# TH400 Problems



## BearGFR (Aug 25, 2008)

So, today Mrs. Bear and I got really brave and decided to make the first road trip in the Beast - about 100 miles or so away from home for the weekend.

We took her step-mom out for dinner tonight, on the way back to her place I started noticing a tranny problem. Oh boy.

Background...
I've been noticing for "awhile" that in drive, on the 1-2 shift, at light throttle it will occasionally make an odd sound, sort of like a brief ratcheting sound followed by a sort of 'clunk' when second engages. Not all the time, just sometimes. I've never experienced it when shifting manually or when being a little more energetic on the thottle. It seems to get better once the trans gets good and warm - maybe. Whatever it is/was, it didn't seem like a horrendous problem so I haven't really dug into it.

Now the real issue:
What happened tonight was, leaving the restaurant something changed. --- Now the 1-2 shift is VERY soft and slow - regardless of whether it's automatic or manual, and it's that way at every throttle opening I've tried. Even worse is now on the 2-3 shift, if it's manual, there's a period where it almost sounds like everything is completely "disengaged" and the engine is freewheeling. The automatic 2-3 shift seems mostly ok, perhaps a tad softer than it was but not much more so. It's definitely much firmer than the now wimpy 1-2 shift.

It's still drivable as long as I treat it sedately, thank goodness, since we're still 100 miles away from home and plan to be for the rest of the weekend.

Are these symptoms ringing any bells with anyone?

Thanks,
Bear


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## 05GTO (Oct 6, 2004)

Maybe a vacuum leak or bad modulator, where are you getting vacuum for the modulator? carb port or manifold?


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## BearGFR (Aug 25, 2008)

I'd love it if it was a bad modulator. It "looks" new but I don't recall for sure if the trans shop replaced it or not. It's pretty irritating because the transmission/converter combo is the ONE mechancial assembly on this car that I didn't build myself, and I've already had to take it back once to get them to re-do the converter because they didn't get the stall speed right. Vacuum is coming from a non-ported manifold source. I supposed I could just replace it and see if it changes anything.

Bear


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## GTO JUDGE (May 14, 2005)

Bear....

Before my valve body was removed and tweaked I experienced:

Had shifting from 1st to 2nd when in auto shift along with a clunk. This was pronounced when the oil was hot. When cold it would shift smooth.

Ratchet shifting from 1st to 2nd, again hard shift and clunk. 2nd to 3rd seemed ok.

The issues: Check ball not in the required #4 spot, other check balls installed and not necessary, they were removed...... 1-2 accumulator spring was incorrect.......2-3 accumulator puck not flipped....separator plate holes were too large which contributed to the hard shifting.....Vac modulator was adjusted in too far which attributed to harsh shifting....and the vac mod valve was sticking to the bore which was also causing hard shifting.....shift kit was also contributing to this. The screw in the vac modulator, if adjust in too far it can affect your mph and harshness.

Someone not knowing what the hell they were doing got their lunch-hooks on the valve body had it all screwed up.

The transmission fluid not flowing properly through the valve body may be the cause of the sluggish shifting plus a separator plate issue?..... 

The fellow that redid my valve body and inspected the rebuild of my transmission is an authority on TH 400's. He diagnosed my issue pretty much by description. As soon as he removed my valve body he could see the issue.

I am NOT an authority on transmissions but I learned much from him, your issue to me sounds like its a valve body issue.

I have the recipe and diagram he used to correct my issue. I have it if you'd like it. If it comes down to a valvebody issue, this diagram and recipe will get you fixed up. My transmission is set up is capable of handling 700HP and is capable and running a high single digit 1/4 mile time. The valve body he modified made a world of difference. I had learned during a typical transmission rebuild the valve body is not typically touched. Not many are versed on the proper set up of a valve body I learned. 

When ratchet shifting at 5K the car just launches. The valve body was the key in getting the trans to respond.


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## Eric Animal (Oct 28, 2007)

Bear, Automatic trannys are basically magic to me. I would TRY to find a good transmission shop and get this fixed prior to the 100 mile drive home...I know it's no help...just sayin'  Eric


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## geeteeohguy (Feb 2, 2008)

Bear, IMO you have a hydraulic pressure problem. Everything Judge says is right on the money. These trannies are fairly simple if you take the time to look at them....basically fluid under pressure directed by and pushing spool valves to apply and disengage clutches and bands. Like a brake system. Not enough pressure at the right time, and you get no, slow, or weak engagement (slippage). I would talk with Jakeshoe or Cliff on the other forum. They have EXTENSIVE TH400 knowledge, and you're pushing a bunch of HP with your combo. Most of the time it's a valve body problem, and usually form the get-go. That it "happened" after a few miles tells me something changed, and not for the better. Do you have a warranty on the trans??


