[birchy]

Hey guys,

So I've done a lot of searching on this topic and asked a few questions, but I'm still a bit unsure.

Can someone describe what rear diff chatter feels like? From most of the searches I've done, most guys are talking about TIGHT turns.. whereas I feel this vibration even on very shallow turns .. I've tried to explain it before but it's hard to put into words.. it's like a clunk (pause) clunk (pause) clunk.. it does feel like two surfaces grabbing, slipping, grabbing.. The truck has done this since I bought it in the summer.. I don't feel this at all when I'm driving in a straight line, and it's a LOT more pronounced when towing the 5th wheel.

I changed my diff fluids a month or so back with Motomaster synthetic 75w90 (Canadian Tire).. didn't put any friction modifier at first because in their Q&A section, someone asked about Trak-Lok additive and they answered with this: "Motomaster Synthetic 75W-90 Differential Oil additive technology contains a well-balanced blend of friction modifiers for limited-slip, so a top-treat booster for service-fill quality limited slip is not required."

I drove it for awhile to let it work in.. did the figure 8's and all that.. but I was still having vibrations in slow turns. Got a couple 4oz. bottles of the Red Line LSD friction modifier and dumped it in.. (so 8 oz... manual calls for 10oz).. been driving it for another couple weeks and I'm still getting vibrations around slow turns. I could add another half a bottle to get the 10oz, but I'm starting to think that differential chatter might not be what I'm feeling..? I don't want to put too much in because guys have said this is bad too.. the LSD slips too much..

Any advice?

If there are any guys in Calgary, AB that have experienced this before, I'd be willing to come pick you up and go for a quick spin to get an opinion...

 

[juiceycummins]

I have the exact same thing with mine changed fluid and everything and still chatter it happens more when i turn left then when i turn right i woukd like to know what the cause is too

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[ezoliver]

First off check and double check your U-Joints on your rear drive-shaft as well as the carrier bearing if you have one.

Also make sure your 4 wheel drive is disengaging and check your front end Axle U-Joints for play.

Almost sounds like 4-wheel drive bind the way you explain it.... :confused013:

 

[juiceycummins]

Its deffinatly not in 4 by and u joints were checked a few months ago but they could need replacing

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[birchy]

First off check and double check your U-Joints on your rear drive-shaft as well as the carrier bearing if you have one.

Also make sure your 4 wheel drive is disengaging and check your front end Axle U-Joints for play.

Almost sounds like 4-wheel drive bind the way you explain it.... :confused013:

I know my 4x4 is engaging/disengaging properly.. Going through a good ol' Canadian winter right now, so I've been using it all the time eh!

I'll check the U-Joints.. do I just grab the drive shafts and shake the crap out of them and see if I can feel any play?

 

[Shainer]

I'll check the U-Joints.. do I just grab the drive shafts and shake the crap out of them and see if I can feel any play?

Start there with truck in neutral and service brake applied. Chock the weeks if the brake wont hold the truck (dont need any more Canadian Darwin award recipients) You don't want any tension on the driveline. Also look for visual clues like rust dust around the joint. Might be hard to tell see with all the crap on the road covering it up or washing it off. While you are under there leave it in two wheel drive and make sure you can spin the front drive shaft.

 

[AKBlacksmoke]

Forget U-joints if its only around a corner in your rear axle. First question would be, do you have a LSD in the rear, or an open diff? As the complaint is chatter only around corner's in the rear, its either damaged spider gears/cross shaft in an open diff, or damaged LSD plates. Basicly if the only time your getting this chatter is when one wheel is spinning faster than the other (corners) its somewhere in your diff. Triple check the axle tag and figure out what Diff is under your truck.

 

[birchy]

Tag says:

52069469AJ PL
3.54 606242-2

Other side has a tag that says to "Use Limited Slip Lube".. so that's pretty obvious.

 

[AKBlacksmoke]

I would assume your LSD is having issues then. seeing as how when your tires need to spin at different RPM's is the only time your chatter occurs.

 

[Clunk]

Here's a downloadable 2001 service manual.
The download is kinda slow but worth the wait.

http://dl.dropbox.com/u/42304/2001DodgeRam.pdf


Now check page 215.

 

[birchy]

Thanks Clunk.. I actually have the FSM on my iPad.. always forget to search it though!!

 

[birchy]

Never did figure this out.. hasn't gotten any worse though. I'm thinking I should try doing the diffs again, and this time just splurge and get the higher quality diff fluid - Royal Purple Synthetic or something. That being said.. I have a few "little things" that need to be done to the truck right now and I haven't had any time to do it myself - that and it's been -20C in Calgary the last few days.. thinking I might just bend over, take it to the dealership, and get it over with.

 

[bigfish95971]

It sounds kind of normal like mine after I changed clutches in it. Some clutch sets do it more than others. Mine has broken in and reduce that a lot after few months. The clutch instructions specifically said to expect it, even a lot. Maybe somebody changed yours. Friction modifier makes them stick together not looser.

 

[nickg]

It sounds kind of normal like mine after I changed clutches in it. Some clutch sets do it more than others. Mine has broken in and reduce that a lot after few months. The clutch instructions specifically said to expect it, even a lot. Maybe somebody changed yours. Friction modifier makes them stick together not looser.

