Buick 3.8 In A CJ5

I've had an SM420 behind a Dauntless, pretty much a bolt up, shortest length of the granny low transmissions, lowest low gear ratio, usually cheap, found in GM trucks from 1946? until 1968, not hard to find parts for, several suppliers of parts like bearings, seals, gaskets and synchros are on line I;e: High Impact etc. My SM 420 was given to me. Inner city folks may have to look a little more to find them, rural dwellers probably have seen a GM truck made between 1946? and 1967.sitting around somewhere. The last year or two had a provision for a back up light switch, earlier transmissions can be drilled and tapped for a back up switch, or a switch can be mounted on the shifter to operate back up lights. There are two ways of adapting SM 420's to Dana 18/20 tcases, a one piece long main shaft and a stubby main shaft, long main shafts require a total teardown of the trans, the stubby main shaft doesn't, AFAIK. I used a long main shaft because I got a good deal on it, and I was going rebuild the transmission before installation anyway. Price, availability, size, adapter cost and planned use all influence your decision. Good luck!

 

Trans is short, but with the adapter, what the overall length? The adapter is long. Did you have issues with your front driveshaft universal joint etc.?

 

I can't tell you OAL for trans/tcase/adapter, I have since parted out my CJ6. I would guess the AA one piece shaft adapter was between 3" and 4" long.

 

I have a SM465 and the rear driveshaft is around 16" long. The Novak adapter is only 1" thick. No problems and I have been running it for many years now. The SM420 adapter from Novak is 4".

 

I have decided to go with the TH350 I have instead of a 4 speed. I have mocked up the engine and transmission, but I have not purchased the adapter for the transmission to transfer case yet. It appears that I will need to move my engine and transmission forward approximately 3" to place my transfer case shift levers in the floor and not in the under seat tool box. I would like to know where others have had their transfer case shift levers end up. The 4-speed conversion would have been about 1 - 2" shorter so I think I would have had the same problem.

 

With a smallblock Chevy and 400 automatic, my shifters are in the stock location. I extended the pivot point and shift rails. I can send you pics if you pm me your email or phone #.

 

I've been thinking about an SC 3800 L67 as a swap candidate; I was also looking at the TH350 as a transmission choice but I figured I would try an get a sm420 bolted to the back of one before I went to an automatic.

 

Once I figure out how to pm I will send the information.

 

pm sent

 

I will be getting my TH350 back from the transmission shop next week. I have the transfer case rebuilt and the engine ready to go. The tub is still on my frame and I would like to know the easiest way to get this combination installed. The motor mounts are installed. Do I split it up or drop the entire assembly as one unit? I do not have a chain hoist, only an engine hoist, and a floor jack.

 

If the grill and radiator are removed, I would bolt everything together and drop it all in as a unit.

 

a really old picture

motor in stock location . rear driveshaft about 13-14 inches long . if I were to do it again I would do as your going
to do move everything forward . one of biggest problems is floor . TH350 is quite large compared to a stock transmission

 

That is what I planned to do, I was just having some concerns about the weight.

 

Sling it over all in one piece if possible. I start with the grill and radiator and set the engine fan an inch back from the radiator. Easy with a v6. Most CJ5 small block transplants benefit from a 72-86 grill that has the radiator inset into the grill. Line it all up, center and level before welding in your mounts. Some turbo 350s need you to offset the whole works for front driveline clearence but you still need to leave room for steering and exhaust. One big ole jigsaw puzzle.

 

One more question. I picked up a shifter from a Ford Aerostar thinking it was for a C4 transmission. Turns out it was for an OD transmission. Can I adjust the detents and still use it, or do I throw it in my "get rid of later" parts bin?

 

MAN - You guys are a wealth of info! Thanks so much. At this point, given all the complexities of making the swap, I'll probably rebuild the T90/T18 combo that's in the rig. I'm tuning up dormant mechanical skills and doubt, time and money are factors. I also really want to drive the darn thing. One of the benefits of this forum to me has been the clarity your knowledge affords me prior to making these commitments to more time and money. Thanks again

 

I put the engine and drivetrain assembly in. The engine is close to the firewall and I have room for my radiator. I used the stock cross member, but since the transfer case has been clocked I had to drop it about 2". Looking at it I am not sure my front driveline will clear the transmission. I can drop the cross member a little more, but I am afraid that will put the output below the differential or I can cut out the motor mounts and move the engine forward abt 2" and that would raise it 2". Has anyone else had this problem?

 

Is the grill from a 72-86 a direct bolt in, or do I have to modify to fit my 1957?

 

Swaps take time and effort, but are very doable. We all want to help and try and give info on what works and what doesn't but it can sometimes make the job sound way more complicated then it is. I went through Novak, they where very helpful and have great info on each swap. I spent about what I would have rebuilding my t18 as I would have my t90. They are not hard to rebuild (swap main shaft on t18). Good luck, just didn't want to discourage you.