Technical Thoughts on '57 Chevy Tranny Options?

Who told you that?

 

Which part? The 2.75 planetary set is used on '79 Caddy Seville, The GMC motorhomes with Toronado drivetrain, some Pontiac performance models......

 

You say mostly street driven..What is the other usage part then?

Never heard of Street Freak Show or whatever.. Anybody with a converter welder and a Sonnax account can build a street and strip 245 mm converter. I'd look for someone fairly local. Don't know where Good Ole is..Sorry

 

All 2.48

 

It would help a bit if you would post complete sentences. Do you mean ALL TH400 are 2.48 1st gear?
If that is what you are contending, you are mistaken. 2.48 is, by far the most common 1st gear ratio, but certainly not the only that was supplied. The 2.75 is listed in the specifications of the models I mentioned and probably a few others.I have seen the specs a few times over the past several years....look it up if you doubt it.

 

I have been looking it up...and looking AT them for 50 years. None of the cars mentioned , or any other ones, came with a 2.75 low gear.
All 2.48 (Like that sentence?)
Aftermarket only (How about that one?)

 

Factory installed standard equipment (how about this one?)'

I have long been aware the planetary set in question is/was available in the so-called aftermarket but it is not at all uncommon for suppliers to re-market OEM performance parts.

 

Well that is the first I have ever heard about .Thank you

 

Thanks for the tip!

Luckily, I've had this one for years, and it is p***enger

 

Well, my friends..Here's a perfect example of what not to believe on the internet:
1979 Cadillac Sevilles came with the 350 Olds V-8 EFI or diesel and the Turbo 200 transmission, not a T400
Note the ratios comparison:

The gearing for the 200(C) is:

• First - 2.74:1
• Second - 1.57:1
• Third - 1.00:1
• Reverse - 2.07:1

Next case, please...

 

Lots of snitzelforking going on. I must say, don't you think a race car should have a race car transmission? And, no one has mentioned if you rev up a 400 in neutral, as many do the check stuff out, it will blow the front pump out. Street driven G***er is an oxy*****. If it is built to haul the mail, it will be a bit over the line to be street. My choice for a race only automatic would be a 'purpose built' Power Glide by a reputable shop. For a stick, depends on the rules. My grandma used to tell me you can't have your cake and eat it too. If it's not full race and ready to rip, why not rebuild it as a cruiser and enjoy it on the road. Some of what I say may irritate you, some may make better sense in the fullness of time. And, then again it may not. Have fun, no matter what. And, I was going to say, Life's a gas. Hmm.

 

I agree with some of what you say here (not the PG) but there's a very good reason nobody mentioned the above ;-)

 

I prefer the T-400. A built T-350 will work and it takes less torque to turn it but a basic T-400 will hold up better.

 

I direct your attention to the heading at the top of the page and then about halfway down the Cadillac list to 'Seville'...and this is not even taking into consideration the TH425 derivative used in the GMC front drive motor homes that also had the 2.75 1st gear.

as I see it, you have made two mistakes here.....1) ***uming you are ALWAYS correct.......and 2) see number 1)

Your move............

 

Sorry your cut and paste proves nothing..Most likely those are axle codes. Are you still trying to prove the 79 Seville had a T400? Look below at some somewhat conflicting facts:
Big car, 425, 368 etc., 2.48 1st = T400
Seville , 350 Olds, 2.74 1st = T200

Or are we still going with the 2.75 factory, or a 2.74.. I'm confused on what you think it is today.


https://www.100megsfree4.com/cadillac/cad1970/cad79d.htm
https://www.100megsfree4.com/cadillac/cad1970/cad79s.htm

The T425 FWD trans used some 400 parts, but had reversed planetary gears , but ALL still used the 400 2.48 first gear ratio.
EDIT...You couldn't use a 2.74 or 2.75 MH planetary, even if there was such a thing.They are reverse direction /thrust and would probably sing a nice song..before they blew apart.
Wiki makes some mistakes, but pretty much accurate here, ...from my hands on experience.
https://en.wikipedia.org/wiki/Turbo-Hydramatic#Super_Turbine_400_/_THM400_/_THM375_/_3L80_/_3L80HD
As I see it, you have made two mistakes here.....1) You're getting your info from the internet or the tastee freeze cruise night.......and 2) You've never actually worked on this stuff.

