Whats up guys,

I have a 98 F150 4.6L. It makes a bad howling noise whenever I am accelerating and it stops when I take my foot off the gas. After researching on here for a while I have found tons of others with the same problem and the fix seems to be a friction modifier. Am I understanding that correctly? I noticed that mostly everyone with this problem has an 04 but didnt see to many with a 98 truck. Is it still the ring and pinion? I believe the rear axle I have is the 8.8? I am not toally sure tho. Is the friction modifier just a liquid I pour in the diff with new fluid?

Also, I have a shell on my bed so would that make it louder than it is? When I drive it is pretty loud at lower speeds.

Any info will really help. Thanks!

D

 

First I would look at your door jam sticker and get the axle code. Once you have that you can find out if you have an 8.8 or 9.75 or if you even have a limited slip. With a 4.6 you most likely have an 8.8 but I think there some 4.6's around with a 9.75. A 5.4 gave you a 9.75.

If you have a ton of miles your rear diff may just be toast or you could have failing axle bearings or a bad pinion bearing but I would change the fluid as it is cheap compared to a new diff and gives you a reason to pull the cover off and have a look inside. Friction modifier is just a liquid you add to your diff fluid. It smells fantastic. I recomend the Ford stuff as it works the best IMO. Some guys have added two bottles for problem LS diffs but again make sure you have an LS diff before you rush out and buy it.

 

If you bought the truck used you never know if the door tag is correct like my truck I added the traction lock if jacked up you turn one wheel and both the other wheel and the drive shaft turn you have a traction lock..

 

In most cases it is the pinion bearings. Modifier is for the clutches and shouldnt cause any whine. If you have a limited slip than you need it if open diff than you dont. axle 19 is 3.55 open, H9 (what I have) is 3.55LS if I remember correctly. I have the same whine issues at acceleration and slow down. Counting down the days before I have to get new bearings and gears .

 

Ah dont tell me that! I don't want to have to do surgery like that. My truck has 171000 miles on it and it still runs strong IMO. I am pretty sure I have looked at the sticker before and it said H9 I believe. Does the door sticker tell you if you have LS or do you have to get it off the ground to check it? And if I don't have the LS I do not need to get the friction modifier?

The guy I bought it from also towed a TT and I tow occasionally so I think that could be another reason it is so loud. maybe just a lot of abuse.

Thanks for all the input!

D

 

The door sticker code tells you the gear ratio and if you have an open or LS diff.

Correct.

That will definately increase the wear and tear.

 

Friction modifier or the lack of will not cause a whine. The lack of it in a LS can cause clutch chatter.

 

Are you sure it isn't your U-joints?

 

If your axle code has a letter in it then you have limited slip. If it is just a number then it is just an open rear end.
The friction modifier is an additive people always seem to put in the rear ends of these pickups when they start having problems with the clutches chattering in their limited slip rear ends. Very very noticable when you are turning corners...a very common problem with these trucks too.

This is not a problem that is pertaining to what you describe though. A whine that comes and goes depending upon acceleration/deceleration is most likely going to be either the gears themselves or a pinion bearing. Under acceleration or deceleration the pinion gear itself will actually want to move forward or backwards, in turn loading either the inner or outter pinion bearing and causing a noise to become apparent.

 

Thanks for all the input guys! I am going to do some work on my truck this weekend to see what the deal is. Ill keep the thread updated. Thanks again!

D

 

I checked the axle code on my door and it says "H9". So just to double check before I go spend some money, that it an 8.8 with an LS correct? I remember there was a thread on here with the axle codes and what they mean but I cant seem to find it.

D

 

That's a 3.55 LS, you don't get the size from that code. However, if you have a 4.6 it is a 8.8.

Limited Slip Differential, Rear Ford & Dana 80......GL-5*
All TEMPS......75W-140 [3] [4]

[3] Limited Slip Identification: Letter & number
on plate on door lock pillar. (Models W/ Traction-Lok Rear
Axle Add 4 oz of friction modifier part no. C8AZ-19B546A
(EST-M2C118-A) or equivalent)
[4] Synthetic oil is required.

Differential, Ford 8.8 or 9 R Rear..........5.5 pints

 

Ah ok got it!

Whats GL-5?

Just to make sure, the friction modifier is C8AZ-19B546A and I need 4oz of it along with 5.5 Pints of delicious smelling synthetic gear oil? Any type particularly?

Thanks!

D

 

Just look for synthetic 75w140 diff oil that is GL-5 compatible. It will say on the back of the bottle. Any brand you prefer as long as it is GL-5 compatible.

I just went into the Ford parts counter and asked for Friction Modifier. No part number was needed. They may ask for your truck Vin #.

 

You need 5.5 pints TOTAL - fluid and modifier. Considering fluid is only sold in quart bottles, you need 3 quarts and you will have some left over.

GL-5 is simply a spec. For what it's worth, Walmart Supertech meets spec.

You will also need a cover gasket and/or RTV. Autozone sells gaskets for the 8.8 for 5 bucks. Everyone around here is all high on just RTV, but I'm old school and find a gasket is a lot easier to work with and I use RTV to help hold it in place while installing the cover.