71 Commando Dana 30 swap

[JeepMedic911]

I searched this page but couldn’t find what I was looking for. I just acquired a 1971 Commando with the V-6 and T 400 automatic. It has no brakes. Master cylinder is dry and rusty. Instead of putting $ into drum brakes I bought a disk brake, narrow track D30. Planning on keeping rear drum brakes. I’ve done some research and it should bolt in but what about the drive shaft? Looks like a GM universal brake booster/master cylinder will bolt in? Is that true? Seems cheaper than Jeepster parts. I know I’ll need a different brake light  switch. Has anyone done this swap? I’m sure I will have lots more questions once I actually start working on it. 
Thanks

[Moses Ludel]

JeepMedic911...See my comments below in colored print.  Let us know where you go with all this:

On 9/18/2024 at 8:00 PM, JeepMedic911 said:

I searched this page but couldn’t find what I was looking for. I just acquired a 1971 Commando with the V-6 and T 400 automatic. It has no brakes. Master cylinder is dry and rusty. Instead of putting $ into drum brakes I bought a disk brake, narrow track D30. Planning on keeping rear drum brakes. I’ve done some research and it should bolt in but what about the drive shaft?

Got it...So, is the D30 from a Jeep with the same side transfer case drop (right side/passenger) as your '71 Jeepster/Commando?  Presumably it's a narrow track '77-up CJ Jeep D30 (low pinion location) that had leaf springs?  If so, the main issues are spring perches, perch locations and the driveshaft, as you hint.  If the axle's companion flange/yoke is the same as your '71 front driveshaft, and if the driveshaft length is still correct, that's the easier swap.  The Commando uses pinion flange U-bolts; later Jeep driveline U-joints use straps with small bolts.  If there isn't a match here, a driveline shop can change, modify or even fabricate a complete front driveline that will attach correctly to your D30 front axle and the transfer case.  (You do need a splined coupler built into the driveshaft like your original shaft.)  For reference purposes, you have a Spicer (Dana-type) 20 transfer case in the Commando if original.

Looks like a GM universal brake booster/master cylinder will bolt in? Is that true? Seems cheaper than Jeepster parts. I know I’ll need a different brake light  switch.

You need is a master cylinder and booster from a disc brake application.  This will proportion for disc front brakes and not have a residual valve at the front brake port.  Whether you use a GM, Jeep or any other brake master cylinder with booster, it needs to be a disc brake/drum brake application.  (The master cylinder's rear brake port does require a residual valve.)  As long as you can get the firewall mounting and brake pedal pushrod length correct, you have a way to go here.  (There are many replacement pedal pushrods from which to choose.)  Make sure the brake pedal pushrod length or adjustment is correct to prevent locking fluid in the brake circuits.  The master cylinder's piston needs to retract completely when the pedal releases. 

Consider a master cylinder along with its "combination valve" (proportioning and safety switchover).  When you get the brakes going, test them for front-to-rear proportioning.  If the master cylinder and its combination valve or proportioning valve come from a disc/drum vehicle with a similar wheelbase and weight distribution/transfer, the master cylinder and its combination valve should work correctly.

There are many approaches to brake light switches that can be activated at the brake pedal.  Some time spent at the parts house and fabrication of a mounting bracket can handle the brake light switch.  Ideas abound at a recycling yard.

Has anyone done this swap? I’m sure I will have lots more questions once I actually start working on it. 

Others may have more to add, including specific parts that would be useful.  Keep us posted on the project, you have a great vehicle for starters!

Thanks