Adapter between SM465 and NP205

[Mark80K15]

Hi all, 1980 GMC K15 with SM465 trans and NP205 transfer case. Trans and transfer case work fine, but when I get to 40 mph and higher the drivetrain sounds like it's rattling and shaking apart. I've never pushed it more than 60 mph as a result. Transfer case shifter also rattles like hell. it's not as bad when I'm in 4H (much worse when in 2H).

I happen to have the engine out right now (for other reasons) and I also removed the bell housing. Sub question: The bellhousing has 6 bolts holes (3 on drivers side and the other 3 on passenger side) but no bolt hole at the top center. I point this out because the 1980-1986 350 engine does have a bolt hole at the top center. Does this mean I have the wrong bell housing?

Anyway, with the bell housing off and the trans supported on a block of wood, I can stand inside the engine compartment and grab the trans and physically move the trans/transfer case by hand. I can't drop it, of course, but I mean it is not rigid, as I expected. I can play it around about an inch or two in side to side and up and down motion. Is this expected? Front and rear driveshafts still attached.

I suspect I have a problem is (at least partially) related to the mount the trans/transfer case is supported by. Does anyone have a diagram of this mount? I'm not even sure if there are one or 2 mounts. It appears the trans/transfer case are not directly bolted together, rather, there is an adapter (?) between them, and that adapter is what sits on the mount(s). Anyone know the part number(s) of the mount(s), or have a diagram? Any knowledge of videos showing a replacement procedure? Thanks!

 

[bucket]

You have the correct bellhousing, the top bolt hole was not used originally. Being able to move the trans around is normal for used rubber factory mounts. You have two mounts, each one is made up of a main isolator pad and a smaller bushing.

Your 465/205 combo has a 10 spline coupler inside the adapter. It is known to wear the splines out and be noisy.

However, it really sounds like your rear driveshaft is out of balance.

 

[Mark80K15]

Hey bucket, thanks a lot for the advice. I'll get the rear driveshaft checked out. And thanks for the confirmation regarding the bell housing.

Is it correct to say that the trans/transfer case are not directly bolted together, rather, there is an adapter between them, and the 2 mounts bolt to the adapter and the cross member? If so, in order to check out the 10 spline coupler inside the adapter, can I just remove the trans and leave the adapter and transfer case in place (of course, supporting the transfer case from below)? Or does the transfer case need to be dropped to check out the spline?

Anyone have a diagram of the trans/adapter/transfer case/mounts? Or at least a part number and/or picture of the mounts?

 

[bucket]

Imho, it may be a bit awkward getting the trans out and off the t-case like that. But yeah, you can do that.

Here's the mount rubbers:

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Here's a source for the coupler:

SM465 to NP205 drive sleeve, 10 spline x 10 spline

SM465 to NP205 drive sleeve, 10 spline x 10 spline

www.offroaddesign.com

 

[Mark80K15]

Thanks very much, bucket. I appreciate it.

 

[Mark80K15]

Hey, sorry to carry this on, but I still need a little more info. Now that I've pulled the x-member out that the adapter sits on, I only have more questions. Attached are 2 pictures of the x-member out of the truck with the one mount in place. On both pictures, the left is the passenger side.

The first picture is exactly as I found the x-member and mount. There is only one mount, on the passenger side. The front driveshaft attaches to the transfer case on the passenger side also. I don't know if there was ever a mount on the driver's side, but there wasn't one when I took the x-member off.

The second picture shows the same thing, but with the passenger side (upper) mount removed. You can see the broken bolt poking up out of the hole, so for this one mount, the adapter wasn't even bolted on! Just sitting on it. Glad I'm working on this.

So, is there really supposed to be 2 mounts? (I've heard yes and no!). If so, is there any significance that the passenger hole is round but the driver's hole is rounded rectangular? Is it the same mount for both sides? Does anyone have a picture of how the mount(s) bolts to the adapter? Does anyone have a picture of the adapter? Thanks!

 

[Mark80K15]

I thought I would include the only 2 pictures from the manual that refer to the adapter. One of the adapter pictures shows the driver's side of the adapter (the rest is cut off!) and there appears to be a bolt hole on the driver's side, indicating there should be a mount there (seems to be visible in the picture). I was hoping to see a picture of the adapter showing both flanges for bolts going to 2 mounts.

