Jeep T-400 shifting, skips 2nd gear - Hot Rod Forum : Hotrodders Bulletin Board
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Old 12-11-2011, 06:31 PM
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Jeep T-400 shifting, skips 2nd gear

I have a 79 Jeep J10 with a TH400 that I converted to 2wd. I also rebuilt it, new seals/gaskets, clutches, bands, but original steels (if you saw this trans, you may not have even put new clutches or bands in it; it was CLEAN with nice bright red fluid)....it was a school project for me. I did the engine this past summer at school too. Anyway...

Seems something isn't 100% because I have no 2nd gear, it goes from 1st straight to 3rd, and holds first for a bit but nothing i would consider excessive. Here is a rundown of the driving tests I did:

-In D, it shifts from 1st to 3rd and skips 2nd.

-I downshift from D, it goes into 2nd, and I put it back in D, and it shifts into 3rd.

-I start in first, and it holds it until it shifts to 2nd due to the safety feature built into the TH400.

-I start in 2nd, and it shifts from 1st to second fine, and holds until I put it in D, then it shifts into 3rd.

Modulator is adjustable and is new, I didn't adjust it at all. Line to it is also all new steel and rubber. I have it hooked to full manifold vacuum. Also, the wiring for the detent solenoid isn't in my truck at this time; I haven't put it back in yet.

So does this sound like a modulator that needs adjusting? Tire size is also 235/75R15 if that helps. If I need to adjust it, I know where the screw is to do it, but how do you set it? Thanks!

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Old 12-13-2011, 06:29 AM
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No, this is not a modulator issue. Manual 2nd works because in manual 2 or manual 1 above the 2-1 downshift speed the intermediate BAND is applied along with the intermediate clutch to provide coast braking. In D range the band is not applied. Only the intermediate CLUTCH (in the case in front of the center support) is applied. In 1st the direct drum is turning opposite of engine rotation at about 7/8 of input shaft speed, and when the intermediate clutch applies the sprag (one way clutch on back of drum) must lock. No 2nd immediately after rebuild suggests the sprag is misinstalled or missing, or broken. The only cause in the valve body for a 1-3 shift would be a sticking 1-2 valve, but this is rare, AND you DO have a manual 1-2 shift. Now, (hint) without the intermediate clutch, a high throttle manual 1-2 will be long, since the band does not have the same braking power as the clutch. You may feel a bump at the beginning of the shift, but the RPM drop is poor.


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Originally Posted by kevinz
I have a 79 Jeep J10 with a TH400 that I converted to 2wd. I also rebuilt it, new seals/gaskets, clutches, bands, but original steels (if you saw this trans, you may not have even put new clutches or bands in it; it was CLEAN with nice bright red fluid)....it was a school project for me. I did the engine this past summer at school too. Anyway...

Seems something isn't 100% because I have no 2nd gear, it goes from 1st straight to 3rd, and holds first for a bit but nothing i would consider excessive. Here is a rundown of the driving tests I did:

-In D, it shifts from 1st to 3rd and skips 2nd.

-I downshift from D, it goes into 2nd, and I put it back in D, and it shifts into 3rd.

-I start in first, and it holds it until it shifts to 2nd due to the safety feature built into the TH400.

-I start in 2nd, and it shifts from 1st to second fine, and holds until I put it in D, then it shifts into 3rd.

Modulator is adjustable and is new, I didn't adjust it at all. Line to it is also all new steel and rubber. I have it hooked to full manifold vacuum. Also, the wiring for the detent solenoid isn't in my truck at this time; I haven't put it back in yet.

So does this sound like a modulator that needs adjusting? Tire size is also 235/75R15 if that helps. If I need to adjust it, I know where the screw is to do it, but how do you set it? Thanks!
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Old 12-13-2011, 10:45 AM
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Thanks for the advice. When I rebuilt the trans, I did check the sprag, and it appeared fine and worked when i tested it (spun freely one way, locked up solid immediately when i tried to spin it the other way.)
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Old 12-13-2011, 10:57 AM
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well, if it was in backward it would bind up on the 1-3 shift, so thats not it. you could drop the valve body and air check thru the center support bolt and see if the intermediate clutch will apply. Are you certain you didn't make a blunder, like put the plates in, then answer the phone and forget to install the snap ring?
That kind of stuff happens all the time to professional rebuilders in shops. they get interrupted or distracted and forget something. While the valve body is out you can check the 1-2 shift valve.
Now i will mention this... on rare occasions we would get a tech call for a 350 or 400 and a 1-3 shift was repaired by replacing the governor. it would be worn in a weird way and at a stop would not make gov pressure, then after getting up to speed the gov pressure would suddenly jump up. but i've only seen that a couple times. check for loose valve, badly worn nails, or weights that are hanging up.

Dean

Quote:
Originally Posted by kevinz
Thanks for the advice. When I rebuilt the trans, I did check the sprag, and it appeared fine and worked when i tested it (spun freely one way, locked up solid immediately when i tried to spin it the other way.)
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Old 12-13-2011, 12:53 PM
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Everything checked out fine as far as the governor goes, but my research on other sites has also shown that to be a possible cause, so i'll be pulling it back out soon as I get a chance. I know the gear looked fine, and from what I recall it wouldn't spin when the gear was meshed with the gear on the output shaft.

Now, I will admit that the valve body was removed from the case but we didn't take it apart, didn't have the time as the semester was winding down and we still had to get it in the truck. I also did not pull the sprag out because it worked fine when we checked it.

