TH350 dragging in low gear

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nxtruck
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TH350 dragging in low gear

Post by nxtruck » Sun Mar 06, 2016 5:11 pm

I recently had a friend of mine rebuild my TH350 and make a few upgrades while he was in there. This tranny was working fine before the overhaul. He replaced the stock forward drum/input shaft with an ATI hardened input shaft/drum combo, replaced the stock direct drum piston with a thinner one from Coan to be able to run 5 clutches instead of 4, and replaced the stock TH350 low/reverse clutch support with one out of a 700R4 to be able to run the wider low/reverse roller sprag clutch. Obviously, all the frictions and steels were replaced, also. Everything else was put back in.
I had a chance to get the truck out and test the tranny yesterday and noticed something strange in low gear. It drags in low gear at higher rpm. Taking off from idle @ 1000, it feels ok. But bringing the rpms up to around 2500-3000 or so, it feels like the brakes are being applied and it seems to get worse the higher you spin it up. Both 2nd and 3rd gears feel fine. One other thing that I noticed is that it doesn't bang nearly as hard when going from neutral to reverse, but this may not be related, or even a problem. The 1-2 shift is not quite as firm as it was before, either. I'm not too concerned about the 1-2 shift or the reverse engagement, but the dragging in low gear has me very concerned. I even noticed the few times that I ran it up in low gear that you could smell something getting hot, kinda like trans fluid.
If anyone has any ideas about what could have been overlooked, please let me know.
Thanks in advance!!

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Re: TH350 dragging in low gear

Post by Greenlight » Mon Mar 07, 2016 7:07 pm

Check the intermediate clutch pack clearance by removing the oil pan and using a screwdriver to move the clutches.

If the intermediate band is binding or does not have adequate clearance, it MAY also cause your problem. I'm not sure you can check this w/o removing the valve body.

If you do remove the valve body, please ensure that all of the check balls are in the correct location.
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Re: TH350 dragging in low gear

Post by nxtruck » Mon Mar 07, 2016 8:48 pm

Thanks for the reply!
Do you know what the intermediate clutch pack clearance is supposed to be? I think that checking this would be easy enough, but I've got a feeling that I'll be pulling the tranny back out.
I do know that this particular valve body doesn't use any check balls anywhere.

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Re: TH350 dragging in low gear

Post by Greenlight » Fri Mar 11, 2016 12:38 am

The intermediate clutch pack clearance should be a minimum of about 0.060", but most have about .080".
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Re: TH350 dragging in low gear

Post by nxtruck » Fri Mar 11, 2016 11:46 am

Thanks for the reply!
I'm planning on dropping the pan this weekend and having a look. I ordered the correct valve body gaskets from TCI and I'll check the int. clutch pack clearance when I drop the valve body. If, in fact, the int. clutches are set up too tight, where do I go from there? Are there select-fit pressure plates or different thickness steels? Sorry for the questions; I just wanna make sure I'm going in the right direction with it.
Thanks again!

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Re: TH350 dragging in low gear

Post by Greenlight » Fri Mar 11, 2016 8:28 pm

The builder MAY have put too many fiber or steel clutches in it.

Most transmissions take 3 fiber clutches. There is the thick "pressure plate" that goes into the case first. Then it's fiber, steel, fiber, steel, fiber , steel, then a "wave plate".

In a race transmission I normally replace the wave plate with a steel plate.
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Re: TH350 dragging in low gear

Post by nxtruck » Sat Mar 12, 2016 3:59 pm

Greenlight,
I wanted to let you know what I've found so far. I removed the pan and filter and measured the int. clutch clearance and have approximately .114" clearance. I'm hoping that's not too much clearance. I have some V.B. gaskets ordered from TCI, but they haven't made it here yet. I did find some material that kinda looks like black gasket shredded up on the filter and that makes me think that could be the issue, but without the new gaskets to look at, I'm not sure at this point.
You had mentioned the int. band as a possible culprit. I'm guessing as long as it's not bound up on the drum that the clearance there is ok?
Thanks for all of your help!

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Re: TH350 dragging in low gear

Post by Greenlight » Wed Mar 16, 2016 6:52 pm

The 0.114" clearance is a tad high, but shouldn't be causing your problem. Once you have the valve body out, you can remove the intermediate band apply piston and use a screwdriver to apply to band through the intermediate band piston pin hole. I think you should be able to get a good feel if it is correct or not.

One more thing, in the direct drum (the drum not attached to the input shaft), there are three seals. Two on the piston and one in the drum. I am not sure what would happen if the seal located in the drum were installed upside down (lip facing wrong direction).

I am also puzzled that there are no check balls in the case. Can you please double check the instructions that came with the shift kit/valve body, etc.?
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Re: TH350 dragging in low gear

Post by nxtruck » Thu Mar 17, 2016 11:39 am

Well,
My gaskets came in Tuesday and I had time to put them in. I did see some differences in the gaskets, as in one or two holes were in the TCI gaskets that weren't in the stock ones. I couldn't tell anything was out of order with the band and reinstalled the valve body with the correct gaskets.
During the test drive, I could tell that the dragging wasn't as bad as before, but was still there. The only difference I could tell was that before the dragging would be noticeable around 2500 or so and now you don't notice it until around 3500 or so rpms. The gear engagement felt about the same.
I did double-check the instructions for my valve body and it says that the 4 Teflon balls sitting on the plate can be discarded. I also removed that seal you referred to, as per the instructions. It says to remove the center seal located in the direct drum, which will make the 2-3 shift a lot firmer.
I believe I'm going to pull it back out and double-check the direct clutch pack clearances and add a bleed hole to the direct piston.
One other thing I noticed while backing the truck into the shop is that, while in reverse, the truck seem to be chattering somehow. Not very noticeable, but I did notice that something didn't feel quite right. It only did that in reverse. So, I'm going to be looking for possible causes for that, also.

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Re: TH350 dragging in low gear

Post by Greenlight » Fri Mar 18, 2016 1:13 am

What year is your transmission? Is it a lockup convertor style transmission (~1980 and up)? If so, it should have 5 check balls.
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Re: TH350 dragging in low gear

Post by nxtruck » Fri Mar 18, 2016 5:04 pm

My tranny isn't a newer lock-up style tranny. It's a mid-70s case, non-lock-up style tranny.

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