THM 300 Transmission

[bbuss]

I have a THM 300 Variable Pitch transmission with a round bell housing.

If memory serves me right the round bell is 1964 only.

The trans has just been rebuilt.

Any idea what this trans might be worth befor I try to sell it?

bbuss

[Mrbuick714]

I have one also,fits 322 engine. You can buy mine for $200/. It is near-new

[NTX5467]

I believe that what you're referring to as a "TurboHydraMatic 300" is really a Buick "SuperTurbine 300". If I am correct, it was built in a Buick facility just as Chevrolet built their PowerGlides "in house".

Just some thoughts,

NTX5467

[Guest norb]

I was working with chuck chapman when the 300,350 & 400 were developed.It did not have a round bell housing however. two pictures of it here.

[Guest norb]

300 Trans booklet

[bbuss]

I was also in the transmission trade part time in the late 60s and full time

starting in 1970.

This 300 trans does have a round bell that was used in 1964 only.

Buick went to the GM style bell housing design in 1965.

There are also 400 transmissions with the round bell for the 64 yesr.

PS thanks for the reply's

bbuss

[Philippe Racicot]

Maybe it is a 300 transmission with the nailhead bellhousing (adapter?) for the 65-66 GranSport.

[bbuss]

The Super Turbine 300 is listed in some later books as THM 300

just like the THM 400 is called Super Turbine 400 in early books.

Could the term Super Turbine have to do with variable pitch converter?

bbuss

[Guest norb]

I just listed a shop manual for the ST 300 3 speed on e-bay. if it does not sell,I will make you a good deal on it. norb 6634549234

[NTX5467]

By observation, in some "later books", the authors might be of a more recent vintage too, such that they might not fully understand the reason that "THM300" is incorrect (as "THM" denotes a transmission designed and built by HydraMatic Division of GM rather than a car division of GM). In more recent times, everything is under the umbrella of GMPowertrain, but it was not that way in earlier times (when each GM division had their own Chief Engineer and other completely unique mechanical designs from other GM divisions).

The first automatic to use the "THM" designation was the fixed-stator THM400, circa 1965. Then followed by the lighter duty THM350 in 1969. There were also THM375 and THM425 versions too.

"SuperTurbine" does relate to the variable pitch torque converter in the ST300s and ST400s. There are extra switches on the carb to affect the "switch pitch" functions, plus specific front pumps and matching torque converters. Olds also used some switch pitch 400s too. "SuperTurbine" nomenclature was unique to Buick.

Enjoy!

NTX5467

[55PackardGuy]

In my experience the THM400 was THE transmission to beat. Had one in my '65 Electra, and if that was the first year for the "400" it was great right out of the box. I absolutely thrashed that trans in that big heavy car and it would not die. I didn't even know you were supposed to change the fluid and filter once in a while--it was never serviced under my watch during the car's second hundred thousand miles. It retired undefeated with about 125,000 on the clock.

[Philippe Racicot]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">

"SuperTurbine" does relate to the variable pitch torque converter in the ST300s and ST400s. There are extra switches on the carb to affect the "switch pitch" functions, plus specific front pumps and matching torque converters. Olds also used some switch pitch 400s too. "SuperTurbine" nomenclature was unique to Buick.

Enjoy!

NTX5467 </div></div>

The <span style="font-style: italic">Super Turbine 400</span> name was first used in the 1964 Buicks and that year, unlike the also new <span style="font-style: italic">Super Turbine 300</span>, it had a fixed stator.

The 1964 400 transmission also had a valve body that was unique to that year and it didn't have two "low" ranges like the 1965 and newer 400 transmissions. The 1964 400 transmission shift selector did show "PRNDL" but the transmission had 3 speeds. The 65-67 400 transmission did have the switch pitch feature and the "PRNDLL" shift selector but in 1968, the Buick transmissions were still called <span style="font-style: italic">Super Turbine 300</span> and <span style="font-style: italic">Super Turbine 400</span> while neither of them had the switch pitch stator.