Friction modifiers allow the clutches to slip, this is needed in a turn as the outside wheel needs to turn faster/more rvs than the inside wheel. if the modifier did not allow slippage the diff would chatter/hop during turns(exactly what happens without modifier)


to the original poster, try adding more additive on my 01 using amsoil 75w110 I needed 2 tubes of additive

or pull the rear diff cover and inspect the rear diff for as mentioned above, damaged/missing teeth or other failed parts

my rear diff was like this for who knows how long , truck had over 500,000kms on it. I think the clutch kit was under 100$ and I had it done in a couple hours

 

[bigfish95971]

Friction Modifier does not make it slip or unlock more, jsut the opposite. The lube oil alone would let it slip too much. The friction modifiers help it grab after it slips to lock up again and give you traction to both wheels again. Read below from Mobile, a manufacturer.

Ask Mobil Ask Mobil
What are Friction Modifiers?

Ask Your Stickiest Question. . . Or ask us something you’ve always wanted to know about using our products. We’ll sort through all the submissions and present the best questions to our automotive experts. We'll share the questions and their answers here.

Question:
What are Friction Modifiers?
Please explain what Friction Modifiers means? Example: Mobil 1 Synthetic Gear Lube LS 75W-90. So LS means it has more Friction Modifiers. Does "Friction Modifiers" mean it has more slippery for LSD's or that it contains more friction for the LSD clutch plates (hence potentially more LSD locking performance)?
-- Steve Lau, San Jose, CA
Answer:
Friction modifiers are designed to do what the name implies, they modify friction. In the case of a Limited Slip Differential (LSD), the friction modifiers are designed to modify the friction characteristics of the fluid such that clutch engagement occurs when you need it for the rear differential to allow the rear wheel to rotate at different speeds. For example, if a vehicle is on an icy road and one wheel is on ice and slipping with no traction, in a normal differential the other wheel would be left with no torque because the one wheel is spinning. In a vehicle with LSD, even though one wheel is spinning, that spinning action causes the clutch to engage the gear (the friction modifiers in the lubricant enable the smooth engagement and disengagement of the clutches as needed), which produces the torque required to power the non-spinning wheel, enabling the car to move.

 

[dozer12216]

quote: (the friction modifiers in the lubricant enable the smooth engagement and disengagement of the clutches as needed), which produces the torque required to power the non-spinning wheel, enabling the car to move. end quote.

Sounds pretty simple to me.

 

[nickg]

Sorry BigFish
no where in that example you listed does it say that the friction modifier makes it grab

here is mobile ones info.you have to digest what is being said the modifier allows clutch slippage, too much in theory negates your LSD function

also note LSD work in different ways, some have to have one wheel spin then it transfers/or locks the other wheel. some locks the two wheels together all the time and allow slippage during turns here is a link to the different types

Limited-slip differential - Wikipedia, the free encyclopedia


MORE TECHNICAL INFORMATION

Limited-slip or Positraction units use plates or clutches to provide the proper amount of lock-up to the differential. Slippery lubricants are required to prevent chatter, but too much slipperiness causes excess wheel spin, reducing traction.
For perfect traction, use Red Line 75W90NS and add the Red Line Limited-Slip Differential Friction-Modifier / Break-In Additive until the chatter disappears.

Satisfies performance requirements of GM 1052358, Ford M2C118-A, 19B546-MA, Chrysler 4318060 and most imports.

Recommended Dosage:
Use 4% for prevention of limited slip chatter in broken-in units (typical one 4 oz. bottle) or 4 to 8% for the break-in of new differentials.

Red Line Limited-Slip Differential Friction-Modifier / Break-In Additive will significantly reduce the friction during break-in of differentials. High temperatures encountered in break-in
can destroy the hardening of the gear teeth causing rapid wear of the softened gears. This additive can reduce the break-in temperatures by as much as 50°F, improving break-in conditions. Compatible with petroleum or synthetic gear oils. Red Line Gear Oils already contain this additive (except the NS).

In non limited-slip racing differentials and quick change units using the Red Line ShockProof Gear Oils an additional 3 to 6% Red Line Limited-Slip Differential Friction-Modifier / Break-In Additive is recommended.

 

[Shainer]

I know nothing about clutch activated traction devices. I've even added LS additive to my automatic transmission with no effects

.

 

[bigfish95971]

Apparently you do not read or comprehend English very well. Read again, that is exactly what it says.

Friction modifiers are designed to do what the name implies, they modify friction. In the case of a Limited Slip Differential (LSD), the friction modifiers are designed to modify the friction characteristics of the fluid such that clutch engagement occurs when you need it for the rear differential to allow the rear wheel to rotate at different speeds. For example, if a vehicle is on an icy road and one wheel is on ice and slipping with no traction, in a normal differential the other wheel would be left with no torque because the one wheel is spinning. In a vehicle with LSD, even though one wheel is spinning, that spinning action causes the clutch to engage the gear (the friction modifiers in the lubricant enable the smooth engagement and disengagement of the clutches as needed), which produces the torque required to power the non-spinning wheel, enabling the car to move.

Without the modifier it slips too much with jsut the oil lubricating it.