C6 - no third gear, control pressure tests...
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Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
C6 - no third gear, control pressure tests...
My main concern is no third gear after my rebuild. I have reverse, 1st and 2nd, but it does not want to shift into third no matter what I do.
Today I performed a control pressure test and the results are surely off. I'm just not sure how to interpret -
At 20"
N = 85 PSI
Forward gears = 80
Reverse = 140
At 10"
N = 140 PSI
Forward gears = 135
Reverse = 220
At 2-3"
N = 180 PSI
Forward gears = 170 PSi
Reverse = 220
I have a decent roller cam in the engine so it lopes and the needle was bouncing around a bit despite the consistent vacuum pump vacuum.
Reverse works just fine and it seems to shift from 1-2 just fine, but never to third. I'm inclined to think I have a governor problem, but maybe the experts can see other possible problems? Any help is appreciated!
Today I performed a control pressure test and the results are surely off. I'm just not sure how to interpret -
At 20"
N = 85 PSI
Forward gears = 80
Reverse = 140
At 10"
N = 140 PSI
Forward gears = 135
Reverse = 220
At 2-3"
N = 180 PSI
Forward gears = 170 PSi
Reverse = 220
I have a decent roller cam in the engine so it lopes and the needle was bouncing around a bit despite the consistent vacuum pump vacuum.
Reverse works just fine and it seems to shift from 1-2 just fine, but never to third. I'm inclined to think I have a governor problem, but maybe the experts can see other possible problems? Any help is appreciated!
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 965
From: Tri Cities, TN
Pressure looks OK, I usually shoot for 80-90 PSI at twice idle in "N" or "P".
Might be the 2-3 shift valve if you put in a shift kit you might want to pull the valve body and check everything. Lots of springs and check ***** in there that can easily get missed.
Might be the 2-3 shift valve if you put in a shift kit you might want to pull the valve body and check everything. Lots of springs and check ***** in there that can easily get missed.
Thread Starter
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Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
I took it for a short test drive today and it's not shifting when in D, has first and second gears, but not shifting. I'll start pulling the transfer case tomorrow to get to the governor.
Thread Starter
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Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
Okay, so here is a question I haven't been able to answer - what is the pressure supposed to be at the test port above the vacuum modulator? Without vacuum it is steady at about 50 PSI. With engine vacuum it varies, starting very low, maybe zero and raises with lower vacuum. I'm not sure where this port is in relation to the modulator... before or after, hence I have no idea how to interpret.
Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 965
From: Tri Cities, TN
That is the throttle valve pressure. It will change with changes in vacuum because that is the job of the modulator valve to make the trans shift harder or softer depending on the engine load. In order to check that you have to use the shop manual for your transmission. It won't stop the transmission from shifting. If it is messed up the trans will either have lazy soft shifts at the low end or harsh hard shifts at the high end. Most transmissions would fall into TV = 25 # + - at 29.5 barometric pressure with 80 # + - control pressure 14 inches or so manifold vacuum.
You need to be more descriptive with what it isn't doing. Reading your posts it seems it is shifting from low to second when in drive but not into third. Sometimes if a shift valve is stuck or the governor is stuck you can just get out on the road and go wide open throttle and wind it up in D and let off of the gas a couple of times and maybe it will break loose.
But I have the feeling that there is going to be some disassembly required.
You need to be more descriptive with what it isn't doing. Reading your posts it seems it is shifting from low to second when in drive but not into third. Sometimes if a shift valve is stuck or the governor is stuck you can just get out on the road and go wide open throttle and wind it up in D and let off of the gas a couple of times and maybe it will break loose.
But I have the feeling that there is going to be some disassembly required.
Lead Driver
Joined: Mar 2004
Posts: 8,922
Likes: 153
My main concern is no third gear after my rebuild. I have reverse, 1st and 2nd, but it does not want to shift into third no matter what I do.
Today I performed a control pressure test and the results are surely off. I'm just not sure how to interpret -
At 20"
N = 85 PSI
Forward gears = 80
Reverse = 140
At 10"
N = 140 PSI
Forward gears = 135
Reverse = 220
At 2-3"
N = 180 PSI
Forward gears = 170 PSi
Reverse = 220
I have a decent roller cam in the engine so it lopes and the needle was bouncing around a bit despite the consistent vacuum pump vacuum.
Reverse works just fine and it seems to shift from 1-2 just fine, but never to third. I'm inclined to think I have a governor problem, but maybe the experts can see other possible problems? Any help is appreciated!
Today I performed a control pressure test and the results are surely off. I'm just not sure how to interpret -
At 20"
N = 85 PSI
Forward gears = 80
Reverse = 140
At 10"
N = 140 PSI
Forward gears = 135
Reverse = 220
At 2-3"
N = 180 PSI
Forward gears = 170 PSi
Reverse = 220
I have a decent roller cam in the engine so it lopes and the needle was bouncing around a bit despite the consistent vacuum pump vacuum.
Reverse works just fine and it seems to shift from 1-2 just fine, but never to third. I'm inclined to think I have a governor problem, but maybe the experts can see other possible problems? Any help is appreciated!
Thread Starter
|
Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
Thanks for the posts guys. I'll have to watch that video.
Crop.Duster - The transmission does not shift automatically. In first it seems just fine, manually shift to second also seems fine, reverse fine, but in drive it stays in first and won't shift. Checked vacuum line to the modulator that's good.
Crop.Duster - The transmission does not shift automatically. In first it seems just fine, manually shift to second also seems fine, reverse fine, but in drive it stays in first and won't shift. Checked vacuum line to the modulator that's good.
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Logistics Pro
Joined: May 2015
Posts: 4,469
Likes: 965
From: Tri Cities, TN
My friend I don't know exactly what to tell you. There are several things that can cause your problem. Depends on how you want to proceed. If you want to try to fix it without pulling it, about all you can do is remove the modulator and make sure the modulator valve and pin are in correctly. Remove the tail shaft housing and install a new or at least a good used governor. There are plenty of used and new governors out there the casting number on the last of them was E4TP-7A300-AA. I've had C6's around for decades and to be honest I've never had a governor fail. Remove the valve body and make sure every piece is in correctly with the correct springs also I would install a (new) separator plate if you didn't do that already.
Good luck, hopefully you have a lift.
Good luck, hopefully you have a lift.
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Thread Starter
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Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
No lift, but I have a decent floor jack. I removed the governor today and larger valve was in pretty rough shape. I pulled another governor that was in much better shape and installed it. I'll finish the transfer case linkage and driveline install tomorrow. I'll be sure to update with any progress.
++++++++++++++++
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Laughing Gas
Joined: Sep 2013
Posts: 1,114
Likes: 103
From: North Idaho
Thanks Crop Duster! It's been quite an adventure! Shifts are very firm. I should probably do a 0 to 60 and see how much time it has trimmed off. It seems noticeably faster. Lower first gear, much firmer shifts, and a little less weight than the NP203.
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