Hey fellas hope you’re having a good week. I ran out to the ranch in my 12 valve 3500 manual dually yesterday. On my way home in traffic I noticed when I’m cruising at 55 mph or faster and I let off the gas the truck shudders? lags? maybe just one quick bump before I feel the engine braking the truck. I’ve checked the u joints and driveline when I got the truck and nothing feels loose. Is this just a normal driveline surge when the load transitions from acceleration to deceleration? There is no knock or bang it’s just a shudder or surge when the weight of the truck shifts forward.



I’ve only had the truck for a month and as far as I know it’s done this since I’ve owned it. I don’t believe it’s a new thing. I think I’ve just started driving more aggressively. I just want to see if there is something I should be looking for or concerned about? Discuss please. Cheers

 

There is some slack in the differential. Put it in N with park brake locked and crawl under it and rotate the drive shaft from side to side. You will fell the free play in the diff but also look at the joints and slip yoke for play. You should not feel movement in the joints. The slack may be more noticeable because of warm temperatures.

 

Thank you! I’ll try this

 

You will sometimes feel it clunk from the free play. The drive shaft will make a pinging sound. It mostly happens when you let off or reapply the fuel going slightly down hill but can happen on level ground. You can sort of reproduce it by shifting back and forth from R to D in the driveway. The free play is for the pinion to allow lubrication in the gear and not make grinding noise.

 

Thank you. I have never noticed the “buck” when I eft of the gas on my 24 valve but my 12 valve 3500 does it. I have’t tried it or noticed anything while the truck is running just when I climb under it while it’s sitting. I can’t get the U-joints to move knock.

The big concern of mine is the very very slow drip under my auto transmission. I can’t pinpoint the location of the leak ( possibly inside the observation cover. I took it off and didn’t see anything out of the ordinary ) When I drive the truck it seems to have a higher pitched noise ( maybe it’s not shifting like it should ) and at a certain speed it shifts up and down through two gears until I get to a certain speed and then it’s fine. Any thoughts???

 

What color is the oil that is dripping. A white rag left under truck at leaking area can help identify color. Black is engine oil. Trans fluid color can vary but usually red.

 

It’s red…. it’s brand new fluid. Not enough to make a ‘puddle” but the underside of the transmission pan and rear of the transfer case are always wet with fluid. It looks to me like it may be coming from inside the inspection cover and blowing backwards. Any thoughts on cause? What is wearing out and is there a fix I can do myself??

 

You have multiple leaks and the transmission will need to come out to repair them with a seal kit. Might as well inspect the whole thing and replace clutches if necessary. Now is the time for upgrades if you want. It is not that bad but if you want it dry.

I see front seal or pump housing leak. Tail shaft leak may be able to be tightened. pan is leaking and may be able to be tightened.

Are you sure the oil on the converter pan is not black? Looks dark in the pic. When apart you can see better. The rear main is not hard to replace.