C6 Shudder

[Sorro71]

My Truck has developed a shudder in 2nd & 3rd gear when I'm coasting
It only happens when it gets up to operating temperature
When its cold it shifts hard and then when its hot it seems to shift softly so much so that when my speed is 40 to 60 km/h and I'm not on the throttle much it drops back to second very easily where I almost cant feel when it changes.
A bit of history
The transmission is about 2 years old since it was supposedly rebuilt, it was an exchange box. Its only done about 10000 kilometres. I first ran a dexron 3 oil in it, I'm pretty sure it was called something like texamatic 1888. Since my engine rebuild last year I have run a synthetic oil in it which is supposed to be compatible

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I've had a couple of leaks that I've been able to fix, the selector shaft seals and around the band adjustment nut was leaking. I was able to squirt a little RTV behind the nut without moving the adjustment. I drove it for a couple of hours after the repairs and everything was fine.
The truck has then sat for at least 2 or more weeks. Now when I drove it yesterday it has started to shudder.
I've checked the oil level and that is ok.
Any ideas on where I should start the process of elimination to try and find the problem?

 

[OLDBULL8]

Adjust the intermediate band. Back off the nut, tighten the bolt to 10 ft lbs, backup the bolt exactly one and a half turns, tighten the nut to 22 ft lbs. That will eliminate any problems with it.

Next, start the engine and check the Vacuum from the Vac pump, you should have no less that 22 inches of vacuum, a new/good Vac pump will pull around 26 to 28 inches.

Next, if the vacuum is enough as above, adjust the VRV according to below attachment. The gauge block is 1/2" thickness, any nut that is a 1/2" will do.

After these adjustments, see how it shifts and if the shudder is gone.

You may have to make an adjustment to the Modulator.

Report back on the results.

 

[OLDBULL8]

More pics of the C6 and band adjustment.

 

[Sorro71]

Ok thanks. Its Friday morning here, Ill try and get a vacuum pump and gauge this afternoon on my way home from work.

 

[dunk]

Indeed intermediate band and VRV adjustment are very important to proper shifts. Mine got slow and slippy and after adjusting the intermediate band it firmed up the shifts and no more slamming into gear on upshifts when cold. I hate slushboxes.

 

[Sorro71]

I haven't got any choice with this one. The LHD to RHD conversion doesn't leave enough room for the three pedals. I would love to have one of those ZF5's instead of the C6 with gear vendors. So far I've checked the vacuum at the pump and there's about 24 inches of vacuum and adjusted the intermediate band. Took it for a drive and there's no improvement. I won't be able to do the VRV until next week, had to order in a hand vacuum pump. In the meantime I'll drop the fluid and pan. While the pans off I'll check the filter and that I did things correctly when I changed the selector shaft seals.

 

[OLDBULL8]

Holy be Jesus, didn't see that your from down under. Lot of auto parts stores have a vacuum pump to bleed brakes, that'll work on the VRV.

One like this. http://www.harborfreight.com/brake-bleeder-and-vacuum-pump-kit-60770.html

 

[Sorro71]

Holy be Jesus, didn't see that your from down under. Lot of auto parts stores have a vacuum pump to bleed brakes, that'll work on the VRV.

Yeah thank god for gravity I tried the 3 auto parts stores and 2 "specialised tool stores and only came away with a gauge. One of the specialised tool stores had a diagnostic kit for over $300 that had a pump in it. A bit over the top for my needs. I ended up ordering a cheaper brake bleeder kit similar to the one you suggested at about $28, it should be here on Monday or Tuesday. I hope the VRV is ok, it looks like they're getting difficult to find replacements for.

 

[Sorro71]

Dropped the fluids out of the torque converter and the pan, the fluid looks and smells ok. Took the pan off and its inside is clean and the filter looks ok. The selector shaft and the indents seem to be working fine.

 

[OLDBULL8]

Be very careful with the VRV. They are obsolete and very hard to find if at all. The VRV for a GM won't work as they are on the opposite side.

 

[Sorro71]

Readjusted the VRV to 7 inches. It was a little over 8 inches with the block under the throttle before adjustment . The vacuum with the throttle at idle after adjustment was 15.5 inches. I then took it for a drive and it still shudders once the transmission warms up. While it was running I checked the vacuum at the modulator it was 15 inches at idle. It only seems to happen below 80 km/h. The only thing I can change now is the ATF back to the texamatic 1888 I had in there before the engine rebuild that was finished in October last year.
The closest transmission shop is at least an hours drive away. Would the trans mission survive the drive?

 

[riotwarrior]

Probably

 

[trackspeeder]

Readjusted the VRV to 7 inches. It was a little over 8 inches with the block under the throttle before adjustment . The vacuum with the throttle at idle after adjustment was 15.5 inches. I then took it for a drive and it still shudders once the transmission warms up. While it was running I checked the vacuum at the modulator it was 15 inches at idle. It only seems to happen below 80 km/h. The only thing I can change now is the ATF back to the texamatic 1888 I had in there before the engine rebuild that was finished in October last year.
The closest transmission shop is at least an hours drive away. Would the trans mission survive the drive?

It should be able to make that trip.

 

[Sorro71]

Long story short, I got to a transmission shop and got them to go through the c6 and check everything that I had done. All was ok. They took it for a test run and narrowed the shudder down to the gv overdrive. It only happens when the electronic controller is in auto mode and only in manual mode when od has been disengaged below about 70kmh. It will shudder and if I accelerate a bit and engage od it stops. I've changed the oil and checked the filter, both were in good shape. The transmission guy said to me it felt like the od wasn,t engaging sometimes in the auto mode. I've checked the control box while driving and it's controling power to the solenoid the way it,s supposed to. I'm hoping it could be the o,rings in the solenoid that I remember reading about somewhere. I just can't seem to pick it up again using the search.
Would you guys have any other suggestions before I pull the solenoid out ?