I would really like a turbo 400 in my truck

jakewalter · Friday at 8:31 PM

I have a 85 K20 that I built up to haul our 3500 pound pickup camper.

It currently has a pretty healthy big block that I built for torque.

The transmission is a 700R4 and a 208 transfer case.

While on vacation a couple of weeks ago the transmission started slipping and I lost reverse.

I never use the overdrive and as for mileage I threw my pencil away a long time ago.

Other than a TH400 out of a 4wd what else would I need?

I would really appreciate any input that you guys could share with me.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

nvrenuf · Friday at 11:57 PM

You need a 4wd th400 from a 400/203 combo. The th400 tailshaft that fits a 203 is super short and only fits that application, nothing else 2wd or 4wd.

You will also need the trans to tcase adapter and kick down switch for the gas pedal.

jakewalter · Saturday at 2:15 PM

nvrenuf said:
You need a 4wd th400 from a 400/203 combo. The th400 tailshaft that fits a 203 is super short and only fits that application, nothing else 2wd or 4wd.

You will also need the trans to tcase adapter and kick down switch for the gas pedal.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

nvrenuf · Saturday at 5:05 PM

You’ll still need the correct tailshaft, I think it sticks out of the case 3.5” but I’m not sure. Also you’ll need the adapter.

Another hurdle will be the tcase input shaft, the th400 is 32 spline and the th350/th700 use 27 spline. I believe the 2 input shafts for the 208 are a direct swap.

Old Guy Bill · Saturday at 5:25 PM

I just changed the 203 to a 208 behind my TH400.
A 6-7” tail shaft is needed, I could only find a good used one from Novak.

nvrenuf · Saturday at 5:37 PM

Old Guy Bill said:
I just changed the 203 to a 208 behind my TH400.
A 6x7” tail shaft is needed, I could only find a good used one from Novak.

Just to be clear, you are talking about total length, correct?
My estimate was just what sticks out of the case.

Rusty Nail · Saturday at 5:51 PM

nvrenuf said:
Just to be clear, just what sticks out of the case?

No. They speak of the whole thing.

nvrenuf · Saturday at 7:18 PM

Rusty Nail said:
No. They speak of the whole thing.

That’s what I asked. See my post, not what you quoted.

Old Guy Bill · Saturday at 7:51 PM

Middle one, bottom row.
The new ones sold by Jeggs & Summit are for drag racing and have no provision for turning the Governor.

nvrenuf · Saturday at 9:08 PM

Old Guy Bill said:
Middle one, bottom row.
The new ones sold by Jeggs & Summit are for drag racing and have no provision for turning the Governor.

Are you sure the 4.5” stick out fits a 208? I thought the stick out was less than a figure 8 205 tailshaft.

jakewalter · Sunday at 8:26 AM

nvrenuf said:
You need a 4wd th400 from a 400/203 combo. The th400 tailshaft that fits a 203 is super short and only fits that application, nothing else 2wd or 4wd.

You will also need the trans to tcase adapter and kick down switch for the gas pedal.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

nvrenuf · Sunday at 11:45 AM

jakewalter said:
I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

No problem but a lot of the previously post items still apply - correct trans tailshaft length, adapter and tcase input shaft spline count.

JD Miller · Sunday at 3:07 PM

Why not a 4L80?

Nasty-LSX · Sunday at 3:48 PM

jakewalter said:
I have a 85 K20 that I built up to haul our 3500 pound pickup camper.

It currently has a pretty healthy big block that I built for torque.

The transmission is a 700R4 and a 208 transfer case.

While on vacation a couple of weeks ago the transmission started slipping and I lost reverse.

I never use the overdrive and as for mileage I threw my pencil away a long time ago.

Other than a TH400 out of a 4wd what else would I need?

I would really appreciate any input that you guys could share with me.

I need to apologize.

The guy that rebuilt my transfer case said that it is a 208 not a 203.

I'm swapping to a 4l80e I NEED overdrive. I have a perfect TH400 that needs no rebuild. No slipping skipping or weird stuff if your interested. the 2500 K20 th400 are 32 spline. I also have the 208 T/C. You can swap your T/C gear from 27 to 32. Its very easy. NOW, contrary to what everyone believes, You can get your 700R4 built to do what you want. I had a 82 k10 with a 454 and a 700r4 and beat the hell out of it with no problems. You just need a builder that knows his stuff. Talking 700R4's is like talking politics or religion, everyone(almost will tell you 700's suck). Not true. as long as its not a 86 or older. They suck!!!87 and newer are upgraded internals. Here is my 85 K20 4x4 with a TH400 and 208.

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Jimmyperf400 · Monday at 11:02 PM

I built my 700r4 with every after market performance part they make and I've towed a 10 thousand pound excavator with the 1990 gmc jimmy its in and I've never had any issues. But up to you you know what you want.

I would really like a turbo 400 in my truck

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