ANOTHER bottle of FM?

[Roots-type]

About 5k miles ago I rebuilt my 04 Cobra differential with new carbon fiber clutches, ring/pinion gears and used Royal Purple 75w90 gear oil with a small bottle of friction modifier.
Everything seemed great.

Fast forwarding about 6 months and 3k miles, and I started to hear and feel the clutches slipping during slow turns. Not all the time, just sometimes. This has been happening for several months now.

Should I add a second bottle of FM or what? I ran RP 75w140 in the differential for years with different gear sets and never had any issues. Should I switch back to that? Is this just a common thing with fresh carbon fiber clutches that's unavoidable?

Thanks for any insight. :beer:

 

[ctrlraven]

I would switch back to the 75w140 since that's really what all has changed.

 

[Roots-type]

I would switch back to the 75w140 since that's really what all has changed.

Actually, the new carbon fiber clutches are another variable that's changed. If I hadn't rebuilt the diff with new clutches, I'd know to just switch back. Royal purple isn't cheap and I don't want to throw this stuff out if this is just how new carbon fiber clutches act.

 

[Roots-type]

Bump

 

[Jimmysidecarr]

Do not throw that fluid away!

The 75w140 and the 75w90 Max Gear both have the same dose of limited slip friction modifier included. It is appropriate for nearly all light truck and car applications including many aggressive high performance limited slip units, though they are stock units.

Did you happen to soak the clutches in the fluid prior to installation?
The Ford and Lincoln/Mercury techs where I used to work would soak new LSD clutches in friction modifier, (sometimes overnight) and then they would do the slow tight figure 8s right after the install.

I recommend trying the slow tight figure 8s to get some fluid in between the clutches and get them treated a bit more with the friction modifier that is already in the fluid.

New clutches will sometimes take a while to absorb the fm and will produce a shudder on slow tight turns. Rather than over dose the fluid and potentially reduce the effectiveness of your limited slip, I think a better path will be to just repeat the figure 8s if the shudder reoccurs. Eventually the clutches should settle down and release properly on turns without grabbing and shuddering.

I don't think it should take too many times repeating the figure 8s, unless you added some extra shims or clutch discs to the diff. Extra shims or clutches increase the clamping force and will make release on turns more difficult.

If the shudder persists after several figure 8 tries, you could try adding a cap full or two of additional friction modifier and work it in with more figure 8s.

I would not just dump in a whole bottle of FM additive however.

 

[Roots-type]

Thanks, Jimmy. I'll give the figure 8s a few shots and see what happens.

And no, the clutches were not soaked overnight.

 

[Roots-type]

Did the slow and tight figure 8s for 3 minutes straight. No luck.

 

[Jimmysidecarr]

Did the slow and tight figure 8s for 3 minutes straight. No luck.

How many figure 8s did that end up being?

If the 8s does not resolve the issue, you can try a couple cap fulls of friction modifier plus working it in with more figure 8s.(not another whole bottle).

However if that does not correct the issue, new carbon fiber clutches are supposed to be soaked in the friction modifier prior to installation. If I am not mistaken there is an actual TSB on this.

A 75W140 being a heavier fluid is also better able to dampen out NVH and I would imagine LSD clutch slipping and gripping would fall well within that category.

You may be experiencing some of the symptoms that actually caused Ford to change over to that heavier gear lube, at a time when nearly all the other power train and drive line fluids are getting lighter.

ATF in manuals transmissions used to be mostly 80w90 gear lubes, 5w30 to 5w20, and yet the rear diffs go heavier???

 

[RoadZOmbie]

Good info in here for future reference. Jimmy, bottle of royal purple 75-140 says it has friction modifier in it already, should we still add the ford 4oz friction modifier?

 

[Jimmysidecarr]

Good info in here for future reference. Jimmy, bottle of royal purple 75-140 says it has friction modifier in it already, should we still add the ford 4oz friction modifier?

Only if you want to run a double dose.:shrug:

You should not need any additional FM.

 

[Roots-type]

How many figure 8s did that end up being?

