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So the title is a bit weirdly worded but basically when I shift into reverse from drive or any other gear i get a really big jolt backwards when the gear engages. now its gotten a bit more violent today when i gave the refurbished Govenor a good test run around town. me and Rich Hanlon have come to a point where we think its being caused by the torque converter.
anyone got any ideas on what could be causing the issue?
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(06 Feb 2023, 15:08)theningiachicken Wrote: So the title is a bit weirdly worded but basically when I shift into reverse from drive or any other gear i get a really big jolt backwards when the gear engages. now its gotten a bit more violent today when i gave the refurbished Govenor a good test run around town. me and Rich Hanlon have come to a point where we think its being caused by the torque converter.
anyone got any ideas on what could be causing the issue?
My other thought was fluid pressure, which can be adjusted, but it would seem to me to be unusual for all the forward gears to shift nicely if the pressure was way out.
The AT fluid level is right, we know.
Richard Hanlon
Derbyshire
DOC 393
1981 DMC-12 VIN 06126
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How long has it been like this, and what work have you done to the transmission lately?
You imply (by omission) that it doesn't do it from park. Is that correct?
June '81 No. 1867
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(06 Feb 2023, 23:19)Justwatching Wrote: How long has it been like this, and what work have you done to the transmission lately?
You imply (by omission) that it doesn't do it from park. Is that correct?
its been like it since I've had the car, but its gotten much more aggressive recently since having the govenor rebuilt and fresh ATF the other week.
if i start the car and change straight to reverse its fine but changing into it after having it running it starts doing it.
i'll upload a video next time I get the car out
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Not an expert on auto boxes but are the engine revs at idle to high?
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Diagnostic chart No.1 for the automatic transmission has check-list items for a "grabs during gear changing" scenario. Not sure if they meant changing gear automatically while in motion, or changing gear like moving the selector to different a ratio or direction, but it's the closest match. Only other possibly relevant scenario is "grabs on moving off".
Anyway, I'll list the items and give my thoughts. Disclaimer - I'm just a dumbass on the internet.
Governor cable - seems plausible that incorrect adjustment would give the computer duff info on throttle position and result in inappropriate commands. However, the governor cable setting isn't unique to reverse, so I'd expect poor adjustment to cause wider operation issues.
Solenoid shift valves - there are only two shift solenoids, neither unique to reverse, so I reason it a poor diagnostic fit as above.
Fluid pressure setting - an incorrect pressure setting should effect all gears, so I'm doubtful, but it can be checked with an in-line pressure gauge. Factory setting is 113 PSI (+ or - 3) at 2,500 rpm, wheels of the ground in third gear, ATF temp at 80c.
Vacuum leaks and/or vacuum modulator fault - from what I understand, the modulator regulates dynamic hydraulic pressure, so it would be responsible for whether a shift is hard or soft. That would make it prime suspect were it not for the fact that, again, it's not unique to reverse.
Valve body - yikes! Let's hope not.
Pick-up screen - not sure how this item relates to gear grabbing, but fairly easy to rule out.
June '81 No. 1867
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(07 Feb 2023, 22:42)Justwatching Wrote: Diagnostic chart No.1 for the automatic transmission has check-list items for a "grabs during gear changing" scenario. Not sure if they meant changing gear automatically while in motion, or changing gear like moving the selector to different a ratio or direction, but it's the closest match. Only other possibly relevant scenario is "grabs on moving off".
Anyway, I'll list the items and give my thoughts. Disclaimer - I'm just a dumbass on the internet.
Governor cable - seems plausible that incorrect adjustment would give the computer duff info on throttle position and result in inappropriate commands. However, the governor cable setting isn't unique to reverse, so I'd expect poor adjustment to cause wider operation issues.
Solenoid shift valves - there are only two shift solenoids, neither unique to reverse, so I reason it a poor diagnostic fit as above.
Fluid pressure setting - an incorrect pressure setting should effect all gears, so I'm doubtful, but it can be checked with an in-line pressure gauge. Factory setting is 113 PSI (+ or - 3) at 2,500 rpm, wheels of the ground in third gear, ATF temp at 80c.
Vacuum leaks and/or vacuum modulator fault - from what I understand, the modulator regulates dynamic hydraulic pressure, so it would be responsible for whether a shift is hard or soft. That would make it prime suspect were it not for the fact that, again, it's not unique to reverse.
Valve body - yikes! Let's hope not.
Pick-up screen - not sure how this item relates to gear grabbing, but fairly easy to rule out.
I can Rule out at least 2 of these. as Rich Hanlon adjusted the governor cable when it was reinstalled, although the spring back is still slightly sticky (could be part of the problem)
and the fluid pressure because all other gears work smoothly so im thinking it could be possible vac related or just lack of use being sat for 15+ years before recently
