I have a perfect running and very strong 394 in my 63 98..The slim jim wont get out of 1st gear.I dont want to rebuild it because from what I read on them, they arent very good..I want to put in a TH350..I need to know what I need for the swap as in new flex plate?, will it fit as far as the body goes?Also where to get an adaptor plate or have a machine shop make me one..?..Any help would be great.P.S. I wont get rid of the original tranny and hope I wont have to make undoable mods to the car..This car is 100% unmolested and original..I want to drive it and not mod it too much..Unless there is anything that can be done to make the slimjim a better tranny i.e. better quality parts or mods to it..

 

this topc has been covered many many times, the search feature DOES work. IMHO keep the car original, rebuild the transmission. a TH350 just doesn't swap in there.

If you are up to it, Tanson Ent. http://www.forwhatyouneed.com/transm...conversion.htm

 

Get rid of the Slim Jim. They are a POS transmission. It would cost about the same to modify a TH 350 to fit your 394 as it would to rebuild a Slim Jim.

 

mine has been going for 80 or so thousand miles... knock on wood, and who knows the history of any rebuilds, but from what I can gather, it's original. Right down to the self changing fluid feature !

 

My slim jim shifts weird from 1st to second like the gear ratio for second is extremely high and goes into third nice and smooth. Without driving a car with a perfect running tranny I can't tell if it's suppose to be that way.
Pat

 

That's not weird, that's normal.

 

I do know this has been talked about before..Its still always good to ask again.Different people will respond and just maybe someone will add something new.Thanks for the info..Im going to just pull this one and go through it.It would be best and a good point was brought up in this thread..Keep it old and the challenge and fun of these old cars is what its all about..

 

Make sure you have a service manual if you are going to tear apart your Slim Jim.

 

Fatsco will be your friend.

 

Tanson Interprises in Sacramento ,Ca. offers a Th 350, 400 or 700 R4 transmission case modified to fit the early Olds engines. Personally, I just cut the bell housing off of a 400 case and built an adapter that bolts to the front pump and mated it up to my 63 394 in my 55 Super 88 Coupe. It's been in the car for 10+ years now without a problem.
Rod Hoover

 

I talked to Bendtsens transmissions at Back to The 50's in Minnesota and he quoted me $3,800 to convert my Slim Jim to a 700R4 on my 61 88. This included the tranny, modifing the floor, and everything so it would be a turn key deal. I didn't think this was too bad considering all the work involved. http://www.transmissionadapters.com/gallery.htm
Pat

 

I think that is a fair price. Bring it to him with $3,800 and pick it up and drive it away with a new transmission. You might ask him if you need to provide a core for the 700 R4. Also ask him if you will get your old Slim Jim back. You could always take the insides out and use the case as a dog house or something. I am sure they must be good for something.

 

The problem is that half the bellhousing of a 394 is actually part of the cast iron engine block. Also, the 394 uses a motor mount under the crank pulley and one on each side of the bellhousing area, while later engines use mounts on both sides of the engine and one at the tail of the tranny. If your 394 gives trouble later, it is harder to find stuff for it than for later engines. If you really want to get rid of the slim jim, consider a 455 with Turbo 400 and change the engine mount setup or use the Toronado front engine mount and fabricate something for the others. Changing both engine and trans will probably not cost more than trying to adapt a turbo 350 to the 394.