Hey guys, I've got a TH400 that requires me to rev to about 2000-2500 to get the car moving. I have verified linkage is adjusted properly and that fluid level is correct. Fluid also looks and feels good no burnt smell. Next step is to measure line pressure, but I am waiting to get a gauge that I ordered. Factory manual says that if pressure is low (less than 95-150 PSI) in reverse at 1000 rpm there is an "oil leak in feed system to direct clutch". Assuming this is the case, how do I find this leak, does the trans need to come out? Thanks for any replies.
Do you have engine braking in 1st gear? If you are driving along at 15-20 mph and downshift to low gear do you feel it go into low gear and then the car decelerate?
OK here I go again, I'm not really an expert on trannies, but I have rebuilt my 400 myself. For what it's worth........when that trans goes into reverse, 2 things happen, the forward clutch applies and the low/reverse band applies. That is activated by the rear servo, so if anything has happened that would cause the servo not to get pressure to apply the band, that could be the problem. If the forward clutch was slipping, she'd slip in drive too. Did you have it apart? Perhaps a check ball is out of place.........or possibly the servo cover has become loose and is leaking pressure......my bet is that if you drop the pan and look, you may have loose bolts on the valve body or somewhere else causing the drop in pressure. Good luck.
I do have engine braking at low speeds dropping into first gear. The trans was rebuilt over a year ago and I have had this problem from the beginning. Yeah, I should have brought it back then but never did it and now I want to try and fix it myself. There is a Trans-go shift kit and a Coan 11" 2600 rpm stall converter in the car. The 2-3 shift is soft also, but I am trying to remedy one thing at a time. Thanks for the help
nailhead is on the right track but has it confused. The low band has to be applied, it is used in reverse and manual low. In manual low it provides engine braking on decel, and this is why I asked about engine braking in manual low. This tells us the band/servo/circuit is functioning. The forward clutches are on in all the forward gears but not in reverse... In reverse the direct (3rd) gear clutches come on. No reverse and a soft 2-3 shift are probably related and point to a problem with the direct clutches. Probably a cut seal in that drum. The TransGo kit usually provides an excellent 3rd gear shift. Here's a help article I wrote on another board. http://www.nastyz28.com/forum/showthread.php?t=58578
Exactly right. Usually, if reverse is gone on a TH400 you will find 3rd gear also out or slipping. The rear band and servo are generally trouble-free. My guess is that probably one of the direct clutch seals is broken and leaking fluid past and yes, the tranny will have to come apart.
That's an awesome article! :TU: That's the first I've heard of putting a setscrew in the 2-3 accumulator. I guess if that don't firm it up, nothing will.
When you dual feed the directs, there is a greater volume to fill. Blocking the 2-3 accumulator results in a crisp but not brutal shift on that circuit with the proper orifice sizing. I leave all the checkballs in on my builds, and my orificing isn't large by huge. The rear band and servo as previously mentioned are not usually problematic, the only time you might have issues is on a fresh build. The servo pin length is selective and if you don't check the band clearance you can get into trouble. I had a 4L80E eat my lunch on that once and I had checked the clearance but skipped a step in doing so.
I'm still not 100% clear on that 6th checkball thing......I remember reading that it is non-functional. Exactly what is it that it's supposed to do.....if it's non-functional, then why did they put it in there? uzzled:
I'm still not 100% clear on that 6th checkball thing......I remember reading that it is non-functional. Exactly what is it that it's supposed to do.....if it's non-functional, then why did they put it in there the 6th check ball was put in to slow oil flow to direct clutches this ball can be left out on 1975 and up thm 400
That doesn't sound right to me.......again unless I'm mistaken.....that 6th check ball is located right next to the intermediate clutch feed hole, so if it was going to slow down oil flow it would be the intermediate clutch and not the direct clutch. I tried mine with the ball in there and with the ball out and didn't notice any difference at all in the shifts.
The checkball is in the 3rd feed passage. If you follow the passage it goes directly to the 3rd feed passage into the center support. I think the plate has a feed hole in a different spot which eliminated the function of that ball. I would have to look at the plate.
