Transmissions and DrivetrainNeed help with your trans? Problems with your axle?
Welcome to ThirdGen.org!
Welcome to ThirdGen.org.
You are currently viewing our forum as a guest, which gives you limited access to view most discussions and access our other features. By joining our community, at no cost, you will have access to post topics, communicate privately with other members (PM), respond to polls, upload content and access many other special features. Registration is free, fast and simple, join the ThirdGen.org community today!
Here is a list of parts and prices for what I used for my TH400 swap. I tried to find a complete list a while ago but couldn't, so this is for all the people that do a search in the future.
The car that I put this trans in is a weekend bracket car so I was after consistency more than anything. There are different ways to do some of the things, but this is how I did it.
Trans; the important part. Luckily I have a friend of a friend that builds racing transmissions so he built mine for me. It's got the big sprag, hardened drum, Alto Red's, TransGo kit, hardened shafts, deep pan, adjustable modulator, he worked the gears a little bit and did a lot of other stuff that's over my head. Guaranteed it for 900 HP so I think it'll do OK behind 430. He sells this trans for $1275.
Convertor; I went with a Hughes since I've always had good luck with them. I called them up and gave them the specs on my motor and faxed over my dyno sheets and car info. They spec'd out a 10" 3500 stall converter and it ran me $680 but I'm a dealer so that was my cost. I'm not sure what retail was. Their off-the-shelf converters hold up well too. I've used them in several cars with good results. They retail for $435.
Flexplate; You can get away with the stock piece but I grabbed a TCI SFI approved piece since my stocker was old. It's up to you, a new one will run you about $80 but spinning to over 6000 rpm's I feel safer with a high quality flexplate. Also swing for the ARP bolts.
Shifter; I rigged up my stocker to work for now since my B&M wasn't here in time. You can use your stocker but your indicator will be off. No biggie. When it stops raining I will be making mounts and modding the shifter plate to fit the B&M Magnum Pro Stick. Figure $175-200 for a decent shifter.
Trans crossmember/torque arm; You can either get the B&M or Hurst kit to adapt the crossmember and torque arm or you can go with the Spohn torque arm. Chances are if you need the th400 then you'll benefit from the adjustability of the Spohn piece. I wasn't about to try to tune the suspension with a stock torque arm so I went with the Spohn piece. It moves the instant center farther back, it gets the torque arm off the trans tail housing and onto the frame and it lets you adjust the pinion angle. Not to mention it's stiffer. For a street that you don't plan on racing a lot, the Hurst kit will work well. Hurst kit is $135, Spohn is $395.
Driveshaft; Most say this is the hardest part of the whole swap but it isn't that bad. The stocker is too short and finding a usable core at a junkyard that you could shorted is a pain. Not to mention it would cost you as much as a new one by the time you get it, new joints and shorten it. Once you get the transmission in and the torque arm installed you need to measure the length for your new driveshaft. Measure from the face of the end of the tailshaft to the center of the rear u-joint. Call up your local driveshaft shop and tell them what you're doing. They will know which joints to use. I called up and told them that I needed a DS with a front yoke for a TH400 and a rear joint to fit the stock 10 bolt and gave them the measurement. Had them make it out of 3' .083" wall thickness DOM seamless tubing. 3 hours after I called them the called me back and told me to pick it up. Total was $260.
Trans cooler; you'll need to add an additional trans cooler, especially with a high stall converter. I used the 2nd biggest Perma Cool trans cooler I could find with -6 an fititngs. That ran about $60, 20 ft. of -6 braided hose, $80 and another $90 worth of fittings. Expensive but well worth it. Cleaner install, more durable and reliable than rubber lines.
Dipstick; I'm sure that you can find a stock GM dipstick/tube that will work but I just got the Lokar braided one. Easier to install and it looks better. $50
Trans Mount; Pick up a good poly mount. Around $25. Energy suspension better than Prothane IMO.
Bolts; Hit up ARP for some good flexplate and torque converter bolts. Just a little extra security. Be sure to use a little blue loctite on them all.
Kickdown switch; I didn't use one, but all you need it a momentary switch up on the gas pedal under the dash to supply 12v. to the kickdown switch on the side of the trans. Search the bone yards for any car or truck and snatch the switch off the pedals and adapt it to your car.
Temp Gauge; Any car with a high stall converter should have a trans temp gauge to keep an eye on the temps, ESPECIALLY bracket cars. Autometer electric gauges work great and can be had for less than $60. Be sure to mount the sender in the pan before you fill the trans with fluid.
Odds 'n Ends; Don't forget all the little stuff! Fluids, nuts, bolts etc.. A drain plug is a good idea and makes fluid changes a lot easier.
This is how I did everything, not to be taken as gospel. Just trying to put most of the info in one place for those doing their own research.
This ad is not displayed to registered members. Register your free account today and become a member on ThirdGen!
