Chevy 3/4 ton Transmission shift problem OD issue

[fbhart@wk.net]

I have a 2000 model old style Chevy ¾ ton pickup with 77K miles. It has the 350 cu in engine and 4 speed auto transmission; I was told it is a 4L80E, not for sure, may be a 4L60E.

From time to time my truck will shift out of OD going up a slight hill, but will not shift back into OD, when this happens, at each stop it will shift hard or jerk as it shift from 1 to 2 to 3 gear.

Most times, if you turn off the engine and let it sit for a while it will work fine for a few weeks or month.

I have added one qt. of Lucas transmission oil for sticky valves and it did appear to help, but the problem comes back.

I was told to have an OBD2 live scan test run on truck, it came back no defects. Apparently this test does not test transmission.

Question:

• How do you determine if you have a 4L60E or a 4L80E
• What test do I need to have run on transmission?
• What codes will tell me if the problem is electrical or sticky shift solenoid.

Thanks,

[75K30]

Welcome to the site.
You are experiencing common problems with the 4L series transmissions.
Both the 60 and the 80E's share similar shifting problems.
The 60 has a problem with shifting and should throw an 1870 code. Sometimes it falls back to the valve body plate itself, or a sonnex valve kit TCC regulator with sleeve is in order.
I have just recently killed a 4L60E in my Tahoe with just over 160K miles without a re-build. These can last if taken care of.
If you have a 4L80E, you may simpy have a speed sensor problem. The input and output speed sensors are known for being troublesome. Luckily these are easy to access, as they are located on the left side of the transmission, and external.
Input speed is the foward sensor, and output speed is the rear. These should be checked before any big money is spent. I have seen many cases where a bad sensor does not throw a code.
Below is a chart of common GM pans to help you identify yours. The ones you are looking for are number 6, and 7. Thiese would be the 60, and 80 trransmissions.
60 has 16 bolts and the 80 has 17 bolts holding the pans on. There is a big difference in size.
Good luck.

[fbhart@wk.net]

Thanks for the reply 75K30

I checked the pan and it has 17 bolts so it is a 4L80E.

Transmission has been working great for the last couple of weeks. Chevy man told me not to add any more Lucus transmission oil, if what I added did not stop stick valves then unit most likely had other problems.

If the transmission if fuctioning properly, will it show any defect codes?

Can these speed senors you mentioned be checked for fuction or do they have to be replaced.

Any time you have a problem that comes and then goes away is much harder to fix.

Thanks again.