m5od and np205 not that I should but I could so I did

Shorty

Well-known member
Had a bunch of parts sitting around and my shop beater truck (1983 f150 with 300, M5od) was getting pretty rusted (seat was trough the floor and on the frame, radius arm mounts had flaked holes through them etc.) So I thought that rather than have a bunch of spare parts in a barn I would bolt/weld until I had a functional truck.
Foundation to build off was a 1981 f250 4x4. Cab was rusty but patchable, frame solid. It has the 300 but with a c6, np208 t case.
Had all the clutch pedal brackets and parts for the hyd. clutch off the rust bucket and a spare 4x4 m5od. In digging out the tranny I came across a np205 transfer case. Measured the 5 speed and the 205 and it's an inch shorter than the c6 np208. rear shaft will work. For the front the first section of the 2 pc shaft out of the 2wd rust bucket will be perfect, it even had the slip yoke I need.
Had to make a few mods to bolt the two together. The aluminum bearing retainer on the input of the 205 hits before things pull together so i chucked it in the lathe and turned it down a bit (first pic) and used a die grinder in the tail housing to make clearance for the bolt heads (2nd pic). I also needed to clearance the flange for one of the shift rails (3rd pic)
I had modified the shift rails in the 205 to make it able to operate the front and rear outputs independently so I needed to add two t case shifters. The M5od and it's tail housing have two convenient threaded bosses that made a perfect spot to work off of. These can be seen in the 4th pic. I used some DOM and some rebar pieces and other odds and bits I scrounged to make the linkages. Fifth pic shows the final result. Found a double boot on amazon that should finish it off nice.
Why this combo of parts? Only because I wanted the overdrive rather than the c6 and this was the parts I had laying around.
I will report back once the rest of the truck is put together and I get a chance to drive it a bit if anyone is interested
 

Attachments

  • DSC04915.JPG
    DSC04915.JPG
    7.1 MB · Views: 4
  • DSC04917.JPG
    DSC04917.JPG
    6.4 MB · Views: 2
  • DSC04918.JPG
    DSC04918.JPG
    6 MB · Views: 4
  • DSC04922.JPG
    DSC04922.JPG
    6.4 MB · Views: 4
  • DSC04921.JPG
    DSC04921.JPG
    7.2 MB · Views: 4

Shorty

Well-known member
Found out the truck had bad motor mounts while tightening the tranny bolts so I changed them out. 205 case has a plate on the side for a mount to the frame rail so I plan to add that as well to help the tail housing of the tranny live a little longer. Discovered many little differences between the f 150 and f 250 as I re assemble the pile of parts. For example on the f 250 the distance between the pivot point and the push rod for the brake pedal is about half inch more making it necessary to remove the pedal bracketry and mix match to get a hyd clutch (85 f 150) and the brake pedal for the 81 f 250 master cyl together. Today I am working at fitting the front drive shaft. Seems the output on the 205 uses a smaller u joint. The output on the 208 case is same spline and seal surface and uses the bigger u joint that is already in the section of the f 150 rear shaft that I am trying to use. Yoke may need slight machining or shimming to work but it's close.
 

Shorty

Well-known member
Got the front output yoke from the 208 case to fit the 205. Had to put a shim about 3/32 thick in first to get the seal to contact the proper spot on the seal surface, and had to die grind a few spots on the bearing retainer so the dust shield would fit without hitting but it's all in there. Now all the drive shaft u joints are the same and I was able to use the 1st section of the f150 2 pc rear shaft (after I cut the hanger bearing off) as the front shaft in the f250.
Also managed to make a mount for the side of the 205 case. Found a rubber mount in my pile of random spare parts that I think was a body mount for something in it's past life. Found a bit of 3 x 1/4" flat bar left over from a job to make the bracket. Found some rusty (authentic patina?) bolts to attach it to the frame so it blends right in from the out side. The L bracket on the t case was already there
 

Attachments

  • DSC04923.JPG
    DSC04923.JPG
    7.1 MB · Views: 6

BigBlue94

1K+
VIP
Supporter 2021
Supporter 2019
Why not? is always a valid reason! Make sure that NP205 is well supported. The M5R2 is not known for case strength. BW4407 (107lbs empty) broke the back of my C6 case after 140k miles.
 