Been driving it a couple weeks now and went to the track last weekend. All is good. Here is an updated list of all the prices that I incurred during the project.
Trans $850
Converter $435
Flexplate $90
Torque arm $395
Driveshaft $260
Shifter $170
Trans mount $18
Temp gauge $40
Dipstick $40
Trans cooler (all -6an lines, you can do it cheaper) $180
ARP flexplate bolts $16
Fluids ( I'm a Royal Purple dealer so I had to use the good stuff ) $65
Total puts you around $1700, give or take a few. You can do the trans cooler for around $50 with rubber lines. You can use the stock 700R4 flexplate and bolts. You can make the stock torque arm and shifter work. I decided to go the more expensive route since it's raced every weekend and need the durabilty and I didn't want to have to try and rely on a 700R4.
Driveshasft is no problem at all. It's going to be slightly different for each car so you'll need to measure it for yourself with your parts.I don't remember the length but it's not hard to measure.
Calculators for RPM at a given speed can be found here ;
I used the short tail version. There is a long tail version that others have used successfully but I'm not sure what is entailed besides different driveshaft length.
There is a th-375 that has the th-400 case with th-350 size output spline and diameter. The length of the th-375 is also right about the same of th-350 with a 9in tailshaft. I think most of the internals are th400 but its not rated as high as the th400. I would think it has less clutches and steels but I haven't taken one apart and haven't seen anything about them regarding that.
I have a th375 and a th400 short tail (4in) if anyone would like pictures.
Hey man I read your post and was about to the something similar. I am wanting to switch from the t5 that is in my car to a th400. I have a few questions...
Pedals?
Will my tranny crossmember that I have now do or not?
I guess that is really it. for now.
If I use the Hurst or B&M fitting kit, what sort of trans mount am I looking for? Just a poly version of the 700R4 mount? Or do I need to find one for a T400?
OK, my swap is slowly coming together... New question tho...
Do i need a one-way valve or something to use the vacuum modulator on my boosted motor? Or once it hits atmospheric is it maxed, and the boost doesnt make any difference?
I think just use a manifold vac port from the motor. not sure though so I would look for a more positive answer. Also with the Hurst kit does the torque arm still bolt up the same? would it be ok for street use for a little while? The 400 kit comes with a crossmember I think I have never used one.
Is the 350 the exact same as the 400 as far as dimenstions and bolt patterns? Will I need to do anything as far as the trailing arm or whatever is is that connects the rear end to the trans? Can I get a link to the b&m or hurst kits?
If Im looking to get a 9" th350, what parts will I all need to get? Will any modifying at all be necessary or will it be simply bolt up? Im looking to maybe convert since my 700r4 is acting screwy and shifting like crap
big bad jonny the long th350 will fit-same driveshaft can be used. no more t.v. cable-now a kickdown cable with the th350 needs hooked up. now a vacuum line to intake needs hooked up. shifter arm will fit but detents will be off not matching the shift pattern of the th350 but could still be shifted-make shure it holds in park and doesn't start in neutral or park or you'll run you or someone else over--splat.. torque converter is different maybe need different flexplate if bolts don't line up. bolt pattern to engine will be same but bolts might be too long-check. just tape off or remove tcc plug on trans harness-should be fine//. third gear will be same 1to1 ratio but you won't have fourth-.7o.d. sad...
What about speedo drive gear , Ive done a few swaps from electrical to drive gear tranny's and still havent figured out a cheap fix for that yet, Much help appriciated.
there are th350's that use the electrical speedo. they are gear driven but have the proper electrical hookup with two wires. they can be found in th350c cores at the junk yard.
This sucks man. I just switched everything in my car over to run the th 350. But ran into the same problem with the driveshaft because I got the short tail transmission. However, there must have been a way to run these without having a special driveshaft made, my brother has one in his 83 but he cant remember what kind of vehicle he got it out of. But, from the tip of the yoke to the end of my driveshaft is exactly 4 feet. But I was reading on ebay of some LS1 driveshafts being about 4 3/4 inches longer than mine? can anyone shed some lite on my current situation?
Im going to be swapping in a TH400 into my car within the next month or two, and I have a question about hooking up the Speedo to it. I am using the GTA 140 MPH Electronic Speedo, so how do I get my TH400 to work with it?
This sucks man. I just switched everything in my car over to run the th 350. But ran into the same problem with the driveshaft because I got the short tail transmission. However, there must have been a way to run these without having a special driveshaft made, my brother has one in his 83 but he cant remember what kind of vehicle he got it out of. But, from the tip of the yoke to the end of my driveshaft is exactly 4 feet. But I was reading on ebay of some LS1 driveshafts being about 4 3/4 inches longer than mine? can anyone shed some lite on my current situation?
Wow all that work, you shouldnt just through it away. Any 4x4 shop worth anything can make you a driveshaft and it should be under $150. If you cant go to a store call up Speedway Motors. They will make you a driveshaft and ship it to you. Just a thought.
) $65
