th350 questions, yes I did a search

I posted this in tech and got no answers and 9 views in 2 days. I feel this is advanced, so here it goes. Any help would be great. Thanks in advance.


I have been going through the searchs of converting to a th350 trans. Two problems I cant figure out. First the speedo. I realized you can get the parts through Dakota Digital for a huge amount of money. But someone also said you can use GM part numbers 8655315 and 8655291 and make it work. But if you use those parts from GM, are you going to have to retain the A4 programming in the ECM? I want to do away with the A4 file so as to avoid the high stall problem associated with OBD1 ECM's. Is it possible to switch from a 40 tooth reluctor to a 17 tooth reluctor and make it work and believe it is a M6? If so does anyone know where you can get a 17 tooth reluctor? Second problem I have is fairly small. I have heard different stories about the dipstick. Will a stock one work? or a stock one from the th350? If not, where can you get a dipstick that will work?

I have done the TH-350 conversion from a 4L60E
Question #1
I used a kit that has a diffrent out-put shaft and comes with a 2" spacer that goes between the tail shaft housing and the tranny case this kit allows you to use the stock DS and use the factory speedo the only thing i did have to do is change the plugin on the wiring harness, (simple change) i got one off an old 700R4 for free and the speedo works like a charm. My local tranny shop built the tranny and installed the conversion kit.
The pice was around 150$ for the conversion kit, I do have the part # and the name of the manufactor i got it from if you need it

Question #2
I used a Lokar flexable tranny dip stick tube they are a little high but they are worth it because you can mount the dip stick any where you want. im not sureif the stock one works or not didnt try it.

One thing to add i just converted to an OBD1 PCM from my OBD2 and i had them delete the A4 tranny so it will stop throwing codes, so now i dont know if the speedo is going to work i guess i will find out this weekend!

Great info, that helped alot. I had thought of the Lokar before but wasnt sure it would work. I would love a link and the part number on the parts you used. And PLEASE let me know if your speedo still works. That is one of the main problems I am having is wondering if it will work once I delelte the A4 program in the ECM. I want to run a high stall, but dont want the problems with a OBD1 to bite me, but if it screws with the speedo I dont know what I can do. Please keep me informed on this one, I look forward to hearing what happens.

Q

I will post the part #'s when i get back from my shop later this afternoon, and i will let you know when i get the PCM put back in this weekend i should get the OBD1 PCM from PCMforless.com tommorow.

Sounds good, I will wait for ya.;)

get the madman dipstick tube, it is more easily accessible and puts in the stock (A4) location in the engine bay. as for those GM part #'s for the speedo, i believe that is for the TH400, not the TH350. i only know of 2 ways to hook up the speedo for the TH350--Dakota Digital stuff or make your own using a Radio Shack operational amp. i have yet to hook up my speedo, but i would like to hear more about what was mentioned above using a plug off a 700r4??

Get a Lokar 36" dipstick....

Most TH350's does not have a lockup converter. If you are installing a non- lock up version, the programming is irrelevant. The lock up version can be controlled manually, probably the best way to do it. TCI also has a kit that will control lock- up automatically. The lock up converters are not as strong as the non-lock up and generate more heat.

This should not be in Advanced Tech as it is pretty basic.

Rich

This should not be in Advanced Tech as it is pretty basic.

Rich
I looked at posts over the last 3 months and couldn't find any regarding a TH350, or any on the Drivetrain forum. I wonder which "tech" forum it was posted in? :)

Moving to "Drivetrain".

You need a vss translator from dakota digital and mine was only 35-40 bucks wired it into the existing harness for the speedo and the thing worked perfectly. as for the trans if you use a TH-350 with a 9" tailshaft it will bolt in using the stock shaft. A 9" tailshaft core trans should be easy to locate if you havent bought a trans yet. I had my trans program eliminated from the pcm and it also cured the stall wall problem from my 3500 stall converter.

You can use the stock dip stick that what i use in my car the th350 is a good tranny what gear are you going to run with it? You can also use the stock crossmember you just mod the mount on it. I hope you get a stout th350 the one in my car had all the best parts in it any today on the dyno i snaped the case right in half at the bellhousing theirs $2000 down the drain.

I never understood the logic of a TH350 swap. If you need a storng automatic and are resigned to losing the OD, just go for a TH400 and be done with it.

Rich

The 400 is stronger but you know that it takes 50 hp to turn over the th400

[QUOTE] i snaped the case right in half at the bellhousing theirs $2000 down the drain.[QUOTE]

If the case snapped then it did not fail internally. Maybe a cracked bellhousing.
I may run a built TH350 just to see if it will last longer than my built 4L60E, which lasted 26k behind my bolt on high mileage LT1.

The TH400 does take more horsepower than a TH350 but a TH400 is 28 lbs LIGHTER than a 4L60E.
I wonder how much horsepower it takes to spin a 60E?

I don't believe that there is any possible way that it would take 50hp more to spin a TH400 than a TH350. Most of the drivetrain loss from adding any automatic is the converter. There is very little internal drag. Yes, the TH400 parts are larger and heavier and therefore have more inertia. But the parts are not that heavy and they are all small radius, so it just isn't going to take that kind of hp to turn them. 50hp would be a 12.5% ADDITIONAL loss for the tranny alone on a 400hp setup and I find that very hard to accept. A TH400 setup might loose ~20% total drivetrain loss, so by switching to a TH350 the net drivetrain loss would be 5%?? Does not make sense.

