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2006 F150 Clunk under mild acceleration at 40-50mph

I have a 2006 F150 with about 80k miles. It has a limited slip rear end. Under mild acceleration, “sometimes” there is a muted clunk at about 40-50mph. If I accelerate harder it does not happen. I cannot get it to happen at lower speeds. I cannot tell if its the transmission or rear end.

Suggestions for further diagnosis?

thanks
Don

Have you considered the possibility that the problem is a worn U-joint on the driveshaft?
I would recommend putting the truck up on a lift in order to check the U-joints.

Thanks, we’ll take a look for that. I am a little concerned its worse than that because the clunk is not consistent like other u-joint problems I have had. I also cannot get the clunk to happen at lower speeds.

Lock out the overdrive and see if that eliminates it…

Good suggestion I will give that a try.

Well I locked out the overdrive and the problem went away. So I guess the next step is into the tranny shop? sigh I have zero trust in those guys…

Go to an independent transmission repair shop.

DO NOT GO TO A BIG NAME, FRANCHISED TRANSMISSION REPAIR CHAIN STORE. THEY WILL SELL YOU A TOTAL OVERHAUL, REGARDLESS OF WHETHER YOU NEED IT OR NOT.

On my Ford truck, U joints and limited slip symptoms show up first at slow speeds, especially when moving from a stop, or coming to a stop, not high speeds. So you are probably right, its a xmission issue. I concur with db above. Every locality has one indepent xmission shop which is the best. That’s where the mechanics take their cars for xmission work. Ask your regular mechanic who this is in your area.

OK, thanks for the help gang.