1984 gmc 3500 new process540 swap

[Rogerhsr]

I have a 1984 gmc 3500 wrecker I swapped the 6.2 and installed a 6.5 turbo the sm465 is shot I bought a np540 5 speed out of a school bus the issue is the np540 doesn’t any mounting area on the tail end of the gear box to mount a transmission mount so I have the original cast iron bellhousing for the 540 but I don’t know how to mount the bellhousing to the frame and another issue is the ball stud for the clutch rod it has no mount for it on the cast iron bellhousing any help is appreciated thanks

 

[MrMarty51]

I know knott one thing about what swaps You have going.
Was the BH set up for a hydraulic clutch slave cylinder ? If so then most likely be easier to go with a hatdrauc master clutch cylinder and plumb it all together.

 

[Rogerhsr]

It was mechanical not hydraulic I do know the older trucks the clutch lever pivot ball was on the engine block not the bellhousing

 

[MrMarty51]

Might need to build some bracketry, weld in a piece of pipe for a pocket and devise a system to mount a manual clutch cross link to, or, bracketry to convert to a hydraulic system on the manual linkage clutch BH.

 

[Rogerhsr]

Thanks I’ll try that

 

[Will L.]

The 540 rear output seal goes into the bracket that mounts the rear of the transmission.
They made multiple mounts for different applications.
Post a pic of the back of your transmission.

 

[Rogerhsr]

This transmission doesn’t have a transmission mount on the output seal housing the transmission mount was originally mounted on the bellhousing

 

[Will L.]

The bolt holes are used to mount the brackets. Here is two pics of the most common type.

You HAVE to have a rear mount, not just the bell housing.
Sometimes the parking brake assembly that was a drum brake on the rear of the transmission which stops the driveshaft from turning- that assembly can have the mount on it in some.

 

[Rogerhsr]

Mine doesn’t have that it has a place for a driveshaft brake

 

[Will L.]

 

[Will L.]

The different years had different options. Different bolt hole locations.
That is why I am telling you post pictures of YOURS.

 

[Will L.]

Some used multiple side locations and had brackets that held the mounts.

 

[Rogerhsr]

This is it

 

[Rogerhsr]

I do know none of the sm465 parts will interchange

 

[Will L.]

That is the rear mount. You need to het a rubber mount under the circled bracket, then go from it to the frame of the truck. Remember, never cut, weld or drill into the flanges of the frame. The flange is the top and bottom part all the way including the bend radius. Using existing holes in the web of the frame is better than drilling your own holes when possible. Never use a torch to cut holes on a frame. The web is the large flat face of the frame. I strongly suggest a crossmember that goes from one side if the frame to the other if at all possible.

 

[Rogerhsr]

i had no clue that was a rear mount because it’s so small I just didn’t think it would hold the weight I appreciate your help

 

[Rogerhsr]

That is the rear mount. You need to het a rubber mount under the circled bracket, then go from it to the frame of the truck. Remember, never cut, weld or drill into the flanges of the frame. The flange is the top and bottom part all the way including the bend radius. Using existing holes in the web of the frame is better than drilling your own holes when possible. Never use a torch to cut holes on a frame. The web is the large flat face of the frame. I strongly suggest a crossmember that goes from one side if the frame to the other if at all possible.
View attachment 73570View attachment 73571

 

[Will L.]

That single sided mount is the weaker design. If you can find one of the dual sided ones like the first pic I posted- it would be worth buying, it shouldn’t be hard to find one. Install a new rear seal while swapping them obviously.

 

[Rogerhsr]

can I use the original crossmember for the truck or will I have to make one?

 

[Will L.]

Using the original would be best. Then use the original transmission mount (replace with new one if worn), and build a bracket from mount to the transmission brace. Seriously pursue the better dual mounting bracket/ seal cover. Well worth a couple hundred bucks.

Because you are doing it custom, inspect if frequently: daily for the first 2 weeks. Then monthly for the first two years. Then every normal service. Sounds excessive, I know. But better safe than sorry. Caught early you plan a repair, missed 1 day late involves tow trucks and possibly damage to even other vehicles.