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Reading an article about the Roto-Hydramatic "Slim Jim" transmissions, and I was surprised to learn they were designed to run on ATF that included whale oil. The article says modern ATF exacerbates the rough shifting problems the Roto is already known to have (yes, I said "exacerbates"- that means "it makes it worse"). I'm looking for input on this- what ATF are you using, do you feel the shifts are rough? Is there an additive you use? I just picked up a '64 Dynamic 88 and I'm doing a pretty extensive mechanical refresh. I've hardly driven the car because when I bought it, it was barely driveable. Now it's in pieces and I'd like to fix everything while it's all apart.
I was never concerned that the ATF I ran in my Slim Jim wasn't made from whale oil. If the Slim Jim in your Oldsmobile shifts properly treat it like a fine porcelain doll and granny foot the car everywhere.
You can read plenty on the Slim Jim Rotohydramatic on our site. Good luck, hopefully you don't have to do a modern transmission swap. 🤞
Last edited by Olds64; January 13th, 2024 at 04:47 PM.
Reading an article about the Roto-Hydramatic "Slim Jim" transmissions, and I was surprised to learn they were designed to run on ATF that included whale oil. The article says modern ATF exacerbates the rough shifting problems the Roto is already known to have (yes, I said "exacerbates"- that means "it makes it worse"). I'm looking for input on this- what ATF are you using, do you feel the shifts are rough? Is there an additive you use? I just picked up a '64 Dynamic 88 and I'm doing a pretty extensive mechanical refresh. I've hardly driven the car because when I bought it, it was barely driveable. Now it's in pieces and I'd like to fix everything while it's all apart.
So, my question is WHO wrote the article and where you saw it ? What ATF did they recommend using now ?
So, my question is WHO wrote the article and where you saw it ? What ATF did they recommend using now ?
It was a hot rod website, and the question was about putting a TH400 behind a 394 in a 1963 Olds. The article said there's "huge jumps" between gears on the Slim Jim, and it said the Slim Jim is a high pressure transmission that is prone to leaking, so swapping it for a modern transmission is a desirable but complicated swap. Here's the link...
I was never concerned that the ATF I ran in my Slim Jim wasn't made from whale oil. If the Slim Jim in your Oldsmobile shifts properly treat it like a fine porcelain doll and granny foot the car everywhere.
You can read plenty on the Slim Jim Rotohydramatic on our site. Good luck, hopefully you don't have to do a modern transmission swap. 🤞
"Granny foot"? Seriously- you're suggesting I "granny foot" my car because I'll blow up the transmission? If you're right, I'm not happy. Better I think to blow it up and move forward to something better
Don't let everyone scare you into spending big money on a "replacement" trans.
Slim Jim's can and have served faithfully for many thousands of miles without "granny-footin" it .
Being a collector car, how many thousand miles are you going to put on this car?
Since you already have the trans out, here's a few things you can do.
Remove the pan, and replace the filter.
Replace the front and rear seals.
Check the damper ( in the middle of the flywheel ). If the springs are loose at all, replace it.
Fill the trans with Dexron III / Mercon . It is the modern equivalent of "whale oil".
If you don't have one , get a 1964 Oldsmobile shop manual . 1964 oldsmobile shop manual for sale | eBay
Follow the instructions there to adjust the throttle to trans linkage.
The linkage adjustment guage is available from Jaswest JASWEST - Home
Last edited by Charlie Jones; January 13th, 2024 at 08:26 PM.
It was a hot rod website, and the question was about putting a TH400 behind a 394 in a 1963 Olds. The article said there's "huge jumps" between gears on the Slim Jim, and it said the Slim Jim is a high pressure transmission that is prone to leaking, so swapping it for a modern transmission is a desirable but complicated swap. Here's the link...
I read the article. You should know that at least one person on here has mated a TH400 to a 394. It was not cheap and it had a few problems. Just remember, anything is possible, with enough money.
Personally, I would talk to some people with good transmissions before making a decision. Your biggest problem will be finding someone to overhaul the transmission. Is it a great transmission ? No. Will it perform sufficiently ? Yes. If you plan on driving it, it would be ok. If your going to race it, you might want a different transmission.
Take it for what you want. The Slim Jim Rotohydramatic is a POS. Any Oldsmobile I considered owning with a Slim Jim would IMMEDIATELY get a transplant. The only Oldsmobile worth keeping a Slim Jim in is a Starfire. Guess I'll never have one of those.
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Last edited by Olds64; January 14th, 2024 at 11:58 AM.
Listen to Charlie rather than the legion of SlimJim haters. Yes it does shift a little weird, yes it does slip a bit due to the lack of a torque converter, but that also why it is part of the 60s 394 experience. The single most important thing that will make it operate correctly is the linkage adjustment. I've owned three cars with this trans, correctly adjusted, and they all drove very well.
Listen to Charlie rather than the legion of SlimJim haters. Yes it does shift a little weird, yes it does slip a bit due to the lack of a torque converter, but that also why it is part of the 60s 394 experience. The single most important thing that will make it operate correctly is the linkage adjustment. I've owned three cars with this trans, correctly adjusted, and they all drove very well.
Thanks Don. I'm sure if it's really bad, I can find someone with enough ***** to try to rebuild it. Heck, I'm not afraid to try to do it myself if I had to, but I'm one of those guys who believes he can do anything until proven wrong. I just want a driver- not a race car. One commenter said "granny foot", and I'm sure he just meant "don't beat on it". That's my plan exactly.
I appreciate everyone's comments. I've never owned a car with a slim jim and I barely drove this one before I tore it apart.
January 13th, 2024, 03:23 PM