Some Oldsmobiles and Cadillacs also used the switch pitch 400 transmission. I'm wondering how it was called when installed in cars from other divisions.

"THM" stands for <span style="font-style: italic">Turbo-Hydra-Matic</span> and and the reason why "Turbo" was added to the "Hydra-Matic" name is because it used a torque converter instead of the fluid couplings of the previous Hydra-Matics.

[Guest John Chapman]

Besides the ST-300 application in Buicks, this transmission also was used in the Olds F-85/Cutlass/Jetstar as the "Jetaway" and in the Pontiac Tempest/GTO as the "TempestTorque". "Jetaway" and "TempestTorque" were marketing names that applied to a number of transmissions over the years, but for 1964-68, referrend to variants of the core ST-300.

Olds offered the transmission with and without the variable stator, depending on application. Pontiac offered one version (1964?) that was aircooled.

Of note, many of the internal rotating parts of the ST-300 were identical to the Chevy Powerglides.

Cheers,

JMC

[NTX5467]

I'll admit that I did relate some things I hadn't thought about in some time, which might not have been completely correct--key word "completely". I recall that when the variable-pitch torque converter was introduced, it was a heralded advancement, but when it was quietly dropped for 1968, the change (in the sales literature which noted the "new" fixed stator torque converter resulted in lower transmission tempeeratures and greater reliability.

In my research, I did find the comments about the 1964 "400" transmission, word for word, on another transmission website. Be that as it may.

In many respects, to fully understand how things happened at GM back then, as compared to more recent times of consolidations/combinations, each carline division was it's own seperate business entity. Each division manager did answer to GM Corporate, but much of what went on was of their own determination (within corporate guidelines). For example, when racer Jim Hall went to Chevrolet for an "automatic transmission" for his Chapparal race cars (mid-late 1960s), he dealt with Chevrolet and not GM per se. In that time frame, Chevrolet was the volume leader at GM and (from some accounts) could do pretty much what they wanted.

Each division had their own engineering and manufacturing facilities too. Much of each division's clientel knew the distinctive feel of each division's vehicles and that was a huge marketing issue back then. With respect to automatic transmissions, GM's HydraMatic Division had the transmission business (typically) for Pontiac, Olds, and Cadillac who used 3-4 speed automatics. Chevrolet had their PowerGlide and Buick had their DynaFlow. Chevrolet (being the lower price and volume leader) probably had no need for the more expensive and heavier HydraMatics and Buick (being a storied luxury brand of powerful vehicles) desired more smoothness than the HydraMatics could provide. And that's pretty much how things laid out until the more modern and efficient 3-speed TurboHydraMatics of the middle-late 1960s took over for the earlier (divisional specific) transmissions.

Considering that all Buick automatic shift quadrants (for years) were "D-L", plus trying to ease their loyal customers into the more modern transmissions with three forward speeds, maintaining the "D-L" quadrant with a matching valve body would make sense. By 1965, though, the "upscale" was the three-speed automatic (of whatever initial quadrant style, whether P-R-N-D-L2-L1, P-R-N-D-S-L, or the (later) standardized P-R-N-D-2-1.

In one transmission website, it referenced the switch pitch transmissions as being in "heavier" cars and the fixed stator transmissions for "lighter" cars. "Lighter" could also be interpreted as Chevy and Pontiac with "heavier" being Olds, Buick, and Cadillac. Be that as it may, but it also gave the higher level carlines something to indicate that they were technically superior to their lower price associates.

In that same general time frame, torque converter and automatic transmission technology was improving, as was engine power and torque. One website noted that the torque multiplication in the switch pitch converter (in "high" angle) was 2.5 with the "low angle" multiplication being 2.0. At that same time, the fixed stator torque converters (of GM, Ford, and Chrysler) were generally 2.0 to 2.2 in torque multiplication factors. Such a small advantage might be worth in on the drag strip, but most people did not really notice. I suspect that smaller difference could be compensated for with some minor engine tuning, at a generally lesser cost and complexity at the factory level.