If the 8s does not resolve the issue, you can try a couple cap fulls of friction modifier plus working it in with more figure 8s.(not another whole bottle).

However if that does not correct the issue, new carbon fiber clutches are supposed to be soaked in the friction modifier prior to installation. If I am not mistaken there is an actual TSB on this.

A 75W140 being a heavier fluid is also better able to dampen out NVH and I would imagine LSD clutch slipping and gripping would fall well within that category.

You may be experiencing some of the symptoms that actually caused Ford to change over to that heavier gear lube, at a time when nearly all the other power train and drive line fluids are getting lighter.

ATF in manuals transmissions used to be mostly 80w90 gear lubes, 5w30 to 5w20, and yet the rear diffs go heavier???

I didn't count the figure 8s, but it was quite a few. I think I'll just go back to 75w140. What really chaps my ass is the shop that did the work recommended the 75w90 over the 75w140 when I told them I wanted the 140.

Only if you want to run a double dose.:shrug:

You should not need any additional FM.

That's another thing they pushed on me
even after I pointed out that the Rp had it already added in. Never used fm in the past with the 75w140, then again I think my old clutches were almost toast.

 

[D2Fresh16]

Not to thread-jack, but I'm getting ready to swap my clutches out for the carbon ones, I will definitely be referring back to this thread! Sub'n!

 

[01cobravortech]

About 5k miles ago I rebuilt my 04 Cobra differential with new carbon fiber clutches, ring/pinion gears and used Royal Purple 75w90 gear oil with a small bottle of friction modifier.
Everything seemed great.

Fast forwarding about 6 months and 3k miles, and I started to hear and feel the clutches slipping during slow turns. Not all the time, just sometimes. This has been happening for several months now.

Should I add a second bottle of FM or what? I ran RP 75w140 in the differential for years with different gear sets and never had any issues. Should I switch back to that? Is this just a common thing with fresh carbon fiber clutches that's unavoidable?

Thanks for any insight. :beer:

OP can you describe the sound, as best you can, that you are hearing? Does it almost sound like the traction control is engaging?

I'm a few weeks away from putting my 3.73s in, along with a new track-loc and RP gear oil. I'm starting to feel as if my diff is slipping. And I've been getting a sound every now and then when lets say I'm out of gear and get on the pedal and it sounds like the traction control is coming on. Only happens if accelerate a little in the wrong gear and it just started about maybe 4 weeks ago.

But I'm rather curious to hear what sound you are hearing that leads you to believe its related to your diff slipping. Thanks. :beer:

And of course if anyone else has any input please jump in. Sorry for changing the direction here but I got people telling me its the clutch hub vibrating that's causing that noise and I don't know how that is possible. My Spec 3+ has almost 60k on it and it has never made that sound before.

 

[Roots-type]

OP can you describe the sound, as best you can, that you are hearing? Does it almost sound like the traction control is engaging?

I'm a few weeks away from putting my 3.73s in, along with a new track-loc and RP gear oil. I'm starting to feel as if my diff is slipping. And I've been getting a sound every now and then when lets say I'm out of gear and get on the pedal and it sounds like the traction control is coming on. Only happens if accelerate a little in the wrong gear and it just started about maybe 4 weeks ago.

But I'm rather curious to hear what sound you are hearing that leads you to believe its related to your diff slipping. Thanks. :beer:

And of course if anyone else has any input please jump in. Sorry for changing the direction here but I got people telling me its the clutch hub vibrating that's causing that noise and I don't know how that is possible. My Spec 3+ has almost 60k on it and it has never made that sound before.

Its been several years since i've actually felt my traction control come on (its been disabled) so I can't really say for sure.

If you are in-tune with your car as much as I am with mine, you'll be able to immediately know that its coming from the rear end. It sort of sounds like a tire rubbing, and at the same time feels sort of like the brakes are dragging. So, yeah, I guess you could say its sort of feels like traction control coming on since braking is part of how traction control works.