 

You are correct about one thing, the internet is often wrong...and I did notice the 2.74 vs 2.75 gear ratio given in the first "cut and paste" posted, but I often see gear ratios off a 2nd place decimal for the same component, depending on the editing of the publication. And, how is it that your 'cut and paste' is any more valid than mine?

Until I can prove myself wrong, and believe it or not, I WANT to know the accurate facts of anything I deal with, I will be doing more research as time permits. But I didn't happen into this notion out of thin air or at the Tastee Freeze, thank you very much. I first stumbled onto the info when an acquaintance was s****ping his old '79 Seville and I got the rear axle and front brakes from it, missed out on getting the trans. However, the very tall rear axle (2.24) caught my attention and looking further, I found information that indicated the trans was a TH400 with a 2.75 1st gear.

The trans codes in my prior post, that you so mockingly say are 'probably axle codes' are clearly trans codes, both because that is the point of the list and, in addition, in some cases the axle ratios given are the same but the trans codes are different, suggesting the trans is 'tuned' in some way for the specific application. I included a cover shot of the book to support the validity of the data as it is highly regarded as a source of exclusively TH400 information, not T200 or T350. When I have found a another (unimpeachable) source for data, whether I am right or wrong, I will post the results.

Lastly, my at***ude in these posts is a reflection of the tone of your initial responses which reeked with 'snark'...I give as good as I get. You don't like it, fine by me. But try being a little less ****y and see if that that yields better results from people, as I doubt I am the only recipient of your hubris. Perhaps being a 'Promoter'...where hyperbole and BS reign supreme....is the underlying issue, but I would guess that to be a 'chicken or egg' proposition.

Ray

 

Okay, Ray
Let's back up here. I don't know it all..far from it, but when I see what I perceive as disinfo on the 'net, I do my best to correct it. If you google T400 , 2.75 low, you'll see several other guys who work on these things, that say the same thing as I do. As for myself, I don't post anything that I don't have first hand knowledge of. Not what somebody told me, or what I read on the 'net, or heard down on the corner.
For instance, in your earlier post, you mentioned high performance Pontiacs.
I'm here to tell you, I've owned over 80 Pontiacs..every conceivable one that came with a T400, and worked on all of them. I've never seen or heard of a 2.75 low Pontiac, in all my dealings. Not first hand , or within the circle of Pontiac enthusiasts that I know. I've never seen a trans code in a factory shop manual for a 2.75 low trans either. As you know , the trans code could change with just one more friction in the direct drum. Certainly a 2.75 would be denoted as such.
Safe to say , that one is out.
Also you mentioned the FWD R/V trans. I've shown you why that would not work already.
This all makes me think you're getting this stuff elsewhere, rather than through firsthand experience. Hence, the reason for my initial question to you.
Anyway , this should be easy enough to settle. You have the Ron Sessions book? Show us what he says about gear ratios. Or, as an alternative, show us a page from a factory shop manual, with the code denoting a 2.75 low ratio and it's application.
Good luck , Ray

 

Ray, et al,
I thought might interrupt anyone still searching and save you guys some time and effort.
Outside of Jim Forbes, who's very busy right now, I didn't figure you'd believe anyone here, least of all, me, so I decided to go right to the source in Ypsilanti :

The three popular GM 3 speed automatics are the THM 400 , 350 THM , and the THM 200 . Both the latter's also came with converter clutches , 350-C and 200-C . The 1st gear ratios were kept the same for each of the transmissions through out their production runs THM 400 was a 2.48 , 350 THM was 2.52 , and the THM 200 was 2.74 . From GM there was not any other ratios put in production . There are plenty of aftermarket companies that made other ratios , both higher and lower for all three of these transmissions . These were never used by GM . Hope that helps .