In another website, I found documentation that in "high stall" mode, in a motorhome with a THM425, the transmsission oil temperature (under load up a hill) was about 30 degrees F. hotter than it had been with a fixed stator converter. Plus that an electronic controller to control the the variable pitch torque converter had been developed for these application (using manifold vacuum and such as we now do for lockup torque converters).

I did find (in my 1968 Buick full line sales brochure) that in 1968, all Buick automatics were called "Super Turbine", with the distinctions of Super Turbine 300 and Super Turbine 400 being engine size and model range specific. As with Pontiac and Oldsmobile, the lower levels of the range could be had with smaller engines and the two-speed automatics than their higher level siblings (with larger engines and three-speed automatics). Of course, these would be fixed stator Super Turbines rather than the earlier variable pitch Super Turbines. I also found documentation that Olds used the ST300 in their Jetstar models (a transition model toward the lower price spectrum of their model line) and Pontiac used it in their larger-engine GTOs in the middle 1960s (for a few years before the THM400 was needed).

Chevrolet used their PowerGlide as long as GM Corporate would let them, probably longer than corporate really wanted them too (from what I've read). The Chevrolet transmissions "claim to fame" would be its lower power consumption than other 3-speed automatic transmissions did. Documented as being 15 horsepower or so, rather than close to 40 for the THM400. It's possible that Chevrolet wanted to do their own 3-speed automatics, but that was not to be.

The HydraMatic products changed in most every year of production. The "dual coupling" Jetaway 315 was used many years in the 1950s and the later Roto-HydraMatic (aka "Slim Jim") was used in the earlier 1960s. Some people have complained that with Chrysler products in the middle 1950s and so, you needed the vehicle build date or VIN to get parts, but these HydraMatics were the same if not worse--some GM divisional HydraMatics had mid-year changes and others did not, for example, so they might have looked the same on the outside, but the internals were different.

Some of Pontiac's HydraMatics were called "Strato-Flight" in the sales literature, but I think that the normal Olds HydraMatics used the HydraMatic name in general (with many Olds V-8s being in drag racing, backed by a B&M-modified HydraMatic). Each GM division had their own unique names and such for these things, which reflected their divisional heritage and orientation.

I think the last of the divisional automatics to survive was the Chevy PowerGlide, which was later used until the inline Chevy 6-cylinder and PowerGlide powertrain combinations vanished. A less expensive version, with a clutch (as many super duty drag racers had done with Chrysler Torqueflites) was known as "TorqueDrive" and used in the base model 6-cylinder Chevy Novas (late 1960s). After that time, the more recent range of TurboHydraMatic transmissions replaced all of the earlier GM carline transmissions with "THM" variants.

Chevrolet, being the "high value" division of GM, seemed to always be trying to prove their customers with features that might have been only available in more expensive cars (and possibly "scooping" Ford in the process!). PowerGlide came out in the early 1950s and was upgraded and modernized many times before the aluminum case (and higher power tolerant) versions of 1962 (when it seemed that all other manufacturers went to aluminum case automatics). All the way from a 6 cylinder to a high power 427 Corvette in one transmission took some doing (if they wanted to go faster, there were always 4-speed manuals, which fit the "performance" image plus the "value" image too).

In the first versions of PowerGlide, "D" meant "high gear only" and did not start in "low" gear and then upshift into "high" gear. Possibly trying to mimic DynaFlow in feel?

