Differential Whine

98mustanggtkid · Sep 6, 2009

So I am getting a whine noise from the rear of the car I think that it is the differential because as I go faster it becomes more high pitched. So if i am going to rebuild it I might as well upgrade it so i dont have to do it later, but what all do I need? I would like to go with the 31 spline axles and upgrade the differential it self, I plan on getting a new differential cover as well but do I need to replace the ring and pinion as well? there is a 3:73 in there now but that was put in before I bought the car.

Any help would be great

Thanks
Chris

Javi · Sep 6, 2009

backslash is not set correctly.

98mustanggtkid · Sep 6, 2009

even though it just started it never did it before up until 2 weeks ago

MustangChris · Sep 6, 2009

^ yes. your backlash is off.

For a budget build, you dont really need to throw in 31 splines, but if you do, you will need to get 31 spline differencial to match up with it.

Jegs has a number of t-lok diffys available in 31 spline. I personally went with americanmuscle's 31 spline eaton true-posi set up and I have loved it.

for a rebuild you will need:
depending on the wear and tear on the gears:

gears
bearing/disc rebuild kit
gear lube
RTV Sealant

if you want to upgrade:
gears (suggest a faster ratio, such as 3.55:1, 3.73:1, or 4.10:1)
differencial (suggest posi differencial)
axles (suggest 31 spline. 33 is overkill and they are hard to find diffys for)
bearing kit (i think... lol its been a few years since i had mine done)
fluid (suggest royal purple)
posi additive (suggest ford racing... *if* you get a posi diffy)
and since you are already there i suggest a differencial girdle
RTV Sealant
and, once again. since you are there... ARP lug nut studs

98mustanggtkid · Sep 6, 2009

Awesome thanks Chris, I always heard if it makes a whine noise it was going bad so thats what I assumed. how does the backlash just become off does something fail or does something in there just catch and throw it off?

MustangChris · Sep 6, 2009

honestly, i dont know. I bought my car with bad backlash (the dealer said "they are aftermarket gears, they are supposed to make that sound.") so i dont know exactly what causes it to go bad other than a crappy install.

When they take your gears out, ask to see them. Touch the edge of the teeth on the ring gear (obviously the round one. lol) they will feel sharp, like the blade to a pair of scissors. This is bad. this is what happens when the ring gear and the pinion gear dont mesh properly, i.e. bad backlash.

I had my rearend rebuilt with the exception of brakes and ARP Lugnut studs.
Ford Racing aluminum driveshaft
SVO 4.10:1 gears
eaton LSD Posi diffy
FRPP 8.8 axle girdle
moser 31 spline axles
royal purple fluid
differencial magnet
FRPP LSD Additive fluid

all i need now is brakes, ARP studs, and speed cal to fix my speedo

Hoseitdown · Sep 6, 2009

It DOES have fluid in it right? have you checked it?

MustangChris · Sep 6, 2009

^^^^^ LMAO!!! good point brotha. lol. no one even asked

there is a plug on the FRONT of your axle housing, next to the driveshaft. use a ratchet and extension to take it out while the car is sitting level. if fluid comes out, its full. if not, add fluid till it comes out.

98mustanggtkid · Sep 6, 2009

nice! i just upgraded to the cobra brakes on mine which went smooth minus being sent 2 front passenger calipers. but I need to find a place to install the stuff, i was looking at the Eaton diff from american muscle as well and getting the moser 31 spline axles, i like the 3:73's that are in there now so if i need to replace the ring and pinion i will probably keep that and i never heard of a diff magnet so i will look into that , there is royal purple oil in there now and i can get the additive no problem i would like to get an aluminum drive shaft but i might to that later with my trans cuz for an auto i think you have to change the yokes on both sides? i could be wrong i havent really researched it much ( i like to look up alot of info and get opinions of people who have done the things i want to go before i do them)

And yes it has fluid i just changed it and filled it all the way, but it was making this noise before i change it

MustangChris · Sep 6, 2009

http://www.summitracing.com/parts/FTM-DM101/

3.73s are a good performing gear.
as for the driveshaft, i didnt realize you had an auto. So, i dont know what it takes to get an aluminum one in there. lol.
let us know how the cobra brake swap goes ;-)
FRPP Additive is like, $4.99 a bottle. i put it in the diffy first when re-filling it.

98mustanggtkid · Sep 6, 2009

its cool i sometimes wish i had a stick but the auto still gets the job done, i just finished the swap yesterday ill try and get pics up later tonight but it was pretty easy