Bye Old Jim, Hello 350
 

I know this subject had been discussed much over the years. I probably should have done it years ago when I might have done it myself. But at 82 the idea of up and down with a creeper is not appealing. And it cost me dearly to have someone else do the work. But h this is what I did.

As I still have the original 1961 389 with a bell housing mounted starter, I was forced to use an adaptor. I had decided to use the Wilcap adaptor as it is a little tinner than the Bendtsen. I was worried that there would be firewall interference at the upper bell housing bolts. With the thickness of the adaptor plus a BOP bellhousing plus the bolt heads it would require a lot of hammer work on the firewall. Then I realized if I used a Chevy bolt pattern 350 I could remove that thickness as those bolts would be lower. I also had not realized that both Wilcap and Bendtsen use countersunk or counterbored bolts at that upper location so there was no problem anyway. The following pictures show really a lot of clearance and likely either adaptor would have worked.

There has always been concern about floorboard clearance when replacing the old transmission in a Catlina/Ventura body. Look close at the picture and you can see some hammer work a the rear tail shaft mount bolts. That was the only real problem and not bad either. The accumulator is close and maybe could have had some hammer work but it has not been a problem. Also the dipstick area should have been worked if we had used a factory dipstick but the Lokar unit seems to have solved the problem

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The rear mount is not the arrangement I might have preferred. The load point is way forward of the cross member and imparts a twist to the cross member. The cross member to frame mounds have been beefed up some to compensate. I didn't want to move the cross member forward as the exhaust pipes would have to be changed. I know I could have had a better mounting point on the transmission with a 200R4 but thane I would have had to change the rear end also. I have a 2.87 rear end and an overdrive with that would not work.

Thanks for posting. This is a swap that is often talked about, but photographic documentation has always been missing.

I got a Chevy, 9 inch tailshaft transmission. With the 9 inch the overall transmission length seems to be about the same as the old Slim Jim. The driveshaft should be about 1/2 to 3/4 shorter that the original which allows for the adaptor thickness. I had a new driveshaft made as I thought the rubber shock absorber in the old drive shaft should go.

For shift linkage a Lokar ACA-1800 works fine.


And a Lokar KD-2350U works for the kickdown. We used the old TV linkage mounted on the rear of the head. May still need a little adjustment as the slide slot is to long for the short throw on the lever.

For the modulator I added a hollow stud to the center carb to get vacuum. The exhaust pipe still needs a little work as it hits the floor above the cross member and is way too close to the starter. The Wilcap adaptor moves the starter location a little and this was a tight place anyway. Don't try to use long branch header with this adaptor.

Neutral Safety switch and shift indicator are another problem. The old safety switch mounts below an actuator arm on the steering column. Nothing quite like that is available for the new PRNDL order of the shifting in the transmission I have seen various solutions to this, but my approach was to buy a PM238X for a 65-68 with console from Ames. That uses the same type of actuating rod but as it was to be mounted to a console the configuration is reversed and it works with the new shift sequence when mounted above (not below) the actuating arm on the steering column. For the shift indicator I was going to engrave a new glass to the new shift sequence. But that got to be a lot of trouble so I went with Lil'Abner's solution with a Shiftworks S147 that I stuck to the background plate so now the pointer is i front of the letters not behind the letters. Looks like the factory did it. But damn it that stuff hard to get out of and back in the dash.

And one more picture of the new shift indicator. I got lucky of the speedometer as my core transmission had the same gears ratios as my old Slim JIm. Reads right and the tranny seems to work properly.

Great info! Thanks.

Very creative and fun to read through. Your adapter and shift indicator solutions seem like breakthrough thinking days!

Nice job, and yes the under dash stuff is tough for us Octogenarians.

What rear axle ratio do you have? With the taller first gear on the T350, do you find it adequate?

Oops, I just reread your earlier post and see it’s 2.87. I guess my question still holds.

For a neutral/backup light switch you can also use one from the street rod companies that mounts on the transmission itself. It doesn't care what kind of car it's in only the type of transmission.

Yellow Banana

I was afraid I would miss the startup ratio of Old Jim as it was something like 3.50 and the 350 is 2.52 in first. The 3.50 x 2.87 is a nice low ratio and something like having a manual 4sp with maybe 4.11 rear end. But the 350 with the converter (I have a fairly conservative OEM stall but I don't know the exact number) still starts out nicely. I'm not racing the thing just cruises. Yet the 1-2 WOT shift will get a nice chirp from the tires.

If I had gone to a 2004R with the .67 OD and changed the rear end I could have gotten back to about the same first gear ratio and still had about 2000 RPM at 60 but I didn't want to go to the trouble and expense of changing the rear end. All things considered I guess I'm happy. Except for what it cost to pay someone else to do what I used to do for myself.

Goatracer1
I considered that. And I think you can get them to do both neutral safety and backup. But I didn't want to have to extend wires from the steering column down to the transmission. All personal preference, I guess.

Thanks pfilean. I need to check my rear ratio for sure, but I think it’s similar to yours.

Keep in mind that many later ‘60s and early ‘70s Le Mans and Tempest of similar weight to the ‘61 big Pontiacs came equipped with a 2-barrel 350 coupled with a TH350 and 2.78 rear.

I had a ‘70 Tempest equipped as such with factory A/C and it got out of its own way no problem.

The TH350 should work fine with the 2.87 rear gear.

MyGrand Prix has the high compression, 4 barrel 389 that was standard in ‘64. Would one of the higher performance T350 rebuilds be required to handle the torque?

A stock rebuild on a TH350 should be plenty adequate if you’re not a racer.

Exactly what’s behind the 8.8:1 421 HO in my loaded Le Mans convertible.

Spending more to upgrade it is fine if you think you might be hard on it, however it does add up quickly to do anything substantial in the strength department. They’re a good transmission and my builder said upgrades weren’t necessary for my application.

I think the GP trim generally got something like the 2,87 as standard. Catalina usually had more like a 2.69 but the factory in 61 (like for GP later) thought that was a buyer that wanted a little more first gear go. Then there was the economy buyer who got like a 2.56.

There are a lot of rebuild upgrade levels that can be had for a TH350. And in general a TH350 can handle the Pontiac torque unless you have a fully built engine. When the TH400 came out it became standard for the B body Pontiac. After the 350 was introduced it was standard behind a lot of Pontiac engines in various body styles. . I told them to give me maybe one step better than a conventional stock rebuild.. I haven't beat hard on in yet and maybe never will but so far I'm good.

I have had a stock rebuilt T350 in my 1964 GP with a 421 4bbl for 10 years now. I don't beat on the car much but do get on it once in a while and I have had no problems.