Clutch or Trans causing my speedometer fluctuate under full load?

What could be making my speedometer fluctuate under full load. I am getting a grown/vibration at the same time. I feel it is in my clutch or transmission, because I get a shake at high Idle also. My mirrors shake in reverse also. I have had all of drive line balanced. Clutch and reman transmission are about 8 months old.

 

Thanks for all the replies. I hope I do not have a valve or injector problem. I just had a platinum out of frame overhaul done less than 25000 miles ago. 2007 Peterbilt 379 with cat c-15 625 factory hp with PDI system on it. Reman 18 speed transmission about 40000 miles ago. With new clutch at that time. I have had ride height checked by two different shops, and they say it is in specs. These issues were definatly not sudden. Things have gotten progressively worse over the last couple years. If I didn't have so much money invested in this truck, chasing this vibration/hop. I would have sold it a long time ago before it gave me so much grey hair.

I feel a hop under light load, and coasting also. Had new rear brake drums put on and balanced 8 drive tires two weeks ago. All this has been going on since before overhaul, clutch, and trans, balanced drive shafts, new dampener on engine at overhaul. I am just grabbing at straws now. I wonder if the clutch has been over stressed, and is now out of balance. It was a factory 2050 torque clutch, and PDI tells me I should be around 2300 now. I just don't now enough about transmissions to know if there is enough fast moving parts inside at Idle to cause a shake. I feel it is clutch, but just don't know how that would make my speedometer jump, unless my ecm/speed sensor are working together to feel slippage, and be over correcting things.

 

I put a new yoke on the back of the transmission a while back, and that was not it. I still have to drop the plate and do a visual on the clutch again. Could the ears being broken on the clutch cause a hop at highway speed also, along with my vibration under load, or do I have two issues. Another wierdo clue to add to this, is that sometimes when I am under full load, and the vibration is going on, my red low fuel light comes on, and my fuel gauge drops to empty, then recovers back to where it is. Is the vibration really shaking things that much. I had some similar symptoms before I had new reman transmission, and new clutch put in, that is the only thing holding me back from trying a new clutch again. I just wonder if the clutch install was not done properly.

 

If I do decide to tear things apart, which clutch do you guys recommend? I have a Cat C-15, 18 speed trans, with 700hp at the back wheels on the last dyno. PDI tells me I am getting about 2300ft lbs torque. I have a 2050 eaton in now. I have looked at PDI clutch, and Pittsburgh Power is saying Lipe, I have heard Eaton does have a 2250. I just want to put together this time with the rite one. Any good clutch experts/shops you guys have good luck with also?

 

Back to the Shake problem. I think we have eliminated rear end problems now. Any one have any ideas on how to determine if the shake could be from my clutch or is it something bent in my transmission. I even get a shake when sitting still and at night when sleeping. They work so close together, I am trying to decide, so I can have a clutch on hand before we take things apart to avoid extra down time. Clutch is less than a year old, and transmission is a reman 18 speed at the same time.