Trying to figure out cross member and trans mount for 1985 GMC Jimmy with NP208 and 700R4

[rpcraft]

Guys, I purchased what I thought was the right Energy suspension PE trans mount for my truck but something isn't right here. The mount I bought was ES part # 3-1129R. I'm not sure if the cross member is wrong, as is the mount, but I have taken some measurements (and photos) and I am getting a little frustrated buying parts only to find they are wrong. I thought I did my research but I think this was a case where the configurator on ebay was not correct so consider that a lesson learned, . At any rate I am hoping you guys can help me here. The truck came with a 305 V8, 700R4 and NP208, as was customary in 1985 (and of course is a 4x4). I am thinking that whoever had this before me grabbed a 2wd cross member not knowing there was a difference so that explains the problem I have there because not only does the mount look pretty flimsy, it doesn't have any holes for the skid plate, which is missing as well, but then the ES mount is way too wide for the TCase adapter.

I'll concede the mount is probably not right, and I can check rockauto or one of the parts stores to straighten that out with a regular rubber one but I am hoping you guys can check my sanity on this cross member and I guess the major question being, will it work? and if not then what should I be looking for. I looked at some of the photos here and on google but its a crap shoot considering what may or may not be stock.

I know its cold outside but I was hoping somoene can help with maybe taking some pictures of their rig as long as its stock and they know nothing is weird about it. I'm wanting to see what the OEM cross member will look like if not this, then also what the mount looks like so I know the wrong one from the right one when I see it. Thanks guys.

This is the new and old PE mount side by side - holes are 4 inches apart compared to about 4 1/2 inches apart


This is showing the width of the old transmission mounting holes, which is right at 4 inches



This is showing the width of the foot of the TCase adapter is @ 6 inches


This is showing the width of the mounting holes of the new PE mount - Roughly 7 1/2 inches and its designed to go against the transfer case adapter


Photo of part of the cross member that goes towards the floor of the truck


Photo of the bottom side of the cross member (only has 1 bolt that attaches the mount)

 

[rpcraft]

Looking like maybe the cross member on the bottom is what I should possibly be looking for?

 

[Hogback Fabrication]

Looking like maybe the cross member on the bottom is what I should possibly be looking for?

View attachment 221279

Top picture is '67-84, bottom picture is '85-87 (up to '91 in the K5's and Suburbans). NP208's spanned both generations. There are minor details within each generation (like most of the earlier crossmembers don't tie into the top frame rail like that one, among others) and 1 tons had flatter crossmember than the rest (because their frames are taller, the crossmembers don't drop down as much).

Adapters are different based on crossmember height (or vice versa), '84 and older adapters hand down a lot more because their t-case mount is lower on the crossmember. It looks like your adapter is the '84 and older style from your picture. I don't recognize the crossmember in your picture, it could be 2WD (IIRC they only have one bolt for the mount but 2WD trucks barely exist in CO).

 

[rpcraft]

So just to make sure I have this correct not only do I need a crossmember, but if I do manage to come across the W version of the cross member then I am also going to need the short version of the Tcase adapter as well, but if I come across the 84 and earlier version crossmember then I can use Tcase adapter I have (aka the tall version) along with the double crossmember bushings from the older style?

 

[rpcraft]

Seems like as with most things Chevy/GMC both setups were introduced in or around 1985/1986 and maybe depending on when your vehicle was produced you may have ended up with find the older Flat style with the "long foot" or the newer W style with the "short foot" (or mine in this case, lol). Probably applies to 1986 models too, kind of like when they switched from the 12 bolt axles and continued using them until they ran out and completely swapped to the 10 bolts....

Took a while of digging but I found some photos of the different adapters on Advanced Adapters and they kind of explained the year changes...

It's got me thinking I may need to go ahead and count the spline's on my transfer case now though.

will check it in the morning when its somewhat warmer.

Thanks for the advice.

 

[Fastereddie]

That mount and xmember you got looks like 2wd stuff.

 

[dyeager535]

Agree with what was said earlier, 1984-down x-member/adapter, 1985+ trans mount.

I'm of the opinion everything is better about the 1985+ setups, if you can get the adapter and x-member cheaply, I'd go that route. If you've got the wrong spline count t-case, could always hunt for the cable speedo 241.

 

[nvrenuf]

To be clear with pics....

The adapter pictured above uses a crossmember from a pre '85 1/2 or 3/4 ton like this - (note the amount of drop compared to the one you have)



and mounts like this -



**** Don't forget to update your wanted post for a pre '85 crossmember, not a "W" crossmember.

 

[rpcraft]

Agree with what was said earlier, 1984-down x-member/adapter, 1985+ trans mount.

I'm of the opinion everything is better about the 1985+ setups, if you can get the adapter and x-member cheaply, I'd go that route. If you've got the wrong spline count t-case, could always hunt for the cable speedo 241.

Considering the PO left me with a cracked transmission housing smothered and hidden in JB weld and finding that that the adapter (and possibly the xfer is out of another vehicle) at this point I am left questioning everything. I was considering rebuilding this unit anyways so we'll see. I've got a couple leads on the W crossmember between here, facebook, and the other k5 forum site so if the transfer is a 27 spline then maybe it will be better to just go ahead and get the short foot adapter. Seems like it will help prevent driveline issues in the long run and it looks like there is an affordable one on e bay right now. It seems like that W crossmember offers a little more space for running exhaust pipes and stuff as well. Not sure when the Blazers got a catalytic converter but maybe that has a bit to do with why they changed it. Mine actually had the original pancake converter on it and I had forgotten how huge those were. Shame it probably doesn't have anything left in it. Either way maybe I can get some money out of it from a recycler because it isn't going back on, lol.

Thanks for the feedback and advice.

 

[rpcraft]

To be clear with pics....

The adapter pictured above uses a crossmember from a pre '85 1/2 or 3/4 ton like this - (note the amount of drop compared to the one you have)



and mounts like this -



**** Don't forget to update your wanted post for a pre '85 crossmember, not a "W" crossmember.

Going to go ahead and try to get the W xmember for now and if it turns out no-one has one close to pick up or ship affordably I'll probably resort to the flatter style.

Lemme go count those splines on the transfer case and make sure I don't have another hairball going on there...

 

[rpcraft]

To be clear with pics....

The adapter pictured above uses a crossmember from a pre '85 1/2 or 3/4 ton like this - (note the amount of drop compared to the one you have)



and mounts like this -



**** Don't forget to update your wanted post for a pre '85 crossmember, not a "W" crossmember.

Thanks for the pictures. It helped answer all my questions. Just another obstacle to overcome when you inherit a project from someone who didn't do things the right way.

 

[rpcraft]

Yay, TCase has 27 splines. Too bad the 2wd crossmember isn't flat. It looks like the W style xmember actually is flat across from the frame rails to where the transmission mount connects to the adapter. I know my Lincoln Handy Mig can't handle doing anything this thick but I am thinking it might be time to go ahead and get some metal and just fab my own up. Tack all the important parts in place and then take it in for finish welding....

 

[rpcraft]

Well, found a contact out south of Dallas that does a lot of parts and sourcing for square bodies and he has the flat style and since I already have the long mount it's probably the easiest solution. May have to drill new holes in the frame rail but that's simple enough with the use of a pair of vise grips. He's got the cross member, the bolts, and the OE rubber mounts for 75 bucks, plus he also has a huge yard full of square body parts, so I'm going to write down a few things on my wish list and see what he's got later today.

Gonna go shut down the Wanted post. Thanks everyone.

 

[thatK30guy]

The very first pics of the OP's crossmember is definitely a 2wd as confirmed by others. Just passing another confirmation on this.