M28/14 A/T No shift problem.
10-27-2008, 06:11 AM
#1
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M28/14 A/T No shift problem.
Hello!
Well, the start of this day has been very sad....
What would you say is/are causing transmission NOT to shift 2->3->4?
It will shift from N to 2, and N to R and also with selector in 2 it will give me the 1st gear. But it will ONLY shift to 2nd back again by selecting neutral first and then into D again. I was going to work, but made U-turn and drove back home, because highway driving using just 2nd gear wouldn´t be a good idea...
Also when the car have been sitting, let´s say overnight, and when selecting D or R it takes about 10-15sec to get the car moving... And it feels like maybe the torque converter is filling up again or something?
It also have been for some time now slipping a bit at 2nd-3rd gears when cold / semi-warm when reaching nearly to shifting points at normal driving arount 2000-2500rpms. It will allow to engine rev to 3000rpm and then I lift the throttle and it will shift the next gear and everything is fine... But it worked perfectly when everything got the operating temperature. Shifted like a dream!
So, I´m quite confused about this.....
Too much / little of fluid? Wrong modulator pressure? Something expensive broken?
Thank you for your replies!
Well, the start of this day has been very sad....
What would you say is/are causing transmission NOT to shift 2->3->4?
It will shift from N to 2, and N to R and also with selector in 2 it will give me the 1st gear. But it will ONLY shift to 2nd back again by selecting neutral first and then into D again. I was going to work, but made U-turn and drove back home, because highway driving using just 2nd gear wouldn´t be a good idea...
Also when the car have been sitting, let´s say overnight, and when selecting D or R it takes about 10-15sec to get the car moving... And it feels like maybe the torque converter is filling up again or something?
It also have been for some time now slipping a bit at 2nd-3rd gears when cold / semi-warm when reaching nearly to shifting points at normal driving arount 2000-2500rpms. It will allow to engine rev to 3000rpm and then I lift the throttle and it will shift the next gear and everything is fine... But it worked perfectly when everything got the operating temperature. Shifted like a dream!
So, I´m quite confused about this.....
Too much / little of fluid? Wrong modulator pressure? Something expensive broken?
Thank you for your replies!
10-27-2008, 07:42 AM
#2
Two conditions come to mind:
1. Condition:
Transmission slips when moving off in 1st and 2nd gear, or moving off not possible in forwaed gear. Reverse gear still good.
Cause/Correction:
1. Service shift valve B2, replacing shift valve housing if necessary.
2. Replace brake band B2 Piston.
3. Adjust brake band b2 by installing a longer thrust pin. Replace brake band in case of excessive wear or broken brake band.
2. Condition:
No power flow in all seletor lever positions for a brief period immediately after starting engine (especially when car had not been used for a while)
Cause/Correction:
Torque converter drains partially via leaky or defective lubricating ring on drive shaft or via leaky lubricating valve in shift valve housing
1. Check lubricating ring on drive shaft, replacing if necessary
2. Check and clean lubricating valv in shift valve housing.
Do you still have reverse gear operating?
Initial thought is that it could be Condition 2.
Tails 1990 928 S4 Auto
1. Condition:
Transmission slips when moving off in 1st and 2nd gear, or moving off not possible in forwaed gear. Reverse gear still good.
Cause/Correction:
1. Service shift valve B2, replacing shift valve housing if necessary.
2. Replace brake band B2 Piston.
3. Adjust brake band b2 by installing a longer thrust pin. Replace brake band in case of excessive wear or broken brake band.
2. Condition:
No power flow in all seletor lever positions for a brief period immediately after starting engine (especially when car had not been used for a while)
Cause/Correction:
Torque converter drains partially via leaky or defective lubricating ring on drive shaft or via leaky lubricating valve in shift valve housing
1. Check lubricating ring on drive shaft, replacing if necessary
2. Check and clean lubricating valv in shift valve housing.
Do you still have reverse gear operating?
Initial thought is that it could be Condition 2.
Tails 1990 928 S4 Auto
10-27-2008, 08:14 AM
#3
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Yes I have reverse gear, and 1+2 gears. But it will not shift from 1st to 2nd without using neutral or reverse.
The torque converter draining problem might be solved with a new lubricating ring...ookay.
