Th400 problems. Help?
Thread Starter
Staging Lane
Joined: Jul 2011
Posts: 71
Likes: 0
From: Sylva, NC
Th400 problems. Help? I just got my car back together after I scattered the bottom end in the 5.3. Now it has a Forged Lq4, s475 turbo ect. Anyway, I had the trans built right before the 5.3 let go. I told the shop to build it to hold 800-1000hp. It has RMVB. 34 element sprag. A brake which is not hooked up yet. And i forget what else is in it. So I drove the car just one night after I got the new tranny in and that was the night the motor came undone. The tranny felt fine then. Pulled hard up top, didn't really notice anything unusual with it, everything felt fine.
So the car has been sitting for almost 6 months now in my shop. Finally get the new motor back and get the car going again. Same Tranny and converter as before. Im driving it around n/a for a while to break the motor in. Now the car won't pull past 4000 rpm in any gear. It revs fine in neutral but when in gear it feels like the tranny is binding up and holding the car back. It starts around 3400 then the motor won't go past 4k in 1st 2nd or 3rd. I called the tranny shop that built it and they said check the shifter adjustment. OK I did that. Pin moves freely in the linkage arm in everygear. Shifts feel firm and solid in first and second and pretty good from 2nd to 3rd. Still hits that wall at 4k.??? We retuned it to run n/a so its not still in the boost tune. So what could be going on What would cause a th400 to act like this?? I've heard of ppl having similar issues in one gear or another but not all 3?? Any help greatly appreciated.
Thanks. -TJ
So the car has been sitting for almost 6 months now in my shop. Finally get the new motor back and get the car going again. Same Tranny and converter as before. Im driving it around n/a for a while to break the motor in. Now the car won't pull past 4000 rpm in any gear. It revs fine in neutral but when in gear it feels like the tranny is binding up and holding the car back. It starts around 3400 then the motor won't go past 4k in 1st 2nd or 3rd. I called the tranny shop that built it and they said check the shifter adjustment. OK I did that. Pin moves freely in the linkage arm in everygear. Shifts feel firm and solid in first and second and pretty good from 2nd to 3rd. Still hits that wall at 4k.??? We retuned it to run n/a so its not still in the boost tune. So what could be going on What would cause a th400 to act like this?? I've heard of ppl having similar issues in one gear or another but not all 3?? Any help greatly appreciated.
Thanks. -TJ
Thread Starter
Staging Lane
Joined: Jul 2011
Posts: 71
Likes: 0
From: Sylva, NC
At WOT around 4k where this is happening timing is 26° and AFR is low 13s.?? I talked to the tranny shop and they don't know what's going on. They just said keep checking the shifter adjustment. But there's no way it would be so far out it'd do it in all three gears? So is there ANYTHING else it could be? Cracked valve body? Messed up case? I dont know, I'm just throwing things out there I'm out of ideas.
Thread Starter
Staging Lane
Joined: Jul 2011
Posts: 71
Likes: 0
From: Sylva, NC
I'll look it over again. But the motor revs out fine when in neutral. Very crisp and clean. Could the converter hold it back that hard like I described? It loads down and doesn't pull hardly at all when the rpms get up. Even if the converter locked it would still pull a lot better than it is now. I mean its a 10:1 365 with a good sized cam in it. Is it possible for a converter to rob that much power? Like I said ANY suggestions helps. I thought about putting a little boost to it and seeing if it does the same thing. The tranny and converter did fine when I first put it in. But I was on 20psi. Ive never drove it n/a. I guess that would tell me if it was a tune issue or not. ??
If there were something in the trans or converter "holding it back" you would be making heat, and lots of it.
Fluid would be burnt.
A failed converter sprag could cause some loss but usually will tighten up the stall speed considerably.
Lots of guys are quick to blame a trans/converter, when they in fact have a tune issue, and I would be willing to bet yours is a tune issue. Maybe it just feels slow N/A.
Fluid would be burnt.
A failed converter sprag could cause some loss but usually will tighten up the stall speed considerably.
Lots of guys are quick to blame a trans/converter, when they in fact have a tune issue, and I would be willing to bet yours is a tune issue. Maybe it just feels slow N/A.
Thread Starter
Staging Lane
Joined: Jul 2011
Posts: 71
Likes: 0
From: Sylva, NC
Haha. That's what I thought at first. But it feels like I'm brake boosting or the e brake is pulled or something. That's how bad it holds back. You can hear the engine loading down and trying to pull but it barely picks up any speed if any at all. Fluid looks new, no burnt odor. Makes a whining sound in first but I guess its a th400 thing?. Cause all three I've had in did it. But everything else functions normal. Tomorrow I'm gonna take some data logs and send to my buddy that knows more about tuning with megasquirt than I do. Well see what he says., maybe I'm missing something. I'm really hoping its the tune. Which seems to be the only thing it could be right now. Thanks alot for your help. I'll post up what we find out