Shorty

Well-known member
Make sure that NP205 is well supported.
That's why I made sure the engine mounts were good and the side mount that was on the 205 was stoutly connected to the frame rail. Not sure there is anything else I could do? Driving style may help it last too.
 

Shorty

Well-known member
Anyone doing a 4pt mount is just asking for trouble. Four points is over-constrained and you WILL break something when the vehicle flexes and your selection of large cast metal objects doesn't. If your engine is installed in a fairly stiff road going vehicle you may get lucky and simply wear our bushings. If your engine is installed in a pickup with a narrow and flexible frame then you will probably break a transmission tail housing or bell-housing.
this is from the "300 dimensions" thread in the big six performance section. When I read this I couldn't help but wonder what you think of this t case side mount? would that fall into the 4 point mount that may cause problems? would there be a better way to support the heavy t case?
 
this is from the "300 dimensions" thread in the big six performance section. When I read this I couldn't help but wonder what you think of this t case side mount? would that fall into the 4 point mount that may cause problems? would there be a better way to support the heavy t case?

I'm not a fan of those mounts.

They pretty much only work because you only ever see them in 4spd trucks that don't have an aluminum tailhousing to crack and the fact that the drivetrain combo is so short you can't get much frame flex over the short length of frame between trans mount and engine crossmember.

You'll notice that GM never did such a mount and that the transfer case adapter hanging off the back of an SM465 is pretty wispy compared to the one hanging off the back of a Ford NP435. That bushing is very much a "we have enough margin for error to get away with it" situation.

The "right" way to reduce drive-train movement to a tolerable level would have been to move the motor mounts outboard or use different motor mounts. I'm sure FTF can speak to why that might not have been a feasible reality in a production environment depending on at what stage the "problems" were raised.

If I were OP and I was worried about supporting the 205 I would absolutely not run that mount. I would run a strut rod from the bellhousing to the side of the transfer case like you see on 73-87 GM trucks (bottom) or I would copy what Jeep did around 2000 (top) with the aft bolt location obviously changed to suit. I think the Jeep solution is better.

Also, note the rear mount on the GM example. I'm likewise not a huge fan of the stock C6-> NP203 adapter which is of the same design.

These over-constrained mounts are very much in the realm of "you can get away with it, probably, but do you really want to try". If you're trying to hang a 205 off of an M5OD or ZF or you're hanging a doubler off of anything you really shouldn't be pushing the envelope like that.

Screen Shot 2022-04-19 at 7.07.23 AM.pngIMG_1636.JPG
 

Shorty

Well-known member
Thanks for the thought provoking response, make a lot of sense to me. The pictures give me a good idea of what I should be trying to do. I also found some leaf spring bushings on Amazon (warehouse deals for 18 bucks instead of the regular 100 dollar price) and plan to fabricate some engine mounts like the pic you posted in the "300 dimensions" thread.
 

BigBlue94

1K+
VIP
Supporter 2021
Supporter 2019
That's why I made sure the engine mounts were good and the side mount that was on the 205 was stoutly connected to the frame rail. Not sure there is anything else I could do? Driving style may help it last too.
The only thing better than what Arse suggested above is a dedicated crossmember with proper rubber/urethane bushings.

Here is the damage to my 96 C6. Both sides are broke, but the left side chunk is held in by the pump bolt.

20180609_154334.jpg


20180606_181629.jpg
 

Shorty

Well-known member
had the chance to drive it around a little bit. So far any time I'm in the yard or maneuvering around tight parking lots I just flip the transfer case lever that controls the rear out put into low. Makes reversing with a trailer a lot easier too. The M5od shifts nice on the road, good gear spread although I don't think my speedometer is correct, I will have to check it with sometime but for now I just go with traffic flow. I ended up removing the side t case mount and plan to take it easy until I get a chance to try fabricating some braces to the bellhousing bolts as suggested. All in all worth the effort since I already had the parts in stock.
 
Top