I need to find out which years are the best to find a 425 tranny for a longitudinal setup. I will have the tranny redone with all the harden parts. What numbers am I looking for? I have the 325-4L on hand but my plans have changed as far as the HP & Torque out put of the motor. I want to get the strongest auto tranny that's out there for my build. Also how do I find out about the final gear ratio for those transmissions.

T I A

Prasad

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"Turbo Cars are like hot women. A little edgy, every guy wants one, some guys can't handle them, and if you throw a little alchohol in the mix they'll rock your world"
1986 GT (waiting for Buick GN setup trasplant)
1984SE 5 Speed W/SBC V8
1997 GTP
1987 Buick GN(10.70@124MPH)
1987 Trans Am SBC 355cid Twin Turbo(no track times yet)
1992 GMC Typhoon(13.20@ 99mph)
Other cars; JaguarXJR, XJ6 & Mercedes AMG 500SEC

The best year would have been 1977, there were lots of TH425's around. LOL. Seriously though, any year TH425 is a good year. They are very stout transmissions. I believe they were made from 1966 thru 1977. might be off by a year either way. The drawback is the Differentials that attach only come in two gear ratios, 2.73 and 3.08:1 I believe. They were also used on GMC Motorhomes as well as Toronados and Eldorados.
Hope this helps. If you need help locating one I may have some links for you.
Tony

TH-425's were used from 66 to 78. For the Olds, and I beleive the other cars were the same,, they have a 2 letter ID like OJ or OM on a tag on the trans. The tag is about 3/4" by 3/4" and the letters should be red or blue.

The EARLY transmissions before 1975 (OJ codes) are a bit better and you may luck out with a 3:08 ratio a bit easier but any 425 can be rebuilt to handle your swap. You can also check Buick Rivera's as well as Toro's and Eldorados.

Olds TH-425 ID's:

ID Year(s) Application
OJ '66-'78 Toronado
OJ '70 4V 455 Toronado, except W-34 (9400 series)
OJ '73-'75 4V 455 Toronado
OM '74-'75 4V 455 Toronado (Calif)

[This message has been edited by 3084me (edited 08-03-2006).]

Buick Riveras before 1979 were RWD and did not use TH425s. Rivera joined the Eldo and Toronado as a FWD platform in 79(?) and uses the smaller and weaker TH325.

Great Info guys, thank you so much!!!!

Prasad

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"Turbo Cars are like hot women. A little edgy, every guy wants one, some guys can't handle them, and if you throw a little alchohol in the mix they'll rock your world"
1986 GT (waiting for Buick GN setup trasplant)
1984SE 5 Speed W/SBC V8
1997 GTP
1987 Buick GN(10.70@124MPH)
1987 Trans Am SBC 355cid Twin Turbo(no track times yet)
1992 GMC Typhoon(13.20@ 99mph)
Other cars; JaguarXJR, XJ6 & Mercedes AMG 500SEC

You should probably just go with your 325-4L unless you are in the 400HP range. It has overdrive to keep the RPm down, and a lockup TC to save you gas. The real weak point would be the narrow drive chain, but I felt that the RPM issues with a big block would be a bigger problem. There's a lot of paranoia about the drive chain, but if you look at the tiny thin little gears cardealer used in how reverse rotation setup, an the power he was successfully putting down, it really looks like a non-issue. Go with what you hav imo, and don't try to put a 472 BB in like I'm doing. It doesn't fit all that well. Actually it doesn't fit at all. the motor is wider than the strut towews, and i will have to notch them out and use coilovers.

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Go with the 273 diff. with a 24" tire the car is more enjoyable with freeway ratio simular to your deep geared overdrive setup.

The car will launch just as hard "big wheelies" with the multiplication of a stall converter. Better yet use a switch pitch 425 tranny out of a 67 toronado then you can turn the stall off during freeway cruise. Use the 12" switch pitch converter out of the superturbine 300, it is much lighter, quicker revs, then rebuild it and modify the servo travel to increase the pitched stall rpm. mine was done for only 200$ at midwest converter in minneapolis.With a flick of the toggle switch stall speed will go back to stock and tranny temps will drop.

motor home trannys have six clutches in the drum.All the rebuild internals are the same as a turbo 400 but dont put the 400 drum and planetary in your 425 because you'll have one forward gear and three backward gears. Your choice then is to mount the drivetrain backward or only race in reverse.

watch out for missinformation about longetudinal fiero swaps.The handling isnt quite as good as a conventional setup but its not to bad. You dont have to cut the shock towers and the motor fits under the stock hood. The only 10 second fieros have longitudinal drivetrains.

It's good to hear talk of the 425. My 454 and trans are mated and I'm getting ready to start the frame mock up now. The only question I have is what did you do for axels? The Fiero spindle set-up looks like the weak link.

Big Block Fiero,
Where did you get your info about swapping the 400 and 425 parts turning the tranny backwards? If it was this simple, then you could just turn the engine and transaxle around and set the chain drive weight forward rather than hanging it out the rear end. This would eliminate the extra gears that Car Delaer had with his drag racing car, and eliminate the flipping of the differential in order to reverse the drive.

Jim

All this talk about the TH425 makes my mouth water. I also wonder why I still have mine. Rebuilt TH425 with diffential & axle shafts. I think I listed it in the classifieds at one time ... maybe couple years ago. If anyone wants it, holler at me. Send me an e-mail in lieu of a PM 'cause I don't hang around this site like I used to.

Still wondering about the 400 clutch drum and planatary in the 425.

Jim

quote Originally posted by Jim_S: Still wondering about the 400 clutch drum and planatary in the 425. Jim

Ditto ... if it is that simple, I may reconsider using my TH425 for a north-south swap. I was under the impression that the only real difference between the 400 and 425 was one was oriented for conventional rear wheel drive while (400), while the other (425) was set-up for front wheel drive ... and that all the internals were the same.

If this works, I'll definitely be heading back to the shop a lot in the next couple months. Another note on that 325-4L you have there. It's roughly half the weight of the 425. Food for thought. Regardless of the power you are putting to it. Stock wheels and street tires will break loose way before the guts do.

Little note to people who don't know much about the trans. The adapter plate to mate a 350 to it is the cheapest I have ever heard of. Somewhere around $60. You space the torque converter with washers that come with the kit, and there are NO other issues. If the mod mentioned earlier actually works, Installing the drivetrain backwards is your best bet. If you put it in facing forward you will be rediculously ass heavy, and you will have to swap your knuckles left to right to move the tie rods to the front of the wheels in anything but an 88.

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[This message has been edited by HellYes (edited 11-29-2006).]