diver64

Ok, I've read the threads here and elsewhere on the differences in gear ratio's.

I have a 2004 XLT (axle code H9) 9.75 with 3.55LS in a 5.4 and the heavy duty towing package. I have a leveling kit and went to 285/70/17 tires. I don't tow more than 3,000-4000 now.

I took off the rear cover to change the fluid and noticed the big gear has some gouges in it which most likely is the culprit for the rear end drivers side hop

So, it looks like new gears. Considering what I have now and the fact that when I'm changing out I can pick about anything what is the opinion on the gears? Stay 3.55 or change to 3.73? Would I notice the difference as one thread said that with every .25 difference in ratio I'd notice about .5-1.0 mpg change which is not enough for me to worry about.

I'm not doing this myself and am going to have all the bearings, spacers etc changed at the same time which is way more than I can comfortably take on.

PerryB

Can you post a couple pictures of the ring gear? I think it's far more likely that your wheel hop issue is stemming from the clutches in the LS unit. As far as ratio, you'd like the 3.73 better with those tires, 4.10 would be better yet. Just remember you'll have to do the front as well, assuming its a 4x4.

Kevinpmac

Spot on advice!

diver64

My photo skills are not great but I will take a picture and post as I've not filled it yet. Clutches in the LS Unit? That's interesting. I'll dig into that and see if it's a change I can do? If I have to change the front then I think I'll stick with the 3.55.

The more I think about it when I bought the truck I changed all the fluids and put 75w90 in the back with the friction mod. When looking around I noticed a tag on the rear that said 75w140 Synthetic so someone had already been there, changed the fluid and tagged it. After reading threads on the LS Clutch I'm going to drain and refill with 75w140 and add a second bottle of friction modifier suggestion elsewhere if I still get the jump as a first step. The drivers side jumps when reaching over 45mph or so like it's going over speed bumps but it comes and goes. the passenger side is nice and flat so I'm not sure that is the problem but it's worth trying

Thanks for the suggestions

PerryB

If memory serves (debatable) we were discussing this in another thread a week-10 days ago. If you're certain its a drivers side vibration, I can't see how its a ring gear problem, or even the clutches for that matter. The clutches will manifest most at low speeds when getting on the throttle while turning/cornering. This will either cause a chatter in the rear end (not specific to either side) and/or make a Whoop-Whoop-Whoop sound. When travelling in a straight line the clutches are static. A badly scarred gearset might whine or growl, but it will most likely be proportional to speed, not just in a relatively narrow range. I still have to go back to suspecting a 1) bent wheel. 2) bent axle. 3) faulty/failing axle bearing. I'd be looking for a dial indicator to check the axle runout, both radially and axially. Axial runout is the one you'll feel first in the seat of your pants.

diver64

Yeah, the symptoms don't match what is described for a LS Clutch Pack. No sound, shudder or chatter either at start, turning a corner or going backwards from a stop. Only when traveling above 40-45mph.

When you say "axle bearing" do you mean the one on the outside next to the oil seal? I was going to change the oil seal since it was leaking a little and thought I'd change the bearing at the same time. Now I've filled the rear with new fluid so I'll run it a bit to see what happens.

The gear was not as bad as I thought and remembered. Just some slight scuffing on the outside rim of the teeth around the circumference. You can feel it with your finger on most of the teeth but not see it much. Probably just normal wear stuff and nowhere near enough to cause what I'm getting i think

If you remember the thread you are describing please post it so I can read it.

thanks

PerryB

Yes, I was referring to the outer axle bearing. If I can come up with the other thread I'll post a link. It may have been over at Ford Truck Enthusiasts (FTE).

diver64

Thanks. I tried that forum and another one but didn't find what I was looking for so thought I'd try here as I've had pretty good luck on this one finding stuff and getting questions on my truck answered.