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Old 10-20-2009, 07:59 PM
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T-400 Shifting Issues

Here is one for the transmission guys.

TH400, recently rebuilt, Transgo shift kit,

This transmission was installed in my jeep and working perfectly. Ran it for about 2500 miles. The ACC Boss Hog converter that was in it came apart and busted the case. So, I found another core th400. I tore my transmission down in order to get the output shaft out of it to go in my "new" core.

So, I put everything back together using a combination of the best parts from my original transmission and my new core. Transmission worked perfectly for about 50 miles then the shifting issues started.

Problem:
Trans shifts good and crisp through all gears. Trans gets up to 3rd gear and it seems to slip out of gear back to second after a while. Take your foot of the gas and the engine idles down. Most of the time, you can pull it back into second gear and then put it back in drive and it will shift back to 3rd for a while. but it will do it again.

This shifting issue mainly happens when the trans gets hotter. I can drive it to work in the morning and it is perfect. Coming home in the evenings it does it just about every day.

Thought I had it fixed (replaced the modulator and vacuum line), so I took the jeep on a 350 mile trip last weekend. 20 miles in, the shifting issue happened. So, I adjusted the shift linkage thinking that it may not be getting completely in gear. Ran perfectly for the rest of the trip plus 50 miles of low range idling and rock crawling. Drove it to work today and it happend again on the way home.

I have checked the governor, installed a new metal vacuum line to the modulator, and installed a new modulator. Going to drop the pan this weekend and see if there is anything obvious going on in there.

Any ideas on what this could be? The only thing that I can think of is some sort of debris that is stopping up some passage some where. Like I said, it ran perfectly for 350 miles after I adjusted the shift linkage alittle. I am out of ideas at this point.

Any help would be appreciated.

cm

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Old 10-22-2009, 06:30 PM
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Nobody want to take stab at this one?

Let me run this one by you all.
When I put the transmission back together, I used the complete transgo shift kit in my new built transmission. I used standard case and valve body gaskets on the valve body.
Right there in the transgo instruction sheet it says that a special case gasket must be used if using the transgo plate. I compared the old transgo gasket to the old stock gasket and sure enough, there are 2 extra holes in the transgo gasket. These holes lead directly to the 2-3 piston.

Does it make since that the 2-3 piston is not getting enough pressure to operate properly since the spring has been swapped out with a stiffer spring from the transgo kit?

This is where I am at. Will pull the pan and valve body and swap out the gaskets this weekend. Is there anything else in there I should look at while I have it apart?

Thanks,
cm
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Old 10-22-2009, 07:22 PM
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May want to inspect Governor & Gov gear on passenger side. Cover w/4-bolts.
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Old 10-22-2009, 08:41 PM
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You need to measure the vacuum at the modulator.

I would check the governor bore for wear , the governor also.

Loose governor gear is bad.

The Trango v-body plate.. is this a 3 thin plate setup? If so , the extra holes in the gasket only feeds the direct clutch with full amount of oil for the whole piston.

Quote:
Does it make since that the 2-3 piston is not getting enough pressure to operate properly since the spring has been swapped out with a stiffer spring from the transgo kit?
nope.... if you are talking about the stiffer spring for the PR system, it raises pressure.

You may have a clutch pack problem or sealing ring problem. A worn pump that is low on pressure

Dropping out of 3rd gear is usually a governor pressure problem or a vacuum problem (low or a leak) . Sounds like you addressed most of the vacuum feed to the modulator.

As I mention the pump may be a problem too

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Old 10-26-2009, 05:04 PM
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Just an update.
Saturday first thing I did was to check the pressure in all gears. All pressures were at or over maximum in the chart I had except for when the shifter was in "D". It was below the minimum in the chart. Took it all apart to change the gasket that I mentioned earlier. Found no problems in the valve body, gov. assembly, or anything else. Put it all back together with the proper trango case gasket on the valve body. Flushed the system and filled her back up. Checked the pressures again out of curiosity, and the pressure in "D" was at the max. in the chart.
So, after a few test miles, it now shifts better. The 12 shift has always been crisp and the 23 was at times weak. Now, the 23 shift feels just as firm as the 12 shift.
It seems to be fixed, but it will take some time before I trust it again.

Thanks for all the suggestions.

CM
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