When I turn my 04 Screw Lariat hard left and excelerate, the rear end seems to shimmy. Any thoughts???

 

Same here. To take it a step further, if I am parked on an "incline" (my driveway) and accelerate really slow I can duplicate the shimmy 99.9% of the time from a cold start, meaning the truck is warmed up but has not moved. Seems like something to do with applying torque to the rear end.

Anyway, I take it to the dealer on the 15th to address this issue.

We'll see what happens. I think the 1st step is getting the Service Dept. to admit that the truck has a shudder.

 

Please let me know what you find out nadams@grifflink.com. I will have this looked at with my first oil change which won't be for a couple of months.

 

Also, there have been "numerous" posts on this very topic. Is it a shimmy or a shudder...???...etc.... There are alot of different opinions on what the exact sensation is when it is experienced, but it all boils down to the same issue, I believe. And that issue is Clutch Packs in the rear end.

 

Take it to your dealer and tell him you need a new clutch pack .Thats what I had to do and it fixed it right up.Mine is a 3:73 LS.

 

My dealer told me they will not replace the clutch packs until we first try the "additive" and I drive it for a couple hundred miles.

I wish I knew exactly what this "additive" is. I assume its to make the differential fluid "not so slick"... They don't want to discuss it too much.

 

My dealer wouldn't do anything about it saying that there isn't a tsb out for it. And now that they have to replace all 4 of my rims since they gouged and scratched them I don't think it will be a priority to them. Good luck getting it taken care of.

 

There does seem to be a problem with some Limited slips on some of the trucks BUT:

All limited slips will "grab" a little when you make sharp turns. The system has clutches in it that need to slip. They need to slip a Lot when making sharp turns and such. You'll often feel this. You can add a friction modifier which will make it slip easier but it will also limit the ****ion of the Limited Slip differential.

If you feel this slipping or grabbing Every time you take off from a stop there's a problem that needs to be fixed.


Is this the first Limited slip rear end you've had?

 

My truck "slips" (shudders) going strait forward at slow speeds.....
I can make it happen at will. This ought to help me out when I take it to the dealer.

It is a 3.73LSD built in Oct 03.

More history:
When I 1st got my truck, I has a terrible shudder every time I accelerated, but after driving it in 4x4 for 100 miles or so during inclement weather, the shudder seemed to subside "completely" for a while. The shudder is now back and is quite noticable to my passangers who know nothing about this issue, or this Forum. So they, my passengers, are not formulating opinions as we may, or may not be, on this Forum.

 

I disagree with your "You'll often feel this" blurb.

I have owned alot of vehicles in my life - everything from Corvettes and BMW M3's to Ford Broncos and Dodge Ram 4x4's and I've never "felt" a posi slipping. Ever.

My FX4 shudders, and its not right. They can put the "additive" in - I'll go through the motions to satisfy them, but those clutch packs WILL be replaced.

Also, Lance - I believe there is an official TSB on this. Search through the forum on "shudder" - you'll find it. My dealer knew EXACTLY what I was talking about.

 

Yea, if it's happening at will, there's definitely an issue. Sounds like the new Clutch pack fixes it.

I stand by my comment on feeling a Posi "Grab" when making sharp turns. The clutch on the inside wheel has to Slip a lot, but it wants to grab, and you can often feel this. I've experienced it consistantly on Many cars I've owned, Camaro's, Ford Rangers...

They've set them up so they "slip" a lot more now than the older ones because people don't like feeling this and don't mind losing a little of the benefit of the posi rear ends.. (sucks for those who really want an active posi-rear end though)

My Dad's got a Chevy 1 ton. You would feel it in sharp turns all the time, but then it got Worse as it got older. The clutches became too sticky. They added a friction modifier to make the clutches More Slippery/less sticky so you didn't feel it on the corners. Now his Posi hardly works at all.

My theory, although I'm not sure, is they made the clutch packs Too light on the new Fords, therefore causing them to slip on both sides and shudder when going in a Straight line during take off. I may be wrong on that one though..

 

I'm not trying to split hairs here, but...

I've owned three Z-28's. All three of them with posi, all three of them with manual trannies.

I drove them all around and around in the same parking garage on the same level and same spot I have been parking in forever.

I went out to lunch last Friday with a co-worker in his 2003 Chevy Dually Quad-Cab Diesel which has some serious mods and is running a posi and he parks one spot away from me - So.. same drill - tight round and round in the garage.

No shudder, no shimmy, no wiggle. Nada.

Sorry bro, I'll argue this one 'til the cows come home. A "correct" posi should not shudder. Straightline or turning.

 

I've also owned and ridden in several vehicles with LS rearends and I've never felt anything like the"shudder" was on my '04. I noticed it on the 1st day of driving it. Mine was only noticeable from a cold start with a left turn or in a pull just like fatboy0103@***. described his. I told the service manger that I knew the problem was with the clutch pack and suggested not wasting time with the friction modifiers and thats was what they did. I was a happy camper.
Hang in there guys and with the info you have you'll get your problem fixed.

 

The friction modifiers That go in a LS rearend is to make the clutch pack slip smoothley. This is so when you go around a curve the carrier wont bust .The service Tech told me that some trucks may have left the fctory without this additive. When they took out my clutch pack I was there so I inspected the clutches . They were a little burnt looking and smelt burnt. The service writer told me they put the additive in about 4 trucks with no luck so now ford lets them replace the clutch pack.

Silver Scab FX4 3:73 LS

 

I have searched this Forum for the TSB but I cannot find it.

Does anyone know what the TSB # is...???

Thanks!