700R4 Swap, Front driveshaft, K20 pickup

[Jack15T]

Hi Folks, I have a 71Chevy K20 with a 700R4 mated to a NP205. It looks like I am going to have interference problems with the front driveshaft hitting the 700R4 Oil Pan. Has anybody else had this issue and if so a fix for the problem? The transmission and transfer case are in their stock mounting positions. I slid the 454 forward two inches to clear the firewall. The 454 was mated to the TH350 when I bought the truck and the engine was hitting the firewall. I thought problem solved with the longer 700R4. Not so fast.

[CUSTOM/10]

Yes, I had the same issue.
I'll elaborate more later, at work right now.

Gary

[Bigdav160]

I have a 2" lift. No clearance issues. I tried to install an aluminum pan in the 700R4 and there was interference.

If your springs are original they've probably sagged enough to cause the clearance issue.

There might be enough space between the pan and valve body to clearance with a hammer.

[Jack15T]

Thanks for the info. Nice looking Vette. I had a 66 convertible, same color, unfortunately I had to let it go about 25 years ago. I might have to get another down the road abit.

[DeadheadNM]

Mine clears but is very, very close on fresh zero-lift springs. I have a K-case example - not sure that makes a difference with regard to pan configuration though.

[CUSTOM/10]

Hey Jack !

My situation maybe a bit different than yours. Because I'm using a later model front output flange, the square 4 bolt type. This type definitely hits the corner of the pan if you use a stock flange. I had Tom Wood build me a custom front shaft using a smaller u-joint and I had the output flange turned down some, and I dimpled the corner of the pan. Now it clears by about 1/4 to 3/8 of an inch.

Gary

[Jack15T]

Thanks DeadHead and Gary, I appreciate the info. Jack

[DeadheadNM]

You bet. Keep us posted.

[Jack15T]

Gary, Here is a pic of my front flange. Does yours look like this?

[CUSTOM/10]

No, that's the original style, mine is a later style ( borrowed pic )

Gary

[CUSTOM/10]

This is a picture of mine and what I have for clearance.

[randy500]

Are you guys using the 700r4 spacer which is about 2” long or so between the trans and th350 np205 adapter shown in post 9. I think the adapter allows use of a 2wd 700r4 and moves the driveshaft back which gives clearance.

[randy500]

http://offroaddesign.com/catalog/700r4spacer.htm

This adapter/spacer

[randy500]

Apparently the adapter just mates a 4wd 700r4 and even then you have to trim the output shaft.
https://www.pirate4x4.com/forum/chev...5-adapter.html

[CUSTOM/10]

Hey randy,

No I use the AA shorter out-put shaft in the trany and the stock 205 auto adapter. This keeps the setup as short as possibe, and just move the engine forward about 1-3/4".

Gary

Originally Posted by randy500

Are you guys using the 700r4 spacer which is about 2” long or so between the trans and th350 np205 adapter shown in post 9. I think the adapter allows use of a 2wd 700r4 and moves the driveshaft back which gives clearance.

[randy500]

Originally Posted by CUSTOM/10

Hey randy,

No I use the AA shorter out-put shaft in the trany and the stock 205 auto adapter. This keeps the setup as short as possibe, and just move the engine forward about 1-3/4".

Gary

Thats what i thought, And moving the engine forward keeps the driveshafts the same length, right? Or i mean doesnt require doing anything with the driveshafts except checking for clearance at the trans.

[Jack15T]

Hi Randy and Gary, Thanks for the info and the pictures. Changing the flange might be the easiest route for me as the tranny and transfer case are already installed in the factory positions. My driveshafts needed work so Tom Woods built me a new front one and cleaned up the back one for me. Gary do you have a part number for that new style flange or the years they were used and or a source for them? I'll look around and see if I can find one. The picture is a huge help, thanks. Jack

[randy500]

Your front shaft will not fit the flange style front output.
The shafts have to match output style.

Read post 6, you need a new custom driveshaft with smaller u joints in the cv, and the flanged front output.

The flanged front output may not (think probably not the same) be the same spline count as your front output shaft too.

[randy500]

The info on chevy stock spline counts is out there on the web, i have it printed someplace. I will look.

[Jack15T]

Originally Posted by randy500

Your front shaft will not fit the flange style front output.
The shafts have to match output style.

Read post 6, you need a new custom driveshaft with smaller u joints in the cv, and the flanged front output.

The flanged front output may not (think probably not the same) be the same spline count as your front output shaft too.

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[Jack15T]

If I can find one of those flanges with the correct spline count then modifying the drive shaft would be the easiest way to go. I would rather not lift the truck or relocate the trans and transfer case. Thanks, Jack
Posted via Mobile Device

[Jack15T]

Gary, did your flange have a spline count that matched your output shaft or did you use a different output shaft? I just finished rebuilding the transfer case and would prefer not to open it up again. Jack
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[randy500]

Ok quick research but read 5 threads at least, 1310 u joint cv and transfer case yoke get it to barely clear. Not a cheap solution at all. New custom made driveshaft at about $400
Assuming your stock is 1330 joint....which i think it is.

You should have a 10 spline front output so this yoke will work at $90
SPICER 2-4-4021X

[randy500]

Im absolutely never swapping in a 700r4 now that i know all this.

[CUSTOM/10]

To go to the flange yoke you need to change the front output shaft also, at least with stock GM parts. You might be able to find an aftermarket yoke.
I had every thing to change mine over, but still had a clearance issue, that's when I had Tom Woods build a shaft for me.

Changing the front output shaft with the transfer case in the truck is a PITA, it can be done but it's much easier out of the truck.

It,s been a few yrs since I did mine, so if I was to do it again I would check places like Torque King 4x4 / Off Road Design / Northwest Fab / Advanced Adapters and such to see what's available now. Maybe call them and describe your issue and see if they have a solution..

Gary