Overdrive sometimes....stops working...? - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 10-06-2006, 05:00 PM   #1
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Default Overdrive sometimes....stops working...?

I've noticed that the odd day my overdrive will just kick out on me while I'm on my daily commute. I'll be tootin' along and then the tac will jump from ~2000 rpm to ~3000 rpm.

I've shifted it back to Drive and then popped the shifter into OD again but it just keeps cruizing along blistfully buring way more fuel then what I'm happy with.This seems to happen on and off, I've had 5-6 days in between incidents.

Transmission fluid is fine, level is fine.

Also, not sure if it is related or not, when I'm coasting down a hill the tac will drop to ~1000 rpm, and then jump up to ~1800 rpm, then back down and back up....Am I in need of changing a sensor...or...what?

Any info would be helpful.
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Old 10-06-2006, 06:10 PM   #2
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Default OD

Check for codes first and let us know. The idle going up and down could be a lot of things like TPS fault, or vac leak, IAC valve dirty etc.
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Old 10-07-2006, 12:53 AM   #3
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I think your SSEi has a more robust version of the 4T60E in my '95 SLE. Don't know if yours is similar enough to share the problem mine had, but.....mine would drop out of OD when the trans got hot. The problem is caused by a piston and bore in the pump body that leak pressure required to keep the car in lockup. Heat aggravates the problem by increasing clearance between the piston and bore. Sonnax makes a "sure-cure" kit to fix the problem for $150. Because the problem was heat related, I installed a trans cooler (4454) and now my trans stays in lockup in all but the very hottest conditions. (I should have opted for the bigger cooler (4490) for $15 more.)
http://www.bulkpart.com/Merchant2/me...e=tru-cool-lpd
This is an excellent, high quality, cooler that bypasses the trans fluid on cold days by design of the passages without valves, or sensors. I also run a drilled 180 thermostat. The trans cooler and 180 stat keep my car running way cooler than it used to. Everything works better. Not saying it will for sure solve your lockup problem, but, even if it doesn't, a cooler transmission will definitely last longer.
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Old 10-07-2006, 01:37 AM   #4
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ive road shotgun in this car..trany feels great, possible vacuum leak? makes me wonder now...
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Old 10-08-2006, 03:08 AM   #5
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I ended up snagging a GM code reader on ebay so soon I'll hopefully have a better idea what'* going on.

It could be a heat issue. It doesn't seem to matter what I'm doing for it to kick out, I've had it happen while passing but I've also had it happen while I'm driving " normal " with no stress upon the drive train. ( i.e no hills or speeding ).

I'll have to snag one of those trans coolers when I have enough pennies. Sure couldn't hurt.
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Old 08-19-2007, 01:06 PM   #6
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Well, turns out I HAVE a tranny cooler installed but the OD still kicks out. It still only happens on warm days.
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Old 08-19-2007, 01:48 PM   #7
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After a good hot drive, let'* have you check the fluid level, color, and smell.
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Old 08-19-2007, 02:46 PM   #8
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Roughness or variation in idle speed is a vacuum leak way over 50% of the time.

Check the little rubber fitting that runs off the front of the throttle body where two vacuum lines, one large and one small, both connect to the throttle body.

Mine was cracked and leaking vacuum. It was about $3 at the stealership.
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Old 08-19-2007, 03:25 PM   #9
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At what temperature does your engine typically run? While the real problem is most likely the worn piston that the Sonnax kit is designed to fix, if you are running around 200F, you may benefit from a drilled 180 thermostat, a new radiator, and/or a larger trans cooler.
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Old 08-20-2007, 03:17 AM   #10
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Default O/D dropout

You know, my 94 SE does the same thing. I just installed a drilled 180 stat today, so we'll see if that helps. Next I guess I will do a tranny cooler. Anyone have more info on the Sonnax fix-kit? Like where to get it, and if I can do it without tranny removal and teardown.

Oh, soon I am adding a crossflow Flowmaster from a 90 IROC with dual dumps, and I am in the process of building an air tube and CAI. Thinking of plexiglas for the CAI box. How heat-resistant is plexi?

Thanks--Chris
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