Jonathan@Tick

iTrader: (5)

We have a 94 LT1 Caprice at the shop that will not shift from drive to overdrive under full throttle. From what I have read, the 4L60e should be able to shift under wot. We installed a transmission in this car for the customer about two years which had no overdrive. He since has had the transmission rebuilt and then gone into again. The car will shift into overdrive just fine now under normal driving and will also hold without slipping on the dyno in overdrive even under full throttle. The problem is it will not make the shift during wot.

On the log, you can clearly see that the comand has been sent for the transmission to shift at about 5100 rpms. I set this low to give the trans plenty of time to shift but it still will not complete the shift. The transmission seems to slip once the command to shift has been sent and the rpms will continue to climb as power output on the dyno falls off drastically. In the log there is almost 1800 rpms of converter slip being shown with no sign of the slip going down and the transmission shows no sign of being in forth gear.

The transmission shop made new lines for the transmission, which eliminated the trans fluid temp sensor. Does this sensor play a role somehow that could create this issue? I set all of the shift tables to match to eliminate any issues in terms of shift speed.

Any ideas on what would cause this issue would be greatly appreciated. The customer doesn't wish to have our local auto trans guy going into the transmission as he still has a warranty from the previous rebuild. I'm thinking there might be something going on with the valve body. I would think that it could also be the 4th gear servo, but it holds the power just fine if you allow it to shift and then get back into the throttle.

I know shifting from drive to od at wot isn't something a lot of people will ever do anyway, but this particular car has a 4.10 gear and with the stock valvetrain it needs to shift at about 105 mph...

RamAirRocket

iTrader: (1)

If the trans fluid sensor is eliminated it might be in HOT mode and on a different shift table that doesn't allow WOT shift.

Can you post the logs?

Let me see if I can find my 4L60E stuff, it IS possible the non HD 4L60E (RPO V4P Fleetwood) does allow it and Vette and maybe F Body, but the std B/D cars (except 9C1) may not be able. Most B/D cars have lethargic 2.56's or 2.93's, even the Impala SS has 3.08's, so the 3-4 shift is already at a very fast vehicle speed, far above the factory speed limiter setting (except Impala SS/9C1).

Edit: Make sure you log slip rpm. That is sure way to know if a 3-4 shift was commanded, as slip rpm will go way up.

Jonathan@Tick

iTrader: (5)

I'll see if I can post a log before the end of the day. I haven't done much with the LT1 stuff in terms of tuning. The car did have a 2.93 rear gear originally, but as mentioned it has 4.10's now.

The car used to actually belong to me. PCMforless did a tune for it back then (probably 3 or 4 years ago) and I'm pretty sure it would shift into od under wot. I started parting the car out and sold a really nice 4L60e and vigilante stall I had in it. The customer purchased the car with no transmission or converter and had us install a used tranny. Since then, he had someone else to tune it. The shift speed settings were really weird....as if they wanted it to shift from 1-2 and 2-3 based solely on rpm. They had these shift speeds set for like 5 mph with near 100 % tps, however the downshift stuff was normal so it had all kinds of weird shifting issues if the car would spin and then catch traction, etc. I can't find anywhere in the program where the rpm of a shift can be altered either. Its an early 94 if that matters that uses the different definition file and im using tuner cats.

I changed all the shift tables to shift at the same values, and it shows that a shift has been made in the log. you can tell its shifting, it just never starts pulling solid in 4th gear unless you let off the throttle giving it time to shift and then get back into it.

RamAirRocket

iTrader: (1)

Are you using TunerPro, Tunercat or LT1Edit?

With 2.93's you are way high in rpm/speed for a WOT 3-4 shift, but 4.10's that isn't so bad.

mrvedit

Are you able to connect a pressure gauge to the trans and determine what it is when the 3-4 shift is supposed to take place?
I'm thinking there isn't enough pressure to the 4th gear servo to properly engage the band; of course the condition and seals of the 4th gear servo should be checked too.

Jonathan@Tick

iTrader: (5)

I'm not an auto guy, but I would think that since the transmission will hold the power when in 4th gear even during wot that the band and servo are doing their job. Maybe it needs more pressure during the shift though?

Anyway, here is a log file. At the very end you can see the car go full throttle in drive and you can see it change to 4th gear and immediately the converter slip goes through the roof while the rpms continue to climb.

http://www.tickperformance.com/content/capricelog3.uni

Hopefully the link works... I'm using Tunercat to tune and Datamaster EE to log.

RamAirRocket

iTrader: (1)

Give Shane Cobb a call, he is owner of Carolina Performance Transmissions. He is the guru of 4L60E's.

https://ls1tech.com/forums/8751324-post3.html

https://ls1tech.com/forums/9014036-post11.html

mrvedit

Holding a gear requires pressure and only enough volume to overcome the small bleeds many circuits have. Shifts also require additional volume to fill servos, clutches, accumulators, and new circuits. So, if your 4th servo had a significant leak, the normal volume might be enough to hold it at full pressure. However, during a shift, the difference between available volume minus the leak, might require a lot of time to fill the servo and engage the band. If line pressure is low, volume will be limited.

Since you say the trans can hold WOT in any gear after the shift, it does sound like your band and 3-4 clutch are fine.

I'm no expert; hopefully more experienced people will chime in here.

RamAirRocket

iTrader: (1)

What does it do NOT at WOT, you get up past the 3-4 shift point at WOT, and no shifty, now you back off, (no power), but still high speed, does it shift into 4th, and now can you stand on it again, or does it kick down? You might need to move the kick down speeds higher so it doesn't kick down. If it kicks down anyway it sounds like a mechanical design on that trans. What is the trans code? Where did it come from?

I am trying to find my material on the 4L60E, I went thru a ton of troubleshooting on a no 1-2 shift and learned a lot. But I never got to 3-4 issues...

Jonathan@Tick

iTrader: (5)

I haven't tried actually easing up on the throttle and then getting back into the throttle after it makes the 3-4 shift (even if it shifts). I have tried easing the throttle down all the way to wot while in 4th without a kickdown. It holds that just fine. It does shift all other gears just fine and it will kick down from od to d, and from d to 2nd when required.

One other thing is the converter will not lock up. On the log you can see tcc pw I believe it is and it seems to cycle from 0 to some other value. I'm not sure if that is signifying that the converter should be locking and unlocking but it never does. The requirements for it to lock up are being met in terms of the tune however...

I don't have any specifics for the transmission. He purchased it used and installed it more than two years ago. That was the last time I saw the customer until a couple of weeks ago. He said that the transmission was rebuilt since we installed it and it has been removed and gone through to solve this issue once again with no luck. It has never worked properly since this transmission was installed however the old transmission and stall that were in the car when I owned it worked just fine including the converter lockup.

mrvedit

Unless you have a triple-disk converter, you do NOT want it to lockup anywhere close to WOT. Most tunes have it unlock above anywhere from 25% to 50% throttle.

RamAirRocket

iTrader: (1)

I was just gonna ask that, when you had it how was it?

I am wondering if it has the wrong valve body (say a 95 or 96-up VB on a 94 Trans or vice versa) or is one from say a pickup or some application where GM mandated the OD not be allowed under any circumstances at WOT. Like a truck or S10/Blazer/Astro. Can you see the trans? 96's had removeable bellhousing, that would be first clue of wrong trans.