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rack 11-19-2012 06:29 AM

1990 Chevy V2500, T-400 to 700R4 swap
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Hello to everyone,
I need some information, ideas and help on my project, 1990 Chevy V2500 Suburban, 4x4, SBC350 TBI, TH400.
First, some preliminary information about it.
I imported the car from USA last summer. It is in really good shape for its age, rust free. I really like it.
I am not in USA, so buying parts is a bit harder and should be done very carefully and from the first attempt, there is no junk yard I can go and get it. I have to import everything from USA. Most European guys here know what I am talking about.

Anyway, I want to make some modifications on it.
I will convert it to dual fuel gasoline/propane and mainly use it on propane. It is because gasoline prices here ($1,67 per liter gasoline, $0,94 per liter propane). This step is more or less clear, I already have Impco setup for it.
For that same reason, I want to change TH400 with 700R4/4L60/4L60E with overdrive, whichever is appropriate for the car. I want to keep 4X4 as well.
Here come all questions and troubles.
Is there 700R4/4L60/4L60E that will directly bolt on?
If not, what should I check for, before I start looking and buying one? What other parts I will need for the swap?
I will be glad to provide you with any information you need.
Thanks for the help,

302 Z28 11-19-2012 07:33 AM

Chevrolets small (first generation) block bell housing is the same for TH400, 700R4, 4L60 and 4l60E, unless the last two came from an LS based engine.


SSedan64 11-21-2012 02:39 AM

You will need a 700R4 for a 4X4 with the correct Output Shaft for your Transfer Case.
700R4's are not a great choice for a heavy vehicle unless it's upgraded with better parts, extra clutches, 2-4 Servo, Beast Sun Shell, Shift Kit etc..
You'll also need the TV Cable & Linkage.
Column shifter will need to be modified or changed if you want to be able to shift into 1st gear manually.

rack 11-22-2012 10:24 AM

1 Attachment(s)
Hi guys,
Thanks for replies.
I checked my transfer case. It is NP241C behind TH400, so it should be 32-spline input. In that case I will need to change it as well.
Are the output shafts the same of 27 and 32 input versions?

Hi SSedan64, helpful as always :thumbup:
I will buy used transmission, so in any case I will rebuild it before installing it.
Do you think kits like these are enough to harden it?



I am not towing or doing any hard staff, it is my hobby car.

What about lockup convertor? How it is controlled? I do not know if I have lockup now...

I will get TV Cable. Please look on the picture (sorry I nave not better one now), is this what I need to connect the TV Cable?

Thank you for your help,

Kawabuggy 11-23-2012 09:45 PM

Ssedan is trying to steer you in the right direction. You are going to spend a lot of money getting that 700R4 into the vehicle. Factor in new transfer case, potentially cutting both driveshafts to get correct length, TV cable, tv cable bracket, Geometry corrector or new linkage to attach TV cable to induction system, moving the crossmember, reworking the mount location, bending or new cooler lines. Then, when it is all said and done, you will have a transmission that will be HALF as strong as the trans you have in the vehicle now. Even when built right, with the best parts, a 700 can only DREAM of being half as strong as a TH-400.

You say you are not going to be towing.. Let's ask another question. How large are the tires on this truck? If they are larger than stock, have the gears in BOTH axles been changed to match the over-size tires? If it has O/S tires, and the gears have not been changed to match the tires you WILL NOT get a 700 to last in that vehicle. Even if you never tow with it. Period.

My advise-stay with what you have! Otherwise, plan on laying out a BUNCH of cash to get a 700 in the vehicle, and then plan on rebuilding that 700 every couple years. The recipe for a long lasting 700 are simple-light weight vehicles, low horse power, no towing, no over-size tires. If you stick to that you can expect 150K miles out of a properly built 700. If you break any single one of those mandates you can expect to soon be a 700 guru after you have pulled it, disassembled it, rebuilt, & reinstalled it multiple multiple multiple multiple multiple multiple times. Are you getting the picture yet? Keep the 400.

rack 11-28-2012 01:21 PM

Thanks Kawabuggy,
You are right, I will think twice before taking this step.
May be I will consider 4L80 later, knowing it is even harder conversion.

First I will finish installing LPG in it. Then I will check MPG and so on...

Best regards,

496CHEVY3100 12-06-2012 08:56 PM

What about Gear Vendor overdrive works great on my rollback ,but it is 2 wheel drive ,i dont know if it is avalible for 4 wd

rack 12-08-2012 05:00 AM

After some more reading, I decided to go 4L80E way. It will not be easy but I am not in a hurry. It is future project that may not even happen :)
I read I can take ECU from diesel truck to control transmission.
Also, the output shafts should be the same and I will be able to couple mt NP241 transfer case.


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