Conversion

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bhempel20

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Nov 11, 2022
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Location
53805
First Name
Brian
Truck Year
75
Truck Model
K10
Engine Size
350
Would like to know how much at a shop to convert 75 k10 from th350 to th400 or 700r4
and np208 t-case
 

waterpirate

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delaware
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Eric
Truck Year
1987
Truck Model
v10
Engine Size
5.7 tbi
Hi and welcome. All they can get. What you want is considered " full on custom work ". They will make you pay. If it is not your daily driver, buy some tools, take your time and learn some stuff. YMMV
Eric
 

Big Ray

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Ray
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1979
Truck Model
K5
Engine Size
400
700r4 is 2" longer than a th350. Move the crossmember back, drill some holes and you're good. May have to shorten/replace the driveshaft. There's enough trucks out there you should be able to get one from a salvage yard. Easy peasy.

Th400 should be a straight swap from a th350.
 

nvrenuf

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John
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1991
Truck Model
K5
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454
Neither trans is a direct swap, especially the th400.

Both the th350 and th700 have 27 spline tailshafts and a 4 bolt pattern on the back of the trans case so these are the more similar of the 2.

The th400 has a 32 spline tailshaft and a 6 bolt pattern on the back of the case.

The tailshaft spline count is important because it has to match the tcase.

All three of these transmissions have different length cases so anything other than another th350 will mean driveshaft changes and relocating the crossmember.

A th350 will be the simplest / cheapest way to go.

Ultimately, you need to contact local shops for pricing because regionally costs will be different and some shops simply may not want to do this type of work while others may have done it many times.
 

Big Ray

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Truck Model
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Engine Size
400
I assumed he was getting a tranny t-case combo as the 208 was not available in 75...my bad.
 

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