1961 Hydromatic

[KQQLCAT]

Is this a good or bad tranny? What are some of the quirks I can look forward to.
Thanks
Pat
61 Olds 88 Dynamic 88 2dr sedan

[Oldsguy]

Some people like it, others don't. If it is serving you well now, why change anything? Welcome to our site.

[Oldsfan]

Originally Posted by Oldsguy

Some people like it,

Name two....

Roto HydraMatics, or Slim-Jims, are very fussy as to fluid level and T.V. adjustment. I think they are generally a poor design. These transmissions were constantly being updated during their 4 years of manufacture. From what I understand, valve bodies tended to wear around the 30k mark. First to 2nd is a drastic gear drop. They don't downshift out of high gear until about 7 miles per hour. In stop and go traffic, it's a little hard to get all that weight moving from 7 miles per hour in high gear. Shifts aren't the greatest, either. 2nd to 3rd can really slide, especially with a worn valve body.

If its working half decent, let it go. If something breaks, then it's time for repair, or time to look for an alternative. Some guys go backwards and replace them with Jetaway HydraMatics, some go newer and replace them with TH400s, etc. Some rebuild them, if they can find someone reliable who is willing to work on them.

Paul

[Olds64]

My 64 98 has a Slim Jim and it is a very poor transmission. I hope to convert over to a TH 400 in the future. Like Paul said, if your tranny is shifting ok now then just make sure you keep fluid in it and keep the TV adjusted. If it isn't shifting properly and it isn't just an out of adjustment TV then you need to consider replacing your transmission. I don't know of anybody that services these older transmissions with a good reputation. Everyone I have ever met or talked to on-line converts to a different tranny instead of having the orignial rebuilt. Parts are expensive. If you are determined to go through a rebuild about the only place you can get parts is Fatsco transmissions.

http://www.fatsco.com/

[59-59-59]

I am curious if anybody here put a Hydramatic in place of the Slim Jim transmission? I thought about this in a '62 I had years back, but I didnt think the Hydramatic would clear the narrow transmission hump in the floor!

[KQQLCAT]

The tranny was rebuilt 2,000 miles ago so the previous owner said but it is very clean so maybe. I just noticed that the tranny has a weird shift when slowing down to a stop almost like a manual tranny down shifting to low at about 7-10 miles per hour. I have a 63 Buick Wildcat tthat I just converted from a dynaflow to a TH400 switch pitch. Can this be done with a 394? I know it's all about bell housings. Are 394's BOP pattern?

[Oldsguy]

No, not the modern BOP pattern, you have to purchase an adapter plate. I think Olds64 looked into that one time, he may have the part number and contact information.

[Modern Motoring]

Tanson Enterprises > http://www.forwhatyouneed.com/transm...conversion.htm

[Olds64]

Yeah, Tanson is the only place I know of that you can get an adapter plate made. Don't forget that you will also have to modify the drive shaft, shift linkage, TV, and motor / transmission mounts. Also, if you convert to a TH 400 you will be going from a 4 speed automatic to a 3 speed automatic. That means that you will be turning higher rpm on the highway while cruising. Of course, this might be desireable in an old car (depending on what you want your car for).

If you want to stick with an automatic with an overdrive you might consider a 200 4R. The only problem with this transmission is that it would need to be built up to handle the torque of a BBO. If you decide to use the 200 4R have Brian Hofer build it for you (he is a transmission guy that builds hi quality 200 4Rs for Buick GNs). If you decide to use a TH 400 then I suggest putting a rebuild kit in it and changing the fluid. The TH 400 is definitely the cheaper way to go. But then again, in a conversion like that who is counting dollars?

[alrandmae]

Hi KQQLCAT,

Here's my two cents on the 61 Olds Roto 10 Hydramatic (Slim Jim)...it's a quirky and weak unit, but in my opinion, part of the fun of owning an older Oldsmobile. If you upgrade, it's like putting a piece of modern car into an older car. Dont get me wrong, I appreciate modern/better transmissions, but I dont see the point in mixing old and new technology unless you are going totally custom, which can be very cool, but is a different issue.

I've had about 14 1961 Oldsmobiles, and two 63 Oldsmobiles...all with the Slim Jim. Have 2 '61 Oldsmobile 98s at the present time. Found that if you avoid doing certain things, they will be much more likely not to break.

#1 most important...upon deccelleration...when the car is coming to a stop and the unit is shifting itself out of second down into first...if you are going to accellerate again (for example if a traffic light turns green BEFORE you are fully stopped), go easy on the gas to let the trans 'catch up' and build pressure. Sometimes in this situation if you suddenly accellerate you can catch the trans 'off guard' and it's like in neutral and then will slam into gear and shock the unit. Yep, self-destructive.

