i'm replacing a Powerglide with a TH350 in a low horse power application (300hp/350lbs/ft when the engine was new 53 years ago). based on advice i received here i'm looking at having a local shop build a transmission for me. i've found 3 shops that have the short shaft core that i need and have quoted a price to do it. problem is the quotes range from $650 to $1200 incl. core and torque converter. also, it looks like these guys are all getting their rebuild kits from the local Transtar warehouse. i need to be able to make sense of these quotes. so my question is: what kinds of questions about the build should i be asking theses shops? should i look at upgrading any of the components? any advice or words of wisdom would be much appreciated. thanks.
I purchased this book...it was very good! slowly walked you through the process with a million pictures...we on the HAMB like pictures! https://www.amazon.com/GM-Turbo-350-Transmissions-Rebuild/dp/1613251890 I worked slowly and methodically and did it my self. The o-ring and soft parts rebuild kits as well as the shift kits are not expensive. When I built mine, I purchased the steels in the necessary thicknesses to bring the clutch packs up to their tightest tolerances. At full throttle shifts, it would bark the tires hard with a very firm shift and under normal acceleration it shifted firm but not annoyingly so. If I recall I might have had a couple hundred dollars or so in the trans and another $100 or so in the torque converter. A lot cheaper than your quotes and you'll learn a new skill. Oh yeah, and another $100 in the necessary specialty tools. There is an internal spring type compressor that pushes down in the case to allow removal of the internal snap rings. I'm not sure what it's called, but I can get a picture of it if you like.
These are fairly easy to build yourself. The main problem is working on them comfortably. You have to shift the trans from working in the main case to working on the valve body. Rolling it around on the bench or the floor is not the way to overhaul a unit. Besides that a shift improver kit, adjustable modulator, torque converter and some time. 2X the select fit steel plates, if you are looking for a firm shift. Vaseline on the seals and do not throw out the thrust spring, it has a job to do. Make sure you have a map of the valve body where the check balls go. It is advised to use the rubberized balls as the steel balls rattle and can blow through the valve body spacer plate.
You could do it yourself. Not real difficult but if you don't feel comfortable the main question I would ask is what converter they are using. Most of these shops use a Dayco or Recon converter. They are J.U.N.K. I've done transmissions for 40 years and wouldn't use either of them. Also, the price will vary depending on the shop. I'd say that 650 figure is reasonable if they are supplying the core. The 1200 figure is someone trying to gaff you unless they are using superior parts. Bottom line is, if it's a good core it probably needs 100 bucks in parts not including the converter. Rest is labor and the core.
Many years ago I taught automatic transmission rebuild. The thing I remember about the THM 350 is that I saw a lot of failures of the of the input shaft where it pilots into the main shaft. I believe that the trans would fail and plug up the intake screen for the pump. The bushing in the main shaft would be starved for lube and fail taking the input shaft surface with it. This is also the lube circuit for the gear train. If you get a core trans, pay close attention to the end of the input shaft. At the time, mid 70's, the input shaft was not available separately. You had to get the assembly with the clutch drums.
I will try and answer some of your questions. I have been in the transmission business for 38 years. Transtar is probably the best supplier there is, for high quality trans parts.. I get most of my rebuild parts from them. Transtar also distributes Dynamic torque converters now, a Chicagoland based business, that has been around for ever. I have used Dynamic for 38 years for stock or mild performance converters, with only a handful of problems over the years. The only times I have strayed away from Dynamic was due to delivery issues over the years. (they stopped delivery themselves, had some other companies deliver etc.) then went back to delivering. That went on a few times over the years. I used other converter companies with a lots of problems during those times. Somehow I always ended up back With Dynamic. Dynamic also sold out a few years ago, so all the original Italians, operating the business are now gone. There are still some of the original employees still there. I have gotten converters from the new Dynamic and so far the quality still seems to be there. They have become real big in remanufacturing converters for auto makers and the aftermarket part of their business (transmission shops) has gotten smaller. Turbo 350 non lockup trans cores are getting harder and harder to find that are rebuildable. They have been out of production for more than 40 years. Most cores we see now have been rebuilt many times (poorly) and many have worn out cases. So good core prices are higher. Based on what you are doing with the car, I would recommend a good quality rebuild with parts from Transtar and install a SK shift improver kit and hardened intermediate race. The shift improver kit will get you two nice positive shifts that are not brutal. The best 350 cores are from 1976 and up. They have needle thrust bearings between parts instead of thrust washers. Remember, the transmission rebuild is only as good as the guy rebuilding it. The best parts used wont fix a poor rebuilder. In Chicagoland, my prices are pretty much in line with companies like TCI, B&M, Coan etc. Good luck, Bill
Here you go, it's a KD-2398. There was also an array of snap ring pliers inside and out (I didn't take pictures of them). I cut a piece of plywood about 12" square, and drilled a hole in the center for the output shaft. I set the plywood on top of a 5 gallon bucket and stood the trans tail shaft down in order to unload and load the case. Anytime I was working on the valve body, governor, accumulator etc, I mounted the trans on an engine stand and turned it over like you would an engine It's not the fancy clamp that the pros use, but it worked pretty well for me.
