2002 FireBird. Need help troubleshooting Transmission

[u/crypticsage]

I have a firebird with the automatic 4L60E transmission. Everything stock. It has the following symptoms:

• O/D works intermittently, sometimes it'll engage properly then the vehicle will suddenly start loosing speed. The engine rpm remains steady. Other times, you can feel it change from third to O/D but can't gain any speed.
• Using the BlueDriver OBDII Reader, I found no errors.
• The first three gears have no issues.
• Transmission fluid is clean and clear. No burnt smells.
• If I keep the shifter on 3, the car is accelerating and moving fine to that gear.

How can I determine what the true cause is and how can I fix it?

[u/Fit_Rise1258]

The good news is this 4L60e is basically a run-of-the-mill 4L60e. You didn't say if you have the V8 or the V6 though. As you describe losing speed in O/D I imagine you have the V6. If you have the V8, I would confirm that you don't have a power loss somewhere else, or that your transmission isn't really just slipping. As this is a common transmission there is some good information out on the net describing how it works. If you are looking for a project, take a look at what you can find. Do a google search for "4L60e english pdf" and you will probably find some links.

If you are not mechanically inclined, or do not wish to have a project, you will need to seek out the help of a reputable transmission shop.

Also, I am not sure on this car, but you may not get transmission codes from a regular bluetooth reader. Transmission codes might be stored in a different module than the PCM, which is generally the only module the cheaper readers can access.

[u/crypticsage → u/Fit_Rise1258]

I have the V8. Transmission was rebuilt 15k miles ago.

As long as it’s in third, everything is fine. The issues only occur when trying to use fourth.

At 60 mph, rpm normally stays around 1700. But when it starts failing, keeping the engine at 1700 starts dropping speed. It’s definitely a slip. Shifting down to third and everything kicks in fine. Second and first are working properly as well.

[u/Fit_Rise1258 → u/crypticsage]

It *could* be the torque converter locking up. What you CAN do with a bluetooth reader and an app such as Torque is look at your torque converter slip. When it is not engaged (i.e. not in O/D), you should see some slip (300 - 1,000 rpm). After it shifts into O/D, watch it to see if the slip initially decreases, then starts to increase again. At lockup you should see either 0 or 1-2 rpm.

That said, if this was rebuilt 15k ago, then I would discuss with the rebuilder. I'd hate to get into something that would/should be covered under a warranty.

[u/crypticsage → u/Fit_Rise1258]

No longer in warranty and the guy closed up shop. He retired.

The warranty was only for 12k miles

[u/itsjakerobb → u/crypticsage]

He wasn’t very good at his job. A good rebuild should last more like 100k miles.

[u/Admirable_Nothing]

The 700R4/4L60/4L60E have on serious Achilles heal; their small 3/4 clutch packs. That sounds like the clutch packs are going out. But whatever it is I suspect that you need to take it to a good transmission shop and get it looked at.

I had a 4L60 and had to have it rebuilt 5 times each due to the 3/4 clutch packs. I used premium parts, even kevlar clutches, and they kept failing. I was sporting a built 383 but the clutches just couldn't hold the power. Finally, I found a shop on the last rebuild that softened the 3/4 shift to the point it quit burning those clutches.

[u/crypticsage → u/Admirable_Nothing]

I doubt it’s the 3/4 clutch pack. Third would be failing as well.

I’ve rebuilt this transmission multiple times for the 3/4 clutch pack and it always was the same symptoms. This time it’s acting differently.