chevelle3504speed Posted November 30, 2012 Report Share Posted November 30, 2012 Hey guys, I bought a '95 Olds Cutalss Supreme 3.1 a month ago with 117k on it. The reverse reactor shell was exploded in the transmission so I pulled it out and had it overhauled. After installing the rebuilt trans, I noticed that it downshifted from overdrive on occasion. I took it on a 350 mile trip. About 100 miles into the trip it downshifted out of OD. I stopped, shut it off and cranked it back up. Trans went back into OD. I drove another 75 miles or so before the same thing happened. I pulled over, shut it off and cranked it back up. It went back into OD no problem for about 60 miles or so before downshifting again. No SES light on. Fluid looks fine. I have inspected all connections. Trans works great otherwise. Has anyone else encountered this issue? Thanks, Andy Quote Link to comment Share on other sites More sharing options...
Galaxie500XL Posted November 30, 2012 Report Share Posted November 30, 2012 (edited) Unfortunately, yes...several have encountered the issue. Some have found that the Neutral Safety switch on top of the transmission was slightly out of adjustment, some found the brake switch under the dash was a problem, confusing the transmission as to what gear it was actually in. More common, though, seems to be a problem with the TCC apply piston in the valve body. It's usually heat related--works fine when the transmission is cool, then TCC is locked out when the transmission reaches operating temps. The problem is the TCC apply piston sticks in the bore of the valve body, leading to insufficient fluid volume/pressure to the TCC. The ECM detects excess slip from the TCC due to the TCC not being fully locked up, then locks out both the TCC apply, AND overdrive. Restarting the car resets the ECM, until excess slip is detected again. Easy to find out...if this is your problem, a code, which does not illuminate the SES light will appear...P0740. EDIT: Since a P0740 doesn't set an SES..the only way you'll know if the car set the error is with a scantool. Sonnax made a repair kit for the TCC apply piston, but my ultimate fix was having the transmission rebuilt. Ironically, the rebuilder ignored the TCC piston issue, and had to rebuild it again, and I've had no further problems. Below is a link with all the stuff I checked in '09, shortly after I bought my car, and details on the ultimate solution. I spent two years researching the problem and looking for other possible explainations, because I didn't really want to rebuild the transmission unnecessarily. Hopefully, the information I gleaned will help you with yours.. http://www.w-body.com/showthread.php/42020-95-DOHC-Cutlass-P0740-no-overdrive-no-TCC-when-hot?highlight=TCC+Apply Edited November 30, 2012 by Galaxie500XL Quote Link to comment Share on other sites More sharing options...
RobertISaar Posted November 30, 2012 Report Share Posted November 30, 2012 ^ TRUTHS you can somewhat band-aid it by installing an aux trans cooler, especially if you bypass the main cooler to keep the fluid temps as low as possible. Quote Link to comment Share on other sites More sharing options...
Galaxie500XL Posted November 30, 2012 Report Share Posted November 30, 2012 Absolutely. I added a cooler from a 3.8 Buick to mine (but didn't bypass the cooler in the radiator). This helped somewhat, by keeping transmission temperatures below the critical point long enough to make my normal daily commute each day without issue--most days. But on trips longer than about 30-45 minutes, the temperatures would rise high enough to once again cause the ECM to disable the TCC, and overdrive, to the detriment of fuel mileage. It doesn't appear, however, that anything OTHER than fuel mileage suffered in the two years I drove the car in that condition...but I wanted to occasionally be able to drive the car on long trips, and for me, spending the money to have everything working properly was worth the cost of the transmission rebuild. Your priorities may be different. BUT...keep in mind, if you're thinking of simply getting another 4T60E from a junkyard, the odds are good that the replacement transmission may have the exact same problem. I'd only consider that solution if I found a transmission in a running car, known to be good by driving it a good bit first, just to make sure. ^ TRUTHS you can somewhat band-aid it by installing an aux trans cooler, especially if you bypass the main cooler to keep the fluid temps as low as possible. Quote Link to comment Share on other sites More sharing options...
chevelle3504speed Posted December 3, 2012 Author Report Share Posted December 3, 2012 Thanks for the information and links. I fixed the issue. It was indeed a bad gear selector (PRNDL) switch. I noticed the airbag light started coming on when I put the trans. in reverse, and it would go out when I shifted to any other position. As soon as the back up lights went out, the airbag light would go out. I took my original switch apart and cleaned it, which did no good, so I bought a new one, and that fixed it right up. Quote Link to comment Share on other sites More sharing options...
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