2005 2500hd Exhaust Vibration And Rpm Question

oldspwr · March 6, 2008

I have an '05 2500HD 8' crew cab that I bought new with a 6.0. I had a bad exhaust drone around 70 and dealer put a weight on the exhaust to change the resonant frequency.

The drone just came back and I crawled under the truck and couldn't find any weight to speak of (or any place that it may have been bolted to for that matter...) I made a temp on my self with a 3" exhaust clamp and a 6" long 1/2"thick x 1 1/4" wide piece of steel. I bolted it to the middle of the exhaust and that reduced the drone by 50%.

I started to think about the drone at 70mph and the rpm. I am taching 2900 at 70mph with 245 75 16 tires and 4.11 gears. If you run the numbers, shouldn't it be taching around 2400 or so at 70mph? I assumed a .75 overdrive ratio with the 4L80E trans.

Any help would be appreciated...

Tom

Killerbee · March 6, 2008

Sound like you are not in OD.

2900 is too high for 70. Maybe the tach is off? I haven't done the numers, but 2600 sounds right. I'm not sure .75 od is a good assumption

ws6_guy · March 6, 2008

2900rpms at 70 is waayy to high, i get ticked off that mine rides 60mph at 2300 while my F150 did like 1700

oldspwr · March 7, 2008

Ok, on my way home last night, I have determined that the torque converter is NOT locking up. After researching this forum, the general consensus is that the converter will not lock up until the trans is over 100 degrees. My trip home is around 25 miles at 70mph, and towards the trip the gauge was over 100 deg, still with no lock up.

So later on last night I plugged in my laptop and checked to see if I have any codes. I have a older version of AutoTAP that works fairly well. I had no DTC's. After a short 5 mile trip, the trans was also at 130 degrees.

So I am guessing that either my brake light switch is bad (the normally closed side), or something else in the trans...

Does anyone have anything else to offer? I would appreciate it...

Thanks,

Tom

oldspwr · March 9, 2008

I ran AutoTap on a 25 minute trip this afternoon and the speedometer on the computer is 10 miles faster that what the speedometer in the truck is saying. For instance, the computer reads 80 but the speedo reads 70. I've checked it against a few of the construction speed signs and it's always been with 2-3 mph. Any thoughts?

Tom

wellinghurst · March 10, 2008

I ran AutoTap on a 25 minute trip this afternoon and the speedometer on the computer is 10 miles faster that what the speedometer in the truck is saying. For instance, the computer reads 80 but the speedo reads 70. I've checked it against a few of the construction speed signs and it's always been with 2-3 mph. Any thoughts?

Tom

Not sure about the AutoTap thing, but my tranny gets up to 100 degrees within a few miles, so that can't be the reason your TC is not locking in. I bet your speedo is incorrect. Construction signs rate my speed all over the place. Could it be part of the gauge cluster recall? 2900 at 80 seems correct. If that's it, it could solve everything.