[sabino56]

I have a basic question about automatic transmissions. I have a TH350 which will not move if started in Drive. If you put it manually in first it will drive and you can manually upshift it to 2nd and Drive. I'm told the problem is likely the sprag clutch (gear?). I've read up on it and think I understand function of the sprag clutch. What I don't understand is how the transmission will run in first when put manually into first if the sprag was bad. Is there a manual mechanism locking the planet carrier when the shifter is put into first gear?
Thanks!
Ed

[scholman]

sabino56,

No, there isn't a mechanical connection from the shifter to low gear. The only reason that I can think of for this transmission to work when you pull the shifter into low is that the oil passes through different passages ways. So you end up with more oil pressure at the clutch pack which causes the trans to work. I think if you do not go into the trans and fix the problem it will quit working one of these days. And if you have my luck it will be when you are on your way to THE most important meeting of your life.

Good Luck
Scholman

[BstMech]

The low/reverse clutch is applied in manual 1st, and released in drive position.

Sounds like a rear sprag to me also.

[sabino56]

Thanks for the replies.
I have transmission out of car and was trying to decide whether to attempt rebuilding myself or taking it to a shop. I've rebuilt engines and manuals but never opened up an automatic. I was thinking if it was something "simple" I might take a shot - but since it's probably the sprag and there is metal everywhere, I will probably take it in to have it cleaned and rebuilt.
I'll have to learn what the low/reverse clutch does - I'm guessing lock the planetary carrier? Does anyone have good links to schematics or tutorial on the TH350 or automatic transmissions in general?
Ed

[Jmark]

Probably one of the best th350 books is by Ron Sessions. It's available cheap on eBay.

Clicky here.

[LordMaximo]

If you have a good aptitude for the task at hand, go for it. I remember my first auto rebuild, it was a Chrysler unit, I was new at this and over torqued the bands. What a mess, it worked well for the first ten minutes, then over heated and died. So, you know what happens next, pulled the pig out and started all over. Luckily we did not do much damage and was able to fix it with another $100.00 towards new parts. This was back in 1978. The T350 is a simple rebuild and worth the experience. I would recommend the heavy duty clutch packages and extra duty parts, over the OEM stuff. You will thank yourself on spending the extra $600.00 + for the upgrade in parts.

Face the facts on this one, automatic transmission rebuilds have gone from $800.00 up-wards to $2500.00 over the past 15 years. Inflation kills everyone.
You save 50% of your investment doing the job yourself. Check out this site for a more concise brief on the extra touch....and good luck....
http://www.transmissioncenter.net/700r4.htm

[sabino56]

just to get back to the group.
I got in touch with person I bought transmission from and he agreed to repair it. It was the one-way clutch which had failed. The outter race had a crack in it and so it could expand and let the teeth or whatever locks it jump.

[Jmark]

That was good of him to fix it!! I hope he put in a hardend race instead of the stock one. That is one weak point in the th350 when adding lots of power.

Makr

[briscoe]

sabino56 am glad to hear your problem is resolved.i am new to this site and certainly happy to read all the great input thats posted.the low sprag keeps the rear planetary held in place so that the planet pinions will turn clockwise,looking at trans from front to rear,this forces the output ring gear and output shaft to turn in a clockwise direction,the low sprag freewheels in a clockwise direction and locks counter clockwise.in manual low the low reverse clutchs are applied locking the rear planetary in place,or doing the same thing a good sprag would do,thought this might be interesting reading for some.tci makes a hardened intermediate sprag race,which will keep you from losing 2nd gear if you have much over 350 hp

[Crosley]

so much information here.

[briscoe]

hey crosley what did you mean,so much information here? I ask because i'm new to this site,in fact new to contributing info to any internet forum,I have enjoyed it so far ,there are a lot of sharp people that contribute to this site,I expect to learn much.you have posted over 2600 times so in your opinion did I bog the forum down with my post,or is this the type of info people want to read?Thank you in advance for your reply,Briscoe.

[Crosley]

Originally Posted by briscoe

hey crosley what did you mean,so much information here? I ask because i'm new to this site,in fact new to contributing info to any internet forum,I have enjoyed it so far ,there are a lot of sharp people that contribute to this site,I expect to learn much.you have posted over 2600 times so in your opinion did I bog the forum down with my post,or is this the type of info people want to read?Thank you in advance for your reply,Briscoe.

my post stands on it's own. I meant nothing special by it.

post away , we appreciate all correct information here on the site