Transmission x-member 4X confusion

[73 cheySuper]

I may have overthought this.....I'm converting my '73 C20 to a K20 using the drivetrain from a '89 Dually 1 ton 3+3. Using the 454, turbo 400 and the 205. The X-member I'm also using from the dually, but the frame measures 8 inches deep, while the frame I'm using is 6 inches deep. The added 2 inches is at the lower rail, keeping all the body mounts in the same location. Well, that lead me to think the crossmember needed to be lowered at the trans mount 2 inches to sit on top of the rails. After fabbing up the driver's side to correct this, I googled the part number and found that everyone's claiming the x-member is used in both cases, just mounted on top of the rail of the dually, and on bottom of the K10/K20 frame. BUTTTTT, that only changes it 1 inch, not 2, the difference of the frame rails. Soooooo confused. Math is math right?

 

[bucket]

You are just over thinking it. As long as the driveline angles are ok and the engine has the typical 3* or so of layback, it will be fine.

What are you using for an engine crossmember?

 

[ali_c20]

I would finish the fab work and put it on top of the rails. Driveline angles have to be adjusted anyways on a custom build.

 

[Ricko1966]

Which 1989 1 ton dually, there were 2 I believe.

 

[73 cheySuper]

It's the square body dually. I'm using the factory 3/4 ton engine x member. Running a 2.5 lift, so this should help a bit. I'll continue the fab work.

 

[bucket]

I would finish the fab work and put it on top of the rails. Driveline angles have to be adjusted anyways on a custom build.

That crossmember is designed to be used below the frame on a K20 or K20. It will be a much closer starting point for correct angles.

 

[73 cheySuper]

If it's too low, I can easily just shim it up. If I put it in the factory "below the rails" position, it would be an inch higher with no adjustment other than shims between the rails and member, which I think is hokey.

 

[bucket]

If it's too low, I can easily just shim it up. If I put it in the factory "below the rails" position, it would be an inch higher with no adjustment other than shims between the rails and member, which I think is hokey.

I'm confused by all that. If it's below the rails, how would it be an inch higher?


That specific crossmember is designed to be bolted below the frame rails (as in, hanging below the frame) on a 10 or 20 truck. If it's mounted above the rails (within the c-channel frame rail) then it will put the trans and t-case mount up too high on a 10 or 20 truck. When it is used on a k30 (such as your donor) it is designed to be mounted above and within the rails, due to the taller frame that hangs lower than a 10 or 20 truck. But you aren't putting it in a 30 series truck.

 

[ali_c20]

I'm confused by all that. If it's below the rails, how would it be an inch higher?


That specific crossmember is designed to be bolted below the frame rails (as in, hanging below the frame) on a 10 or 20 truck. If it's mounted above the rails (within the c-channel frame rail) then it will put the trans and t-case mount up too high on a 10 or 20 truck. When it is used on a k30 (such as your donor) it is designed to be mounted above and within the rails, due to the taller frame that hangs lower than a 10 or 20 truck. But you aren't putting it in a 30 series truck.

As I understand it 73cheySuper modified the crossmember to be 2 inches lower to make up for the frame rail height difference.

 

[bucket]

As I understand it 73cheySuper modified the crossmember to be 2 inches lower to make up for the frame rail height difference.

Ah, yep. I re-read it and looked at the picture again. Right now, the crossmember is only modified on one side.

If it were me, I'd just get another crossmember, bolt it below the rails and call it good. There will be more exhaust clearance with it below the rails. Actually thinking about it... below the rails might be required for front shaft clearance.

 

[73 cheySuper]

Front shaft is fine, at least it was in the dually, and wouldn't change in the new frame. By doing this mod, it assures me everything from the transfer forward will be the exact same. The dip in the x member on the passenger side clears the mount ring of the front drive shaft, and the angle will be a bit steeper from their forward being it's a 2.5 inch lift. Finished the fab yesterday, so just need to paint some of these pieces and begin bolting back together. I'll leave the x-member hanging loose on the rails until everything's happy in it's new position, then drill the rails and bolt it in place.

 

[Strick]

I just used an SM465/NP205 from an '80 K30 and put it in my '78 K20. The frame difference is a couple inches and when trying to use the K30 crossmember it was hanging too low; a couple inches from the frame. I had to dig through my stash of parts to find a K10/20 crossmember that would work. I took my parts pen and marked the K30 unit so that I would know later on down the road.

HS

 

[Old Guy Bill]

Need pics....

 

[73 cheySuper]

Dug out a 454 block and got the trans back from the fabricator, mocked the drivetrain up and it's about 2 inches too low at the trans/transfer mount. Not understanding this, since the frame is 2 inches narrower and that's what I added to the crossmember. I'm just going to stuff 2 inch square tubing on the lower rail and call it good. That'll put the engine 3 to 4 degrees downward. It also levels out the trans pan. This puts the front half of the rear driveline sloped down about 1.5 degree till it hits the carrier barring. That sounds good, but I'd appreciate feedback on that. 2.5 inch lift kit from skyjacker came with tapered rear blocks, and that put the pinion angled up at 9 degrees, seems a bit much but I'd appreciate feedback on that also.

........the trans bell had to be welded, since I had to pry it away from the corroded dowels on the dually, so hard that it cracked the crap out of it. All's good now.

 

[bucket]

OK, so that looks like a factory K frame... not a C.

What exact combo of parts are you using then? Is that your modified crossmember? Is it installed above the frame channel, or below? What engine crossmember is being used?