I have a used F-150, two wheel drive, long bed. The limited slip differential is jerking. The Chilton's manual says to drain the rear end using suction gun. I can't fit the tubing in past the clutches to drain it. I want to put in synthetics and need to empty the case.

I'm ready to pull the case cover. The problem is, I don't know if a gasket is needed. It is the weekend. If I pull it and find a torn gasket, can I safely use silicon sealant instead?

Previous owner threw away the ID tag describing the differential serial #, so even if I wait until Monday when Ford is open, what do I tell them.

The truck is too old and is not in their computer ID system, so original equipment is a mystery. Don't you just love guys that work on mechanical things and burn the bridges behind them? Tossing the ID tag. Makes you wonder.

Gary Curtis
Trinity County Calif.

 

most diff covers don't use a gasket they use a RTV silicone.

 

Should be a 9" rear end, at least that is what was on my '88 w/ 302 motor. Pull the cover so you can inspect the gears and flush out any metal shavings in the bottom of the pumpkin. Check with Auto Zone (or whatever) to see if they carry a gasket for it, otherwise use silicone.

 

A 9" doesn't have a cover it has a carrier housing so you'll have to suck out the fluid. A Dana has a cover.

 

I should have specified my truck. 302 V8, EFI, Manual 5-sp. The rear end has a pressed steel cover attached with small bolts. I don't know if it is a 9", but definitely limited slip.

So if the cover comes off, will that drain it? Otherwise, the 1/2 diameter hose on my suction gun doesn't bore into the cause through the fill hole. Or, do I just force it and twist, etc. like a madman? Get a smaller diameter hose?

Love the truck, though. Came into California from West Virginia with 85k miles. Has a Flowmaster, headers with smog control, free-flow air cleaner. Amazingly clean. Have all repair records, so the mileage is true. Amazing for an '88. My first truck. Love it.

Gary Curtis

 

loosen the cover bolts and then pry the cover away to allow the oil to drain. this is going to be some nasty smelly oil. once its drained remove the cover and clean the mount surfaces. inspect the insides and if all is ok then reinstall the cover with a quality RTV or gasket. you will need to refill through the small plug.

 

Thanks Lee, and the others who responded. This truck has to make a 650 mile trip soon to my new home north of San Francisco. This maintenance is a preparation for that trip.

It dawned on me that the rear end is low on fluid. Yet it was lubed at the dealer 6 months ago. That must mean that the seals are probably leaking. The expensive Amsoil synthetic would probably run right through the seals. I'm going to simply fill it with Dino hypoid oil and make the long drive.

When I get to my new town, I'll check the fluid level again. If it is low, I'll have the local garage replace the axle seals and have them pop the rear end cover, then clean things up and replace the hypoid with the Amsoil. I avoid a big mess, and it gets done right.

So, my nervous about this got me thinking hard and asking questions. It revealed a problem that I've caught early, and probably saved me from having to replace the entire rear end.

You guys have been great.

Gary Curtis

 

I think I have bigger problems with the limited slip diff. Thinking it was low on hypoid, I added some an immediately it began overflowing from the fill hole. I let it stop, and then squeezed in some of that STP Limited Slip additive and quickly buttoned up the fill plug.

So, the truck was jerking and lunging for a bit. That was why I decided to change fluids to synthetics, and to add some Limited Slip compound as well. Even though the Amsoil specifies that it is rated for limited slip duty.

What's causing the jerking, then, if not low fluid? This came only a few days ago. Coincided with colder temperatures here in Los Angeles.

 

are you sure its the rear end?
what make you think it is?
jack up the rear and turn it by hand. see if its smooth and listen for noise. if you turn the drive shaft both wheels should turn. turn a wheel and have someone hold the other and see how it feels.
Maybe the parking brake is holding on. you could check and inspect the rear brake shoes

 

The gears were partially broken, and the splines on the end of axles stripped. A fair amount of metal debris in the bottom of the case.

Clutches seem to be ok. It needs all the bearing surfaces, axles and a few gears replaced. No alternative but to have Ford repair it. I can fly jets, but I don't have the knowhow to undertake the biggers jobs on a car or truck. Swapping out the sparkplugs on my inline 6 Toyota took me 4 hours and a lot of skinned knuckles.

Thanks for your suggestions.

Gary Curtis

 

maybe you can get a good used axle from a junk yard and have a local mechanic install it.
sorry about the bad news.

 

The rear axle in your truck would be a Ford 8.8 not a Ford 9". I have a 1988 Ford F-150 Lariat with only 86,500 original miles on it and it has the Ford 8.8 axle with limited slip and 3.55 gears. My truck has the 4.9L Inline 6 with a 5 speed. You can get a build sheet for your truck from Ford if you call their toll free number and ask to receive one. It is free. The number is 1 800 392 3673. Call them and ask them if you can get a build sheet for your truck and tell them your VIN. They will mail it to you. Hope this info helps.