4.6gt-2-ls1ta

iTrader: (3)

I have a 94 formula stock tranny, supposed to be stock stall too. The problem now is the car will shift through out all the gears just fine, but only when manually put in first and then manually shifted out. Goes into second, then drive, then overdrive, and will even lock up convertor. Problem is when you put it into OD it will shift from 1 to 2 then on the 3 shift it acts like it doesn't engage the gear all the way. Also thats not even under WOT under WOT it bangs rev limiter. Tunerpro, and freescan show no codes, has new EPC, and 3-2 downshift solenoid. Any help is greatly appreciated and sorry for the book. Oh and anytime you stop if you put it in 1st again take off and then shift the gears out it shifts solid and engages cleanly. Thanks again for any help.

Gilbert@Ace Racing

There is a better than 90% chance that your 3/4 clutches are smoked. If it's a stock unit and spends much time at all at WOT, and is more than a few years old... it's time for a freshen up or rebuild to a higher level depending on what your goals for the car are.

What is the fluid condition? Have you removed the pan to inspect it for debris?

I know it's not what you want to hear but I hope that helps you understand your next decision...

g

4.6gt-2-ls1ta

iTrader: (3)

I have actually had the pan off a couple times. Car sat (or was a 1/4 mile car not sure) for 5 years then I bought it. Didn't want to shift into drive when I got it, so we changed filter and fluid shifted fine after, but had a harsh shift into R and D from P or N, then developed the crazy flare up on 2-3 intermittantly, and an intermittant 4-3 issue. So I just changed the 3-2 downshift sole, and the VSS (was leaking fluid), and the EPC. No longer harsh from P or N to D or R, but now the crazy shift from 2-3. Fluid wasn't too bad had some black in it, and saw no kinda debris. Been fearing 3-4 clutches too. Thanks for your help.

Gilbert@Ace Racing

Well I believe the defining clue here would be the dark fluid. It only becomes dark when a clutch pack or bank slips. It's just like seeing brake dust on the front wheels of a car only that dust has nowhere to go in a transmission so it circulates with the fluid.

The reason for the symptom is the 3/4 clutches have excessive clearance and are no longer able to hold the power that they are being fed.

Hope that helps!

g

4.6gt-2-ls1ta

iTrader: (3)

Thanks for the reply, one other question though is if the 3-4 clutches are about shot (and I'm not doubting you, you know more about autos then me for sure) how come when I manually shift the car starting from first it will shift out into drive and overdrive and seems to hold quite well. Meaning if I shift 1-2-3-4 it will hit every gear and will hold acceleration as long as I don't hit it enough to make it downshift? I know it's hard to diagnose something over the comp so I apperciate your time and help, just don't really have the money for a built tranny so trying to rule out everything before I have to face the reality it might be done for. One other thing do you think it could be anything to do with a vertor problem? Thanks again for your time.

4.6gt-2-ls1ta

iTrader: (3)

Any other thoughts on my problem?

mrvedit

I'm no trans expert, but here goes...
My first thought was that your forward (overrun) spag is slipping. The sprag is like the freewheel in a bicycle, it allows the car to go faster than the engine as when you are coasting. When you give gas the sprag engages and accelerates the car.

However, when you put the shifter into [1],[2] or [3], the overrun clutch is engaged which basically locks the forward sprag. This lets you use engine braking to slow the car, e.g. going down a mountain.
Therefore, even if the forward sprag is slipping in [D]rive, there will be no slippage in [1], [2] or [3].

Speaking of the overrun clutch, I think there may be a mistake in the ATSG Manual Page 3 which lists when the Overrun clutch is engaged. It does not agree with the GM 4L60-E Technicians Guide (Copyright 2000) Page 11 which lists the same info/chart. In the GM manual, the overrun clutch is always applied in [1] and [2], but only for 3rd gear in [3]. Also Sonnax makes a custom shift valve which applies the overrun clutch for all gears in [3].
(Yes, I am a crazy person that reads such manuals cover to cover.)

4.6gt-2-ls1ta

iTrader: (3)

Mrvedit, thanks for the reply I appreciate all the help I can get.

4.6gt-2-ls1ta

iTrader: (3)

Alright I unhooked and hooked the connector and now, it will still hit all the gears good when manually shifted and has hit them all when it automatically shifts some today too. Seems if I take off with shifter in OD if I am on the throttle say 15-25% it will shift out through 1-2-3-4 but if I ease out on the throttle it shifts 1-2-then I feel it shift to 3rd but doesn't seem like it holds the gear and is slipping. The other way though when it goes to 3rd it holds good and solid??? Confused, bad 3-4 clutches, bad torque convertor, or bad electronics? Thanks guys.

Calebfmf

I have a 1996 Chevy 2wd truck. It use to have 4.3 V6 w/ 4l60e ..I have a 1992 lt1 that is going in the truck. Can I use the same 4l60e?

mrvedit

I don't have the experience to reliably answer this, but let me take a shot...
Under full throttle the PCM will instruct the EPC (also called force motor) to increase line pressure to the max. It appears your trans then works fine.
However, at e.g. 3/4 throttle your PCM programmed line pressure is a bit lower and things then start to slip.
It could be that wear in e.g. the valve body is giving you lower line pressure all around; or perhaps your trans is just worn. A trans shop can check line pressure for you.

Instead of these costly repairs, you might consider installing a different boost valve to raise your overall line pressure. A trans expert should verify if this is a good idea.
I don't know the exact steps, but you might also be able to program your PCM to run full line pressure starting at e.g. 1/2 throttle. Perhaps someone could chime in on that idea.
This might give you more life out of the trans before it needs a rebuild.

BTW - here is a good list of basic 4l60E troubleshooting:

http://www.gmtruckhq.com/?q=node/93

4.6gt-2-ls1ta

iTrader: (3)

Thanks mrvedit, I appreciate all your help.