 

[bucket]

Yeah, there should be two mounts. '85 and later trucks had a single, large interlocking mount in the middle. Unfortunately I don't have pictures handy and I'm not at home to take any.

 

[Bextreme04]

I have a 1980 K25 with a NP205. I replaced all my mounts recently while redoing the whole suspension and drivetrain and rebuilding everything. You should have both mounts, one on each side. The big curved piece that you can see on top of the crossmember goes on top like that and the adapter sits on top of the mounts. The smaller piece that @bucket posted(second picture) goes on the bottom inside the curved up portion of the crossmember piece and sandwiches the crossmember between them. The adapter is threaded and the bolt then goes in from the bottom and through both mount pieces and the large hole in the crossmember before threading into the adapter and pulling everything together. The holes are meant to be large ovals like that to allow both mounting pieces to line up easily on multiple different adapters and transmission/t-case combos. The wild shaking and vibration of your shifter was 100% from that mount being missing. I would bet that was what broke off the other bolt as well. You will need to extract the broken bolt piece from the adapter and get two NEW grade 8 bolts. I would also suggest using blue loctite and torque the heck out of both bolts as well when you put it back together.

I would suggest you put the bolts in loosely at first and then get the entire drivetrain including driveshafts installed first. Then make sure the entire drivetrain is installed in the correct alignment before tightening all of the bolts down.

 

[Mark80K15]

Hi everyone, that totally resolves my questions. You provided excellent explanations and advice, thank you!

I'll see if I can provide pictures as I move through this. I haven't decided if I'm dropping the transfer case, if so that may provide more opportunity for better pictures.

 

[Bextreme04]

Hi everyone, that totally resolves my questions. You provided excellent explanations and advice, thank you!

I'll see if I can provide pictures as I move through this. I haven't decided if I'm dropping the transfer case, if so that may provide more opportunity for better pictures.

If you still have everything in the truck(trans/T-case) and just pulled the crossmemebr, I would leave it up there unless you want to rebuild everything. Its a pain in the butt and that thing is very heavy and awkward. If you can't get the bolt extracted from the adapter, you might have to remove something, but it is still easier to strap the dang things up there to the frame rails and remove a few parts that need to be worked on instead of the whole thing.

 

[bucket]

Also check the bolt holes in the t-csse adapter, for the mounts. The one mount may be missing because the threads are stripped in the adapter.

 

[Mark80K15]

Looks like the bolts from both the left and right side mounts are broken and the remnants are stuck in the t-case adapter holes. Any suggestions on getting them out? There is no bolt sticking out the bottom of the adapter, but there is about 1/2" sticking out the top.

Also, there are 8 bolts holding the adapter to the transmission. In my case 2 are missing and a third is broken off. It also appears there is a 1 mm gap between the adapter and the transmission. Would this cause transmission fluid to leak, or is the transmission isolated (from a fluid perspective) from the adapter? Is there supposed to be any fluid inside the adapter at all?

Here's a few pictures to illustrate wheat I'm seeing. The first is a view from inside the cab, passenger side, looking to the driver's side and forward. The hole at the missing top bolt from adapter to transmission is visible, and so is the gap between the two. The second is a view from inside the cab, driver's side, looking forward. The driver's side transmission mount bolt hole is visible at the bottom of the adapter, with the broken bolt visible. The third is looking down on the adapter from the top, showing both transmission mount holes, with broken bolts.

 

[bucket]

Try to grip the bolts from the exposed area and see if they will turn. If so, screw them up and out of the adapter.

If you remove the adapter, you will find that it exposes openings into the case, via the shaft bearings.

 

[Mark80K15]

Bucket was kind enough to include a reference to a source for the coupler above, from Off Road Design. I was going to buy one but Off Road says they are having problems sourcing it. Does anyone know where else the coupler might be available? Here is the reference Bucket provided again:

SM465 to NP205 drive sleeve, 10 spline x 10 spline

SM465 to NP205 drive sleeve, 10 spline x 10 spline

www.offroaddesign.com