Bad rear end gear oil experience.

Discussion in 'Mustang Chit Chat' started by Anti, Aug 9, 2019.

  1. Anti

    Anti forum member

    I don't know about you all, but I read up on rear end gear oils and heard Royal Purple was good. I went with that, and it stated it has friction modifier in it already. Running stock gears. 100k miles when I changed over.

    Well, 20k+ miles later, my rear end whines ALL the time. Acceleration and Deceleration, in neutral, high speed, or low speed. ALL the time.

    So, I changed it for Mobile 1 with friction modifier. The noise hasn't gone away, maybe because damage is done, I don't know, but now my clutch packs wirr and almost sound like whales whining when I turn. I noticed it first at low speed sharp turns. Now that is real bad and does it at medium angle, medium speed turns too.

    Been googling for a bit and watching youtube. Found supporting evidence that the friction modifier could be to blame. Found one guy who has the EXACT same noise 1 month after he had replaced his rear end gears. He found out they didn't add friction modifier. He added it and the noise went away. I will be doing that this weekend.

    So as stated on my subject on this post, my experience has been bad. I DO NOT recommend Mobile 1 for clutch packs, at least not without adding your own friction modifier. As for Royal Purple, I can't rule out other things being the cause. It is possible my drive shaft carrier bearing could be going out, only because it is ALLLLLLLL the time I hear whining. So, I am not sure Royal Purple is to blame there, but Mobile 1's friction modifier is garbage so far.

    Any other thoughts or experiences from you all?
  2. 01yellerCobra

    01yellerCobra forum member

    Friction modifier doesn't do anything for the gears themselves. It just keeps the clutches from chattering. If you under filled or used the wrong weight it could cause issues.

    I ran Royal Purple in the past and didn't have any issues. But I still didn't think it was worth the price. I've had good luck with Valvoline too.
  3. Macman45

    Macman45 Resident Geriatric

    I ran RP with the Ford motorcraft friction modifier despite what RP says it has and it’s been golden. 80K miles
    WJBertrand and Anti like this.
  4. Anti

    Anti forum member

    I filled it exactly as I was supposed to with what is required. I also agree, I am not saying anything fried the rings because of missing friction modifier. I said Mobile 1's "added friction modifier" is what caused that, for sure. I intend to add modifier to see if it saves them. Also, like I stated, I am not 100% that the gears are whining. May be the carrier bearing for the stock drive shaft. So I obviously can't say RP caused the whining. Just suspect since that is all I changed in the rear end.

    Yea, I wish I would have added it in this Mobile 1 I am using.
  5. RocketcarX

    RocketcarX 95% of my weight is fuel

    Add a bottle of friction modifier, no matter what oil is used.

    Side note, Royal Purple products are junk.
    WJBertrand likes this.
  6. 08MustangDude

    08MustangDude Resident Fuktard

    If you have a factory open differential, adding a friction modifier
    is useless, just in case. You didn't mention what kind of DIFF
    you had; Open, LSD. I guess we're to assume a limited slip,
    but just in case, OPEN diffs don't have anything that the additive
    would benefit.

    Whining is for a different reason, it's a mechanical issue... Whining
    on deceleration is a pinion bearing preload issue. Whining on acceleration
    is worn carrier bearings. Generally, worn out pinion bearings can create
    whirring noises at various speeds, be it may during deceleration and/or
    acceleration. If the pinion bearings are the problem, they create more of
    a whirring noise than a rumble because it turns several times faster than
    the carrier assembly.

    If you have removed the two weights on the axle ends, the drive-line
    may whine. They were put there as dampers. They are tuned to
    absorb the frequencies produced by the drive-line.
  7. 86GT351

    86GT351 forum member

    Over the years I have used all the different oils. No matter what the bottle says, I have always added a Friction Modifier. Inexpensive Insurance that can't hurt anything. The Friction Modifier is for your clutch packs. For a driving noise, maybe because it is over 100K there is just a wear pattern on the gears? Changing the oil just "Disrupted" what as working?
  8. 08MustangDude

    08MustangDude Resident Fuktard

    I have the stock gears, and axle. I changed the gear oil in mine, and
    that's when it started to whine when coasting. I used 75W90
    full synthetic gear oil. Mine is the stock open diff, so I don't need any
    friction modifier. The oil I took out wasn't all that dirty either, so it
    must have been done before. Mine is also well over 100,000 miles.
  9. Badd GT

    Badd GT forum member

    what kind of mustang do you have with an open diff?
  10. Pentalab

    Pentalab forum member

    They all come with a LSD, no open diff......unless the LSD is trashed. Oem LSD uses 80W-140 full synthetic... PLUS friction modifier. Oem diff is piss poor at the best of times. The rebuild kit was like aprx $80 a few yrs ago.... and the GT-500 rebuild kit (which uses carbon fiber discs) was $100.00 The CF would melt. When the LSD is trashed, it becomes a permanent open diff...... then you get the ...'one wheel peel'.

    I replaced my oem LSD with an Eaton tru-trac. (VMP, etc, sells em). Tru-trac relies on friction, so
    plane jane 85W-140 dino gear oil used. Bob's auto sports rear axle catch can installed, otherwise the
    vent on pass side of axle (05-10 cars) will puke oil. BMR adj PHB + brace replaced with a Whiteline watts link. Watts link + tru-trac installed at the same time. End of rear end issues. Tru-trac is a zero maintenance item.

    Axle weights are removed when the BMR lca re-locate brackets installed...which use 3 bolts on each bracket.
    Last edited: Aug 10, 2019
  11. 08MustangDude

    08MustangDude Resident Fuktard

    My '08 V6 indicates "3.31 RATIO REGULAR AXLE." They do not come with Limited Slip
    diffs. Maybe the GTs do. That information on the axle is right on the window sticker.

