would be an 11" x 2" rear drum brake conversion in conjunction with disc front brakes.  This is a time-honored approach that Jeep and the aftermarket have taken.  There are conversion kits and numerous other parts readily available from sources like this one:  http://www.the-jeep-guy.com/brakes.htm.  The only caveat with drum rear brakes is drying out the brakes after stream fording.  This would be less pronounced with disc front brakes and 11" x 2" drum rear.  Jeep CJs used 11" x 2" drum brakes to good effect in the '70s.

Note the other upgrades suggested for disc front/drum rear brakes, including a properly sized dual master cylinder and booster (each specifically designed for disc front/drum rear brakes if disc/drum brakes are your choice), a proportioning valve if needed, an 11" x 2" drum brake conversion kit for the rear, etc.  Think "system" upgrade...Make sure the master cylinder is ported for disc/drum brakes if you do disc front/drum rear brakes.  If you do the 4-wheel disc brakes, make sure the master cylinder is correctly ported for disc brakes front and rear.  You don't want drum brake residual pressure to cause drag on disc brake pads and rotors.

Moses

 

[53HiHood]

Moses,

I have an offset 44 with 30 spline 1 piece axle shafts. The jeep was set up with front discs and rear 11” brakes and the proper master cylinder. I looked at the full float kits but I don’t want to get that involved and spend that much. I’ll likely end up purchasing weld-on caliper brackets and sourcing a pair of e-brake calipers. After watching a couple videos it looks pretty straight forward.  

[Moses Ludel]

53HiHood.  As you describe, the concern would be properly welding the caliper brackets in place.  There is a large amount of rotational force weighing on the caliper bracket.  The brackets must be able to withstand this force.  Additionally, the caliper must center over the rotor while also allowing the range of float necessary to compensate for brake pad wear.

Who makes the weld-on bracket kits, and what is the fit-up?  I'd like to see where the manufacturer recommends running the weld beads.

Moses

 

[53HiHood]

The brackets I'm looking at are from ruffstuffspecialties. As far as set up, the best video I saw on youtube, the guy mounted the caliper to the bracket and set the unit on the axle with rotor installed. He used compressed air to center and hold the caliper on the rotor before tacking it to the axle housing. The project is going on hold yet once again. I'm taking a temp transfer to Durango CO at the end of the month.

[Moses Ludel]

Ugh...Delays...Your season is coming up, I can understand the need to prioritize. 

Durango is fantastic country, access to Red Mountain Pass, Telluride/Ouray/Silverton/Animas Forks, Imogene Pass and my favorite view via Last Dollar:  Ridgway toward the San Juans.  You need your bike or Jeep there!  Once you get settled, that will surely be the plan.  There are more complex, "challenging", i.e. hazardous routes, too, you'll hear all about them.  I guided for Chevrolet/GMC in that region during the mid-'nineties media launches of new 4x4 trucks and SUVs, some of my favorite work!  The country was most memorable and so was guiding the media.

 

[53HiHood]

Well I'm back home for the winter and ready to finish this disc conversion, but first I need to start it. I'm still looking at the 3/8" weld-on brackets. I can't seem to find bolt on brackets anywhere except for one complete kit that is way above my price range. The other thing I'll need to look at is a space to take the place of the backing plate I'll be removing. I could either cut up the backing plate or have a spacer made.

[Moses Ludel]

Hi, 53HiHood!  The 6-stud axle flange pattern is common to all Dana/Spicer light axles and also used by others.   There may be a flange ring used for spacing or as a bearing retainer, etc.  Poke around, see what's out there, maybe early Ford or an F-truck with a Spicer 44 rear axle (1949-56).  '55 (Second Series) to mid-'sixties GMC light trucks also used Spicer 44/45 rear axles.   Lincoln, Studebaker and others also used the Spicer 44-type axle, too.  Bearing retainer rings might work.  Or backing plates could be TorchMate/plasma cut to make flange rings.

Plasma cutting two plates with a TorchMate would not be difficult, you can use the original axle flange ends or Jeep axle bearing end-play shims as a pattern.  You're simply creating a spacer, not a support/safety member like a caliper mounting bracket...Use the right metal for the application.

Moses

[53HiHood]

I finally found the brackets with spacers, $100. Nice 3/8” brackets. R&P 4WD in Oregon City has a lot of great older jeep stuff, Rich is the owner and I ended up calling him and he was more than happy to sell me just the brackets with spacers and told me what calipers and rotors to use. I should be able to make the complete conversion for around $200.

[Moses Ludel]

Do these brackets work with GM S/T truck calipers and OE replacement (late '70s to '86) Jeep CJ rotors?  If so, they could be the brackets or at least similar to the type Warn produced.  (As you know, Warn has been based at Clackamas and Milwaukee, Oregon.)  I used that style bracket with Warn's recommended GM single piston calipers and the correct diameter and thickness rotors...$200 for the complete conversion is terrific!  Good job...

[53HiHood]

Samurai rotors(86) and Chevy or caddie calipers. I’m not too concerned with adding an e-brake so I’ll go with the standard ones.

[Moses Ludel]

So, Samurai front rotors for the rear and front of your 3B or for the rear only?  Another approach at the front?  This should be adequate at the rear. 

You may need a proportioning valve although the short wheelbase (80" in your case) often offsets vehicle pitch.  A mechanical proportioning valve is available from Wilwood and others if you need it.  

If you're still running the Model 18 transfer case, you do have an E-brake on the rear driveshaft.  In good condition without oil on the shoes, these brakes are tried and proven.

Moses

[53HiHood]

The front is already disc, I’ll just need to upgrade the master cylinder and set up the proportioning valve I got for it.