#2...fast throttle movements, sudden acceleration at any speed that results in stress on the unit should be avoided. You can still do full throttle acceleration, but dont mash the pedal...

#3...keep the idle on the engine nice and low...will avoid 'holding onto' second during decelleration to stop...can be annoying if the idle is too high and also adds stress to the unit.

I drive fairly hard, and have had pretty good luck keeping these working by going by those guidelines. I drive long distances with these cars (for fun) and I trust them. Have even done standing 1/4 mile drags with a 63 Starfire with stock trans - held together.

On point to some of the other comments...I am pretty sure that most upgraded units will require that you cut the trans tunnel part of the floor as the THM400 and the 4 spd Hydramatic are physically larger. One of the reasons that GM built the Slim Jim was to reduce the size of the transmission hump in the passenger compartment, so therein lies a problem.

Regarding the comment about resultant gear ratios, unless you are using a much more modern overdrive automatic you wont have any difference in engine rpm on the highway. The final drive ratio in the Slim Jim, the 4 spd Hydra and the THM400 is 1:1 - the number of gears does not matter, its the final ratio that matters and they are all 1:1.

On the Slim Jim, also try adjusting the TV rods. They look like downshift linkages but are actually the up and downshift actuators. There is a small one up near the carb. I forget which way is which but lengthening and shortening it changes the shift points. Can make a world of difference; generally speaking delaying the shift point on the Slim Jim makes for a smoother shift.

If your shifts are extremely rough (jolting) from 1st to 2nd, inspect the dampening plate between the engine and trans. It is a spring loaded plate that is meant to cushion the shift. If the springs are broken or the plate is jammed it will cause a hard shift.

Lot's of guys will complain about this transmission, and truthfully they have valid reason because they are not the greatest units out there, but in my opinion it's part of the whole package of the 61-64 Olds. I'd give it a chance.

All best,
Alan

[Oldsfan]

Originally Posted by alrandmae

It is a spring loaded plate that is meant to cushion the shift. If the springs are broken or the plate is jammed it will cause a hard shift.

About those springs...

Are they supposed to rattle? I've got one out of a parts car, and if you shake it, they rattle. Don't know if they are supposed to (wouldn't think so), or if I should just pitch it.

Paul

[Olds64]

Paul, when I rebuilt my engine I could see physical damage to the dampening plate that bolts to the flywheel. The srings were actually broken. When I ordered a new one the springs were all in good condition. They jostled back and forth a little bit when I moved the plate but it wasn't very noticable. If yours is rattling alot, I would say toss it and buy a new one. I think Fusicks and Fatsco carry them.

Also, Alan has a good point. You have to decide if you want to keep your car original or do a custom street rod. An engine or tranny swap is a big job, make sure you have good motivation before setting out to do this. Also, I stand corrected. I didn't think about the final gear ratio of the two transmissions I was talking about if they are both 1:1 then they will have the same cruising rpm on the highway. DOH!

[alrandmae]

Hi Paul,

I believe that the springs in the spring plate do rattle a little bit (they are not preloaded). I'd do just as Olds64 suggests, if they are really loose, toss it; if they just rattle a little, is probably good. I know that is a subjective answer, but I couldn't begin to suggest how to bench test the part.

Had an NOS spring plate that I put into a 61 Starfire a couple of years ago, and the trans ended up shifting really well. My 61 98 conv has 14K original miles and that also shifts nice, but my high-school car, a 100K mile Super 88 gave me whiplash on every 1st to 2nd upshift. So I think that wear/weakening on these plates truly does affect the shift performance.

Catch you guys later...

Alan

[88 coupe]

Originally Posted by alrandmae

Here's my two cents on the 61 Olds Roto 10 Hydramatic ........

I have asked several people, what makes that trans junk? The question was ignored.

Yours is the kind of answer I was looking for.

Thanks.

Norm

[PetChemMan]

Despite the odd gear ratios and somewhat slushy shifts, the Slim Jim can hold up pretty well to abuse, as many Starfire and 98 owners can confirm. Incidently, in some literature the factory called them "4S" transmissions , which many folk took to mean 4 speed. Actually, they were 3 speed transmissions with a small fluid coupling that gave some initial torque multiplication off the line. I agree with alrandmae above that the Slim Jim helps give those cars a unique personality, and I wouldn't trade mine away for any other transmission. On the other hand, the 4 speed Hydra-matic in my '55 Olds was my favorite transmission of all.

[Starfire61]

I couldn't put it any better than Alan did in his posts.

Folks unfamiliar with the quirks of the Slim Jim often think it's broken, when it's actually working the way it's supposed to work.