    Under OPTIONAL equipment for an '08 GT, it says "3.55 RATIO LIMITED SLIP AXLE" $300
    $395 in 2011. I have seen a lot that don't even list the axle under OPTIONAL equipment, or

    Mine is OPEN differential...
  12. Badd GT

    Badd GT forum member

    You have a six popper? You have a totally different rear end! Your in the wrong section lol
  13. Pentalab

    Pentalab forum member

    Those V6 auto rental cars came with a 7.5" rear end, not the 8.8".
    They put out 180 rwhp..when new. The oem tune also put a max speed limit on the V6.

    The GT's all came with a LSD. The option was for the 3.55 / 3.73 gears.

    GT's won't function..with an open diff...... or a trashed oem LSD.
    Last edited: Aug 10, 2019
  14. 08MustangDude

    08MustangDude Resident Fuktard

    I know what the V6s come with, just making conversation. Was not sure though,
    on what the GTs had, LSD or whatever. I said, I guess the GTs come with LSDs...
    I knew the V6s were 7.5" open... I put 7.5". but it didn't look good with:
    7.5" "3.31 RATIO REGULAR AXLE", so I edited the 7.5" out... Should have
    left it in...

    Seed Limiter:
    People are saying the GT can't go faster than 145,, Bullitt 151 regardless
    due to drag. I also read there is a limiter because of the 2-piece driveshaft.
    The V6 has a one piece with a slip yoke a little farther up the shaft, not at
    the differential flange. GT has a carrier bearing, and two CV Joints. The carrier
    bearing fails. I saw a video where a guy tuned his GT, and the rear shaft came
    up through the floor... On a Dyno, no drag, tuned, the GT hits 194MPH at the
    rev limiter. There is a video on that.

    V6 is 115 limited, 142 tuned out, with drag...

    The speed limiters are set, based on the speed rating of the tires from the factory...
  15. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

    Just in case anyone comes across this thread in the future:

    • Clutch LSDs require friction modifier. This includes all factory units called "TracLock" by Ford. Even if the oil you're dumping in says it has the modifier in it, add it regardless.
    • Gear-type differentials such as Torsen and Eaton TrueTrac do NOT require friction modifier and may even recommend use of NON-SYNTHETIC gear oil to prevent lowering of the bias ratio from decreased shear. This is the case for the Eaton and is recommended by their engineers.
    Pentalab likes this.
  16. Pentalab

    Pentalab forum member

    The oem speed limiter on my 2010 GT auto was set to 150 mph. VMP shuts off the speed limiter in the tune. If the (115 mph) speed limiter is shut off on the 2011+ V6, the oem DS will wobulate, like a skipping rope, then explode @ aprx 123 mph.

    I replaced my oem 2 piece DS with a 1 piece DSS-DS, 900 hp rated aluminum 3.5" DS. Universal at front end, CV joint at back end. They come balanced and tested to 9300 rpm. The CV rear joint is field replaceable for $100.00 Pinion angle is not critical on these 1 piece DS... with the CV rear joint. I had zero vibration at 162 mph on the dyno in 4th gear... 1:1 ( 6500 rpm eng speed, 3.31 rear gear, and 27" tires.)

    W rated tires are good for 168 mph. ( like Nitto NT-555's , 555-G2 etc. )
    Y rated tires are good for 186 mph. ( MPSS).

    Never thought of winding it up in OD... on the dyno.
  17. Sky Render

    Sky Render Stig's Retarded Cousin S197 Team Member

    Yeah, wasn't it something to do with the 2011+ V6 having a thinner driveshaft to hit that 30mpg mark, but as a consequence of its reduced mass it would oscillate above a certain speed?
  18. 08MustangDude

    08MustangDude Resident Fuktard

    Which ones are the 2011 V6s using? A 2011 Ford Mustang 3.7L V6
    Driveshaft failed at 135mph. It caused major damage including a hole
    in the metal floor-pan, the exhaust system and muffler damage,
    broken transmission shifter, broken parking brake, and broken interior
    plastic trim parts. He had said he ran it, then backed off before this
    happened, and he had a drive-line vibration on deceleration from 75
    mph. It was when he opened it up AGAIN, that the shaft broke.

    He spoke to an engineer at Ford and he inquired about the reasons behind
    the 113MPH speed limiter before removing it. He was told that the 113MPH
    speed limiter was programmed on all of the new V6 Mustangs only because of
    the speed rating of the "standard model’s" tires. Well, the car he had was ordered
    with pirelli Z rated tires, so he removed the limiter... So, even after tuning it to
    remove the seed limiter, Ford repaired his car under warranty after the damages
    caused by doing so.

    He took the video down...
  19. 1950StangJump$

    1950StangJump$ forum member

    I took the time to call Royal Purple, and the guy was adamant that you do NOT add any more modifier to their gear oil; it already has it. I realize there is lots of experience on this forum, but I don't know how anyone here can just generalize and say all Royal Purple products are junk or that you always want to add additional modifier unless someone has sent the fluid away for analysis. After all, too much modifier can also be bad also, no?

    I didn't add any to mine when I did the RP. My 4.10s always whined a little if I listened close enough, and exponentially more once I did multiple BMR suspension components with poly bushings -- to be expected. To my knowledge, I don't have an "chattering" that would occur if I needed more modifier.
  20. eighty6gt

    eighty6gt forum member

    friction modifier won't do anything to the gears/metal parts, or much at all, actually. You can run without it, it's primarily for NVH

    before you changed oil your brain had cancelled out any whining/mechanical sounds

    i'm fairly sure you could run bleach or veggie oil in the diff for a while without wrecking it, so it wasn't the RP

    Good luck and ford has always had issues with whining wagon axles, at least they don't blow up like the chevrolet 10 bolts.
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