4L80e install - Questions

[Steve Chryssos]

I prefer the dashboard. You have a computer that is reading sensors (TPS and VSS) and using that information to tell the transmission to operate (Line pressure and shift solenoids).

Use the dashboard to confirm that the trans is picking up data and asking the transmission to function. Also check to make sure your manual mode toggle switch is in the off position (automatic mode). Throw the switch both ways and watch for change on the dashboard.



For example, if you see the computer ask for a gear change, but nothing happens, you are likely to have a transmission problem--not a computer problem.

[critter]

And for those keeping score at home, you do NOT need the bushing. We put it in, bolted up the transmission it jammed the converter up against the crank so tight you couldn't turn it. We yanked it out, bolted it up using the washers as per the instructions with TCI's adapter plate and it fit like a glove.

I wondering if I've answered my own question here? I forgot about this and I'm wondering if we damaged the pump when we did this?

Also, I realized I forgot to hook up the tach wire for engine rpm. Might that be affecting things?

[Steve Chryssos]

I wondering if I've answered my own question here? I forgot about this and I'm wondering if we damaged the pump when we did this?

Also, I realized I forgot to hook up the tach wire for engine rpm. Might that be affecting things?

Possibly on the pump and no on the tach wire. To the best of my knowledge, RPM input is only important for WOT upshift on that system and totally unnecessary for Compushift.

Did you jam the converter in there?

[critter]

Sorry, I'm not following your question regarding the converter. If you mean, was it jammed against the flywheel pretty tight, yes, tight enough that I couldn't spin it by hand so we backed it off.

If you mean did I jam the converter down onto the input shaft to seat it, I did it and then had my brother in law check it. I was pretty sure we had it seated properly but I'll check it again.

I'll try to get back in the shop tomorrow and hook up the laptop. By dashboard I'm guessing you mean the screen with all the real time virtual gauges displaying, correct? They call it the "Monitor" screen now.

[Steve Chryssos]

Yup, the screen with real time gauges.

The converter must spin freely before installing bolts.

[Steve Chryssos]

What's the good word big bird?

[critter]

Sorry, Steve and all. I've been stuck at work and not able to get into the shop. Momma says no toys until the work is done! I'm hoping to get back up there tonight.

[critter]

I did what you asked tonight. I also data logged it.

Watching the real time display it seemed everything was normal. The TPS was responding, the RPMs looked normal and it appeared to understand what gear it was in.

Reverse works but the forward gears just seem to not want to move under load as if the stall on the converter is WAY up there. Looking at the data logs I can see where it shifted all the way into OD but the logs show a lot of transmission slippage. It is a used transmission and I took the seller's word for it being solid. Looks like I might have been burned. Bryan says we need to get the gauges on it and I agree. If the ice storm doesn't stop me I'll be back there tomorrow night.

[Jake's Performance]

Chris,
Reverse requires more pressure than any forward gears and also makes more due to the reverse boost function.

The only clutch that has to come on for 1st gear to work is the forward clutch. If it is working, the trans would at least have 1st gear and drive the tires.
It is also required to be on for every other forward gear.

If you have reverse, and it is driving the tires backwards, it tells me you have a properly functioning low band and 3rd gear clutch pack.

The converter installation sounds a bit scary to me, if the tran was bolted up to the block tight enough that the converter couldn't be turned, it has pretty good odds of having broken the pump gears.

If the stall was really loose, it would show up in reverse as well as forward. The converter can't differentiate the gear.

If you need any tech assistance for the trans side you know the number, give me a call.

Jake

[critter]

Thanks Jake. I might be calling. The gauges should tell the tale. What should I look for on the gauges? Bryan will probably know or be able to find out via All Data but you guys are the experts.

[critter]

So here's where I stand as of today.

TCI had looked at the data logs and asked that I recalibrate the base profile in the TCU. I went back through the wizard and created a new data log that I'll send to them. Unfortunately, with the ice and snow we have on the ground, all I was able to do was run the car in the shop, moving it back and forth. If anyone else has experience in reading these and wants to peek, let me know and I'll be happy to send it along.

The results were no different. The car seem fine in reverse but all the forward gears seem to slip. I then used the voltmeter to confirm the TPS was working. It is. We then hooked up a pressure gauge.

In reverse we had between 85-90psi at idle. It would increase with throttle increase.

In all forward gears it was 50psi and didn't budge with throttle position unless we stabbed the throttle. When we touched 3000 rpm or more it would suddenly spike the pressure over 100psi. I couldn't hold it there because I was still in the shop and I wasn't taking chances. It didn't actually feel like it was pulling against the brakes, I was just scared it might suddenly grab. I wish we hadn't had any snow, I could have put it on the parking lot and tried.

So I'm asking for opinions again. Is this electrical or mechanical. I'm open to going into the pan if need be. After that, it may be time to yank it and head for the tranmission shop.

[critter]

How critical is fill level on these transmissions?

[makoshark]

My TH400 would start shifting soft at 1/2 a quart low. It would slip big time at 1 quart low. Proper oil level on autos is important to function properly

[Steve Chryssos]

I don't think you have a fluid level issue. Or a computer issue. I think it's time to yank the trans and converter.

All of the bad smells are wafting from that direction.

[critter]

Agreed. Internal seal issue allowing it to bleed off pressure in the forward gears. I'm going to drop the pan tonight for a quick look and then, probably take it out and trot on down to the transmission shop, checkbook in hand. Sigh.

[Steve Chryssos]

That bad news will be good news in the long run. You will be much happier since a well built 4L80E will shift better. Stock 4L80E's can be very lazy regardless of the electronic tune.

[critter]

Any suggestions on what to ask the shop to pay attention to on the rebuild. Do I need a shift kit?

[critter]

And the winner is...

Burned clutches and steels all the way through. Reverse and second were the least damaged. Second gear being the least damaged kind of surprised him. He said he normally sees that one go first. The pump was fine. He suspects, since the car never really moved for us, that they were gone before we put it in.

I've learned my lesson. I'll only buy new transmissions from now on. No more used units for me.

[JeffT]

Chris, who's going through the trans for you?

[critter]

Superior in Jacksonville. They did a TH400 for me that did pretty good. Avoid Rob's at all cost.