tigercrazy718

ok so i just installed my new rear end (8.8) with brand new 3.73 gears. on teh drive home i heard nothing out of the ordinary. i let the car sit for about an hour, then ran to the store. when i did that, this chattering, groaning noise started to happen when i turned below 15 MPH. the sound comes from teh side im turning into, and doesnt happen at higher speeds or when going straight. bc of this im convinced its coming from the LSD. i wanted to get yalls opinions on this and if this is supposed to be normal for a rear end that had all its guts replace, but i seriously doubt it is. also im wondering do you have to separatly lube up the axles from the diff? bc right after i got the gears put in the shop didnt put in any lube bc they thought i was taking out the axles, and i had another shop do all the fluids later. let me know if you need more info. thanks!

Ricardo

Are you saying you drove the car without any gear oil in the rear end for any length of time? If so it's probably toast; especially with the heat the gears will see as they are broken in.

Did they add friction modifier?

New clutch pack; did you soak them overnight in gear oil?

tigercrazy718

Sorry I need to clarify that. The rear end was moved around shops out of the car. And this rear came out of a new 2011 v6 so it should have hardly any miles on it. As far as a new clutch pack, is that something that is normally replaced in a gear swap?

tigercrazy718

O and the shop that did the fluids was a mustang only performance shop that is very reputable in my area. He put in royal purple and I asked him about the friction modifier bc I know some people say you still need it even though its supposedly included, but he said he's done over 50 gear jobs with just the RP and hasn't had a problem

Ricardo

The clutch pack is changed only if you buy one or the rear is rebuilt. I was on the fence about upgrading to the ones used in the GT500 to handle future mods but they said no-go unless I wanted the car to sit overnight so the discs could sit in gear oil. I have RP and it also has the friction modifier in it, no issues after a few thousand miles.
Maybe getting ahold of the shop and asking them for help would get it fixed. I hope they work with you, most reputable shops should.

grabber blue gt

Yeah sounds like there was no friction modifier, but if they said they used royal P I'm at a loss.

When the dealer effed up the rear end on my 2010 it grinded/groaned/dragged extremely bad when going straight, so if its only happening when you turn than its the limited slip

wcgman

+1 its LS.

tigercrazy718

So what I'm wondering is if the lack of the friction modifier on a brand new rear end is making it hard on the lsd bc its not worn in. I've talked to several people and they all agree that the lack of the friction modifier is probably the issue even tho RP has it in it. Maybe there isn't enough built in to the oil to account for the brand new rear end. I'm gonna call the shop tommorrow and talk to them about it

wcgman

I've heard from several people that RP does not need a FM when its used. However my differential guy swore off RP as cr@p and he's been building drive trains for race cars and DD's probably as long as I've been alive. After my install, I had no issues and he said change the fluid at 500miles which I did. I had a local lube shop do it and handed them my friction modifier (FORD FM mind you) and they said they put it in. Within a 1000 miles I started hearing grinding on turning, so I called my gears guy back and he said they probably screwed up and didnt put the FM in it. I took it to him, he did a fluid change and I havent heard a peep in that rear end since and thats probably 8k ago.

timmbo

Add a 4oz bottle of friction modifier. Royal Purple or not the rear end needs it. Period. Thanks us later.