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Slipping auto transmission and dead alternator?

BerlinaBoy

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Yesterday morning I noticed my electrics warning light come on for a few minutes when I started my '94 VR Berlina sedan. Then, driving home from work, the engine warning light came on as I pulled off the highway. Next thing I know the transmission is slipping really badly as I go to accelerate away from some traffic lights. I was only a couple of k's from home by then and I managed to nurse it back.

Checked the transmission fluid and everything looked pretty normal. Went to start the car...almost a dead flat battery! Grrr, getting really pissed off. :mad: Put the battery on charge overnight and while its not fully charged yet a quick trip around the block and everything is fine with the transmission, :w00t: but the engine warning light is still on. A quick check with a mutlimeter shows that there is about 12V on the battery circuit with the engine running and slightly more with it off, so I'm guessing something in the charging circuit (e.g. alternator) is dead.

I know nothing about auto transmissions, and it seems far-fetched to me, but can the lack of electrical power be associated with the transmission slip? The transmission has never really exhibited any real substantial faults in the past.
 

Tree cutter

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You should have close to 14V at the battery with the engine running if the alternator is working properly. It is possible that low voltage could upset your trans because shift points are electronically controlled, but i have never seen or heard of it before. I would say it is an alternator or regulator problem.
 

Patrio7

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well i dont know about engaging ( figuring it was mostly done though forces within the engine itself but perhaps with the low voltage it wasnt operating completly. )

would of thought that slip is fluid level related.
 

BerlinaBoy

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I just checked the ALDL and only got code 75 = "System Voltage Low - Auto Transmission Only". Hmm, what a surprise. Never done that before, so at least I learnt something!

At least if no-one else knows of a link between the slippage and the lack of voltage I don't feel so thick, although it does leave me wondering what was going on. Thanks for the quick reply posts.
 

TheForgotten

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never seen it myself, but yeah if the alt is shagged then the trans can be a ****, fix the alt problem then you'll have gears again
 

hako

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When the ECU sensed low voltage it should have gone into "limp home" mode which would make it feel like it was slipping. You can thank your cars ECU brain for this - if it didn't go into "limp home" mode, the electronically operated transmission you could have self destructed.
As said before - check the alt.
Good Luck.
 

WILD VR CLUBBY

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hmmm i got a prob thats almost identical.
well heres whats happening while the cars iff the gears are fine then i start the car and put it in Reverse and the car goes no where then put it in Nuetral and the drive like its in drive then all the other gears are fine.
i also got a flat battry all the time but register 14.7v when the cars runin and 12.7v when its off. so i thought it could be a prob with a selector switch or somthing is this possible.
I need help thanx
 

hako

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Sounds like your selector linkage is either loose or totally out of adjustment. Your car is a VR and I think the selector mechanism is the same as the VS but the inhibitor switch is mounted on the gearbox and not in the Tbar console.
You should check underneath....get someone to move the selector backwards and forwards whilst you have a look under the car at where the selector arm mates up with the transmission - you may find the trunnion locknut loose ot the selector arm on the transmission.
If you are getting 14.7V running and 12.7 when off then that's OK. If it was 12.4 or less when off then that would indicate a flat battery but 12.7 is quite OK (unless this measurement was taken immediatly after turning the engine off ---you should wait 30 minutes or so to allow battery to stabilise).
 

BerlinaBoy

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Just to add some closure to the original post, the problem was indeed a lack of voltage due to worn alternator brushes causing the car to go into 'limp home' mode.

All fixed for minimal cost, which was just as well given my Astra blew a transmission hose on the weekend and repair has been costed at $300-$400. Grrrrr.
 

avill

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i found the problem. on my vt auto i had the problem where 4th gear kept slipping,(jolting, chuttering) but when u dropped it into third it went away. the reason is because when u drop it back the rpm raises and the engine is firing and smooth, but at low rpm (in 4th) the car struggles to deliver. this was also noticeable when i was going uphill in fourth and i applied the throttle without making it downshift, the car trans was slipping and jolted back and forth like crazy. Anyway after stressing for ages about it. i nutted out the possibilities and it just came down to my spark leads and spark plugs. they were brittle and old, and they weren't firing correct at low rpm (under 2k). then i replaced them for 54$ and it works like a gem. i know it sounds ridiculous but the reason why it slipped is coz when it was under load it need power and that is when the engine would cut off and my car jolted crazy. thank god its resolves and i have saved excessive money.
Hope this help anyone with the same problem.

Cheers Avill
 
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