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Why no up-shift (auto transmission)

Hello all !

I was diagnosing why my A/C was not working and decided to go to the parts store for freon ... I backed out of the driveway, put the selector into Drive - there was a slight hesitation (before going into gear), then a "clunk" sound - very similar to the sound of driveshaft u-joint [cups] that are missing all the bearings - or as if you rev the engine slightly and drop the transmission from Neutral to Drive.

So I push on the accelerator and the car speeds up, but it never switches into 2nd gear (or any other gear). I stop, try again, this time letting my foot off the gas to "coax" the transmission into switching into 2nd. (reverse works).

I drive back to the house and check the fluid - it's about 1 quart low, so I put in a quart - still same problem. (I had just driven the car home from the office and had it parked about an hour with no signs of issue).

The only thing I did prior to leaving for the store: to determine if the compressor was not running because of too-low freon, I jumpered the low-pressure cycling switch plug to engage the compressor clutch.

My thoughts for next step is to change out the tranny filter and new fluid .... and possibly "blindly" purchase the two shift solenoids (1st to 2nd, etc) and replace them while I have the tranny pan down. (no filter change in 50k miles).

Any other thoughts/diagnosis?

Thanks, Calder ...

1995 Chevy Camaro Z28, 150k miles.
Reply to
calder.cay
Loading thread data ...

4L60E? Put a scanner on it and see what it's doing. Or pay someone to do it.
Reply to
Steve Austin

I would first suspect I knocked something loose or even blew a fuse when nosing around....

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's - Gone to the rust pile... Canadian Off Road Trips Photos: Non members can still view! Jan/06
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(More Off Road album links at bottom of the view page)
Reply to
Mike Romain

Hi Mike ... I checked every single fuse, whether they were related or not - all area fine. I also took a look around the engine compartment (loose wires) - everything looks fine.

Thanks! Calder.

Reply to
calder.cay

I haven't verified the tranny markings yet, but I suspect that's the model.

I've since disconnected the battery, so I suspect that if there were code(s), they,re gone now, right?

I'll give it another check tomorrow.

Thanks, Calder.

Reply to
calder.cay

Does the speedo still work? Could be a failed speed sensor.

Reply to
Steve W.

Hi Steve ...

Does the ECM depend upon the speed sensor only for shifting, or does it additionally rely on engine RPM and or vacuum??? Just curious. It would make sense that the ECM takes all inputs into consideration.

Regards, Calder

Reply to
calder.cay

Not ONLY the VSS, But if the VSS fails the ECM thinks the vehicle isn't in motion and will not shift the trans.

Reply to
Steve W.

Okay, now I am really confused.

Yesterday, I disconnected both terminals from the battery - dont ask me why - I'm thinking that it will "clear the ECU" or something.

Today, II hook it back up, start the car, re-check the tranny fluid level, back out into the street and put it into Drive, and it works! The car shifts up from 1->2, 2->3, and so on.

There is still some sort of "soft clunk" when I move away from a complete stop - almost like something is loose or maybe it's the driveshaft. It's a very slight bump. Dos not happen in Reverse.

One other thing - the tranny shifts "harder" going from 1st to 2nd. It always did exhibit the same behaviour as if a "shift kit" were installed, but it seems now it's a stiffer shift going into second.

Is this a sign of eminent failure?

One other strange thing. A few days ago, the A/C stopped working on the way to the office - after I got home, I checked the fuses, relay, etc. Nothing. The clutch would not engage. I jumpered the low pressure switch to coax the compressor to life.

This is when I was going to the auto parts to get freon and the incident with the tranny not shifting out of 1st happened.

So *now* the A/C works too (?!?!?)

So if the tranny now works, which didnt 2 days ago, and now the A/C works, which didnt 2 days ago, is this a sign of a goofed ECU? Did disconnecting the battery somehow "reset" the ECU - I know it sounds crazy, but ... ?!?!?

Reply to
calder.cay

A punky body ground will cause all kinds of strange 'unrelated' problems to appear and disappear.

On the Chevy, this is a mesh strap from a bellhousing bolt to the body.

If bad, the secondary ground which is a small wire from the battery negative to the fender will start to melt the insulation before it fries it too.

Mike

86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail > Okay, now I am really confused.
Reply to
Mike Romain

========== ========== clean the battery terminals....

and call me in the morning.

That'll be $129.00 please..... cash,no cks, no credit cards!

~~ oo L O

~:~ marsh ~sips his mushroom tea..........mmmmmm.....good stuff~ ~:~

Reply to
Marsh Monster

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