VE 5 speed auto trans 'thumping' issue..

[Gareth]

Hi all, was hoping for some ideas or thoughts on this little head fuck...

This is my WM 6cyl LY7 5 speed that has this issue, as per the title under certain conditions the trans will thump, often like a machine gun. The trans is less than 2000ks old and was recoed by a very reputable builder, the issue was present prior to reco so I figured that it was an engine or harness related issue.

The following are the conditions that need to be met before it will happen,

- drive for 30min, mostly highway
- light throttle
- slight incline
- in fifth gear

The issue is random, i just drove 50mins today, perfect, yesterday, same drive, didn't think that we would get there... i have used tech2 logging the trans 5-4 shift condition and can't see anything wrong. I have ran it on the dyno but wasn't able to replicate it. I have logged the missfire graphic also with no issue.

The thumping is best decribed as the diff pinion hitting the floor, fuckin bad... no fault codes are logged in any module and all modules are fully updated. I have found that acceleration makes it stop and also manually shifting to 4th.

I feel that the issue starts to occur only when i think the trans should be getting ready to kick back a gear to deal with the higher engine load of the incline.

Any thoughts appreciated

[Jayme]

what you describe could also be related to the Torque converter clutch? the conditions you describe, sounds like when it would kick in, then going up a slight incline would up the load to the point where it should disengage the torque converter clutch. maybe somethign stuffed in that mechanism and/or the solenoids or wiring around it? not properly disengaging until you kick it back manually? did you have a look at the TCC items on the tech2 while replicating the issue?

[Gareth]

Hmmm, makes sense.

Didn't look at TCC data at all, wouldn't have thought the torque converter clutch was capable of the violence im seeing... but as the timing is spot on for that to be coming off and on then yeah, i need to check it out.

Thanks

[psyolent]

you're describing something my old VT2 used to do.

- drive for 30min, mostly highway
- light throttle
- slight incline
- in fourth gear (4L60e)

it would not do it all the time. but, when it did, would scare the piss out of me. tell you what though, i found if i ran the car on premium fuel, it would not do it as often. i didn't get to find out what the problem was it felt like spark breaking down, so, coil or lead was my vote. however, premium fuel masking that issue, i'm not so sure.

sorry i'm not much help.

[immortality]

Our old VS did something similar it was a combination of to lean, lean cruise and ignition breaking down. Giving it a good boot full would unlock converter and get it out of lean cruise and it would come right. Solved it (eventually) by changing to a different brand of leads and enriching the factory lean cruise settings a little.

[vlad01]

Are you sure its the auto? We has the same issue with my mates VY and it was the center bearing on the trailshaft would start to wobble out of center and makes to rapid pounding noise like you describe coming from the the auto. I would describe it like driving with square wheels lol

[Gareth]

Thanks guys,

Greg & Immortality, lean missfire is a valid thought but the fuel trims on this say this isnt a problem here, as did the missfire logging.

Vlad, not certain its the auto but pretty sure, the centre bearing is fine.

[psyolent]

my VT would do it going up the westgate bridge on the way home from work (ie: pointing west) - probably about 1/2 way up to the top it would start. would continue doing it all the way up the bridge until the top, on the coast on the other side down, no issues. although your issue doesn't sound spark from your logging.

the only other thing is perhaps one of the line pressure solenoids in the auto - i know it was 'rebuilt' dude which is probably more steels, clutches and the like, but, were the original sensors used that were there previously? they can and do die dude?

[psyolent]

hey

https://forums.justcommodores.com.au/th ... ge.201122/

5L40E g banger?

[psyolent]

whoah

http://www.cadillacforums.com/forums/ca ... 23274.html

Correction
A new transmission control module (TCM) calibration update has been released to correct this
condition. This new calibration changes TCC full lock operation to a higher vehicle speed. Reprogram
the TCM using SPS. This new calibration is available on TIS2WEB.