[Moses Ludel]

Knew you had the front earmarked for disc brakes, was that a Jeep-parts conversion?  Are you keeping the master cylinder beneath the floorboard? 

The master cylinder needs to be 4-wheel disc brake application;  drum brake master cylinder outlet ports will have residual pressure valves.  On my '55 CJ 4-wheel disc conversion, the drum-type dual master cylinder required removal of residual pressure valves from the master cylinder's outlet ports.  (Valves are behind the removable flare seats.)

 

This is a 1972 Jeep CJ master cylinder for a four-wheel drum brake system.  Note the two residual check-valves, one for each end of the vehicle's braking system.  Converting to disc brakes,  I removed these residual check valves and springs then carefully reinstalled the flare seats.  The first Jeep CJs with disc front/drum rear brakes have a check valve at the rear drum port and no check valve at the front disc brake system.

 

This 1973-80 Chilton image shows a tandem master cylinder with one check valve on the rear (drum) brake circuit and no check valve on the front (disc brake) system.  Late model vehicles have residual (very low pressure) devices just to keep pads next to the rotors and prevent lag on brake application.

Late disc brake applications do have low hydraulic residual pressure, just enough to keep pads close to the rotors.  This pressure, however, is lower than drum brake residual valve pressure.  Drum brake residual pressure keeps the wheel cylinder cups expanded and sealing.  Stout brake shoe return springs overcome the residual pressure and keep the shoes from pressing against the drum and dragging. 

Typical residual pressure for a drum brake Jeep master cylinder would be 10-12 psi.  (Aftermarket Wilwood residual valves for drum brakes are around 10 psi.)  This is well below the shoe retraction spring tension.  This residual pressure level, however, would be high enough to cause disc brake pads to drag on the rotors.  This amount of residual pressure will cause premature pad wear, overheating of the rotors, brake drag and even wheel lockup if applied within a disc brake system.

Speedway Motors offers a 2 psi residual valve (inline mounted) for disc brake systems that use a beneath-the-floorboard master cylinder.  They hint that the firewall mounted cylinders have enough gravity feed pressure (not sure about this one) to overcome a spongy pedal or slight lag when applying the disc brakes. 

My dual drum brake master cylinder, mounted beneath the floorboard with both residual valves removed, feeds front and rear disc brakes without timing/lag issues or pedal sponginess.  Earlier OEM disc/drum systems have no residual pressure valve on the disc brake portion of the braking system although these systems do have firewall mounted master cylinders.

The 2 psi residual valve would be like late four-wheel disc systems.  You can watch for any signs of lag or pedal sponginess.  These 2 psi valves are available if needed.

[53HiHood]

On 1/28/2019 at 9:38 AM, Moses Ludel said:

Knew you had the front earmarked for disc brakes, was that a Jeep-parts conversion?  Are you keeping the master cylinder beneath the floorboard? 

The master cylinder needs to be 4-wheel disc brake application;  drum brake master cylinder outlet ports will have residual pressure valves.  On my '55 CJ 4-wheel disc conversion, the drum-type dual master cylinder required removal of residual pressure valves from the master cylinder's outlet ports.  (Valves are behind the removable flare seats.)

 

This is a 1972 Jeep CJ master cylinder for a four-wheel drum brake system.  Note the two residual check-valves, one for each end of the vehicle's braking system.  Converting to disc brakes,  I removed these residual check valves and springs then carefully reinstalled the flare seats.  The first Jeep CJs with disc front/drum rear brakes have a check valve at the rear drum port and no check valve at the front disc brake system.

 

This 1973-80 Chilton image shows a tandem master cylinder with one check valve on the rear (drum) brake circuit and no check valve on the front (disc brake) system.  Late model vehicles have residual (very low pressure) devices just to keep pads next to the rotors and prevent lag on brake application.

Late disc brake applications do have low hydraulic residual pressure, just enough to keep pads close to the rotors.  This pressure, however, is lower than drum brake residual valve pressure.  Drum brake residual pressure keeps the wheel cylinder cups expanded and sealing.  Stout brake shoe return springs overcome the residual pressure and keep the shoes from pressing against the drum and dragging. 

Typical residual pressure for a drum brake Jeep master cylinder would be 10-12 psi.  (Aftermarket Wilwood residual valves for drum brakes are around 10 psi.)  This is well below the shoe retraction spring tension.  This residual pressure level, however, would be high enough to cause disc brake pads to drag on the rotors.  This amount of residual pressure will cause premature pad wear, overheating of the rotors, brake drag and even wheel lockup if applied within a disc brake system.

Speedway Motors offers a 2 psi residual valve (inline mounted) for disc brake systems that use a beneath-the-floorboard master cylinder.  They hint that the firewall mounted cylinders have enough gravity feed pressure (not sure about this one) to overcome a spongy pedal or slight lag when applying the disc brakes. 

My dual drum brake master cylinder, mounted beneath the floorboard with both residual valves removed, feeds front and rear disc brakes without timing/lag issues or pedal sponginess.  Earlier OEM disc/drum systems have no residual pressure valve on the disc brake portion of the braking system although these systems do have firewall mounted master cylinders.

The 2 psi residual valve would be like late four-wheel disc systems.  You can watch for any signs of lag or pedal sponginess.  These 2 psi valves are available if needed.

Moses, I realized I never replied to your last post, but better late than never huh. My front discs are CJ7 if I’m remembering right, it’s been a few 3-4 years since I replaced those parts. There were two different rotor thicknesses I believe and I’ll have to check which I have.I do have a wilwood proportioning valve that I will be using, and the master cylinder is a large bore dual reservoir that mounts on the firewall. I need to replace it due to it’s condition.

Jon

[Moses Ludel]

Gotcha...Sounds like the popular conversion.