Not to be upstaged, Chevrolet had their TurboGlide in 1958. I normally associate that with "DynaFlow" (as a role model), but it could well have been spured on by the Triple Turbine Flight Pitch DynaFlow. As with many things "new and improved", there were problems and the TurboGlide was not well accepted AND not pushed when it was found to possibly hurt Chevrolet sales. The later "sales" claim to fame of the TurboGlide was the "Grade Retard" feature (mentioned as something that heavy duty truck automatics had to help with controlling speed in hilly driving, downhill), in the same quadrant location as "L" would have been, but noted to NOT be a "Low" gear as it was in the PowerGlide. You might say it's mission statement could have been "Buick smoothness at a Chevrolet price". I had an uncle that had a 1961 Impala 4-door Sport Sedan with a TurboGlide in it. It was smooth and all of that. By that time frame, much of the earlier problems had been taken care of and it was generally as reliable as a PoweGlide. TurboGlide became a "low production" option that might be somewhat rare today on those cars.

One used car dealer I know stated that (in the later 1950s), he'd buy rental fleet Chevys with broken TurboGlides and put PowerGlides in them and then put them on his used car lot. PowerGlide was a significant selling point for Chevrolets back then, but the early TurboGlides were just the opposite.

Some of the things that happened "back then", which might seem a little strange in more modern times, have to be considered in the orientations that were in place and operative in those earlier times. NOT try to position them against things which have been more recent, which can lead to some incorrect situations. By observation, once one incorrect piece of data is configured (intentionally or not), it gets into "publication" and is then repeated many times by those that might not be cognizant that it is incorrect. The more it's "referenced", the more it's accepted as fact.

A specific instance of that was when I was researching "POA Eliminator Valve" a few years ago. One Camaro parts vendor had a picture of the "eliminator valve contraption", with pressure switches hanging off of a somewhat crude brass "pipe", and called it a "POA Valve" rather than the contraption that could replace the POA Valve and convert the system to a cycling compressor system from the earlier "continuously running compressor, freon gas throttled" system. Such things make me look for another vendor that better know what they were selling.

It might be possible to translate the earlier "THM" designations into the current GM Powertrain designations (where a THM400 becomes a 3L80, and a THM700 becomes a 4L60,for example), but to add the "THM" designation to a Buick-built 2-speed automatic (variable or fixed stator) is not (in my way of thinking) correct.

So, I'll concede that I was incorrect to associate the "Super Turbine" nommenclature to be exclusively for variable stator angle torque converters rather than to also encompass other years of Buick automatic transmissions (of the same transmission family) that did not have the variable angle stator. I did find some noted transmission websites and articles that had the variable angle stator used in Buicks of model years '64-'67 and '65-'67. When something new comes out (i.e., the THM400), we somewhat expect it to be "full bore" rather than otherwise, which makes the variable stator not being in there seem incorrect, but as they also apparently used the "D-L" quadrant only in Buicks, possibly somewhat shielding the new transmission from DynaFlow loyalists (who might NOT want a Buick without a DynaFlow in it), that would increase the possibility that the '64 model year Buick-use THM400 would have had a fixed stator torque converter. As with some other things, it's those pesky side issues that can make or break things.

In my research, I also found a THM400 valve body that used different kickdown valves. With the "single stage" valve, the transmission would not downshift into "1" at WOT unless the vehicle speed was below 20mph, at WOT. The "two stage" valve would allow a WOT downshift to "1" or "L" as long as the vehicle speed was below the WOT 1-2 upshift speed. Both of the valves would interchange, but probably had something to do with vehicle application (i.e., car or light truck) and model year than anything else. Another example of something being "the same, but different".

Enjoy!

NTX5467

[Philippe Racicot]

Another reason why Buick had variable pitch converters in it's Dynaflow from 1955 to 1963 and reintroduced it the 1965 400 transmission after a one year abscence was the nailhead engine. To compensate for the small valves, a hotter-than-usual cam was used in these engines and the switch pitch transmission had less drag in high stall while the engine was idling. The transmission switched to low stall when you touched the gas pedal before the carb linkage even moved.

The situation where the switch pitch feature is the most noticeable is when te engine is cold and the fast idle is still engaged while you're driving the car. When you release the accelerator pedal the engine revs faster because of the swith to high stall and when you're not used to it, it can lead you to think there is something wrong in the transmission. I know someone who thought that his '65 LeSabre's 300 transmission was slipping when cold while it was just variable pitch torque converter that gave him this impression as there is a small delay when getting in low-stall mode.

