I just wanted to give you a guys a heads up about how important friction modifier is in your rear end. I had 4.10s installed about 3,000 miles ago ... then took them out and had 3.55s put back in. I asked the last installer many times if everything looked ok, cause both the 4.10s and the 3.55s whined. I recently took my car to the dealership, and had them look at it. And the whole rear end was ruined, all because friction modifier wasn't used. I don't know if it wasn't used for the 4.10s lifespan, or just the 3.55s (100 miles), or both. But, it is key that you guys have this. Just wanted to make sure people out there know this info. I've read it on some other threads saying that it is good to have or is required, but I figured it should be stressed that each person who has their gear changed, make sure their installer does this. My modified days are done for the mustang for a while, but I will be back .

 

Why did you take out the 4:10's ? What is a friction modifier?

 

Ford has used friction modifier in every rear end it has produced for like 20 to 25 years. It is a $10 bottle of liquid gold when it comes to the clutch packs it these rear ends. It is very simply an enhancer for the rear end lube. Extremely important stuff. It is hard to believe that anyone that works on Ford rear gears doesn't know about it.
Scott

 

I can see it hurting the clutch packs, but not ruining the whole rear end. It has nothing to do with the ring gear or the pinon gear.

 

The friction modifier is there for the benefit of the clutch packs and only that. All differential gear oil has other extreme pressure modifiers for the benefit of the gears. Lack of the friction modifier for the clutch pack wll affect the operation (won't slip) and wear of the limited slip. If the gears and bearings are toast too, something else is wrong.

 

Quick question does royal purple gear oil already have the modifier?

 

RadBOSS and Cobrakev are correct the friction modifier has nothing to do with the Ring and pinions themselves.

Shaun81 Yes the RP should already have it in it as does Redline Oil

Richard

 

Royal Purple does come with the additive in it. I think that there might have been more than 1 problem in this situation...

3,000 miles, when set up properly should have little wear. Of course this depends on driving habits. Furthermore, we've put in plenty of gears in 8.8's, and "whirring" is unusual.

CR
Tillman Speed

 

Set up properly might be the key word here ... i.e. contact patch in the right spot, bearing preload correct, and the ring gear carrier w/o excessive run out.

 

Tell your dealer that that's a load of horse poo.
I have 11,000 miles and 400 runs on my 05 without any friction modifier for a total of 22,000 miles and 800 runs.
The purpose of the friction modifier is to quiet down the clutch packs from groaning PERIOD.

If the dealer is trying to charge you for repairing the rear end you can purchase a complete new rear end for a fraction of the price at newtakeoff.com
http://www.newtakeoff.com/index.asp?...S&Category=424
Notice that you can get it in either 3.31, 3.55, or 3.73.

 

Thump rr

Great Link Thanks for posting it.

Richard

 

Wow you guys said a lot. Don't worry about how much it cost me to fix. I'm paying zero dollars for the fix ... don't really want to go into the details. Basically, from the 4.10s for 3,000 miles it would make a whine noise from 45 mph and up. I had the 3.55s put back in, and asked the installer place a lot if everything looked ok ... and they said yes. The 3.55s are OEM, and when they were put in, it made a horrible noise like low groan from 45mph and up. I took it back to them, and they said they couldn't do anything about it. So, this is when i took it to the dealer. I put it back to stock, cause basically I was going to drag it, but with an engagement ring coming soon, and trying to buy a house ... my funds will go bye bye real soon , and i won't have the money for any mods (thus, i've given up on my run for a while). Anyways, I can't wait to have my car back in one piece. I haven't gotten to drive it in over a month (having gears changed, and been at the dealer while I was on a trip). Basically the dealer said the reason the whole rear-end was ruined was because of the modifier. I don't really know if that is the case ... and my dad said this morning that the clutch packs should have been the only thing ruined without the modifier. And he said that something else must have been wrong. Anyways ... just giving a heads up out there. And, I don't think I'll ever get gear changes again in my area. I'll need to find someone that is more trusted that others suggest.

 

If the friction modifier was to prevent groaning, how come its not called 'anti-groaning fluid'? The groaning is a symptom. The friction modifier is there to ensure oil has the correct lubricity so they slip and grip as necessary...

 

If you're ever in the PA area, stop by and we'll set you up for cheap. With a guarunteed installation!