1970 Gear Change / Transmission Swap

[ecbert]

Ok, so I'm tired of going 55 mph on the freeway @ 3100 rpm in my medium duty and I wanted to keep it semi-original, so I did a bunch of searching as to the parts I may need.

I figured the best way would be to raise the gear ratio from my current 6.50:1 to some other factory available ratio. So, over the past year or so, I bought a higher geared third member and a Clark 280VO HD transmission to install.

The transmission is NOS and will need nothing, I rounded up the parking brake assembly for it and already found a used shifter assembly off eBay.

I will have to rebuild the third member, pictures of that are going to be coming as I do it.

Currently I just have the two parts shown and I have not torn anything out of my truck yet. The process of rebuilding and doing the swap is just starting, so here goes...

[c60clf]

Keep us posted, this is a great thread to follow, Pat

[Bigdually]

Oh man, I'm drooling over that Clark! What rear gear ratio are you going to swap in?

[Campbel45]

Wow, awesome snag on the Clark. I'm curious what the gear ratio is too. Any plans to update the brakes too?

[Pvmt-Pndr]

I'm along for the ride. I hope to be doing a gear swap before too long also.

This seems like a relevant place to ask, not trying to hijack, someone feel free to pm me instead. How can you tell if you have a locker or not? I have a switch in the cab that says wet/dry.

[sweetk30]

jack up rear axle . trans in neutral . parking brake off if air . spin tire if the other spins 180* of the way you spin its open .

flip the switch and re-test . if both spin the same way = air locker for big trucks being air .

[Pvmt-Pndr]

Thanks sweetk30

[ecbert]

Ok, did the tranny swap.

Couple of issues, the parking brake is totally different and the rear prop shaft has to be shortened by 3.125"

Pulled the shifter, removed PTO shaft, removed front of prop shaft, removed transmission. You DO NOT have to remove bell housing to remove transmission. You CAN get to the two bolts that go into the trans from the front. Remove inspection cover and they are right there!

I have a 5.57:1 T170 axle, tore it down also. Found a Detroit "no spin" for this axle on ebay!

[ecbert]

Removed shifter, removed PTO shaft, removed front prop shaft, shot of clutch linkage / bell housing

[ecbert]

Shifter removed, transmission sliding out, pic of SM 465 next to the Clark. I cant wait to drive this thing!
I was surprised, I thought the rear main was leaking oil but it turned out to be the bearing retainer cover was loose on the SM465 so that was the source of my leak, go figure.
The new shifter location is about 1" further rear than the original one, I'm thinking of having the hole moved south 1" by a good body guy I know...

[ecbert]

Also got the T170 torn down
The case half shows some wear as does the anchor and sliding clutch. They were off to the machine shop to get jet washed.
What do you guys think of the rust on the ring gear?

[ecbert]

I have not been getting any emails! I'll have to check my settings...

[Katrina/10]

Originally Posted by ecbert

I have not been getting any emails! I'll have to check my settings...

Neither have I.

[sweetk30]

take a scotch bright zippy pad on die grinder and buff the teeth on the gear and if they have no real pits showing i say run it . if heavy pitting then its up to you .

[ecbert]

I'm going to media blast the ring gear to check and see how deep the rust is, once I get the pinion out to check the bearings.

[sweetk30]

no no no ... watch what media you use .

thats a polished surface now and you might trash it . do like i said and just zippy pad scotch bright wheel those teeth only . you will be able to tell just fine this way .

[ecbert]

I wasn't thinking sand blasting!
I media blasted the ring gear with glass shot, removed the rust, did not damage the mating surface(s).
I'll post pictures of the ring gear now but I'm having trouble getting the pinion out of the support. Need to put some heat to it to the pinion flange. I had it in my 25 ton Dake press with 20 tons on it and it will not budge.
Transmission is installed, found a shifter for it and had the rod powder coated semi-gloss black. Looks like I may need to move the boot hole back 1" or so or maybe bend the rod (of course after I had it coated I discover this).

[ecbert]

Ok, back on this project again (finally). Everything is pretty much cleaned up, found all the necessary parts and ordered all the bearings / seals. The carrier is back together and I'm working on the pinion support.

In the process of making a fixture to hold the T170 housing so I can easily work on it using my engine stand. 3/8 thick high tensile steel with triangular braces to help keep it from folding up on me! This drop out third member is very heavy! I figured out the bolt pattern for the carrier housing (it's not uniform, aka it's not perfectly round) and I will post pictures of the completed unit holding the carrier during final assembly.

[jumpsoffrock]

I found a two speed RPO J13 : 15000-LB. 2 SPEED AXLE 4.86/6.61 RATIO on ebay back east and put that it my truck. My truck originally had a 20,000 lbs GVW so the lighter duty carrier kinda ate into that, but it should be fine for the rest of it's life.

Honestly I don't mind if you don't wanna talk about it, but how did you find a NOS 280VO? Back 8-10 years ago I couldn't find one of those used!


And you actually rebuilt the carrier, which shows much more knowledge than I have. I just threw it in used(the place I bought it from said I was A-OK).

You are basically doing what I dreamt of. Can we see the rest of the truck?

[ecbert]

Sure, here is a picture of the green rig from the front.

[rkn463]

Originally Posted by ecbert

Sure, here is a picture of the green rig from the front.

She's beautiful!

[Campbel45]

Beautiful indeed!

[ecbert]

Ok, I got the rear end fixture made / welded up and I'm starting to put it back together. Carrier installed, I just need to do the pinion support sub assembly and install that, set the bearing preload and backlash. Then I can install it, looking forward to lower RPMs!

[ecbert]

See below

[ecbert]

Originally Posted by jumpsoffrock

I found a two speed RPO J13 : 15000-LB. 2 SPEED AXLE 4.86/6.61 RATIO on ebay back east and put that it my truck. My truck originally had a 20,000 lbs GVW so the lighter duty carrier kinda ate into that, but it should be fine for the rest of it's life.

Honestly I don't mind if you don't wanna talk about it, but how did you find a NOS 280VO? Back 8-10 years ago I couldn't find one of those used!


And you actually rebuilt the carrier, which shows much more knowledge than I have. I just threw it in used(the place I bought it from said I was A-OK).

You are basically doing what I dreamt of. Can we see the rest of the truck?

I found a rebuilt one at a medium duty truck dealer back east, when I called them and started talking to the parts guy he told me that he also had a new, never installed one that he'd sell me for a few hundred dollars more (but the new one had no core, so it was a wash). I think they still have the other rebuilt unit that I was originally going to buy, if anybody's interested - I can forward contact information.