The high-stall mode was also activated by another switch when you floored the accelerator to improve the performance.

I don't know why the 300 transmission had the switch pitch feature in 1964 (since it was exclusively used that year with the newer generation of small engines which didn't need a higher stall at idle like the nailhead did) but I'm thinking that the Buick division was probably more involved in the development of the 300 transmission than it was with the 400.

[55PackardGuy]

I'm learnin interesting new things about my old '65 Electra that I never knew while I had it, including the fact that it had a "switch-pitch" transmission and a somewhat radical cam. The cam makes sense now, because I agonized over trying to get that car to idle as smoothly as some other V8s I had known. I always thought that initial timing advance was the trouble, but now I'm pretty sure it just had a slight rumpty-rump from the cam. Thanks for the insights!. <img src="http://forums.aaca.org/images/graemlins/smile.gif" alt="" />

[Guest norb]

How many of you remember that the 67 300 transmission had an extra attachment on the valve body to operature the cruise control with hydraulic pressure from the trans.? A plate covered the space if the cruise was not ordered. A bodies only. Two complicated & too expensive so it was gone next year. I worked on it in 66 but never had a car with it.

[Philippe Racicot]

Guy, I was told that the 65 401 had a milder cam than it had in the early sixties (but still not so mild). I know that many complained about the rough idle of the 401 (even the 65-66 models) but those I have driven idled very smoothly. Strangely, the 401 in my Wildcat has an even less noticeable idle than my 430 and 455 engines, the fact that it doesn't have A/C and that the idle speed is set a bit higher than specs probably helps it too.

I really like the feel of this 401! Nailheads are by far my favourite engines.

Norb, about the Auto Cruise Control, I think it was available in 1966 too. If I remember correctly, there was a special service manual for 1966 cars with Auto Cruise Control. Some 66-67 LeSabres with the 300 transmission also had the Auto Cruise Control while the LeSabre 400 could have been ordered with the Electro-Cruise like the other 66-67 full-size and pre-1966 Buicks. I have never seen a pre-68 LeSabre with the cruise control, it must have been a rare option on this model.

[NTX5467]

An interesting situation you mention, there, regarding the cold start/fast idle issue! I can see how that might happen, too.

In the Petersen Publishing Company's book on the 1965 cars, it notes in the section on the 1965 Skylark GranSport (with the 401 V-8 and ST300), that it has a wilder-than-normal cam in it, but that in conjunction with the smaller intake valves of the Nailhead, that it makes for a huge mid-range torque curve so that passing gear maneuvers (remember those???) and higher speed cruising were enhanced. I remember thinking that it was a pretty wild stock cam, compared to other engines of that era.

In those earlier times, cylinder head port flow was not fully understood, unlike the 1980s when flow benches became more accessible for many high performance engine builders and "flow quality" became a concern. What looked like it might flow like gangbusters really didn't--key example was the Pontiac RamAir IV round port head, which looked fantastic, but actually flowed no better than a stock port head did (when it was finally flow checked many years after it was produced).

In the case of the Pontiac 389/421s, the intake ports "stalled" at about .425" lift. Therefore, higher intake valve lift did not produce any more power, so they went to longer duration camshafts to counter that, but with about .430" lift. If we might use the small block Chevy V-8 as a general guide of an engine that has decent cylinder head ports and then look at the cam profiles that make it "work", when you see another engine with similar valve sizes and "different" valve timing specs, you can pretty well figure that something is amiss in either the port flow characteristics/sizing, the valve sizes, or combinations thereof.

Intake valve shrouding (by the edge of the combustion chamber) was a known issue, though, which is allegedly why the Ford Y-blocks did not breathe as well as the similar small block Chevy V-8s did (in spite of their generously-sized intake ports). In the small block Chevy V-8 cylinder heads that used 2.02" intake valves, from the factory, it's the same head casting as for the 1.72" intake and 1.94" intake valve, just with the valve seats cut for the 2.02" intakes . . . PLUS a radius cut on the side of the combustion chamber to better clear the larger intake valve and not shroud it.