The RPM drop between first & second can be precipitous- if your carb floats aren't set to spec it can bog the engine to the point that the car dies. To reiterate what Alan said, the downshift out of high when coming to a stop can be downright uncomfortable unless the idle is set low- this is crucial to a smooth downshift. Furthermore, I agree 110% that this is not a trans that you want to start mashing the gas pedal with, especially during shifts. Your car will look like it's from the AAMCO commercial with a trail of transmission parts behind it.

It's no TH-400, but it's probably not quite as bad as a lot of folks make them out to be. I had a Slim Jim rebuilt by a retired trans guy who upgraded it to the last set of '64 specs & it works just fine. Back in the day my dad pulled a loaded boat, motor, & trailer all over the place in a '62 88- he did that for ten years with the car & had no trans problems with it of any kind.

I too tend to believe that if you want a car with a new trans then you should buy a new car. If all of these cars were transplanted with SBCs & 700Rs they'd be mighty boring. I think there's a value issue at play here, too. Unless you're keeping the car forever, or you're dropping big, big money into a '61-2 Olds & turning it into something Chip Foose would admire, you're probably better off keeping it original.

I saw a very nice '61 Super 88 bubble top on Ebay awhile back. Black with a red interior. The Super 88 is considerably more scarce than the Dynamic 88, has a nicer interior, plus it has the same 325-horse Skyrocket motor that was found in the Ninety Eight. Some nose-pickin' fool had yanked out that sweet Skyrocket engine & plopped in a- you guessed it- SBC with a TH-350. This otherwise good-looking, southwestern car attracted few bidders, failed to meet the reserve, & didn't sell. I don't think the bidding went much over 5 or 6 Gs. I couldn't help myself & sent the seller an email saying that I'd be very interested in the car if he could come up with the original drivetrain......

Chuck

[Olds64]

[88 coupe]

Originally Posted by PetChemMan

......... in some literature the factory called them "4S" transmissions ........

That is because they actually had four speeds.

Originally Posted by PetChemMan

......... with a small fluid coupling that gave some initial torque multiplication off the line ........

A couple of things wrong with this:

• All Hydramatics, from '39 until the last Jetaway, used two planetary sets. Each used one clutch pack and one band, giving it two gear ratios, for a total of four speeds.

• During the redesign, they did add a fluid coupling, but they did not add a torque converter.

• No torque converter, no multiplication.

• If the coupling worked in the manner you described, the front and rear planetary units would add up to four gears, and your coupling would add a quasi fifth.

• If, they had eliminated one of those units, the same scenario would have a two speed trans, with your magic coupling supplying a third.

Where is the missing gear?

Norm

[PetChemMan]

Nope; the Slim Jim, as installed in 1962 Starfires, is a three speed transmission, and not a four speed. Note that the 3 speed Roto Hydramatic ( Slim Jim) came after the 4 speed Jetaways, although there was some overlap in production depending on car make. And according to the factory service manual, the "fluid coupling" , as the factory called it, did in fact add some torque multiplication for the first few seconds of first gear, which is why they chose to label it a "4S". Note that a torque converter is simply a special type of fluid coupling, and the factory did not choose to call it's small coupling a full torque converter, even though it had a third element and did provide some torque multiplication. The mislabeling of the transmission as a "4S" was a controversial marketing ploy . The issue was much discussed in several trade publications of the day, ( some of which I have in my library) and GM came under criticism from the industry back in the early 60's as a result.

[Olds64]

When I tore apart my Slim Jim I noticed the fluid coupling had a stator in it. I also noticed that the transmission pump was a pressure compensated vane pump. If I remember correctly a pressure compensated vane pump wasn't used again until the early 80s in the Ford AOD transmission. Unofortunately, the transmission in my car has excessive wear and leaks internally. That is why I don't think very much of the Slim Jim. Truthfully, I would love to drive a car with a properly operating Slim Jim.

[88 coupe]

Originally Posted by PetChemMan

........ Slim Jim, as installed in 1962 Starfires ........

Following is from the opening post:

Originally Posted by KQQLCAT

........ 61 Olds 88 Dynamic 88 2dr sedan

The topic is not a '62 Starfire.

Originally Posted by PetChemMan

........ according to the factory service manual ........

The coupling is filled, the neutral clutch is applied and the sprag, or roller clutch, is effective, placing the the transmission in first.

The reduction in first is due to the 2.933 rear unit gear reduction, times the 1.2 coupling torque multiplication, less the .3 engine torque acting on the output shaft through the accel-a-rotor

That should make it a 3.32:1 first gear.

The coupling is filled, the neutral clutch is applied and the sprag, or roller clutch, is effective, placing the the transmission in second.

The reduction in second is due to the 2.933 rear unit gear reduction only.

That should make it a 2.933:1 second gear.

