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Old 09-15-2005, 12:14 AM   #1
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Default Diagnosing Reverse Slam Disease

This forum and a FSM were instrumental in helping me figure this out so I put it all together in this posting. Feel free to correct where I am wrong.

Begining stage: My 95 SL1 would do the reverse slam only when the tranny was at full operating temperature, and only when shifting from drive into reverse. A brief pause in neutral would usually prevent the slam. All other shifting was fine. The wolfman cure, faithfully followed 2 times, did not work. The reason this happens is there is a design defect in the upper valve body, presumably of all S series automatics. The pressure regulator wears out its bore and when the fluid warms up it will flow easily around the regulator piston, causing improper control pressure leading to slam. The lasting cure is to "Sonnax Sleeve" the regulator bore. The sleeve is not prone to wear like the aluminum valve body. Since down time was an issue, I went with a remanufactured valve body for $300, about $100 more than I could do it for. Saturn wanted almost $600 for a factory reman. I highly recommend you re-torque ALL bolts according to factory specs. The operation took 2 hrs and solved the problem for me.

Middle stage: Repeated slamming into reverse WILL cause the input shaft nut to back off. You will know this has happened when you must rev your engine to get into revese at all. The check engine light may come on. Because you have waited too long to take care of this, you now will have to remove the end cover to re-torque this nut. This procedure is not for the uninitiated and at this point you may want to get out the checkbook and let the specialist do it.

End stage: You now have no reverse at all. The check engine light is on. Forward gears, especially second as it shares its clutch with reverse, are not working right. You have let it go on so long that the second clutch is worn out and/or broken. You have also stressed the hard parts and your CV joints. Good work. You now need a total rebuild.

One last point of interest: The OEM tranny filter I took off the '95 says "Manuf'd for Saturn Corp by Fram". I cut it open and found Fram's trademark cardboard end caps. This is crap and not acceptable to me, especially from Saturn. The one I bought from Napa has steel end caps on the filter element and I think is made by Wix. It cost $2 more than the Satty filter and was well worth it. I hope this helps.


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