hey guys, I was looking at my ID sticker in the door and it says that the differential in my truck has a code of H9. I've been looking around and I've read that the H9 is the 3.55 ratio with the limited slip. Is this right?

My trucks a 1998 F-150 with the 5.4.

 

Here is the link to the axle codes.

https://www.ford-trucks.com/forums/s...d.php?t=297637

 

Thanks, I actually found something similar to that chart when I later on searched on Google, but nothing with as much information. Alright, so I've got an H9 3.55 limited slip, so next question is lubes. The chilton manual says to use an 80w90 synthetic while the owners manual says to use 75w140 (I'm guessing dyno). Does it really matter which one of these I use? I've been looking around and can only find the 75w140 in brands that I've never heard of and am weary about putting an unknown brand in my truck. I was told by the guy at O'Reileys that if I used full synthetic that it wouldn't really make that much of a difference...is this true? Which brands do y'all like the most?

My truck is out of warranty, if that makes a difference.

 

I just visited the local Ford dealership and told them what I have for an axle which, by the way, is identical to yours. They gave me Motorcraft 80-90. Don't forget to pick up 2 bottels of friction modifier for the limited slip. Just add it to the rear when you fill it. Comes in 4 fl oz bottles. Use both.
Frank
89 F150 3.55 LS

 

Thanks for the reply. I'm going to go and try to visit a Ford dealership sometime, and hopefully they will help me like they did you.

 

I know the dealership is a wee bit more expensive on a lot of supplies, parts, fluids, etc. but it bugs me when I go into a chain auto parts store and get blank stares on what should be a simple question. Not all are like this but I have come across this a lot.

 

I have a 94 with a 300, 5spd mazda😥manual transmission, 3.55 rear end and 35's. I have no problems at all down low. The only time I have an issue accelerating is with 20mph wind in my face going up a steep steep hill. Other than that, I pick up speed just fine. 5th gear is a bit broad in range but that just helps the gas mileage. Oh yeah, forgot to mention that I also have over 1,000,000 miles on it and still running like a top.

 

I have a 91 with 300, also the Mazda m5od. Rear end is 3.08 with 31's. Have you done any towing with your rig? I'm worried about stressing the clutch starting out on a hill.

 

That guy was one and done. He's never been back to the site to even look.

I think you will be looking at a towing limit under 3500, maybe as little as 1500.

This says the limit for the a '91 with the six is 5800. That would be with an automatic, maybe 4x4, and probably 3.55s, and tires shorter than 31s.

https://ford.boatingmag.com/

IMO you need 3.73s or 4.10s.

(think about reverse, mighty tall in your trans iirc)

 

I bought it more as a farm truck that I will use occasionally to tow a 12 ft tiny house I'm building for my teenager. The more I got in to it the more I realized that the gearing is absurdly high for a truck...imo. I've been seeing a lot of 3.55 axles out there but no 3.73's. Reverse is mighty tall, as well as first gear. 7.8 mph at 1000 rpm. So, yeah, all the evidence is pointing to higher gears as the way forward. 4.10's would put me at 1955 rpms at 55 mph. I don't imagine a lot of highway time so I can live with those revs.

Thanks for the input...it's a great forum!

 

I use the cheap Walmart gear oil, they have it in both 75w140 or 80w90, you can use either one.