Transmission problems...

I have a '99 chevy Z71 and the engine light recently came on. I stopped into an Autozone and they diagnosed it to be a transmission problem. It wasn't driving or shifting bad and I was going to have it looked at soon. The other day I was going to church and the engine would rev when it was shifting into 3rd gear. It would shift through 1st and 2nd just fine but will not work in third. I am going to have it flushed and a filter and fluid change and hope that will fix it. I think there may be a valve stuck or plugged. Any thoughts?

The fluid/filter change is a good place to start.

What model trans is in your truck? I can ask a few of the mechanics at work if there are any "regular" problems with it. I know one of them is known for bad valve bodies, but I'm not sure which model.

If you want, PM me your VIN and I can run it through the computer too.

Check your fluid level. Start the truck, step on the brake, put the truck in reverse, then drive, then park, and check the fluid level while it's running in park. While you've got the dipstick out, check for anything obvious(visible contaminants, burnt smell, dark color, etc.). I'd go to a good independent(not the dealer or AAMCO or other chain)tranny shop and get a diagnostic done, not just a fluid and filter change. You'll get an expert opinion and it won't cost much more than a fluid and filter change. A diagnostic will require a fluid and filter change anyway.

:buddies:

How many miles on the truck?
Do you plow or tow?
Sounds like the normal wear/early designed parts. In 2002 GM made big changes in the 4L60E.

P.S. I rebuild a few of GMs Transmissions.

Hi Diesel,

That's exactly what I plan to do. When I first checked it it was 3 and a half quarts low. I dunno how it got that low in two months as its not leaking ANY fluid. Anyhow, I filled it and it still slips in third gear. I hope it's a simple fix but time will tell. The local transmission shop here I trust isn't open until the first of the new year....

Jake, It is used for casual driving only. it has 62000 miles on it.

Walt, A big thanks. I might do that next time I am out at my truck.

Not sure what model the transmission is though. Is there an easy way to find out?

tiktok 22 said:

When I first checked it it was 3 and a half quarts low. I dunno how it got that low in two months as its not leaking ANY fluid.

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What does your coolant look like?

As I'm sure you know 3.5 quarts low is pretty low and since the fluid is the primary way the trans has to get rid of heat it is likely a band or clutch in there is cooked. Or if the seals get too hot they get hard and don't work very well. I hope for the best for you fixing this problem, I know things are expensive to fix nowadays. After you get it fixed I would recommend an aftermarket trans cooler if it doesn't have one.

JimmyM said:

What does your coolant look like?

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I just checked it and it looks a tich red(the coolant is normally orange) but it's hard to tell. Certainly doesn't look like 3.5 quarts though.

tiktok 22 said:

I just checked it and it looks a tich red(the coolant is normally orange) but it's hard to tell. Certainly doesn't look like 3.5 quarts though.

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If you had fluid in the cooling system, you have brownish foam too.
Take some out and put it in a glass dish to see if you get separation.

JimmyM said:

If you had fluid in the cooling system, you have brownish foam too.
Take some out and put it in a glass dish to see if you get separation.

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no foam, no separation...

If the trans was 3.5 qts low it will have a hard time shifting and cooling. That would also be most of the fluid in the pan. Does the fluid smell burnt? You should have a 4L60E in your truck. Check you cooler lines that run to the front of the truck and connect to the Radiator. Might have a pin hole. Any other odd shifting?

Thanks Jake,

It doesn't smell or look burnt. But it was really low. I will inspect the lines tomorrow as its dark now. Hope this doesn't cost a fortune to fix.

Does the 700R4 or the 4L60E have a vacuum line on the tranny the way the older TH350s did?

JimmyM said:

Does the 700R4 or the 4L60E have a vacuum line on the tranny the way the older TH350s did?

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I don't know about the 700R4, but I'm pretty sure the 4L60E doesn't.

tiktok 22, you can tell from the option label. By running the Vin through the VIS system, I can find out every option the truck was built with. Makes my job MUCH easier. You'd be suprised how many people can't even give you the year, make and model of what they drive, never mind which engine, etc.

I went to the tranny shop today. They took a look and the third and overdrive gears are gone. Long story short...rebuild the tranny. $2k...

thanks for all your responses.

Ouch, especially for only 62k miles.

Buy manual next time, no more fuss.

A lot of trucks these days don't have a manual option. The Automatic allows the factory to program the computer to protect the driveline to reduce warranty claims and build drivelines that aren't as strong to save money. The computers today pull back spark and fuel when the tranny upshifts. They also take the edge off the off-idle torque when starting off. It rolls back in pretty quickly, but it reduces drive line stress when "punching it" from a dead stop. This isn't necessary for small engines, but for 6+ liter V-8s it helps.
Which driveline has to stonger? An automatic that can be computer controlled, or a manual transmission running an all-wheel drive. On 2WD cars, you can count on traction to limit driveline stress. Not 4WD/AWD.

This is my first automatic in 20 yrs. It really makes me question the quality of these products now being manufactured.

The automatic in my '01 Denali has 109K on it. I am not easy on cars. I think you had a failure that is more the exception than the rule.