Along about 1985, Ford used a small block cylinder head that deliberately shrouded the intake valve, with the "intent" induce more "swirl" into the mixture as it entered the combustion chamber. When I saw that, I wondered if THAT was what the Ford Y-block engineers were trying to do in that earlier time, but didn't know they were doing it? But for the next model year, the Ford small block had a different casting cylinder head on it.

In some cases, ports are deliberately undersized to get a greater port velocity at lower rpms at the expense of ultimate higher rpm power (5000+rpm, typically), which might have been one factor in the Nailhead engine design. Just like too big of a port results in poor lower rpm performance, similar to a camshaft with a too long duration for good torque output at lower rpms. So if an engine designer figures that lower to mid-range rpm torque is of more general importance to the vehicle's customers than 5000+rpm power, they can play to that audience in the port sizing/design/valve size of an engine. When you saw that a supercharger or turbocharger made huge power increases in many engines of that earlier era, you knew it was really pushing the air through the ports and past the intake valves to better compensate for the smaller port sizings, as was generally noted to be what happened with the Ford Y-block 312 V-8s in NASCAR competition, circa 1957, as it took the supercharger to even out things with the naturally-aspirated power of the Chevy fuel injected 283s.

I have some dyno charts of 1972 Chevrolet engines, which I found in a 1972 Chevy light truck order guide. In many years, Chevrolet put 1.72" intake valves in their light truck engines rather than the 1.94" intake valves that went in the car engines with the same size and camshaft. The smaller intake valves were allegedly used on the truck applications for better low rpm torque characteristics (aka "pulling power"), with some having governors to limit higher rpms anyway. Yet the dyno charts show that there's not a whole lot of difference in the ultimate power of two comparable motors with different intake valve sizes (in a 350cid V-8)--not quite as much as you might expect. In 1965, there was a 250 horsepower 327 4bbl and a 300 horsepower 327 4bbl, with one of the main differences being the 250 horsepower engine used the smaller 1.72" intake valves (probably with a smaller cfm carburetor too, but with the same dual exhaust system). Yet the 1972 "net" horsepower dyno charts didn't show that much difference, probably about 15 horsepower for similar 350 2bbl V-8s.

There are many very interesting interactions with the specs of the various manufacturers' engines of the 1950s-1970s. If you know what you're looking at in the specs, you can draw some interesting conclusions about various aspects of the engine's design (and how some design areas were compensated for with particular spec camshafts).

Enjoy!

NTX5467

[55PackardGuy]

"passing gear maneuvers (remember those???)" <img src="http://forums.aaca.org/images/graemlins/grin.gif" alt="" />

NTX,

Your points make me think of shade-tree engine "builders" and how they need to do their homework. Like the 327/327 Chevy SB having larger intake valves AND higher CFM carb. How many fellas you suppose tried to duplicate an HO Chevy by just installing the bigger carb? And all the exhaust work in the world won't help if there's a "restriction" on the intake valve side.

Seat-of-the-pants observation on the 401 "nailhead"--indeed top end was limited, and now that mystery is solved with the intake valve design information. Great torque off the line, but I could always feel when I hit that "flat spot" at stoplight jamborees, toward the end of the first block down the street before the first shift.

On the "Y" block I only have personal experience with the 292 in my boat, with dual side-draft carbs. It works fine, but who knows how it would perform in a car? I have to think the Ford engineers DID know why they were shrouding the intake valves--higher air/fuel mixture velocity in the cylinder. Interesting, though, that flow testing was still such an arcane business in those days, even at the factory.

Wasn't NASCAR a great place when they could add a supercharger to a stock engine (presumably after "homologation") to "even things out?" Nothing like that would happen today. <img src="http://forums.aaca.org/images/graemlins/frown.gif" alt="" />