4l60 bumpy shifts - slippage?

[Boost]

On my '03 Silverado with a 4.8 and 100k+ miles, after some aggressive driving with quicker shifts and less torque reduction tuned in, it now bumps into part throttle up-shifts, as if there was too much line pressure. My theory is that the clutches are slipping and then suddenly grabbing. It even does this when milder settings were tuned back in, and filter and fluid changed. Especially bad in tow haul. Truck is stockish and nothing immature like neutral drops or extended burnouts was done, just some regular aggressive driving and some one tire fire rain accelerations that would sometimes bang real hard into gear when the throttle was varied. Maybe the clutches are just glazed? Bands?

[joecar]

First do these:
- check for any DTC's (including engine DTC's),
- check fluid level.

[Boost]

Right on Joecar, sorry I did not mention in my original post that I've already performed those two checks before asking, found no engine or trans. related DTCs, and fluid level is about 1 quart over. Of course I am working on removing the extra fluid, meanwhile I suspect that it would have to be a lot higher in order to aerate (foam) and slip? I am also running a 50/50 mix of new (correct type) synthetic fluid and old nasty factory fluid. I really doubt however that this is the culprit. Also, it bangs into upshifts worse when it's cold. Thanks!

[etmotorsports]

It sound like either a pressure fluctuation on the shift or could be the clutches slipping, i would try a complete tranny service and see if it improves. It is possible the clutches are worn causing that but that should be more of a slip than a bump if you have efi live on it try bumping up the line pressure on part throttle shifts that might help.

[Boost]

Thanks and will try that. So the quality of the fluid can affect slip through the pressures, right? It definitely feels like a fluctuation during the shift, as if my foot was wobbling on the pedal. As I mentioned I have about 60% old nasty fluid and about 40% new Amsoil Dextron VI equivalent, with a new filter. I will further experiment with eventually doing another "mini" service, and for now slightly upping the shift pressures. Thank you

[etmotorsports]

Well the the problems could be trash in the systems, do use any type of flush i personally have never been a fan of those but that is just me. Change the fluid in the pan, converter and the filter all at once, it might not fix the problem but it might make is last a bit longer who knows, if it is clutch wear then raising the pressure a bit could help with that for a few months or longer. If your converter doesn't have a drain, you can crack a return line loose from the cooler to the trans and spin the motor over with the starter, but don't let the motor start you cannot let that happen. That will pump some of the fluid out of the converter but you don't have to do that.

[Boost]

Well David I raised the pressure 10% up to 250 lb/ft on the 1-2 up-shift to see and the "rubber band winding up / then bang into the next gear" effect is reduced but it still shifts fast and a little hard for being de-tuned to .5 second shifts and 30% torque reduction. Similar to when the shifts are sped up too much for comfort of a MAF issue but is is clean with no codes. If it could be junk I'll keep messing with the fluid, but I want to mention this variable:

A short while ago I had the pan off and it got caught on the exhaust and banged into the solenoids pretty good several times. However, none of them came too loose or got noticeably damaged. Just a couple of pretty hard bangs with the pan on the solenoids that had little clearance from the pan while I was fighting in into place. Any thoughts on this please? Like I said, no tranny codes. And I could have disturbed all the metal shavings cleaning the magnet and the pan, definitely possible. Thoughts are appreciated while I keep experimenting. Thanks guys

[joecar]

To replace the fluid in the converter, I repeat this sequence 4-5 times:
- overfill by 2 quarts,
- start engine;
- run engine until 2 quarts have drained out of cooler return line into "calibrated" pail;
- stop engine.

[joecar]

You can test the solenoids using the scantool: from the DVT tab you can command each one on/off, it will make a click sound.

[Boost]

Thanks Joe, that's a good method and I will definitely do it. But if my solenoids weren't clicking, I think I would have more serious issues?

[joecar]

Yes you would detect some problem like only 2 gears or max pressure or no TCC apply.

[Ritch]

you can try adjusting temp/pressure table all to zero. Sounds like it only bangs when it warms up or is cool.

[Boost]

Thanks, I'll try that. An update on this issue, I was able to improve it a great deal by re-flashing the trans settings to completely stock. The problem is barely noticeable now. Perhaps is was my expert tuning that was causing most of it... still bangs a little harder than stock but just a tiny bit and I wouldn't be surprised if it improves even further when I finally fine tune the engine with a wide-band for headers and exact conditions.

[Boost]

Still shifting crappy, especially pronounced when cold, humid, and on part throttle shifts when I am not floored but depressing the throttle just enough to make noise and not downshift. I suppose there is no reason for me to post further until I swap the fluid and filter again and turn-off temp. compensation and let the tranny learn for a few days.

[joecar]

After you swap fluid/filter, if you have a pressure gauge, measure the line pressure while driving (masking tape to hold hose/gauge to where you can see it).

[slow67]

(masking tape to hold hose/gauge to where you can see it).

Hanging it over the mirror works too ;)

[Boost]

Cool, thanks guys