The front clutch is applied and the coupling is empty, shifting the transmission into third.

Because the coupling is empty no power is transmitted through the torus members and torque multiplication is due to the 1.56:1 front unit gear ratio.

That should make it a 1.56:1 third gear.

The front clutch remains applied and the the coupling is filled.

Both planet carriers and the output shaft are connected. The front sun gear and the rear internal gear are connected, and the front internal gear and rear unit sun gear are turning at approximately the same speed, thus the entire train must revolve as a unit in direct drive.

Finally, according to your FSM, that should make it a 1:1 fourth gear.

I count 4 gears, how many do you count?

Originally Posted by PetChemMan

........ the fluid coupling did in fact add some torque multiplication ........

Of course the torus assembly slips. If it didn't, it would not be possible to put the trans in gear, with the engine running.

Originally Posted by PetChemMan

........ for the first few seconds of first gear ........

Normal idle/off idle slippage at the torus wheels. Nothing to do with the number of gears, or gear ratios.

What am I missing?

Norm

[PetChemMan]

The topic of my comments is the Slim Jim transmission, regardless of what car it is in. The Slim Jim was a three speed transmission with a small fluid coupling that acted as a limited torque converter. Three speed transmissions with torque converters are still only three speeds, regardless of the torque multiplication of the torque converter. The earlier four speed hydramatics with torque converters weren't called five speeds because of the torque converter effectively adding a gear, and no other transmission with three mechanical speeds plus a torque converter has been called a four speed. A three speed transmission with a lock up converter is still only a three speed transmission. Buick Dynaflows and Super Turbine 300s were only two speed transmissions with a torque converter, even though the torque converter provided tremendous amounts of torque multiplication on acceleration, and acted as a continuously variable transmission during acceleration.
Yes, the fluid coupling in the Slim Jim gave increased torque briefly in first gear, but that is not usually considered a separate gear. There was no shift from what they called first gear to second gear; it was only the torque multiplication of the fluid coupling running out. It's a matter of semantics, and GM chose to call it a "4S" , while everyone else in the industry said it was only a three speed with a torque converter.

[Starfire61]

Taken verbatim from the 1961 Service Manual:

"Two planetary units are used to obtain neutral, three forward speeds, and reverse."

"A fluid coupling is used to provide additional torque multiplication for first and reverse gears and to lock members of the two planetary gear sets together to provide third speed (direct drive). A multiple disc clutch is used to lock the drive torus and front unit internal gear together to provide reduction in the front unit for second speed. This clutch is also used with the fluid coupling to lock the front and rear units together to provide third speed (direct drive)."

"A sprag clutch is used to lock one member of the front or rear unit to the case to provide reduction for first and second speeds."

It's quite clear in the '61 manual that this is a 3-speed transmission. From '62 on, things get fuzzy, which coincides with the advertising people calling it the 4-S Hydramatic. Indeed, if you look at a '62 service manual, they recycle most of the same diagrams that were used in '61- it's obviously the same trans, yet they start referring to four forward speeds.

If you read between the lines in a '62 or '63 manual, it's apparent that Olds viewed the torque multiplication in the "Accel-A-Rotor" (limited torque convertor) as two distinct forward gears, while they made no such claim in '61. This makes things very confusing when discussing the functions of this trans with people familiar with different sets of semantics. In '61, when the fluid coupling empties & the mechanical clutch locks the drive torus to the front unit internal gear, this is considered the 1-2 upshift. The very same function from '62-'64 is called the 2-3 upshift.

If you look at the manuals from year to year, the ratios change very slightly. I don't know if this is due to them calculating different degrees of torque multiplication or if they used different gearsets in different model years (or both).

I've had several needlessly heated discussions over the years about just how many speeds were built into this 46-year-old obsolete transmission. Once I had to hand a guy the service manual & say "show me where it says there are four speeds." He stood there reading it for a good 10-15 minutes before he gave up- his buddies laughing at him the whole time. I'll be honest & admit that I don't know a whole lot about the workings of automatic transmissions. Nonetheless, I've talked shop with a lot of folks smarter than me about these things & the general consensus is that the Slim Jim just has some weird & unique features that put in in a class all by itself as far as auto trannys go.

I have three 61's & two 62's- all with Slim-Jims. There is no difference in the performance of the trannys in the two different model years. All of them have two distinct shift points, with the first shift being most pronounced. This is the point at which the fluid coupling empties & the mechanical clutch grabs hold. In some cars this can be quite rough depending on the condition of the clutch itself & the damping plate between the trans & the engine. Furthermore, the significant ratio change causes the RPM drop so characteristic of a Slim Jim.

So, I guess it has as many speeds as whichever manual you want to believe!

Hope this helps....