Mostly I´m worried now why the trans will not shift from 2->3->4 at all?? I suspect it would downshift from 4->3->2, because it will shift from 2->1...?
I have to check the ATF fluid level at first later today.... Maybe a turn or a couple more modulation pressure also and see if it starts shifting gears like it should....
The torque converter draining problem might be solved with a new lubricating ring...ookay.
Mostly I´m worried now why the trans will not shift from 2->3->4 at all?? I suspect it would downshift from 4->3->2, because it will shift from 2->1...?
I have to check the ATF fluid level at first later today.... Maybe a turn or a couple more modulation pressure also and see if it starts shifting gears like it should....
10-27-2008, 06:23 PM
#4
I would suggest that just turning the modulator adjustment screw is not good enough. Any adjustment should be done to obtain the correct operating pressure as per the specifications for the modle of the auto gearbox.
I made up a nipple to fit the test pressure point on the auto gear box and fitted a pressure gauge and I found my modulating pressure was approximately double the specification value IIRC. It need many turns of the modulating valve adjusting screw to get the "spot on" pressure required. Prior to any adjustment I had harsh gear changes and now I have very smooth gear changes. The modulation valve only affects the type of changes -harsh or soft or spot on as designed
I would get your WSM and do a complete adjustment of throttle linkage settings, including cable to gear box, check vacuum to auto box and adjust your gear lever setting to gear box and also check the safety start switch for "P" & "N" starting.
Check ATF level cold and hot, check no leakage from torque converter and then analyse the results to the trouble shooting guide included with my post #2 above.
Tails 1990 928 S4 Auto
Tails 1990 928 S4 auto
I made up a nipple to fit the test pressure point on the auto gear box and fitted a pressure gauge and I found my modulating pressure was approximately double the specification value IIRC. It need many turns of the modulating valve adjusting screw to get the "spot on" pressure required. Prior to any adjustment I had harsh gear changes and now I have very smooth gear changes. The modulation valve only affects the type of changes -harsh or soft or spot on as designed
I would get your WSM and do a complete adjustment of throttle linkage settings, including cable to gear box, check vacuum to auto box and adjust your gear lever setting to gear box and also check the safety start switch for "P" & "N" starting.
Check ATF level cold and hot, check no leakage from torque converter and then analyse the results to the trouble shooting guide included with my post #2 above.
Tails 1990 928 S4 Auto
Tails 1990 928 S4 auto
10-27-2008, 06:51 PM
#5
Rennlist Member
Tails,
Sidebar message. You've got some serious technical knowledge on all aspects of these cars. I don't know where you hail from, but thanks for helping the rest of us.
CT
Sidebar message. You've got some serious technical knowledge on all aspects of these cars. I don't know where you hail from, but thanks for helping the rest of us.
CT
10-27-2008, 06:59 PM
#6
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If you want quick, easy and "cheap" fix Niklas has extra '90 MY automatic box without diff in garage which is for sale. It appears to be in very good condition and shouldn't have too much miles on it. But we don't know how well it actually worked when it was in use in UK some years ago.
10-28-2008, 08:22 AM
#7
Chris,
No problems and thanks for the compliment.
Have owned my 928 for 9 years this November and fortunatley I have only had it to one mechanic for the original TB and WP failure nearly 9 years ago. I have had to call into a couple of place to get my rear wheel nuts tension checked as I dont have a 350 ft/lb tension wrench.
I have collected a wealth of knowledge from this and other forums and by 'surfing' the web and fixing my own car's faults.
My first workshop manuals were on microfische, followed by the first Tech CD issued by Jim Moorehouse and then his last Tech CDs which are invaluable. CD workshop manuals and PET are the way to go. I have a CD copy in my car folder.
I do all my own servicing, including all fluid changes etc., and the bigest job I have done is repaired my own auto box with a B2 piston failure, I removed the valve body and checked the B2 brake adjustment and it condition whilst car was on jackstands.
If needs be (touch wood it never happens) I would undertake a full engine strip down and rebuild myself, no problems. All it would mean would be that I would probably be forced to put my bed into the garage as well.
