Transmission Swap Mishaps

[DBinWW]

I bought an '89 4WD Suburban for its 700R4 transmission and swapped it into my '79 Sierra Classic, pictured here. There have been a number of challenges but that side of the transaction seems to have gone okay and the PU is like a new rig.

On the other hand, the 350 going into the Suburban is a different story. The transfer case is very noisy, I think the front driveline spinning might be causing problems with the automatic hubs.

The Suburban got stuck in 4-Low so I had it towed back to the shop. When I went to pick it up a tooth in the rear diff seems to have broken and now needs replacement. Might the shop have mis-installed the tranny or driveline to cause that gear to break? And do I need to change the hubs? Should I put auto hubs on my '79?

 

[Strick]

What transfer case is used in the '79 now?

Strickland

 

[DBinWW]

I cannot find a tag. I'll get the VIN and look it up. ...will be back

 

[Bextreme04]

I'm assuming you swapped trans/t-case between the two vehicles together... right?

A 79 could have only been a 203 or 205 from the factory. An 89 Suburban would be an NP208. They are completely different mounting patterns, so you would have had to buy special adapters if you kept the T-case with the truck.

 

[DBinWW]

That sounds right. Yes, we did need to adapt the NP208 to fit with the cross member. The 205 went into the '89.

 

[DBinWW]

What transfer case is used in the '79 now?

Strickland

NP208

 

[Grit dog]

You don’t have to put locking hubs on the 79. It’s just like driving around with hubs locked in. The 208 won’t care.

And imo there’s no reasonable connection between chipping a ring gear tooth and anything forward of it in the driveline.

 

[DBinWW]

The '79 has manual hubs and you're right, the 208 doesn't care. But the '89 now with the 205 has auto-hubs, and that's the rig that lost a tooth.

 

[Grit dog]

The '79 has manual hubs and you're right, the 208 doesn't care. But the '89 now with the 205 has auto-hubs, and that's the rig that lost a tooth.

My bad. I don’t see the problem with the 89/205 combo either. Part time 4wd case and locking hubs (but auto).

 

[DBinWW]

I believe the 205 is always spinning, while the 208 is not. No?

 

[Buck69]

A synchronizer is required in the 205's when used with auto locking hubs. They were not added until the early 80's. Is it possible yours does not have it?

NP205

www.offroaddesign.com

I am not sure you can necessarily put the sole blame on the shop for swapping components you asked them to, if that caused your problem. These are also 30-40 year old components.

 

[DBinWW]

It is entirely likely that the '89 with the 350/205 does not have a synchronizer.

For me, this is not a blame game. But I don't ant to repair the diff and repeat the breakdown.

Thanks!

 

[Grit dog]

I believe the 205 is always spinning, while the 208 is not. No?

Negative. 205 is a traditional part time case.
Idk about synchronizing the case or hub locking. But I do know that you can’t shift either case on the fly into unlocked front hubs.
I dunno much about the auto lockers except I removed a set once and walked them to the garbage can and installed a set of manual hubs…lol.

And again, imo there is no reasonable connection to the broke tooth on the rear diff and the front half of your 4wd system.
But need some pics of that ‘79 dumper! What part of WW you in?

 

[DBinWW]

So there's no way that the unsynchronized 205 with auto-hubs kajanked the differential? (I wonder what did it)

 

[DBinWW]

But need some pics of that ‘79 dumper! What part of WW you in?

I'm just a mile east of downtown Walla Walla, near Wildwood Park.