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## GTO JUDGE (May 14, 2005)

The guy that did my work is on the PY forum as well. He is out of Lansdale PA. I can give you his user ID if you like Bear.


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## BearGFR (Aug 25, 2008)

Thanks guys. - yes PLEASE on the diagram. It seems better today -almost normal, which is odd, but now I'm spooked about it. I've got a spare at home in the garage, maybe it's time for Bear to learn transmissions. 

Bear


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## GTO JUDGE (May 14, 2005)

Bear, I emailed you the diagram recipe hope it helps.


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## Rukee (Feb 8, 2007)

BearGFR said:


> Thanks guys. - yes PLEASE on the diagram. It seems better today -almost normal, which is odd, but now I'm spooked about it. I've got a spare at home in the garage, maybe it's time for Bear to learn transmissions.
> 
> Bear


Did 2 for myself and they worked out. I have one bench with a thick metal top, I welded a bolt facing up right on the edge and then hung the tranny on it by one of the bell housing bolts. Made it much easer installing the internals. Biggest thing is keeping everything clean, even the fibers from a cloth rag can botch things up. Don't ask me how I know...


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## ALKYGTO (Mar 29, 2010)

Eric Animal said:


> Bear, Automatic trannys are basically magic to me. I would TRY to find a good transmission shop and get this fixed prior to the 100 mile drive home...I know it's no help...just sayin'  Eric


^:lol: Yeah, I've always said tranny guys are like Voodoo Witch Doctors!

Good luck Bear, hope you can get it resolved. My car always likes to act up when the Missus is with me .


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## geeteeohguy (Feb 2, 2008)

Bear, I did mine in March of last year, and so far so good. Used a 16 gallon oil drum as a holding fixture (garbage can technique). There are about 3 "special tools" that make the job much easier, used to install the seals on the apply pistons. Judging by what you've done so far, and by your aptitude and smarts, you could easily rebuild the trans that you have already "sitting on the bench". Go slow, and step by step. It is NO harder than building anything else, just a big "model kit" for grown ups. The cost of my kit was about $200 and it had everything....and you can use your expensive converter. The big myth is that you need special frictions, etc., but you can do extremely well with regular stuff. The pressures have to be up to snuff, and the case and sprags have to be top notch. With the help of the real experts (Like Jake and Cliff) you'll get 'r done. And then, there will be NOTHING on the car you can't do!!!


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## NorwalkNugget (Aug 5, 2011)

If i had my own house / garage with a bench I'd rebuild my tranny myself. Tired of these suspect looking shops robbing me of my money.:shutme


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## BearGFR (Aug 25, 2008)

Back home safe and sound now. They story gets weirder. Saturday morning after sitting overnight, it seemed a lot better. Today it was still fine - even after driving 100+ miles home (dang I love driving this thing!!!! :cool).

Manual 1-2 and 2-3 shifts were nice and firm/quick at part throttle. I didn't get very agressive with it while we were still away from home, after what happened though. I know broken parts dont' fix themselves, and it would have been just as hot after driving home today as it was Friday night. Weird. :confused

I'm off tomorrow so mayhaps since it's home I'll attempt a bit of more aggressive testing.

Bear


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## geeteeohguy (Feb 2, 2008)

Bear, if it's an intermittent, more likely it's hydraulic related and not a mechanical hard parts failure. That would have stayed broken, and gotten worse. You could have had a sticky valve in the valve body hanging up and causing your woes.....driving and the action of the hot, high-detergent ATF could have cleared it up. If nothing else turns up, you might want to drop the pan and change out the filter....and take the opportunity to check the pan for debris or dirt.


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## BearGFR (Aug 25, 2008)

Good idea that - examining what evidence might be lurking in the pan.

Bear


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## Hot_Rod (Feb 10, 2011)

If you need a tranny guy I got one. He's good. Used to be a GM tech, rebuilt my TH350 for 579$ and replaced everything in and around it. With new stock converter.

No issues with my trans whatsoever. 

He's a real big hot rodder, some really nice cars are always at his shop. I trust his work. 

Hope you figure out your issues.


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## BearGFR (Aug 25, 2008)

Thanks Hot Rod, I may take you up on that. Since it seems to have settled down for now I've put the trans mystery on the back burner.

Bear


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## Hot_Rod (Feb 10, 2011)

No problem. Youve been helpful with your knowledge so if I can help, I'll gladly oblidge.(sp?)


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