650 today for the core, kit, converter, extras and labor probably equals the buy a kit and converter and have the local transmission mechanic who did a couple of side jobs a week do the rebuild. Still price aside it comes down to the shop that has the best reputation for turning out quality work locally. Sometimes the far higher price relates more to that shops overhead costs that have to be met than them being that much better than the other shops.
G'day, You couldn't give me a TCI transmission. I bought one from them for an OT project and it was properly set up and failed in less than 70 miles. Summit authorized us to open it up and see what had failed. The core had been under water at some time and was junk. TCI was horrible to deal with so Summit took care of it.
The pictures of the clutch compressor tool is the same one that I used when I built transmissions professionally. I did that for around 30 years. Yes the 350 TH isn’t that hard to rebuild, there are books out there that you should buy to help you through it. You can do it and save money
The TCI tech guys are the salesman ..Don't know shit from Shinola . If I buy a core that had water in it, I get my money back . The higher priced guys are covering their asses for bad hard parts. I price them at so much + options and hard parts.
I had one rebuilt last year by a local transmission shop, i took them the transmission, they called about 2 weeks later and told me it was ready. $350. It worked great, but that was me reusing my old converter. Guess prices vary a lot depending on the size of the town you're in.
what he said !!! I built transmissions when I first started in the trade, the TH350 is an easy trans to build. Seeing as your going for mild performance a stock rebuild should be fine, a shift kit, valve body work , better then stock converter, are all up to your preference and wallet. I know back 25 years ago we got $1800 to build your transmission. My cousin owns a shop and now does the odd one for around $650 if you supply the core. up here on the classifieds a TH350 core goes anywhere from $100-400 bucks. $650 suppling the core sounds cheap, I’m guessing he’s not using a kit but I can’t say for sure, probably opening the trans and replacing what needs replacing. 1200 sounds better for supplying and building a complete trans.
What kind of warranty are these folks offering? Does it include labor to R&R the trans? Do you have to have a new cooler and lines to keep from voiding the warranty?
Along with everything above, at the very least, be sure to replace the sprag race with a hardened one. Personally, I'd replace that entire drum assembly with one modified to take the TH-400 style, 36 element, sprag race, or with the fairly new diode/drum assembly. Update the bushings with wider and doubled up bushings where appropriate, dual feed the clutches, and always use a new/rebuilt torque converter. An external cooler is added insurance. I don't care for the 2 to 3 shift lag of TH-350's, and prefer the TH-400's. A stock level rebuild is fine for a light car or one that's not driven hard. JMO. I am Butch/56sedandelivery.
Since you are starting from scratch, go with something that has overdrive like a 2004R or a 700R4. You will enjoy driving your hot rod a lot more with an overdrive. One of the first things you should realize is that there are certain parts needed to make the trans perform better and increase its strength. The cheapest builder will most likely not be able to upgrade at the lowest price. Talk to the local rodders and see who has a good reputation among them for building transmissions. Sometimes there is a local guy who does it on the side. That can be a blessing or a problem, so make sure they have a very good reputation.
thanks guys for all the thoughtful and informative replies. i've got a lot to learn but it sounds like the key is finding a shop i can trust and that knows what they're doing and then reach an agreement about the parts they'll be using. i might buy that book in the meantime. thanks again.
The Jalopy Journal
