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97 47re Trans Problems Random Downshifting

12K views 8 replies 4 participants last post by  jtaubrey 
#1 ·
Hello everybody new to the forums so bare with me here.

About a month ago I bought a 1997 12v Cummins with the 47re auto tranny. Truck has 148k miles. Test drove it before I bought it and had no issues. Drove it home 3 days later still no issues. A few days after that I started noticing problems...

I drive about 12 miles to work every day so the truck does not quite reach the 180 degree operating temperature (Cincinnati summer been about 70 degrees or so each morning). When the truck was still cold it would start downshifting and upshifting erratically from 2nd to 3rd and back to 2nd around 30mph. If I floor it still does it, if I let off totally and feather the pedal back up to speed it sometimes won't do it. Also tc is locking and unlocking randomly around 45-50mph, but I understand this issue is very common and am not so concerned about it right now. The unusual part about all this is that after cleaning some grounds and checking connections everywhere I discovered that a wire on the PCM connector closest to the driver's side had been completely cut, and another on the same connector had a ground spliced into it. I repaired these trying to return the tranny to somewhat stock operation. After a few test drives and few days later I realized that after about 30 minutes or so of stop and go traffic the truck wouldn't have any issues at all. TC didn't lock unlock randomly and it didn't randomly jump between second and 3rd. But every morning on the way in back to its usual ways.

I did some reading over the last few weeks about the myriad of potential reasons why it would do this and started with easy stuff trying to resolve. Cleaned all my grounds and connections. Checked the tps for proper voltage
(.914v truck off in park key on). Checked fluid level multiple times topped it off with the lucas stop leak stuff truck idling in neutral after it was warmed up
(was still within hashmarks previously). Checked for codes with the freebee autozone deal and no codes unsurprisingly. Last night I noticed that there was some excessive slack in the TV cable so I pulled it towards the cab about 1/4 inch, still about 1/16 of slack in it. Checked the tranny end of the cable, spring seemed to be working right on the linkage, and foot to the floor on the pedal moved it all the way forward. Drive it in this morning and the issue has compounded. Now it downshifts randomly in any gear at any speed and will not stop until I let off totally and again baby it up to speed. Also shifting very late now which seems opposite of what I thought would happen. When rolling to a stop downshifts are harsh I can feel it happening. I have not done anything that involves dropping the pan (governor, od solenoid, temp sensor, etc) or adjust the bands or replace the brake light switch or speed sensor. The man I bought it from claims it has a shift kit and trans was freshly rebuilt, but had no receipts so I trust that about as far as I could throw the receipt if I had one...has anyone else experienced this issue with the shifting being effected by the temperature and just the erratic downshift upshift in general. Getting to be very annoying and I may have to drive on the freeway occasionally this winter...not looking forward to the drop from od to third at 60mph. Thanks for the help.
 
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#3 ·
Just got home so I'll get on the grounds cleaning. Some pertinent information on the drive home-If I baby the throttle as much as possible (accelerate at a snails pace) it won't act up or very minimal. Soon as I give it fuel goes crazy again.
 
#4 ·
Well after cleaning all the grounds I could find in the engine bay and all the connectors on the tranny again I took it for a spin and got it up to temp. Did not act up the whole ride. Whether I gave it hell or went slow and steady no random shifting OR TC cycling. The last time this happened I had cleaned all the grounds and it behaved for about a week but TC still randomly locked and unlocked. Hopefully this time it will not act up again after a week. Thanks for the suggestion jfox.
A separate issue I noticed (now that it actually shifts regularly) is that the shift from 2nd to 3rd seems early - 1750 rpm at about 30mph - and the shift out of 3rd seems really late - 2250 rpm at about 50 mph? Also if I get on it and let off suddenly the shift out of gear is still pretty harsh. TV cable still has some adjustability left in it. Any suggestions on other causes for weird shift points/harshnes? Thanks again
 
#5 ·
Did you get this fixed? I am looking at a 95 tonight for my son and seller says occasionally it will downshift when the brakes are applied at highway speeds.
 
#9 ·
I ended up buying it for my son. It's seems to drop out of lockup and go back in it when going around 55mph. The previous owner said he changed the throttle position sensor. I read somewhere i thought that said if that was replaced it had to be recalibrated. Does that sound right?
 
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