dkm004 11 Report post Posted June 23, 2014 Just had a new Yukon rear end installed and its making severe rubbing/grinding noises from the clutches during slow turns, it really sounds like something is ready to break off back there. No issues in a straight line. Im taking it back to the shop that did the work tomorrow and Im assuming from what Ive found online that they neglected to put in friction additive. Can anyone recommend a particular brand to me? Quote Share this post Link to post Share on other sites
Wycked69 20 Report post Posted June 23, 2014 I prefer the Motorcraft friction modifier you get from your local Ford Dealership. You can also get it from Amazon. http://www.amazon.com/Ford-XL-3-Friction-Modifier-Additive/dp/B000NU5LP6/ref=sr_1_1?s=automotive&ie=UTF8&qid=1403530650&sr=1-1&keywords=friction+modifier+additive Quote Share this post Link to post Share on other sites
LoneWolf2U 136 Report post Posted June 23, 2014 +1 on Fords modifer,even with it added you will still have some noise when tight turning slowly. Quote Share this post Link to post Share on other sites
stangnet33 88 Report post Posted June 23, 2014 I like Red Line's modifier/break-in on new installs/rebuild's and then go to Royal Purples Max Gear after break-in (had modifier already). All of the domestic's modifier's are Ok also (save some money) but use a synthetic gear oil. Quote Share this post Link to post Share on other sites
stangnet33 88 Report post Posted June 23, 2014 True unless to much modifier is added. 4-5 % modifier on broke-in diff's. +1 on Fords modifer,even with it added you will still have some noise when tight turning slowly. Quote Share this post Link to post Share on other sites
dkm004 11 Report post Posted June 24, 2014 (edited) Thanks fella's, however it looks like it could be a bigger issue, they claim that the friction additive was added, if thats the case then something is very wrong back there. As a reference, just how much noise is acceptable and to be expected while turning with a clutched posi? They cant see it till Wednesday, my concern is that there has been some damage done to the clutches or gears. Edited June 24, 2014 by dkm004 Quote Share this post Link to post Share on other sites
fredfordguy 16 Report post Posted June 24, 2014 On the same lines, I recently had a trac loc installed, when turning slowly tight to the left only, there is a bit of a shudder, slight. Is that normal??? Thanks Quote Share this post Link to post Share on other sites
SA69mach 39 Report post Posted June 25, 2014 Tru trac is quiet. Detroit or Yukon posi are both noisy. Totally different systems. You will not break anything, and it can be very disconcerting if you are not familiar with the very noisy clicking on almost all turns. Don't worry until the shop tell you to. Quote Share this post Link to post Share on other sites
SA69mach 39 Report post Posted June 25, 2014 On the same lines, I recently had a trac loc installed, when turning slowly tight to the left only, there is a bit of a shudder, slight. Is that normal??? Thanks Yes that is normal. You have a series of 'springs' instead of clutches (in simple terms) to lock your diff, and it can be felt and heard on very tight turns, but not noticeable reversing or in normal turns. Dont sweat it. It is the ability of the unit to unlock that is the key. At some point, and with plenty of space, you should get on it hard and see how the lock affects your control with spinning tires and in hard power turns. these things are pretty cool, and very strong. Quote Share this post Link to post Share on other sites
dkm004 11 Report post Posted June 26, 2014 It turned out to be the synthetic lubricant. They changed it out and tried a few different types with the additive and now its all quiet back there...Pheeew! Quote Share this post Link to post Share on other sites