Where does that 50hp figure come from?

Rich

Rich...you know the answer...the "internet"...:D

Rich...you know the answer...the "internet"...:D


:D

Rich

I diden't say 50 more the 400 take 50hp were the th350 uses somewere around 30hp

I diden't say 50 more the 400 take 50hp were the th350 uses somewere around 30hp

You're right, you didn't say "more". But I also doubt 20hp more for the 400 than the 350. Most of the loss is the converter, nothing to do with the planetarys/pump/etc. So, 20hp more would imply 2-3x the loss. If you look at the internal parts, the 400 is beefier (that's the point) but not 2-3x as massive.

Anyway, you pays your $$ and you takes your choice. I am not trying to insult anyone who has a TH350 swapped in. If it works for you, great. And if it's not a hi-po car, then I am sure it would be fine. However, if it's not a high-po car, why not get a built 4L60 or 4L60E and keep the OD and lockup converter?

Rich

Because some of us are once bitten twice shy.
I have spent 1200 dollars (built tranny and stall) on a 4L60E and had it last 26k behind a bolt on LT1. I don,t expect it to last forever but 26k seems kinda low to me.
I know there are people on here who have guys build them a 60E (like Frank) and it lasts but I have had very few problems in the past with TH350s and 400s making decent horsepower.
I gave the 60E a chance and it failed, maybe a better builder would give me better luck but I don,t have 1500 dollars or more to take the chance.
My car is not a daily driver and it just makes more sense to me to go with a proven tranny, given the amount of money they cost.
TH350? I have beaten the crap out of them with much heavier cars and stock trannys to boot and never had them blow up the way these OD trannys do.
Just my 2 cents.

I have heard power losses with a turbo 400 over a 350 to be more in the range of 20-30 hp due to parasitic drag from the heavier internal parts and have experienced a loss of a couple of tenths in the quarter using a 400. As far as the strength of a turbo 350 mine holds up fine reason why is the main inherant weakness of the th-350 is the second gear sprag that can strip and freewhell resulting in a total loss of 2nd gear Im using a heavy duty aftermarket unit that will hold 30-50% more then a stock 400 sprag. Its good for well over 700 hp and that added with aftermarket planataries results in a trans that will hold just as well as all but the most extreme 400 trans.At the level my th-350 is built it will hold close to 1000hp and If I was going to give it anymore I would probably switch to a pro-built glide,For those interested the aftermarket sprag is fairly new to the market (last few years) and can be bought from a few different companies such as TCI and hughs.

Are the stock th-400s jus stronger?Could I get a stock 400 have a good rebuild and have it hold up to a 10 sec car better then a half bulit th350?

I put a performance built 4l60e in my Impala less then a year ago, worked great on a bolt on motor. Then I did a LE2 setup and less then 30 days later the 4l60e died. If you check on the Impala board this seems to be the norm with high powered LT1 and 4l60e in a 4100lb car. I've got a th350 on the way to replace the 4l60e. A friend recently put a rebuilt th350 in his Impala and gained 3mph and .5 second in the quarter go figure!!! This was the primary reason I chose the 350 vs 400. If they can live behind a Impala or a wheel standing Roadmaster then I'm sure a 350 will be ok behind a f-body.

Jason

I'd say yes. It is a bigger, stronger tranny. I had one in a 1996 421 Pontiac Catalina 2+2 kinda like this one.
http://www.musclecarclub.com/musclecars/pontiac-catalina/images/pontiac-catalina-1966a.jpg
That thing must have weighed 4,500lbs and had 376hp. Tranny never missed a beat and I really wailed on that thing. Nowadays, the high stall converters in use do put more stress on them though and the tires are stickier, so YMMV.

Rich

I never understood the logic of a TH350 swap. If you need a storng automatic and are resigned to losing the OD, just go for a TH400 and be done with it.

Rich
how i wish i would have known how much i would miss 4th gear after the swap. cant run up top on the interstate anymore :( I guess knowing you wont break anything off the line (with the exception of a 10 bolt) is some piece of mind, but no OD blows. I'm considering buying a 400 off of a good friend of mine that rebuilds cars for a living. He'll sell it to me for $200 w/ a 3000 stall...awesome deal but i dont look forward to doing a trans swap by myself.

I had 3 yes 3 rebuilds on my 4l60 by 2 seperate shops, the second of which is a very reputable builder, and when it failed the first time he rebuilt it for free because i had spent right at $1000 for a 'performance rebuild'. Unfortunately alot of stuff i read on here about local guys not knowing how to rebuild an electronic trans. is apparently true. I went with a bullet proof, warrntied, and respected racing companys product and I havent been able to break it so far.

Just cruising I can understand missing OD. But racing I rarely if ever got into 4th gear. In fact having the car shift into OD at WOT in my opinion did not help the trannys longevity. I have been at a buck forty in my car and its something I really don,t ever need to do again. If I ever get the car to trap 130 I will call it finished and quit modding. With 28 inch tires, 3.73 gears, and it being a weekend warrior I don,t believe I will have any problems living without OD.

awesome deal but i dont look forward to doing a trans swap by myself. I did a trans removal, hop-up, and reinstall all by myself, and I'm a weakling. (Of course, it was in a 1970 Nova, so there was actually some room to work.)