The only problems that have so far that has got the better of me are some of the electronic equipment, like a LH ECU failure (insufficient schematic drawings and the concept of repair by replacement), but with people like John Speake and Alan our electrical boffin, Bill, Wally, Constantine, Steve our resident auto gear box man, Dr Bob, Garth and many others mechanical minded people (sorry I cannot recall all the name at this moment), who are only too willing to help others out, so there is a formidable force out there that can keep our cars operating for years.
The only thing that sometimes annoy some of us, I believe, is when some owners have a problem and don't or won't use the search function before jumping onto the forums and can ask a question when the answer is in another thread on the same page, or has been discussed and solved a few day ago. The secret is to keep checking the 928 tech forums ever opportunity you have, as the knowledge contained in the various post is indeed formadible.
Great cars, great forum, great people with a common interest world wide.
Tails 1990 928S4 Auto
No problems and thanks for the compliment.
Have owned my 928 for 9 years this November and fortunatley I have only had it to one mechanic for the original TB and WP failure nearly 9 years ago. I have had to call into a couple of place to get my rear wheel nuts tension checked as I dont have a 350 ft/lb tension wrench.
I have collected a wealth of knowledge from this and other forums and by 'surfing' the web and fixing my own car's faults.
My first workshop manuals were on microfische, followed by the first Tech CD issued by Jim Moorehouse and then his last Tech CDs which are invaluable. CD workshop manuals and PET are the way to go. I have a CD copy in my car folder.
I do all my own servicing, including all fluid changes etc., and the bigest job I have done is repaired my own auto box with a B2 piston failure, I removed the valve body and checked the B2 brake adjustment and it condition whilst car was on jackstands.
If needs be (touch wood it never happens) I would undertake a full engine strip down and rebuild myself, no problems. All it would mean would be that I would probably be forced to put my bed into the garage as well.
The only problems that have so far that has got the better of me are some of the electronic equipment, like a LH ECU failure (insufficient schematic drawings and the concept of repair by replacement), but with people like John Speake and Alan our electrical boffin, Bill, Wally, Constantine, Steve our resident auto gear box man, Dr Bob, Garth and many others mechanical minded people (sorry I cannot recall all the name at this moment), who are only too willing to help others out, so there is a formidable force out there that can keep our cars operating for years.
The only thing that sometimes annoy some of us, I believe, is when some owners have a problem and don't or won't use the search function before jumping onto the forums and can ask a question when the answer is in another thread on the same page, or has been discussed and solved a few day ago. The secret is to keep checking the 928 tech forums ever opportunity you have, as the knowledge contained in the various post is indeed formadible.
Great cars, great forum, great people with a common interest world wide.
Tails 1990 928S4 Auto
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10-28-2008, 08:55 AM
#8
Race Car
I have a ?:
My friends 85 Euro has done the following twice.
At a light went to accelerate briskly and the Rpm's went up like it was in neutral. He went into a lower gear still no power then the car stalled. Once restarted it ran fine. I don't know a thing about auto's any feedback or where he should look?
My friends 85 Euro has done the following twice.
At a light went to accelerate briskly and the Rpm's went up like it was in neutral. He went into a lower gear still no power then the car stalled. Once restarted it ran fine. I don't know a thing about auto's any feedback or where he should look?
10-28-2008, 11:19 AM
#9
Under the Lift
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Member
Lifetime Rennlist
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It could be stuck shift valves in the valve body.
When was the fluid last changed?
You might change it and add a bottle of transmission varnish cleaner that is intended to be left in (not used as a flush solvent).
These trannies are VERY sentitive to fluid level, either low or high. You need to get the transmission hot and raise the car off the ground so you can check the level. It must be between the two upper marks on the reservoir, engine running in park or neutral.
I had some real bizarre shifting recently only a week after a fluid change. I found the level was about 6-8 ounces low. No problems since correcting that.
When was the fluid last changed?
You might change it and add a bottle of transmission varnish cleaner that is intended to be left in (not used as a flush solvent).
These trannies are VERY sentitive to fluid level, either low or high. You need to get the transmission hot and raise the car off the ground so you can check the level. It must be between the two upper marks on the reservoir, engine running in park or neutral.
I had some real bizarre shifting recently only a week after a fluid change. I found the level was about 6-8 ounces low. No problems since correcting that.
