nierd

Hey guys - I got my dad a 2004 F150 Heritage and was told by the owner pre-purchase it needed a drive axle seal. Well I took a look and it seems more like it's a differential seal leak - here is a pic:




So onto questions:

Does anyone think that this is something other than a differential seal?

Gasket seal or silicone? Does it really matter?

I've seen people use break cleaner to clean the surfaces - is this generally recommended?

Anyone have the torque specs for the bolts that could pass the information on?

grss429

Drop Punkin, let the fluis drain out, take break clean and spray the entire diff out real good.. then use rtv and seal the punkin back up.. dont need a tq spec just makr aure they are tight

Rear diff 3 quarts of 75w-140 synthetic with 4-8 oz of friction modifer if you got lsd

PerryB

That's a perfect example of why you should not jack a truck up by the differential housing. I realize this doesn't answer your question, but thats the #1 cause of such a leak. It springs the housing.
As stated above, use a chemical stripper to clean it. I would follow up with a wire wheel and sandpaper and then a final washdown with brake clean. Atfer sealing up the joint, let it sit overnight to cure before refilling with oil.

grss429

Rtv drys rather quick no need to sit overnigjt

PerryB

I like to let it fully cure before exposing it to petroleum products. Maybe unnecessary but that's what I like to do.

nierd

You think that's the cause? T'wernt me I just bought the sucker - got a dream deal on a truck that otherwise is in fantastic shape and I needed to get my dad a daily driver so all in all I'm not upset about having to fix it

I was planning on using a razor blade and pliers to clean off the mating surfaces - Other than that I'm just waiting on my parts to show up and get 'er done.

I appreciate the look overs from everyone - thanks for the advice - and while I know many here most likely can do it by feel - in case in the future someone is reading this thread for information the called for torque on the bolts is 33 ft/lbs.

PerryB

Yes, I do. Look at the physics involved. Assuming it takes 2000 lbs. of lifting force to get the rear wheels off the ground, the stress on those bosses is roughly the equivalent of putting a 5000 lb. load in the bed, in the opposite direction of course . I don't know how this terrible practice of jacking them up by the "punkin" ever got started, but it doesn't happen on my trucks. When I go into a tire shop, we have a little chat about how there are going to be jacks used under each end of the axle (assuming both wheels need to be off the ground).
I didn't mean to imply it was your fault, and I realize most people are unaware of the damage potential because its such a common proceedure, but it puts a LOT of stress on those axle bosses that they weren't designed for.

Rick's 06

I agree with you that I don't think you should jack up the truck under the diff, but I can't really back that concern up with numbers that really make the case. If it does take 2000 pounds to lift up the back of the truck under the diff, that's only 1000 pounds going through each joint. To me that's just not that much, and I would think that the impacts the rear axle sees under any moderate off roading would exceed that. Anyway, good discussion. I love to understand how things are loaded which helps see why things are designed the way they are.

PerryB

It's the distance from the fulcrum to the load that counts. The leaf spring is the fulcrum, and the load is normally applied at the axle flange, a distance of about 12". When you jack it up by the diff. you are increasing the length of the arm by a factor of roughly 2.5.

Martian

Same. Overnight into the afternoon. Chances are I didn't have plans to drive it anyway which is why I'm doing it when I am.