First off, this is a 4L80E with a vac. modulator. I got the trans for basically nothing and had it rebuilt, replace the steels, clutches, bands, bushings and seals. The rest of it stayed as it was. Trans has been fine on the street for about 6 months now.

Took the car to the track and launched it, right off the bat hit the rev limiter pedaled it and it grabbed second.

Before the next pass lowered the 1-2 WOT shift to 6200 rpms rev limiter at 7000. Same results only this time it would not grab second after pedaling it.

Let the car cool down & the car down the road, half throttle the car shifted fine .

Lowered the shift point to 5000, saw the tach headed towards 7000 let out a little bit and it shifted into 2nd.

Was going to make one more pass, put the shift point at 4000. On the way to the staging lanes the car wouldn't shift into 2nd part throttle. If I put the shifter in "2" it goes into 2nd but it would not shift on its own.

Any ideas? I have HPT and can scan the car, but I'm not sure what to look for.

I haven't done anything with the car since it's cooled down overnight, but will probably take it for a test spin this afternoon.

 

Just took the car for a little spin.

Manually shifting from 1-2 it will only shift if I let off the gas, even part throttle. If I then put it in D it will shift into 3rd. If I put it down to 2 it will drop down.

I'm not sure, but I' guessing something in the trans is toasted.

Some of you gurus out there please give me some insight of things to try, things to scan, etc..
I really don't want to pull this thing until I'm sure I have to.

 

Anybody?

 

You have lost the 2nd gear clutches here. It will have to come out and see what has happened. Did the 2-3 shift get softer? Any other changes?

 

No, 2-3 shift feels the same just driving normal. It did seem a little late at the track though.

I wonder why this went out so fast. I had it built with the "red" clutches.

I'd say I'm only making 600 - 650 rwhp, though I've never had it on a dyno. Thats what my trap speed is telling me anyway.

I thought a 80 would take the kind of power I'm making in stock form.

Trans swap isn't normally too bad, I think this is going to be a bitch with the APS system on the car though. I was hoping somebody would say something in the valve body.

 

Look to see if the vacuum line colapsed. If it has, this would cause a high vacuum condition at the modualtor. This would cause a "low line pressure" condition, which in turn would tear up the clutches. Before you tear it down, put a pressure guage on this and "see" what the readings are. This will give you an idea of what to look for.

 

Put a gauge where? A vac guage at the end of the line running to the modulator?
I don't think the line collapsed though, it has metal spring running through it so prevent it from collapsing.

 

There is a pressure port on the transmission, not the vacuum line. Get out the book on these and see where the pressure port is and go from there.

 

OK, I know what you're talking about now.

 

Make sure when making adjustments to the tune that you lower the RPM and MPH as well. Might be something to consider. Vince

 

The MPH for the 1-2 WOT shift is set low, 36 mph I think. I'll try to zero it out and see what it will do. Now that it won't shift into 2nd part throttle I'm thinking it's a mechanical problem though. I did not make any changes to any of the part throttle tables, only the WOT tables.

I looked at the vac line, it looks fine. I'll check the pressure port before I start pulling it out and see what I find.

 

You also need to make sure that the vaccum source is throttle responsive .
It should drop with throttle opening or it will not be raising line pressure !!!

 

I have my vac/boost gauge hooked to the same place as the vac modulator line (brake booster) and the guage works just fine.
I am using a check valve so the modulator does not get boosted.