I'll try to keep this short. Last year I figured I would do the truck a favor and change all the fluids in the truck. It's a 2001 F350, 7.3L, crew cab Dually, automatic. Everything worked fine before this point. Yea I know, don't fix it if it isnt broke.

Anyway all went well with the changes, I can turn a wrench pretty well. First thing I noticed was a clicking noise coming from the rear diff. I also noticed when backing up that the rear wheels where jerking with the clicking noise. Second thing that became an issue was that the trans would intermittently slip from a stop and would stop after letting off the throttle and you cound feal it thump into gear and would then work fine.

Figuring I might have not used the proper fluid in the rear and trans I tok it to the dealer right away and had them re-do what I had just done. New fluids in trans, both diffs and transfer case, to the tune of $700.+ They found nothing else wrong. Hmm, problems still persist.

I'm now noticing that the trans seems do do it's slipping mostly after being in reverse. The more I back up the worse it will slip and the rear diff clunking is worse in reverse and doesn't do it whhile driving forward at any speed, just while parking etc with steering.

Anyone know what this could be? I don't want to change the trans if it might not be the problem. Rather costly hunch.

For the rear diff, if you have a posi you will need to add the posi additive,the dealers rely on just the fluid and they say their fluid has the additive..But in your case it may not be enough so the clutch pack is sticking..

if you have a Detroit locker style rear diff then they all make a little bit of noise when they get some miles on them..

Trans,, if you had allot of miles on your trans and the fluid was brown then the new fluid is striping the built up tarnish off the clutch packs and theirs nothing you can do about it..If its starting to slip in reverse i would have to say that you trans is on its way out so your going to have to rebuild it..

Thanks, no it's not slipping in reverse at all. it only slips in forward and only does it once in awhile. I've noticed though that it does it more after being in reverse then once it grabs, it works fine. As for the rear. I do have a posi and figured it was the clutches. I'll get more additive into it and see if that helps. Thats why I took it to the dealer after I relied on the posi fluid, figures they replaced it with the same stuff. I thought there might be some sort of modulator in the trans causing the slippage issue. it seems to be more of a shift problem like not being all the way in gear or something like a bal valve not seating all the way and bypassing?

i remember if the rear speed sensor gets full of crap it wont let the truck go into gear..but usually the over drive light flashes or quits working which is usually that sensor..

the same sensor on top of the diff will cause eratic shifting also..

pull the sensor out and see if theirs a groove cut into it,if their is then you may have a carrier bearing going out.

Whats the mileage on that truck, Ive had a few of them, and they seem to lose the tranny right around 190k-210k, I did have the shifting issue, and put the additive in, it didnt seem to help at first, but an hour drive at highway speeds must have helped it blend, and it ran fine after that.

OK, I'll look for the sensor, I didn't notice any wires going to the rear diff but i wasn't looking for them before It's raining today. Is there an additive for the trans or was spk1 talking about the rear? 169,000 miles on it.

at first he was talking about the trans coming loose then the additive for the diff..i would check both..and about those sensors,i have seen where water gets in them and when the temp drops below zero they will freeze,crack and get pregnet lol...it may come out in pieces..also if your speedo is bouncing that will also be a bad diff sensor..

Pretty sure I see a wire loom in between downpours. I'm not usually that lucky but I will pull the sensor on Saturday and post the findings. Thanks guys.

A friend of mine had the ring gear bolts back out on his Ferd, made a nice mess of things. Might be something worth looking into.

John