A friend has a code reader (which I can borrow) that can read live data - A model he bought from harbor tools. He gave me the model number, Zurich 11. It can view live data, but I don't think it can log. Is this something that viewing live data would be helpful for, or are we looking for a needle in a data haystack?

-Ray

 

I think it's the proverbial needle..... There are a LOT of things going on as you roll to a stop, TCC should disengage shortly after you take your foot off the gas..... (and you should see a bit of an RPM bump.) I wonder if it isn't disengage completely...... not sure the PCM would notice that.

If you can, see if it is any particular RPM that the vibration occurs at. I wonder if it isn't just a heatshield that isn't quite loose enough to rattle at other times.... yet..... Might crawl around under there and poke at stuff, and rap on things with a rubber mallet, see if anything presents itself.

 

Might be a good time to adjust the bands and change the fluid and filter. Our transmissions don't pump fluid in park, you have to put it in neutral or a gear for it to pump fluid. Are you checking the fluid in neutral? Checking in park gives a false high reading because it's not pumping the fluid into the transmission. ATF+4 fluid

 

I changed fluid/filter/adjusted bands last november - about 1500 miles ago (I don't drive much - and when I do I don't drive far).

When I had my first issue with the truck not 'going' in R,D,2,1 - I checked the fluid and it was still find (I would notice a leak - but it was worth a check). I have not had that problem since then, though I have gotten into the habit that if it's the first start of the day I always give it about a minute before shifting into gear...maybe longer.

I was out driving again today - and was able to reproduce the problem. I think I mis-characterized the sound as a vibration, it's more like a thump that I feel in my butt/back. I even wondered if my family threw something in the truck bed that I didn't notice - they had not...that thunk you feel when something hits the cab end of the bed...but with little or no noise. It doesn't happen on every stop, but if it does happen it happens about 2 seconds after the stop. If the RPM moves at all during the 'thump it's a nearly non-existent bump of less than 100 RPM - basically it happens at idle, and I'm not even sure I saw the needle jump that much (it only did it twice when i was looking at the RPM needle).

I do question if it happens more often than I realize when I'm slowing down and nearly stopped (slowing up to a stop light, but not quite stopped yet) the thump is enough to feel when you are sitting still, but with no sound to hear - I questioned if I was feeling it in the last few seconds of slowing. The truck rides rough enough on cruddy okie roads that it would be hard to tell the difference between the thud/clunk/whatever and just normal driving. It almost feels like my drive shaft it thunking forward during a stop.

 

If you get an RPM change when you hear/feel the thump, I wonder if the tcc isn't releasing properly.

 

You could pull the driveshaft and see if it's worn on the outside or seems loose in the transfer case bushing. Try a little oil or grease on the splines, they could be sticking when you accelerate.

 

I have my twice yearly oil change coming up this month - I'll be down there looking around at things anyway, so going to follow that advice about seeing what moves.

The RPM change - going to need to keep driving and watching it. It was so subtle and I only had my eyes on it twice, that I can't swear I saw the needle bump. A few more times and I'll know for sure if I really did see the needle jump just under 100RPM.

I'm googling around a bit and there are some chevy problems out there where people lube the splines to avoid what sounds like a similar issue. I would have thought the transfer case fluid handled that issue (also changed last november). Not sure if that problem is on any rear wheel drive vehicle or a brand specific design issue.

-Ray

 

sorry - didn't see this when I posted last...yes that seems to be prevailing advice I see people giving for similar symptoms on other rear wheel drive vehicles.

 

Yes, my Ford Excursion did that. You would think enough fluid would work it's way into the splines, but that's not always what happens.