Stock Torque Converters, 3 Speed Gears and more - Transmission Forum

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Stock Torque Converters, 3 Speed Gears and more
Friday, June 02, 2006 3:42 PM
Many on here want to put down the auto transmission in the Js as useless for racing. Nothing could be further from the truth. The Autos that came in the Js were designed more for fuel economy, than performance, especially the 3 speed. With the right combination of gearing and the proper torque converter, some unbelievable(to the uninformed) gains can be made.

If you've ever read through a Crane Cams catalog, you should have read how important the correct gearing is to matching the power band of the cam(and motor) is to performance. If you look into their catalog they show you hoe to determine the correct gearing for the cam you are using, if it's a Crane Cam. Talk to your cam manufacturer or engine builder for the best gearing for you car.

Yank Converters also has a Converter Selector, that can aid you in the selection of a torque converter that matches you motor. For best results though, talk to your high performance/race torque converter builder.

The following charts come from the DACCO Transmission Parts Torque Converter Catalog. These charts are good for someone looking for the gear ratios in their own car or what car has a particular gear ratio that someone may be looking for. Although these charts don't show what car they came in, if you find a car of a particular year and what motor it has and/or the transmission ID Code, you can see what gearing it has.

For example: My car (a '96) has code AKC(on the metal tag on drivers side, located under the brake master cylinder). Under that number is a stamped set of numbers, 96_6046. The first two numbers are the year, the next are the serial number. in the serial number, the third digit is the prefix number(if my memory serves correctly, someone correct me if I'm wrong), so my code would be 4AKC. Then look under the '92-up section for the 2.2L motor and code 4AKC. There you'll find I had converter code FZCB, with a stall of 2375rpm, 2.84 final drive and sprockets 33-37. These will be explained later.

You can also look up you RPOs(under the spare tire cover in the trunk, if you still have it) and look them up on some of the may RPO Decoders that can be found on many sites.

Final Drives, Sprockets and Effective ratios:

If you look at the charts, you'll see that the 3speed TH125C/3T40 transmission came with three different Final Drives(Differentials), they are: 2.84:1, 3.06:1 and 3.33:1. When Combined with the four different Drive Chain Sprockets (38-32, 37-33,35-35,33-37, fist number is the drive sprocket tooth count, second the driven sprocket tooth count), you have a wide range of Effective Drive gear ratios. These range from a measly 2.39:1(High geared, good fuel economy, better have a ton of torque) all the way up to a 3.73:1(Low geared, great acceleration, high cruse rpms/poorer gas mileage). To determine your effective ratio, take the driven sprocket tooth count and divide it by the drive sprocket tooth count. take that number and multiply it with the gear ratio. This will give you the effective ratio.

Example: Using my transmission information in the above example, divide the driven number by the drive number:37(driven)/33(drive)=1.1212121 for the multiplication factor. Now multiply that by the gear ratio, 2.84*1.1212121=3.1842423 or 3.18:1 effective drive ratio.

I know there are multiple Final drives for the 4T40E, but sorry, I don't have that information. For those who do, please fell free to add to this thread.

Torque Converter Codes:

These codes apply to the torque converters(TC) used in the 3 speed automatic(TH125C/3T40) and the 4 speed automatic(4T40E), as well as other transmissions not used in the J-Bodies. (Remember these are STOCK torque converters!) These trannies used a 245mm TC. These TCs used a four digit code of numbers and/or letters to identify them, such as my example listed above of FZCB. The definitions for these codes can be found on the last image, below. The first digit is for the trans type, in the case of the J-Bodies they all used code F, for FWD 125C(not listed, but the 4T40E uses the same). The second digit is for the stall speed. In my case it was the letter Z, for a 2375 rpm stall. The third digit is for the torque converter clutch(TCC) style. Mine was C, for Carbon Filled. The third digit, which is common for all stock J-Bodies is for the bolt circle. Ours being B, for 237mm bolt circle for the 125C(and 4T40E).