Funny you should mention the snap rings....when we were putting it together, we did forget the spacer snap ring that goes under the center support. BUT we took it back apart and put it in, so every snap ring is where it belongs in the case. the only leftover parts were the extension housing bolts from the old transfer case adapter; they were too long for the 2wd extension housing.
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Old 12-13-2011, 03:43 PM
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ok but you need to check the weights, and see if they wobble on the nails, as if they are worn thinner, dig? try to move the valve around and see if there is bore clearance inside. but the bottom line is, if you change the governor and still have the problem, we are probably looking somewhere else.
Do you have an air compressor so u can do the int. cl. air check?


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Originally Posted by kevinz
Everything checked out fine as far as the governor goes,
...it wouldn't spin when the gear was meshed with the gear on the output shaft.
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Old 12-13-2011, 07:15 PM
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Yes I do have a compressor and can do checks on the intermediate clutch. Now, I took it to school tonight and did some modulator adjustments, but the problem is still there; I did it cuz it was quick and easy enough to do so I figured it's worth a shot. I have the adjustable screw in the glovebox because i took it out as suggested on another forum; still does it.

Now, here is something else that may help: it WILL shift through all gears if i am barely on the throttle. You can clearly feel 1-2 and 2-3 upshifts. But anything more than 1/4-1/2 throttle and no 2nd. My teacher seems to think, as have many, that this may be a problem with my governor. Does that help you any?
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Old 12-14-2011, 10:09 AM
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> Yes I do have a compressor and can do checks on the intermediate clutch.

OK good, next time valve body is off we’ll air check it.

> I have the adjustable screw in the glovebox because i took it out as suggested on another forum;

What?? I don’t know why in the world someone would suggest that. That just drops modulator pressure below the minimum safe range. Put it back in!!
And its a pointless test. You already know it will 1-2 at minimum throttle. And do yourself a favor. Don’t get advice from that source about trans stuff. That person is obviously not a transmission professional.

> it WILL shift through all gears if i am barely on the throttle. You can clearly feel 1-2 and 2-3 upshifts. But anything more than 1/4-1/2 throttle and no 2nd. My teacher seems to think, as have many, that this may be a problem with my governor.

doubtful.
Here’s what I would do. Put it up on the rack, or on stands with wheels off the ground. Put a vacuum pump on the modulator. Pump up about 16” vac and spin the wheels up. 1-2, 2-3. Then drop it to 10” vac and spin it up again. The shifts should be a little later and firmer. Repeat at 5”, then at 0”. If you can continually feel distinct 1-2 and 2-3 shifts in the air with no load, just a little firmer and later, then the problem is related to TORQUE and LOAD. The clutch is slipping under load, probably due to a leak in the int clutch circuit (cracked 2-3 accu piston or damaged seal ring, cut int cl lipseal, broken center support bolt, etc) or possibly a mechanical problem like broken case lugs, snap ring partial out of the groove, or something like that. This rack test would also show the governor is ok, but the real problem is slipping int clutch. And if you left the modulator line disconnected and plugged, and test it at light throttle on the street, you will have high rpm shift, but you could feel the 1-2 then immediately after the shift increase torque and it would start slipping. Dig? Thats proof the clutch is in trouble.

And by the way, did you use any valve body kit? Some of them risk breaking the case lugs on hi throttle shifts. For this reason i always use a torqueflight .106" thick hi clutch snap ring in the case lugs (it's more rigid) to help prevent breakage, and also use the waved steel (NEVER all flats). The wave helps to load the case lugs more evenly and without shock at the front end of the 1-2 shift.

Dean
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Old 12-14-2011, 10:42 AM
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Thank ya much again for your help! I'll put that screw back in tomorrow or next time weather allows, truck isn't going anywhere for a bit so I can work this issue. I will do as you suggested with the vacuum pump since I have that and can do it easily. Now, as to your other suggestions, I can safely say the case lugs were fine when I rebuilt it and the snap rings were all very secure in their grooves. Granted the truck has been used since then but not much; maybe for about 3 or 4 miles. I specifically remember that center support bolt because for whatever reason, we went through hell trying to find a socket thin enough to fit it; it's in place and torqued down. All lip seals are new, but who knows; maybe I boogered that intermediate one up (just so I know what we are discussing, that is the piston on the center support itself, right?)

The 2-3 accumulator piston...is that the little plastic one that always breaks? Mine was broken when I pulled it so I put one of the aftermarket aluminum ones in it. I had heard that can possibly cause problems, but I don't see how...it's exactly like the plastic one, only metal.

No valve body kits, if you mean shift kits. Just pulled it off, replaced the gaskets and made sure the passages were clean and the case not warped. So it's all stock.
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Old 12-15-2011, 01:46 PM
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OK, so i put the screw back in and did the above test with a vac pump. Found that it only shifts once, and you can BARELY feel it, its almost like a bump instead of an actual shift. No shift after that. Manually shifting back down into 2nd and then back into D does allow a 2-3 shift. Did this with vac at 16, 10, and 5 in, and it acted the same.

Is it usual for people to have these problems if they replace the small plastic accumulator piston with an aluminum one? That's the only "upgrade" this trans had over stock, because the plastic one was broken.

Sooo....does this mean I'll be pulling the trans back out of the truck to fix a bad int. clutch piston seal or sprag? Or is it the governor?
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