Information Request: What is the interchangeability for a '98 F-150 4.6L auto trans, 3.55 rear end ratio? Tag is 3L55 88-8-E30

Problem: The center section is getting HOT, even with full and correct fluid, 75-140 synthetic with friction modifier. Fill plug retains a massive amount of finely ground metal, like soup.

Situation: About 2500 miles ago, the spider gears lunched themselves, so we replaced them and the axle bearings with seals. Ring and pinion gears looked fine, no chafing or unusual wear apparent. There are slotted or tabbed spacers(??) between the spiders and the housing, I think we put them back right. Some were bent, but I straightened them out. Cleaned out the center section and all went back fine. Did not remove the ring or pinion, just the spider gears and all.

Advice, recommendations and or analysis is most welcome.

 

Any axle from the 97-03 F-150s will work fine... as long as they use the same brakes. I dont think the pressure required for drums is enough for disks.

The 5.4 trucks have a 9.75 axle while the 4.2/4.6 trucks use the 8.8. Either should work for your truck.

Those tabbed spacer things are your clutch packs for you Limited slip axle. Currently you have the 3.55 Limited Slip 8.8 axle.

 

Just look for a carrier assembly from a 97 to 03 that has a reluctor ring for the rear abs. You can put in either an open carrier or a limited slip like you have now. I bought one off ebay for $75.

 

If you are just replacing the carrier assembly or "center section" you must find one from an 8.8 rear end.

 

Thanks for the assistance; I got one today for $400 out of a '99 with 60K miles, with nothing cut. All the lines and cables are intact, which is very nice.
It is different in that it is a strange gear ratio, 3.31, but that is close enough to 3.55 that there should be no noticeable speedometer difference.
Thanks again for the help!

 

Is it a limited slip? Does it have disc brakes compared to your drum brakes? Is it an 8.8? Is your truck 4X4? You willl notice a difference in the speedometer. If it has disc brakes and your old truck had drums in the rear you have a lot of work ahead of you there also. What size rear end did you buy?

 

Fordmerc: I got an open 8.8 with drums; it is a 4x2, so I need not be concerned with ratio compatibility for the front axle. A rear disc conversion is really more of a wow factor, unless one is constantly hauling heavy loads, which this truck does not. A locking rear end was going to cost more than I felt justified for something I never need. My Superduty has rear drums, and I can tell the difference with rear discs when hauling steel.
You are correct, changing to disc would involve quite a bit of additional work. Changes would be required to:
Master cylinder
Proportioning valve
And probably the ABS.
Discs require a different proportioning valve than drums. Additionally, the master cylinder handles both pressure and fluid volume differently for discs than for drums. Shoes are allowed to retract, and are kept adjusted using a mechanical setup - the star wheel etc. Pressure is released when the brake pedal is released, and springs retract the shoes.
Not so for discs. Although one of the functions of the piston boot is to retract the caliper piston a bit, slight pressure remains to keep the piston (and pads) close to the rotor. If the caliper piston were to pull too far back, the master cylinder piston would be unable to supply enough fluid to overcome a large gap between the pads and rotor, due to the much larger volume behind the caliper piston. The brake pedal would go to the floor in that situation, and would feel sorta like stepping on a plum - according to the song.
So - no rear disc conversion for me.
I did brake conversions on my '66. It came from the factory with a single reservoir master cylinder, manual drum brakes with a pressure activated brake light switch - the last year those features were allowed.
Using a '76 donor truck, I installed power disc brakes with a dual master cylinder and mechanical switch (off the brake pedal). The lights come on instantly now, by the way. Earlier I had installed power steering in the front, from the same donor as well as the wider '76 rear drum brakes on the '66 axle. The '66 master cylinder couldn't supply enough volume to larger rear wheel cylinders, so I had to double pump the brakes until I installed the correct master cylinder.