Fixed to slip yoke

I've got a bolt on yoke on a trans from a 2007 5500 truck and need to go with a slip yoke. Anyone have any advise on how to proceed? It's a 2WD Allison trans.
Thanks, Hal

I'm curious why you would need to. What application is the tranny from, and what is it going into?

Many light truck models were updated (recall campaign) from 2-piece shafts to a single. It should be a matter of sourcing the correct single propshaft assembly if it's for a compatible model. Only specific cab, drive and bed length combinations were included. Otherwise, you'll have to build a custom shaft with the slip-yoke. If this is for use in a 5500, it will be very different, as the propshafts are different, and may include a shaft-mounted E-brake system. The 5500 tranny may not have a parking pawl, so you'll have to consider that, as well.

It's a very unique build. The motor and transmission I sourced from a 2007 C5500 truck. I'm installing it in a 1977 GMC Motorhome that came with the Toronado FWD drive train. I'm mounting the engine/trans in the back, driving a 9.75" Ford IRS differential flipped driving the center wheels. The drive shaft will be quite short so adding a slip in the shaft might be a problem but a slip yoke would be fine. Hence the interest in a slip yoke. It will be a custom shaft for sure and most likely a two piece at that. The trans has a parking pawl but no tail shaft parking brake. I will be using a Tesla electric caliper clamping a home built rotor attached to the pinion flange for parking. All wheel disc's make parking brakes practically useless in these Motor homes. Just a fun project.
Hal

OK. That does sound like a fun, unique project. You should only need the OEM slip-yoke, then (such as from a 2WD short wheelbase or updated long truck). There is no distinction between the fixed and slip output shafts or seals that I could find in my LT manuals. There may be a difference due to the 5500 application, but I'm not finding any. Just replacing the fixed with a slip yoke should be all. The torque on the fixed yoke bolt is published 90 ft/lb, but may have thread locker (may be a bear to remove, don't torque against the parking pawl).

You might have a look at Robyn's "Van-Cat" thread in the Community Forum. A lot of discussion regarding custom drive shaft, angles, joints and such there.

Thank you very much for that information. It's exactly what I was looking for. This is my first introduction with a Dmax and Allison. I've played with Diesels for more years than I care to mention. Drove a 180D Mercedes in high school, had a number of the Olds 5.7's, many VW's (have one now) Chevy 6.2's, Ford 6.9, 7.3's, and even did a bus conversion installing a 14 ltr Detroit S60. I recently installed a 6.5 in another GMC using a 4l80e, Moorse transfer case, 9.25"AAM late front Chevy IFS. That was a fun project also thats proven itself over 25,000+ miles.
This one is a 'little' more of a project.
Hal

With regard to the yokes, could a person weld up the bolt hole on a bolt in type yoke and use it as a slip? Is the slip yoke longer than the bolt in style? I'm having quite a challenge finding the part numbers for these pieces. Guess I just don't know where to look.
Hal

Simply, no. The fixed yoke is too short. Maybe not simple, but you can find a slip yoke. I'll give it a shot in the morning.

Definitely not simple. Looking for hen's teeth, I think. Can you measure the output shaft? I need the shaft diameter, inner seal diameter, spline count, how far it protrudes from the tail housing, and the length of the spline, if it's possible.

What I'm finding is there may be a significant difference between the fixed and slip output shafts, as well as a possible difference between the tail housing. I'm also finding no reference to any of them 2WD and slip-yokes not on the propshaft, and no confirmation of the size or spline count outside of that. Either the part never breaks, or it isn't a common option.

How long (short) do you suppose the drive shaft will need to be?

OK, the shaft is 1.744", seal dia-OD looks like about 3.5, hard to get exact with it still installed, 2.56 od of yoke @ seal, 34 spline, yoke has 2.7" stick out from tail shaft, length of splines approx 2.5", yoke is 4.7" overall long.
I guess me not finding much isn't uncommon then?
If they were changing over to one piece shafts, you'd think the tails/shafts would be the same wouldn't you? I can't imagine them pulling a trans apart for the recall but then....
Thanks, Hal

The shaft will probably be about 24" but two piece.

You may have to get creative with this. I'm not finding any Allison application with a slip-yoke option, and a likely reason for no slip-yoke. It's one of those questions no one ever asked, until now.

The propshaft recall replaced the 2-piece shaft with a single, and the replacement shaft is delivered with the U-joint and slip-joint attached for 2WD, or just the U-joint for 4x4. The transfer case has a slip-yoke, but the size and spline count is different than the Allison output shaft. There are 2 Allison output shaft options, fixed and slip, but the slip is for mating to a transfer case. The output shaft looks easy enough to replace, but I think your problem is going to be finding a compatible yoke.

There is also another recall that replaced the 4x4 transfer case slip-yoke with a nickel plated version to address a spring-wrap issue, but it only applies to 4x4.

With a shaft only 24", why does it have to be a 2-piece? The angles may be excessive single, and worse as a double. Just thinking out loud.

The trans has to ride high in the chassis for rear ground clearance and the diff will be as high as possible with it being even with the inside floor. The shaft will need to drop from the trans immediatly to hide under the floor to keep the floor flat forward of the bed. The motor/trans will reside under a bed at the rear.
These motor homes are built close to the ground, only a 14" step in height from ground to floor and about 8" under the frame. The new fame will bring it up a couple inches but things are tight. The shaft may need to have a slip in it although it will be tough. The diff will be mounted solid (almost, with isolators) and the motor on typical mounts so the need for slip is really minimal but I'm afraid to do without.
I really appreciate your research and help, things don't always go the 'easy' way for sure.
Hal

Why not a little hump in the floor? I'd certainly want a shield above the propshaft, but that's just me. I've seen some blow up. Had a U-joint come apart in a V-Drive race boat once (4" from my right hip). The aluminum tube contained it. It would have sunk me and the boat, otherwise. The coach floor can't be all that well armored.

Anyway, also consider how you're securing the shaft. You can't just hang a U-joint out in space. A 2-piece requires a center carrier. I think 24" isn't enough distance to get all the parts in there, and account for enough deflection to clear the floor. Maybe channel your inner Rube Goldberg?

I can probably make the shaft longer as I'm adding two feet to the length of the RV. I can move the rear axles a bit and maybe get 30-32 inches of length. I'm aware of the need for a carrier bearing support. The C/L of the pinion is 4 1/2" below the floor so there is plenty of room for a shield.
The unit has a very unique design rear, hard to explain. Here's some drawings to give you an idea:
http://www.gmcrvparts.com/v/vspfiles...s/REACTION.pdf
I've built new control arms with 4x4 front hub/bearing assemblies for the drive.
Fun project.
Hal