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Old 03-11-2019, 11:33 AM   #1
rcazwillis
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TH400 No 2-3 Shift

Last big hurdle on Zane's 71. Transmission will not shift into 3rd.
History: I built it. Have built many without issue, mostly for track use. Have built some with issues, but always managed to sort my error.

Symptoms:
Won't shift into 3rd. 1-2 shift is good.
Reverse shutters a bit at first, does not engage quickly, but will engage. Does not slip once engaged.

Two "upgrades" during build:
Dual feed direct clutch: Removed seal between two chambers. Failed to plug the reverse hole in case. Assumed this was the cause of both issues. Plugged it over the weekend, still won't shift into 3rd. Checked governor, All weights move freely, valve moves freely, teeth are all good, gear on output shaft all good.
Plugged 2-3 accumulator piston in valvebody removed spring under piston. Verified it was correct this weekend.

Ordered pressure gauge and will check pressures per the ATSG manual this week.

So where do I go now? Seal problem in the direct clutch pack? Valve for 2-3 reassembled wrong? This would not make reverse shudder, not engage well. Burned up direct clutch pack when case not plugged?

Is there anything I have not checked before tearing it all back a part.
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Old 03-11-2019, 02:27 PM   #2
rcazwillis
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Re: TH400 No 2-3 Shift

One other symptom. Sometimes it whines when it goes into 2nd gear. No whining in low or reverse.
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Old 03-11-2019, 08:42 PM   #3
Steeveedee
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Re: TH400 No 2-3 Shift

Shuddering in reverse might be related to the vacuum modulator? Is the 1-2 shift late and harsh?
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Old 03-11-2019, 09:00 PM   #4
rcazwillis
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Re: TH400 No 2-3 Shift

1-2 seems to be fine. One of the punch list items is check the vacuum and verify the valve is moving behind the modulator.

Also wondering if I assembled the 2-3 valve in the valve body correctly. Will pull the valve body and take the valves apart to see if I assembled them correctly before pulling transmission.

Will also be checking pressures.
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Old 03-13-2019, 08:47 PM   #5
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Re: TH400 No 2-3 Shift

Direct drum seal issues will give you slow to react Reverse and no 3rd....

Did you air test it on the bench?

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Old 03-13-2019, 09:31 PM   #6
rcazwillis
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Re: TH400 No 2-3 Shift

Quote:
Originally Posted by AussieinNC View Post
Direct drum seal issues will give you slow to react Reverse and no 3rd....

Did you air test it on the bench?

I don't recall. It has been 6 months. I always have in the past. Wondering without the case plugged if I ruined the clutch pack.

Plan:
1. Check vacuum at modulator, modulator, and valve. Shift 1-2 is good, so don't expect to find anything.
2. Check pressures. Expect low pressure in D.
3. Pull valve body, check 2-3 valve and all other. Wondering if I put it together wrong.
4. Pull trans, tear it down and and rebuild. Expect to find problem with direct clutch pack, whether a seal or burnt clutches.
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Old 03-14-2019, 08:36 PM   #7
AussieinNC
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Re: TH400 No 2-3 Shift

Sounds like a plan to me....

I have built maybe 400 of these...

I always set direct clutch clearance at 1/16" - 3/32"...

These direct drums usually don't cause major issues....but if you have another one, maybe build that one and use it...to eliminate a possible bad drum?

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Old 03-15-2019, 12:58 AM   #8
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Re: TH400 No 2-3 Shift

No vacuum to the regulator? Or is it modulator. Been a long time.
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Old 03-15-2019, 09:20 AM   #9
rcazwillis
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Re: TH400 No 2-3 Shift

Quote:
Originally Posted by AussieinNC View Post
Sounds like a plan to me....

I have built maybe 400 of these...

I always set direct clutch clearance at 1/16" - 3/32"...

These direct drums usually don't cause major issues....but if you have another one, maybe build that one and use it...to eliminate a possible bad drum?

Thanks for the info. I don't recall the clearance. I know I checked it against the book I was using and it was in tolerance. Had to buy feeler gauges as I could not find mine. When I put it together, I will use your #s for sure.

I have no spare parts at this time. Have been watching craigslist for a core thinking I would build it and do a swap. Have not found a short tail housing yet.
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Old 03-15-2019, 09:21 AM   #10
rcazwillis
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Re: TH400 No 2-3 Shift

Quote:
Originally Posted by franken View Post
No vacuum to the regulator? Or is it modulator. Been a long time.
The 1-2 shift works and it requires vacuum at the modulator. I will be checking it, but don't expect to find an issue there. My best guess will be the direct clutch pack seals.
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Old 03-15-2019, 10:24 AM   #11
rcazwillis
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Re: TH400 No 2-3 Shift

Quote:
Originally Posted by AussieinNC View Post
Direct drum seal issues will give you slow to react Reverse and no 3rd....

Did you air test it on the bench?

How is the best way to air test the direct? Where do you pressurize the assembly? Could I test this by blowing air in the direct clutch feed hole? The reverse side is plugged. I should be able to hear the assembly pressurize and hold pressure? Correct?

How do you do this while it is on the bench?

Just thinking ahead to make sure I do it correctly. I have not had problems checking seals with compressed air in the past, but you never know.
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Old 03-22-2019, 09:56 PM   #12
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Re: TH400 No 2-3 Shift

Resolved the issue. Started the morning by backing the truck into the garage.
Truck was reluctant to back up the drive. Had to drive up the neighbors drive and floor it to get up the drive. I knew I was going to find something..

Pulled the trans, rebuilt it, and reinstalled it today. The 3-2 down shift valve in the valve body was assembled wrong. The direct clutch pack was toast. Thirteen hours later, truck shifted into 3rd as expected.

On the test drive, something was going clunk. Found the left upper a-arm was loose. All the shims were laying on top of the spring bucket. Time for an alignment.
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