When running in OD with the torque converter locked up, my truck will sometimes vary by about 150 rpm. This is usually between 45 - 50 mph. It doesn't do it often, but has been doing it for a few months. I had the problem with the torque converter unlocking and locking when cruising down the highway and fixed that with a new TPS. This is different, because you can't actually feel it, it is only noticable on the tach. I had the problem before I installed the Hypertech and it is still occuring. I actually thought it was just the tach bouncing and a problem with the guage, not actual rpm change. Now that I installed a new air filter intake, I can hear it. The stock intake muffled the sound before, but now with the louder intake noise, I can hear the rpm's change.

It's strange that I can audibly hear the change, but don't feel any variation in vehicle speed. So I don't know if it is tranny related or if it is in the engine only. Reprogramming the PCM with the Hypertech didn't make it go away. It doesn't really bother me, but I was just wondering if anyone else had a similiar problem and got it fixed.

BTW, I'm planning on having my tranny serviced soon, new filter, fluid, and shift kit installed. I have a problem with driveline/tranny vibration that I'll describe in another post. So we'll see if that might solve the problem.

 

You are having the same problem I am - your torque converter is slipping. I have 300,000 miles on mine - I have even done some racing and quite a bit of heavy hauling, and it's starting to really show it's age now. I have done minor service to mine - new fluid, filter, tightening the bands - but have not replaced the clutch disks or torque converter yet. I am seeing more and more metal in the fluid each time I change it, but for now everything is running fine - if you call slipping fine. I just drive in O/D less now. I don't have as much power getting to the rear wheels though (read: can't spin as easily now ), and the top speed I can get now is only about 110, and that's in 3rd Gear for me. If I go into O/D, it drops to around 96... That's how much power I'm losing...

If you can do the work yourself, it should only take you a weekend - a day if you know what you're doing - and cost you only a couple hundred dollars. You will need a rebuild kit to get the disks and clutch packs, and a torque converter to stop the slipping in O/D...

Having done transmission rebuilds on other vehichles, I can tell you that it will be like driving a new vehichle, and if you have added any major mods within the last 50,000 miles or so, you will notice a much greater effect after you have the transmission to handle the power.

Good luck!

 

Thanks for your reply. I hadn't thought about the tranny slipping, but that makes sense. As I described in another post, I am also having problems with a vibration in the tranny, the two might be related. I am going to have a friend of mine who runs his own tranny shop put a shift kit in next week. I spoke to him about the vibration and he thought it would be the torque converter. He said the problem might go away with the installation of the shift kit. One of the things you do is enlarge some of the valve openings, and this should help eliminate the shudder. He has a flush machine, so I might just have him go ahead and replace all of the fluid in the tranny while he is doing the work. Originally I was only going to replace what was necessary with dropping the pan and the valve body.

I have some hauling to do in the next couple of weeks, so I want to get the tranny work done before I get into too much hauling. Now I'm excited about how much better it'll run. I've been doing some mods to the engine, so it'll be interesting to see if it does seem more responsive with the shift kit.

 

Just be aware that a shift kit affects the valve body, not the disks or converter directly. The kit could be made useless if either of these were to fail.


However, let me know how the shift kit works for you.

 

Before spending money, try this while driving in overdrive.

Lightly depress the brake pedal while lockup is engaged. If you see the rpm change match you tapping the pedal, then the stoplamp switch is out of adjustment or the pedal linkage is worn.

Also, if holding the brake pedal upward with your other foot removes the rpm variation, same thing.

If you have cruise control on, this light application ( and I mean LIGHT) would cause the cruise to disengage. It should require intentional application to disengage.

Just sharing a $2800 lesson (someone else's).

Dealer replaced tranny ($2800) and problem remained. I adjusted pedal freeplay

Hope that helps

 

sound like your TC. is on its way out. that could explain the vibration too. have the dealer to a " stall test" on it.