And just to clarify, you want your clutches to release and slip during turns. Mine are very grabby and not slipping like they should. Its kind of a situation where you want your cake and eat it too. We want the clutches to lock up during spinning to get the power to both wheels, but at the same time we want them to slip during turns (when the outside wheel has to travel at a faster speed than the inside wheel) so we don't have to feel/hear the clutches.

 

[01cobravortech]

Its been several years since i've actually felt my traction control come on (its been disabled) so I can't really say for sure.

If you are in-tune with your car as much as I am with mine, you'll be able to immediately know that its coming from the rear end. It sort of sounds like a tire rubbing, and at the same time feels sort of like the brakes are dragging. So, yeah, I guess you could say its sort of feels like traction control coming on since braking is part of how traction control works.

And just to clarify, you want your clutches to release and slip during turns. Mine are very grabby and not slipping like they should. Its kind of a situation where you want your cake and eat it too. We want the clutches to lock up during spinning to get the power to both wheels, but at the same time we want them to slip during turns (when the outside wheel has to travel at a faster speed than the inside wheel) so we don't have to feel/hear the clutches.

Thanks. :thumbsup:

 

[Roots-type]

Thanks. :thumbsup:

No problem. I definitely recommend the 75w140. A separate bottle of friction modifier is optional.

 

[gen.turner]

Friction Modifier

[/QUOTE] And just to clarify, you want your clutches to release and slip during turns. Mine are very grabby and not slipping like they should. Its kind of a situation where you want your cake and eat it too. We want the clutches to lock up during spinning to get the power to both wheels, but at the same time we want them to slip during turns (when the outside wheel has to travel at a faster speed than the inside wheel) so we don't have to feel/hear the clutches. [/QUOTE]

I have used and serviced the different types of 8.8's alot and in my opinion the problem could be that there is too much FM in your gear oil.

The purpose of the friction modifier is to allow the clutches to grab. Too much is a bad thing because the prevents the clutches already under pre-load (Z spring) from releasing smoothly when the torque bias or variance in wheel speed at the diff is reached. (~30-60ft-lbs if I remember correctly)

If you haven't done anything you could try soaking the clutch-packs before re-installation. If you are having a shop do this it is a toss up on fluid and installation procedures. Just because someone is a mechanice does not mean he knows everything about every car.(true story) And you can re-use the fluid for your daily drive as long as there is no metallic shavings in the rear. I have have used only 75W-140 for a while now and have not had any issues.

Best of luck,
Taylor

 

[Jimmysidecarr]

And just to clarify, you want your clutches to release and slip during turns. Mine are very grabby and not slipping like they should. Its kind of a situation where you want your cake and eat it too. We want the clutches to lock up during spinning to get the power to both wheels, but at the same time we want them to slip during turns (when the outside wheel has to travel at a faster speed than the inside wheel) so we don't have to feel/hear the clutches.

I have used and serviced the different types of 8.8's alot and in my opinion the problem could be that there is too much FM in your gear oil.

The purpose of the friction modifier is to allow the clutches to grab. Too much is a bad thing because the prevents the clutches already under pre-load (Z spring) from releasing smoothly when the torque bias or variance in wheel speed at the diff is reached. (~30-60ft-lbs if I remember correctly)

If you haven't done anything you could try soaking the clutch-packs before re-installation. If you are having a shop do this it is a toss up on fluid and installation procedures. Just because someone is a mechanice does not mean he knows everything about every car.(true story) And you can re-use the fluid for your daily drive as long as there is no metallic shavings in the rear. I have have used only 75W-140 for a while now and have not had any issues.

Best of luck,
Taylor

Unfortunately the statement in red quoted above is not true.
A limited slip friction modifier reduces the grip of the clutches, to facilitate release when turning.

Without friction modifier the clutches want to stay gripped together and will tend to shudder as the release more suddenly and abruptly instead of smoothly.

 

[Roots-type]

Unfortunately the statement in red quoted above is not true.
A limited slip friction modifier reduces the grip of the clutches, to facilitate release when turning.

Without friction modifier the clutches want to stay gripped together and will tend to shudder as the release more suddenly and abruptly instead of smoothly.

Exactly.