4l85e upgrade issues

[Keister101]

1980 K5 Blazer 4x4. I have upgraded the engine to a 383 stroker with 460 to 480 horsepower and torque. The current upgrade is adding the 4L85e transmission and finding fitment issues with the crossmember not being long enough across due to extra transmission length.
Any ideas appreciated as I’m contemplating total new fabrication of the crossmember.

 

[Keister101]

Sorry, has NP205 already upgraded to match the new transmission

 

[CalSgt]

Perhaps a photo of what you're dealing with will help, also what crossmember do you have now (what transmission was in it before)?

 

[CalSgt]

I know the K5 is shorter WB than the SWB pickup but I would think there would be enough room to slide the crossmember back and re-drill the mounting holes. How much more do you need to move it back?

Here's my 1980 K-10 with 4L60e & 208 mounted to a SM465 crossmember that I've moved a few different times for different transmissions over the years. I had to fab a motor mount adapter to accommodate the short mounting foot on TC adapter, my 205 had the tall foot:

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[Keister101]

Sorry will add pics soon. The truck had a TH350 with the NP205. I added 4L85e with the advanced adapters kit for the NP 205 to mate. The only crossmember bolts to the base of the 205 faceplate and to each side of the frame rail. The 4L85e is approximately 4 1/2 to 5 inches longer than the TH350. As the crossmember moves back the frame flares outward and is not reaching

 

[CalSgt]

Sorry will add pics soon. The truck had a TH350 with the NP205. I added 4L85e with the advanced adapters kit for the NP 205 to mate. The only crossmember bolts to the base of the 205 faceplate and to each side of the frame rail. The 4L85e is approximately 4 1/2 to 5 inches longer than the TH350. As the crossmember moves back the frame flares outward and is not reaching

Oh okay, not being a K5 guy I'm assuming they are like that because the gas tank sits inside the frame rail instead of the outside like the trucks.... My frame is near parallel the whole way back after the exhaust manifolds.

Looking forward to pictures...

ETA: Did they ever offer a K5 with a TH400? Supposedly they're like 5" longer to the mounting location than the 350.

 

[Keister101]

I think you’re onto something with the fuel tank being insi the frame rails as opposed to the outside

 

[Keister101]

The crossmember also appears to be 2 inches below the frame rails for the driveshaft angle to be close to the rear axle yoke

 

[CalSgt]

The crossmember also appears to be 2 inches below the frame rails for the driveshaft angle to be close to the rear axle yoke

Are you shooting for pinion and tailshaft to be parallel or are you running a double cardan?

FYI I looked a bit and read articles about guys having same issue putting TH400's in K5's even though it was an option up until '80. Maybe there was a wider crossmember for the 400ci & TH400 option.

 

[Keister101]

So, the 4L85e is 5 inches longer than the TH350/TH400. For anyone wanting to do this upgrade to their K5, you will have to move the motor mounts forward. On the passenger side of the frame there is another set of bolt holes that are 3 3/4 inches forward of the factory motor mount bolt holes but you will have to mark and drill the holes on the drivers side. If there’s another way…I don’t see it! If you leave everything in the stock position you lose 5 inches between the transfer case and the rear axle and that totally screws up the drive shaft angle and would probably require a double knuckle or 2 piece drive shaft and the crossmember will be too short because the K5 frame flares out. Enjoy

 

[Keister101]

This is after moving the engine crossmember and motor mounts forward 3 3/4 inches. I will still have to deal with the 1 1/4 inch at the transfer case.