Most, but not all, of the 3rd Gen J's came with with 2375 rpm stall TC. In my experience, the 2560 rpm stall TC would be a good choice for a stock to very mildly modded (bolt-ons only) J, but not worth the time and/or money to just change it out. If you got to have the transmission or engine out for any reason, then it would be a good time to install it. If you've done more than the basic bolt-ons, then you should use one of the 2760/2795 rpm stall TCs or an after market performance TC. When you have a TCC type that has a number and pound sign never use a lower number. This is the clutch pressure and if you use a lower pressure slippage will result. My recommendation is to stick with the Carbon Filled and Woven Graphite TCCs, which are what come stock in the 4T40Es.

Now for the reason for this post:
Click on the image for larger view.









A few additional notes:

When changing the final drives, don't worry about getting the speedometer re-calibrated. The VSS signal is picked up from the FD's outer housing and all housings use the same gear tooth count to signal the VSS. You should only need to recalibrate if you change tire diameter.

The TCs listed above are only stock replacements, they will not have the tight tolerances as a true performance TC, don't expect to run a serious amount of boost or nitrous with these, but lower power levels, they should be fine.

While you have the transmission out, you might want to consider a rebuild, especially if you have a lot of miles (100K+) on the it and/or if you drive really hard. If you do drive hard on the TH125C/3T40, look into the Alto-Red Eagle rebuild kits. They make about the best frictions and steels, used in racing this transmission. The Master Kit is a complete rebuild kit(click on the Hi-Performance catalog, under the catalog button).

There are three Shift kits, that I know of, for the TH125C/3T40. The Superior Shift Correction Package, which is more like it's name implies, a shift correction. I would consider this more of a Stage I type kit. There is also the TransGo Shift kit, which, from what I understand, has three levels to chose from. Finally there is the J-Body Performance Shift Kit, which I hear is the same as the TransGo kit, just costs more.

For the 4T40E, there are two electronic shift modifiers, The AutoTrans Interceptor, who are out of business and the B&M ShiftPlus Electronic Shift Improver. I don't have any experience with them, so I'm just going by what I've heard about them. The AutoTrans Interceptor had, I believe, 10 settings of firmness. It had a lot of good reports. The B&M ShiftPlus, reportedly can cause problems if used all the time, so save it for the track.

I hope this helps those with some questions about the automatic transmissions. Good Luck!






Re: Stock Torque Converters, 3 Speed Gears and more
Friday, June 02, 2006 3:59 PM
nice write up man


good stuff





RIP JESSE GERARD.....Youll always be in my thoughts and prayers...



Re: Stock Torque Converters, 3 Speed Gears and more
Friday, June 02, 2006 4:38 PM
I SAY STICKY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!



Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, June 06, 2006 7:17 AM
I second the STICKY! All the info I was just looking for in one spot...talk about good timing.



Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, June 06, 2006 7:20 AM
Wish I could edit that post...only question I really have is, how do we figure out which convertor to use and what will actually fit?



Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, June 06, 2006 7:56 AM
The best way to figure out which TC to use is to get dynoed.

What trans code do you have? That will tell me what TC and gearing you have.

Too low of a stall speed and you will bog on acceleration, too high and you miss the torque peak of the motor, which is what gets you off the line. GM typically will put a slightly low stall in a car for more fuel efficency, so stepping up one stall speed will help performance.

With the mods you have listed in you profile and what you've got in you rfuture mods, your right between a 2560 stall and a 2760/2795 stall. I would say when you do the P&P, do a 1.6:1 roller rocker conversion, you'll be getting into the range of the 2760/2795 stall converter. I wouldn't go any higher than this, which would be an aftermarket tc anyways. Remember though, this is more of an educated guess.

Page 54, lists a 2, 3, 4PXC trans code, there you'll see a TC code FACB, which has a 2795 stall and the carbon filled damper(TC Clutch).

As for gearing, I think you'd be good as long as your effective ratio is between 3.18:1(for more fuel efficency) and 3.43:1(for performance). 3.43:1 is pushing the limit for the stock cam, so a 3.33:1 would be a good compromise.





Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, June 06, 2006 11:58 PM
Cars with a lot of mods like cams and heads often bog or hestitate on the stock TC which I believe you had problems with that right Madjack?

You would be suprised how many people roll around in 4000 stalls.


--------------
Yea, ummmm. I used to have a J-body...
Re: Stock Torque Converters, 3 Speed Gears and more
Wednesday, June 07, 2006 6:24 AM
Yep! I had the 2560 stall, but that was nowhere near what I needed, for what I've done to this motor. I tried to be conservitive and ended up being too low.





Re: Stock Torque Converters, 3 Speed Gears and more
Monday, June 12, 2006 5:57 PM
I got a PM the other day from a JBO member who has a 2nd Gen J. It made me look up the info on the TH125C transmissions behind the 60* V6s. Many of the trannies came with a 2.84:1 effective drive(only one came with a 3.18:1 effective drive) and a 2060rpm stall (one had a 1630 rpm stall) TC. Any of these motors that are moderatly modded would do good to have atleast a 3.18:1 (2.84:1 FD & 33Tooth drive, 37T driven sprockets) effective drive and about a 2560 stall TC. You would definitely notice a good gain, converting over to this set up, especially if you do a good rebuild with the Alto-Red Eagle master kit and a shift kit!

Remember, these transmissions came in all three generations of Js and they could all use some mods like these for better performance.





Re: Stock Torque Converters, 3 Speed Gears and more
Monday, June 12, 2006 11:28 PM
I am actually thinking about getting another J body. Yes, an automatic.


--------------
Yea, ummmm. I used to have a J-body...
Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, June 20, 2006 3:00 PM
For those who may not have seen it, heres a link to Event's post about his transmission.






Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, July 09, 2006 6:01 PM
Ok... I have an extra 125 in the garage from my wifes now retired sunbird. If I were to rebuild it, how hard would it be to change out the chain and gears in the diff? I have rebuilt a few RWD trannys but never tried the FWD. Its a toss up right now between a rebuild, lower gears and higher stall... or swap to a stick. If I decide to go with a rebuild.. will my local trans parts house have the diff gears and chain... or will I have to go searching online???


I plan on living forever... so far so good
Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, July 09, 2006 6:42 PM
Get Hayne's GM Transmission Repair Manual (got mine from Pep Boy's). It has a full step-by-step teardown. If you can do a RWD, you can do it. The Chain drive is mounted between the Valve Body and the Pump. The Diff is in the deepest part of the tranny, so a full disassembly is required.

Use the charts above to find the ratio you want and find a (sub)compact GM or Isuzu with the TH125C and get the differential from that. It will probably be cheapest to just get the whole thing and pull the diff yourself. Depending upon what chain you have, you could reuse it or use the on from the parts tranny. The chain is the same part irrregardless of the drive/driven gear, but you should be able to get the gears from any parts/tranny shop that carries/uses TranStar Industries parts.

While its tore down, you might as well do a full rebuild, using the Alto-Red Eagle Master Kit, for a damn near bullit proof tranny. I haven't checked in a while, but see if the Team Green Racing LSD is ready for the TH125, if not you can look into the Phantom Grip 904-Green LSD(the gold spings aren't quite stiff enough, but does help some). You will need to get one of the blocks machined for the retainer clip and assmble the diff with the axle shaft in it, then assemble the tranny around the shaft to get it back together. Sounds like a PITA, it is, but it will help the traction of that extra drive torque. You'll be less likely to spin on a hard launch.





Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, May 27, 2007 2:52 PM
(A shamless bump, to keep this thread for dying and) Just an update on my tranny. The generic heavy duty rebuild kit is holding up fine, the Yank converter is working great, but I do need more gear. Looks like its time for the 3.33:1 differential. Time to start scowering the Junk Yards. My cruse rpm at 60 mph will be 3000 rpm, but I can live with that ( just imagine crusing at 75mph!).





