I recently did a ratio change on our '09 F-250 SD, 330 C.I., 4X4, CC, LB. We went from the 3.73 limited slip to a 4.30 limited slip. This truck is under warranty and since the 3.73 limited slip was acting like an open rear end we contacted the local dealer and upon their inspection they deemed it necessary to order out new limited slip clutch packs to be installed with the new 4.30 ring & pinion.

That got both rear wheels pulling together and we've got the new ring & pinion broke in for towing, did the 500 mile differential fluid change and took a short trip (200 miles) pulling our 25.5' fifth wheel. This gear change brought the little 330 to life, I'd say it even made it just a bit of a beast. I'm not silly enough to say this ratio change put it is in a class with the diesels or even a V-10 but it really does very well with what we'll be doing with it. Ford really should offer the 4.30's as an option with the 330, but I suppose it's an average fuel consumption issue.

I put Valvoline Synthetic 75-140 gear lube in after the 500 mile break-in period and went to the local Ford Dealer and got a bottle of the genuine Ford friction modifier. I put about half of it in after talking to some guys that have done the ring & pinion/limited slip deal told me to use the genuine Ford FM but not to put the whole bottle in at once. I'm now wondering if I should put the remaining half in or leave it the way it is. It doesn't seem to chatter while turning short or shudder from a dead stop upon acceleration or anything like that.

What has been you guys experience? Since we spent the money to get the gear and got the dealer to warranty the new clutch packs we don't want to leave anything to chance.

Thanks guys!

 

If it's not chattering I sure wouldn't add anymore. In fact, you might already have too much in there - check the bottle of Valvoline but I'll bet you find that it already has the friction modifier in it. So long as the LS is working and not chattering I wouldn't change a thing.

 

You probably added more than enough already. Only add more if you get "chatter".

 

Honestly, if you were not wanting to leave anything to chance you would have left the oil in it that came with the gear swap. It was done by the Ford dealer, and therefore the repair didn't compromise your warranty. Not sure why you changed the oil, as it's not supposed to be changed for 100,000+ miles even under severe service.

But I guess that's water under the bridge at this point. Follow the above advice, if it's not chattering you should be just fine. In the future I highly recommend consulting your owner's guide for the factory maintenance recommendations before getting any better ideas. Just my opinion, your mileage may vary.

 

I have an '08 with similar setup (except not 4X4). I have thought many times of going to the 4.30 ratio setup. I tow a 5er that goes about 9200 lbs. fully loaded and at times, am left wanting a little more pulling power. My concern as always is that this is also my daily driver and I don't know that I could stand a big hit on the fuel consumption. I average 14.8 on my daily commute now. What kind of mileage drop did you experience when you made the change?

 

chazworth, I only checked the mileage a couple of times prior to changing out the ring & pinion and it was getting just shy of 16 mpg mostly highway, empty, driven like my 88 year old Mother would drive it and figured with a calculator.
Since I went to the 4.30 it gets just shy of 15 mpg driven under the same conditions as with the 3.73.

That's the bad news, the good news is that when towing our 8300 lb. 5th wheel camper we now get just shy of 10 mpg with the 4.30's as opposed to 7.5-8 mpg towing the same trailer with the 3.73's. The improved towing fuel mileage along with the increase in it's load pulling capability and the ease and enjoyment the 4.30's made in our towing experience more than make the ring & pinion swap worth every penny.

The difference is I'm probably going to use our truck as an empty daily driver very, very little. Obviously, how much you're going to tow is the determining factor, but the 4.30's really made our truck a great tow vehicle.

Crazy001, the new ring & pinion had a break-in procedure that needed to be followed, not following this BI procedure would result in voiding the warranty on the ring and pinion. I followed the procedural guidelines to the letter and they said specifically that the differential lube be change out at 500 miles following installation. Not even the tech's or service manager at the Ford dealer could tell me exactly how much of the friction modifier to use. They said to put 'bout half of the bottle in and if it chatters put a little more in. I haven't experience any chatter but I thought maybe you guys here would know from experience how much to use.

 

Huh, maybe there is a break in procedure that's done at the factory that we don't know about. In that case good call on the oil change. From what I've read over the years you want enough friction modifier to eliminate chatter and no more, so it sounds like you did good on this one.

I will be doing the same thing in two weeks when I get my next truck. Changing all the fluids and this one has a LS rear end, and that's why I'm interested in this thread.

 

Crazy, just curious. Will you use a non-genuine Ford fluid that contains the friction modifier and ad a smaller amount of the Ford FM, or do you intend to use the genuine Ford lube and add the full amount of FM to the refill?

 

I have three quarts of generic synthetic 75w140 that I have sitting on a shelf, and I'll buy whatever I can get cheap to make up the shortfall. So I'll probably add half a bottle of FM and see how it drives.

 

Can someone describe what you mean by "chatter"? I changed my rear end oil about 2 weeks ago I used Royal Purpal 75w-140(I wanted to get mobil 1, but could not find any in town), the bottle said it was for LS diffs. I only drove it a couple times around town and everything seemed normal, then the other day I was on the interstate and at 75mph I kept getting a vibration. I have an appointment Monday to have my tire's balanced, but the vibration seemed diffrent then the tires.

Thanks.

 

This can't be your LS differential. The purpose of a differential is to permit the wheels to travel at different speeds, this is necessary during turning because the outside wheel will always spin faster than the inside wheel. Your LS differential has clutch packs that engage when there is a high speed differential between the two, and this allows more torque to be applied to the gripping wheel than the spinning wheels. When friction modifier isn't used, the chattering occurs because the clutch packs are too grabby when you're turning.

When going down the freeway and going straight the wheels are going the same speed, so the clutch packs aren't engaging. Not sure what your issue is, but this doesn't sound like LS chatter to me.

 

Thanks Crazy001.

 

Thanks Reb, great info!