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Paul S

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Hello All,

I was changing my oil in the '99 STS this week end and with two cars and a one car garage the '88 corvette had to get parked in the street during the job. As always I don't just move the corvette I take it around the block a few times to get the engine warmed up and blow any water out of the exhaust as it doesn't get driven very often and not at all in the winter months.

Everything was fine during the trip around the block the engine sounded good the transmission was shifting well and right on target as far as the shfting points. So I parked it next to the curb in the street and went about changing the oil in the STS when I returned to put the corvette back in the garage the only part of the transmission that operated properly was park. There was no gear selection that would do anything or move the car.

My question is, what in the world could have happened to have made such a radical transition in such a short time and by mearly starting and stopping the car?

I have never had transmission trouble before in my life, I guess I am lucky, but the down side is, because of that I don't know much about them.

Any suggestions or comments would be greatly apprectiated and welcome.

Thanks in advance

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That transmission is the THM700R4, which is bulletproof, so I would expect a cobweb issue, not an internal issue. If the shifter cable is OK, and the fluid level is within reasonable limits, I would check the vacuum modulator, if it has one (I don't see one listed on Rock Auto). Anything else that goes to the transmission, like any wiring, I would also check out.

If everything looks good externally, you might try servicing the transmission. It's possible that the pickup pump lost its prime or some such. Failing that, you can check the line pressures and see if the front pump has quit.

The most likely reasons that a transmission will not engage are loss of line pressure (bad front pump), sticking or bad clutch (or engagement servo), and empty or bad torque converter. Most torque converter turbines have a sprag clutch that, if it slips, will prevent the torque converter from passing drive torque.

Sometimes a car that is driven rarely can have a shift servo stick, or air collect in the front pump or torque converter or some such. A transmission service with fresh fluid and a new filter and screen can sometimes clear that up. If it does, I would make it a point to take a bit longer drive to circulate the fluid in the transmission a bit. Remember, it takes the transmission a lot longer to warm up than the engine.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks for your imput Jim,

A bit of history on the car, last year I noticed there was delayed shifting out of 1st gear on a coulple of instances and I also had one incident where it slipped, After that I immediately took it home and did some inspecting. I found the transmission fluid was dark. I removed the transmission fluid and replaced it with new. and the slipping went away and after a bit of a delay coming out of first gear the first time it started shifting properly.

A local transmission service company tells me that because I changed fluid I hastened its demise and it needs pretty much a total rebuild to the tune on $1,600.00 to $1,900.00.

Is this guy just trying to make a fast buck, or is there some credibility to what he is saying?

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...

A local transmission service company tells me that because I changed fluid I hastened its demise and it needs pretty much a total rebuild to the tune on $1,600.00 to $1,900.00.

...

:bsmeter:

Note that you must flush the transmission to get out about half the fluid, which is left behind with a drain and top-off. If you noticed near-terminal cobweb issues last year that a drain and top-off did fix, I would try a transmission service now as a first cut. If it comes back, give it a few weeks to settle down and either flush the fluid yourself or take it to a GM dealer to make sure that new fluid is used in the flush. Be sure and use Dexron VI when you flush to get the advantages of longer transmission life and more consistent shifting with temperature.

CTS-V_LateralGs_6-2018_tiny.jpg
-- Click Here for CaddyInfo page on "How To" Read Your OBD Codes
-- Click Here for my personal page to download my OBD code list as an Excel file, plus other Cadillac data
-- See my CaddyInfo car blogs: 2011 CTS-V, 1997 ETC
Yes, I was Jims_97_ETC before I changed cars.

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Thanks for your imput Jim,

A bit of history on the car, last year I noticed there was delayed shifting out of 1st gear on a coulple of instances and I also had one incident where it slipped, After that I immediately took it home and did some inspecting. I found the transmission fluid was dark. I removed the transmission fluid and replaced it with new. and the slipping went away and after a bit of a delay coming out of first gear the first time it started shifting properly.

A local transmission service company tells me that because I changed fluid I hastened its demise and it needs pretty much a total rebuild to the tune on $1,600.00 to $1,900.00.

Is this guy just trying to make a fast buck, or is there some credibility to what he is saying?

My opinion... based on what you have said and assuming the transmission guy hasn't yet actually inspected the transmission...

:bsmeter::bsmeter::bsmeter:

he wants you to bring in the car and your checkbook...

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ok, lets start to see if you have any line pressure. Loosen a tranny cooler line and start the engine. Is fluid coming out?

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