Shifting late Th400

[Burbra]

New here guys, I just got this 1990 suburban 4wd 2500 and it won't shift to 3rd (I think) until about 45 or 50mph and it's taching hard by that time. If I let off before it shifts when I hit the accelerator again, it feels like it slips for a few seconds before I feel it accelerating again. I dropped the pan and changed the filter, didn't help. The old fluid was filthy and very fine metal dust covered the round magnet in there but no real large shavings. . What is next on the trouble shooting list?

 

[HotRodPC]

Kinda sounds like you might be saying no engine braking either. The filthy and very fine metal dust like material, and/or sludge sounds to me as if it's burnt up clutches. Off the top of my head, for some reason I'm wanting to say you might have a burnt up band too. Again, my flow charts are not handy to look up what clutch packs and bands are needed for which gears to make a diagnosis. However, the diagnosis doesn't matter much when the trans needs to come out and be taken apart since you're going to do the whole transmission of you do that. But yeah, I hate to be the guy with the bad news but it sounds like a wore out or burnt up clutch pack and/or band.

What gear ratio do you have in the rear end? Are you sure it's not shifting from 1st to 3rd and skipping 2nd? Reason I suggest that is cuz you mention the slipping before it grabs again if you let off it. As if it wants 2nd gear but it's not there, so it goes onto 3rd. You can manipulate a transmission to skip a gear by using high rpm then letting off. That's usually in the Th350 for example when you have a broken intermediate roller clutch.

 

[74 Shortbed]

I wouldn't mess around with it, I'd be tearing it down before it gets worse..

 

[Burbra]

Yes, I should have put that in there too, when I let off the throttle, it does not engine brake. Sounds like a rebuild is needed. Damnit. This is the first vehicle I've ever worked on really, and of course I don't think I'm ready for that level yet. I'll ask around my buddies and see if any of them will help me. I assume this isn't something a beginner should do alone?

 

[74 Shortbed]

The 400 is about the easiest thing to rebuild, this manual has step by step with pics on disassembly and assembly, pay attention to detail and you won't have any problems, I did my first one many moons ago with this and I only needed it once..

http://files.dpbrands.com/bm/instructions/20229.pdf

 

[crpntr78]

I agree. Transmissions sound intimidating but in reality they're pretty simple. IMHO.

 

[Burbra]

Well that's good news guys. I found a used one for $150 the guy said he'd take it back if it didn't work, at least that will give me time to rebuild the original.

 

[HotRodPC]

$150 for a working Turbo 400 is a steal. The core alone is worth $100. If you're mechanical at all, and can develop some patience, with some help here, you can probably do it yourself. Th350 and Th400's are about the easiest transmissions to build.

 

[Burbra]

Turns out the one I can get for 150 is a heavy duty version from a motorhome. This shouldn't effect anything short of swapping the output shaft right?

 

[Burbra]

Well, lessons learned, lessons learned.
So, I got the transmission, start going through the disconnecting things to begin and realize the vacuum modulator isn't connected. Reconnected it and everything works fine again.

Saved several days of work, and the guy took the transmission back no questions asked.

 

[Rusty Nail]

Uhhh... I would have bought it.

 

[Burbra]

Uhhh... I would have bought it.

I thought about it, and would have, but holidays you know... got the burb some brownie points with the wife too.

 

[HotRodPC]

Well, lessons learned, lessons learned.
So, I got the transmission, start going through the disconnecting things to begin and realize the vacuum modulator isn't connected. Reconnected it and everything works fine again.

Saved several days of work, and the guy took the transmission back no questions asked.

Uhhh... I would have bought it.

Hell yes. I woulda bought that motorhome transmission.

 

[87scotty]

on a side note when i change tranny fluid i usually put one bottle of lucus stop slip. not because it says stop slip but it has the most friction modifiers. which you lose when you change the fluid just imho