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#1
04-26-2002, 06:44 PM
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Is there a big difference in performance between these two?
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#2
04-26-2002, 06:44 PM
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Is there a big difference in performance between these two?
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#3
04-26-2002, 07:09 PM
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A HUGE difference!The only thing these units have in common are the selector pattern.The Roto looked great on paper.It had no torque converter and went into direct lockup in 3rd gear.But the govenor and aluminum bowl(torus)were the weak links.
The Super HM was and still is a much better unit.It just weighs twice as much.If you have one rebuilt by someone conpetant,it should last forever.It is great for just cruising.Not great for racing. Both are very expensive to rebuild,(if you can find someone in your area to do it.)
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#4
04-26-2002, 07:56 PM
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A few corrections, as mentioned the 4sp Super Hydramatic is a great transmission, its cast iron predessor was the trans of choice for pro racers in the 60s. It has a low (3-1) first gear ratio to get it rolling and has NO torque converter instead it has a hydraulic coupling featuring _NO_ torque multiplication. The big Hydro was used on the upscale B bodies, Bonneville and StarChief.
The Rotomatic on the other hand does have a torque converter, the first used by GM. It was used on the GrandPrix and Catalinas. Narrow trans as reflected by the narrow trans tunnel which is a close fit for any other trans. Hence its nickname, the "SlimJim". Its a 3sp, though the salesmen used to like to refer to it as having an "effective" 4sp due to the multipling effect of the converter with is actually internal. Its a real P.O.S., when it is functioning properly it is usable on a street cruiser, dont expect any performance from its wonky shifting 1st to 2nd. If it dies, salute it and replace with a th350 or 400.
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  My Daddy bought me a car but all I got was this old Pontiac.
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#5
04-26-2002, 08:13 PM
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will the super HM fit in a catalina?...is the roto HM inferior enough to not be worth its "authenticity"...if you had one of each, and you were "restoring" a catalina would you opt for a T350 ?
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#6
04-26-2002, 09:18 PM
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The Hydromatic will fit a Catalina.
You have to dimple the floorpan for clearence. The Hydramatic has a Torque converter! The Roto has none! The Roto or Slimjim is a weak trans and is great for grandma but not a healthy 389! 
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#7
04-26-2002, 10:41 PM
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Blackcat, you need to do a little research.
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My Daddy bought me a car but all I got was this old Pontiac.
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#8
04-27-2002, 12:18 AM
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Um, not really
Can you show me a Slim Jims Internals and the Torque converter? I've taken many out and the main shaft copules to a dampener plate attatched to the semiflywheel on back of the motor. Is the converter inside the transmission housing? 
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Try calling CRUSHPROOF! 512-386-9889 |
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#9
04-27-2002, 01:54 AM
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I understand the confusion on the part of folks, myself included til I really got into them. Looks are deceiving, Yes it is internal, an actual converter, it doesnt look like contemporary ones on the outside but once you get in far enough to see it you are in the belly of the beast. the multiplication is there as it has the same components a modern converter has. The 4sp Super Hydramatic has what _appears_ to be a converter, its actually a simple fluid coupling. A hydraulic clutch.
A Motors Manual or Factory Service Manual has excellent cutaway draWINGS and photos of the internals. Parts are still available from several sources for both trannies but finding a transmission mechanic who has ever seen one or worked on one is not easy. They are all either dead or retired. I have done th350s and 400s but when I got into a ROTO I freaked and backed out. I would need a more experienced person to handhold if I were to rebuild one.
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My Daddy bought me a car but all I got was this old Pontiac.
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#10
04-27-2002, 04:46 AM
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Say a prayer and replace anything pre-69 in any street car other than antiques and trailer queens with a 400/350/700 transmission and in the long run, [img]smile.gif[/img] I promise you will be happier.
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A Government big enough to give you everything you want is strong enough to take everything you have. - Jefferson  "If ever a time should come, when vain and aspiring men shall possess the highest seats in Government, our country will stand in need of its experienced patriots to prevent its ruin." - Samuel Adams Right and wrong doesn't need facts all the time. -Lighthouseman ("lawyer") Starnes Performance Automatics www.Starnesperformance.com |
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#11
04-29-2002, 09:50 AM
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FWIW,Stevep, Member#100, who was first to answer this thread, is a good transmission mechanic and a good source of information on 'any'Pontiac transmissions. JMHO
Jerry I originally posted this due to some questioning Stevep's credentials. I did not post to start an arguement. I have had many 'Slim Jim' transmissions apart and as BVR421 stated, they do have a torque convertor. There is a stator in addition to the turbine and impeller which creates the torque multiplication. This has been cussed and discussed and I just wanted to clear the air. Jerry [ April 30, 2002, 06:55 AM: Message edited by: Jerry Brock ] |
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