Re: Stock Torque Converters, 3 Speed Gears and more
Friday, December 14, 2007 7:40 PM
not so shameless, good info. i assumed my 3.1 Z24 auto had the 3.18 FDR. at 65 mph i turn about 2600 rpm. i'm currently do a 4T65E swap in my j-body and will have the 3.69 LSD in it. i thought i was going to gain ~16% acceleration, but if i have the 2.83 in the 125, then i'll have a gain of ~30%!! with the mods i have in the 3.1, that effectively equates into ~50HP and 60FT/LBS gain. sound right?


He who dies with the most toys wins!
Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, December 16, 2007 9:45 AM
Jack, any chance you could re-host those images? Or send them my way?




fortune cookie say: better a delay than a disaster
Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, December 16, 2007 10:02 AM
Also, according to this site, neither the Superior or TransGo kits are "performance-type"...why?




fortune cookie say: better a delay than a disaster
Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, December 16, 2007 2:41 PM
SO IS THE PHANTOM GRIP WORTH GETING ? I WAS TOLD THAT THEY WHERE NOT WORTH IT
I AM LOOKING TO MAKE A TWO TIRE FIRE AT THE TRACK WILL THAT DO IT OR ?
I KNOW THAT e.p limited slip would be better but i dont have the cash for that so i wanted a limited slip of some sort so would a phantom grip be good for me ??
Re: Stock Torque Converters, 3 Speed Gears and more
Thursday, December 20, 2007 6:51 AM
Interesting...

jean-louis manuel wrote:

SO IS THE PHANTOM GRIP WORTH GETING ? I WAS TOLD THAT THEY WHERE NOT WORTH IT
I AM LOOKING TO MAKE A TWO TIRE FIRE AT THE TRACK WILL THAT DO IT OR ?
I KNOW THAT e.p limited slip would be better but i dont have the cash for that so i wanted a limited slip of some sort so would a phantom grip be good for me ??
The Team Green LSD should be available sometime after I figure out how to get my driver's side axle out of the tranny...5-foot pry bar didn't work




fortune cookie say: better a delay than a disaster
Re: Stock Torque Converters, 3 Speed Gears and more
Thursday, December 20, 2007 9:56 AM
so the team green would be a better one that phantom grip then ?
Re: Stock Torque Converters, 3 Speed Gears and more
Thursday, December 20, 2007 9:30 PM
or EP. don't short cut with something that's 1/2 the cost. you'll be happier in the long run.


He who dies with the most toys wins!

Re: Stock Torque Converters, 3 Speed Gears and more
Saturday, December 22, 2007 11:10 AM
yeah i guess you are right ?
Re: Stock Torque Converters, 3 Speed Gears and more
Sunday, December 23, 2007 4:53 PM
OHV notec wrote:

Jack, any chance you could re-host those images? Or send them my way?

i've actally have been planning on reposting them, but I just haven't had enough time to sit down and scan the all over again. The original scans were in my old PC that got toasted by lightning, Summer of last year.





Re: Stock Torque Converters, 3 Speed Gears and more
Tuesday, August 12, 2008 7:04 PM
MadJack wrote:

OHV notec wrote:

Jack, any chance you could re-host those images? Or send them my way?

i've actally have been planning on reposting them, but I just haven't had enough time to sit down and scan the all over again. The original scans were in my old PC that got toasted by lightning, Summer of last year.
Any chance you have a little more free time now
I've been trying to find out what I can pull a 3.33 from, with no real luck. The Dacco catalog suggests an 89-91 Lesabre may have had it as an option, but I can't find out what numbers on the casing may give the specific transmission away?




11 speaker JL Audio stereo setup for sale:
http://www.j-body.org/classifieds/audio/52021/

Re: Stock Torque Converters, 3 Speed Gears and more
Saturday, January 03, 2009 6:21 PM
I finally got around to rescanning these pages. They were on my old toasted PC, so I had to scan them all over again. These are from the 2002 DACCO catalog.









If you wish, DACCO now has a 2008 catalog available for downloading here. See pages 6-36 for the application charts, 71 for the Torque Converter Code Explanation and 80-82 for the description of the TCs for various 245mm FWD applications.






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