If I remember correctly, your truck should use 75-140 synthetic rear end lube.

 

so the 90w is too heavy for it? it is still doing the same vibration thing when I turn... the drive shaft was removed and there was nothing wrong with the slip yoke or the u joints

 

Does this feel like hitting the rumble strips on the side of the road? Does the truck do it when turning under power only, or also while coasting?

If it's conventional oil, it's the wrong stuff. You need the synthetic. If the mechanic didn't put in 75W140 like the manual and tag on the diff say to do, then take it back and tell him to do it right. I use 75W90 Valvoline Synthetic in mine. I chose to deviate from the specs after carefull research and my driving habits. That and I do my own maintance and the 75W90 was way cheaper.

The friction modifier may take some time to soak in. But like I said, your diff needs sythetic lube. It's "slipperier" than conventional to start off with. So check what type of lube the guy put in. Also, don't ask him if he put 75W140 in, just ask what type. If it's not 75W140 sythetic with friction modifier, have him redo it right this time.

Mike

 

My guess is the transmission torque converter is shuddering. This is caused by fluid breakdown. When was your last tranny fluid service?

 

sounds like the tranny to me too.. mine shudders when you stop, and lopes bad, sometimes stalls after you stop. watch you RPM's, see if it pulls the engine down when you stop... If I put mine in park right after I stop the engine races to about 1500 rpm's, I'm taking it back to the transmission shop this week, hopefully they can get it right this time... third times the charm.

 

Conventional oils are no less "slippery" than synthetic oils....You'll prolly be suprised to learn that quite a few synthetics are in fact conventional or dino oils. I would suggest a tour of the Oil and Lubrication forum.

Any 75-140 weight oil, dino or synthetic, will function just fine in the rear end as long as the proper amount of LS additive is mixed in. If you are topping it off that is when the dino vs syn is important.

I learned the hard way once, by putting in a lighter 75w90 oil, my whole rear end leaked like a sieve at operation temps....the high side 90 was just not heavy enough at operation temps and just squirted out the seals.

I ended up relacing all the seals on the rearend and the rear brake pads even though they were new, cost me $100 bucks plus two days time that I wouldnt have had to pay if I would have just follwed the xxW140 req. in the owners manual.

You may be able to get away with it on a newer rearend, but heat is the reason that Ford requires the heavier xxW140 grade gear oil.

my .02

 

HI

thanks for all your replies... my Dad thinks it is the tranny as well... I am going to take it in next week to change the tranny fluid.. there are 73K miles on the original fluid... hope that helps.

Should I be worried about internal damage to the tranny?

 

If it turns out that the torque converter is bad (like mine is) then yes you may need to worry. Flush and fill isn't a bad idea, but if the problem persists get it on a diag. machine asap. Metal shavings flowing through the transmission are never good so if your converter is coming apart it can trash the rest of the transmission if you continue to drive it. I think they are supposed to start on mine tomorrow, I hope there's no metal shaving in the pan or filter screen... if I'm luckynot I should get by with just a new torque converter, if not I'll have to have the whole transmission gone through.

 

hi
I took some info off the oil and lubrication link and someone there stated that they were having the exact same problems with his truck that I am having with mine... and he said that the rear diff needed the clutch packs replaced... so that is what I am going to do.... may cost a lot but at least this should solve the problem....

 

Hi

a couple of days ago i was stopped and turned the wheel halfway to the left and slammed on the gas... the truck took off like a shot and after that I really haven't noticed the grinding when I make corners from a dead stop now... It still does it but not vry bad......maybe that friction reliever is working its way into those clutches.... I really don't want to spend any more money on it than I have to ...

 

I am not positive on this but I believe that your tranny and diff fluids are supposed to be changed every 2 years. Also if you are planning to change your clutch packs you may want to opt for an aftermarket one (ex. eaton top spec) They usually last longer and hook up better. I put one in my last truck an would never go back,If I remember correctly it only cost me about a hundred bucks more

 

Sounds like we had too different problems... mine was definately trans. Sorry if I scared ya a bit... strange how much they sounded like the same thing though. I'm glad you got it fixed, and without having to tear into the trans.

My truck also started loping like a had a big cam in it... It would do it when you stopped at a light or something and it had to sit still for a bit, the rpm's would bounce from 500 to 700, then from 500 to 1000... and the whole truck would start to rock. When you tried to take off after that the whole truck would shake and the trans would growl when it shifted to 2nd. Hopefully it will all be fixed when I get it back.

 

my 99 F-150 had same chatter after turning a corner.wouldn't chatter all the time. but once it started, it wouldn't quit untill I came to a full stop, and wouldn't start again untill I turned a corner. twice my wheels locked up while backing out of a parking space. I thought it was in the differential. turned out to be the parking brake,the lining came off and was floating around inside the drum.