Russ Abrams Sr. Staff Engineer , Hydramatic Div. GM

 

If you're going to miss that 4 speed, consider a manual valve body with a trans brake on that TH400. I expect you would not miss the old muncie that much. Even if you don't race, trans brakes are fun and the manual valve body you still get to shift. It's a $500.00 upgrade for a decent trans-brake manual valve body. Of course you need a bad *** shifter to bang on, i prefer the Hurst quarter stick.

 

You mean like this one?

I've been stashing parts in prep for this changeover for years

 

That's what SHE said.....

 

Mark Yac,

Difficult to refute that testimony...........Guess I have to concede I mis-interpreted information....or put more succinctly, I wuz wrong!

I do appreciate your approach in the two most recent communications......."sugar makes the medicine easier to swallow".

Regards,
Ray

 

TH350 output shaft is the same size as a PG and Muncie, the slip yoke is 1.50" diameter, the TH400 is 1.885". I looked this up when I was putting my car together.
https://www.qa1.net/driveshafts/how-to-order-a-custom-driveshaft/whats-my-transmission-and-slip-yoke

 

Yes, and the driveshaft length should work also with a T 350, but he's got a 400 and has to use it, doncha know.

 

Contact Alan Pope Racing .com for one the best convertors and one of the nicest guys who will give you the best service out there. He is in Florida and has built my convertors for years.

 

No problem, Ray
I forgot to mention about the BS thing earlier.
Yes, you are correct. I've heard it all. Several hundred times.
When my business partner and I were doing the drags promotions, we'd go to I don't know how many shows and cruise nights to hand out flyers.
Yes, we'd hear the hundred dollar bill on the dashboard thing,...The lady with the Corvette sign in the back window, the guy who got kicked out of the local track for going too fast, etc. , etc.
My personal favorite was the guy who walks up to my 56 Pontiac 2dr ht Catalina, blue and white, and says he had one just like it ,except it was a 4 dr, and oh yeah, it was dark green, and oh yeah, it was a Buick!
It got so boring that we'd park our cars, put flyers on them, and then proceed into the Mexican restaurant for a Margarita, or two , or four. We'd flip a coin to see who had to go out and re-stock the flyers. ( I made that part up..Had to come clean with the BS)
Anyway, keep up the good fight.

 

Holy smokes....that was a good duel and well worth reading. I am now fully edumacated on t400 1st gear ratios

 

Turboglide, T-56 O/D, 4L-60, TH700r4, TH200, TH250, TH350, TH400, POWERGLIDE

 

I maybe would like to say something here that is going to shake everyones world to the core. @Wildman1 said that he has 2 cores one a T350 and the other a T400. While the powerslip info and the T200 and all the other info is nice what he has to work with is the T350 or the T400.

Someone mentioned that a manual valve body will make him feel like he is driving a 4 gear. Actually close but no cigar and in his original post he mentioned that he is not interested in shifting any more. In the T400 that is race prepped and gets street driven regularly we are using an old auto-stick valve body out of a Firebird. Now some of the experts were not around back then but one selling point on the Firebird was that you could drive it like an automatic or shift it like a stick.

I mentioned the valve body for a reason and it has nothing to do with bragging about my ****** I could but that is not the point is it. The auto stick makes for a car that can be driven in lazy man mode or hot rod mode. Now I realize that sourcing one from a Pontiac would be difficult today (not so much when this transmission was built) but they actually sell aftermarket versions of the valve body, they run about the same price as a manual valve body and from what I have read they are an improvement over the original Poncho version (although I am not sure how???).

Someone mentioned revving one in neutral knocking the front pump out. I guess I would need to see some do***ented proof of this. I have only been racing and driving the T400 since the early '70s so not as long as the experts but I have never ever knocked the pump out of one. Maybe I am revving them wrong.

 

Thanks P&B - how have you been?

Same here my friend - looking for tips on making this changeover work as best that I can.

Went & pulled the old TH400 out in the barn today - it's a damn truck ******! Luckily I called a buddy & now have a good p*** TH400 core for the re-build. Thanks to all that warned about a truck trans - I've ad this one in the barn for nearly 20 years, and never checked it (was told it came out of a Camaro - yeah, right!)

On the reverse vale body issue - with the shifter shown above, will I need one or not?