366 with Allison in G749?

[USMC 00-08]

Has anyone put a 366 with an Allison transmission in a G749 series vehicle? If so could you post pics and tell me what modifications are required, how you like it, etc.? I have searched this forum for the answer but nothing with the detailed info I need were found.

The reason I am asking is the tranny in my M135 is shot but the engine is fine. I was going to try to have the Hydramatic rebuilt, but then my dad gave me a 366 with the Allison out of a late 70's early 80's school bus that he is going to scrap out. I am trying to decide what to do here. Convert over to the 366? Leave the 302?

I had also thought about taking the 302 with Hydramatic out and restoring it over time and use the 366 with Allison to drive around with in the meantime.

What are your thoughts gentlemen?

 

[gimpyrobb]

I know a guy here in Cincy put a 366 in an M35 and loved it. I never got to drive the truck, but I would imagine it should work fine in a 135. You'll have to keep the stock transfer case as the front axle is reverse rotation.

 

[11Echo]

Someone intalled this in an older MV. I don't remember who or what model truck.

View attachment 452891

 

[hendersond]

I'd go 366 and Allison, 20 gallon fuel cell between the frame rails in back, mechanical fuel pump, dual stacks. Modify the suspension by having to remove the top dogbone that goes from frame to axle (you know the one where your starter will be) remove the front shackles and make solid spring mounts (yes, there are shackles on both ends of the springs). If you don't the front axle will roll forward and backward about 4 inches when you step on the brake because it rotates and the center of rotation becomes the front mount where the axle attaches to the lower dogbone. Also every time it rolls, it effectively changes the angle of the position of the axle in relation to the steering box and the wheels turn left (Kind of like bump steer). Don't forget to add a spinner knob on your steering wheel so when it rips the wheel out of your hand, that knob comes around and whacks you a good one in the side of the elbow.

And that is my story of how I was able to purchase a really cheap parts truck from a guy who kept rubbing his elbow. (Except it was not an Allison or a 366, but the engineering will be the same)

 

[jdknech]

keep in mind that the low-range is in the transmission, not the transfercase.. so if you go with the allison, you will lose your low-range

 

[USMC 00-08]

I had heard that first gear with the Allison may be sufficient to act as a low range. Does anyone know if there is any truth to this?

 

[Gunfreak25]

Paul, what model Allison do you have? Low range is really only a must if you plan to off road her quite a bit. The 366 was an industrial motor designed for heavy trucks so it's a good choice. There was a fireman here a few years ago that posted a picture of his GMC with a 366, I had it on my old computer but it's gone now. I would totally try to rebuild the Hydramatic later, worth holding onto. As for the new swap, the most time consuming part will be fabbing your new motor mounts and adapting the air compressor to the 366 unless the truck it came from had one already. Everything else is pretty easy and can be done in a weekend.

When you drop the hydramatic you'll have to re rig up the linkage for the transfer cases reverse shifter shaft, or just say to **** with it and drop the front driveshaft for a dedicated 4x4 until you get the Hydramatic rebuilt.

 

[USMC 00-08]

Hi Tom! Good to hear from you again. I hadn't seen you on here for a while.

I believe the Allison is the AT545. I have not seen the engine or transmission yet so not sure if it has the air compressor. Next time I am at Dad's I'll look at everything.

On Friday night, I spoke with a man that I have known for a while and found out he used to drive M135's in the Army back in the late 50's early 60's. He said he may be able to help out on some of it and also thought there was a guy locally that could rebuild the Hydramatic, so I am exploring all of my options right now.

 

[hendersond]

Tom??????
I may be wrong on the starter/dogbone issue. It may not be an issue with a small high torque unit. I willlook into it further.

Tom, where u been?

 

[Gunfreak25]

AT545 is a stout unit, 4 speed no lockup just direct drive. By all means if you can manage to rebuild that Hydramatic I vote rebuild, now that my own GMC has taken more of a "project toy" status like it should have been from day 1, I wish I had scrounged up an original 302 and Hydramatic to restore it with. But, i'm happy with whatever makes her rumble.

If you need any help you have my email, phone too.

Nice to see you guys again!!

 

[USMC 00-08]

I finally got a chance to go visit Dad and took a peek at the 366. I'm still trying to figure out what I want to do. Here are some pics of the engine. It is in a 1979 Ward School Bus. It seems like it should fit into the M135 ok.

 

[11Echo]

The motor won't look so cramped in your engine bay after taking off the non-essential items.

366 in my M1008.

 

[USMC 00-08]

366 in my M1008.

How do you like the 366? What modifications did you do to make it work? Do you think it would work well in the M135?

 

[11Echo]

How do you like the 366? What modifications did you do to make it work? Do you think it would work well in the M135?

It is an improvement in all categories except fuel mileage. Lots more power.
Around me gas is a lot cheaper than diesel right now so that helps offset the lower mpg.

The motor bolted right up to the T400 transmission. I changed to a 454 water pump and the huge oil pan to car/light truck pan,(the large truck oil pan might work in a M135). I had to make the brackets for the dual alternator setup. I've been running a 12V starter with the 24V solenoid for the last 4 years without problem.