Th400 slips in first

[down4thakrown]

I had a thread about my trans but can't find it. On my th400 its slipping very bad in first, but will eventually shift to 2nd and 3rd not problem and run great in those gears. I'm going to drain some fluid since it looks a little over full but I don't think it would cause it to act like that. If II down shift it manually it hardly slows down. And when I shift from 1st to 2nd manually, it takes right off like it should?....

 

[diesel4me]

Overfilling can cause weird things,the fluid will foam and air trapped in the valve body can cause shifting troubles...usually if it is way overfilled the excess fluid gets peuked out of the vent on top of the case though..

There are troubleshooting charts online that list many symptoms,yours are slipping in first on takeoffs,and no "engine braking" if you manually downshift into second or first ?...I dont have my books handy but I think a band and or a servo problem can cause that,also an "overrunning clutch" or one way sprag ,if I remember right..

Many troubles can be caused by a filter being clogged ,or just the vacuum modulator not getting enough vacuum,being hooked up wrong ,so it gets ported vacuum instead of manifold vacuum,or the diaphram inside it ruptures and lets fluid get sucked into the engine,and it wont control the shifting properly...might as well start with the easy and cheapest things first..

Greg Ducato is the man here to talk too,he really knows his stuff..he helped me with my diesel's TH400 ,and sent me a modified govenor to make it upshift sooner without the vacuum pump that runs the modulator working well..I would ask him !..

 

[down4thakrown]

The fluid don't look foamy and it looks good. The trans has sat for 3 yrs since the rebuild. And has a new tc I bought when the trans went in. I'm going to order a new vacuum line. The one on there is from a th350 and bent up pretty bad. Thx alot for referrel too. I'll try to find the charts

 

[diesel4me]

All you need for the vacuum modulator is a length of 1/4" brake tubing and a few inches of rubber hose to connect to the modulator and intake manifold fitting..a new modulator is about 10-15 bucks,might not hurt to get one in case the old one does turn out to be junk..

If it was rebuilt ,then sitting may have let something like the valve body spools get gummy and stick,or a servo,etc.....did it work OK after the rebuild,or was it never driven to find out ?..

 

[Greg Ducato]

Lack of Vacuum should not affect 1st gear operation, it will cause a no upshift condition and high line pressure.. I would pop the pan and make sure the filter hasn't fallen off the filter neck if she is slipping in first gear only, though it should create the same problem in reverse.

 

[down4thakrown]

The fluid don't look foamy and it looks good. The trans has sat for 3 yrs since the rebuild. And has a new tc I bought when the trans went in. I'm going to order a new vacuum line. The one on there is from a th350 and bent up pretty bad. Thx alot for referrel too. I'll try to find the charts

Will do once the ground dries up. I think reverse is good. It doesn't slip. But I'll check when I get home.