Is there an advantage to using synthetic axle lube when changing the fluid? Can I use one grade of fluid in both front and rear axles for simplicity. I don't believe that I have the limited slip rear axle.

Personally I don't see any reason for synthetics lubes but use standard 80w-90 GL-5 gear lube for my standard open differential axles. If you have a Limited Slip then you have to consider lube with the friction modifier or get buy the friction modifier separately. Being that petroleum lubes have done a excellent job up to 224k miles and no failures and excellent MPG's (Highmark at 27.2 MPG last summer).

Usually less friction and longer service interval...

 

I'm pretty sure you could use same weight oil for both as well.

I have used the 80w90 GL-5 in both the front and the rear for about 40k miles now with no ill effects. Mine is a LS and I added the friction modifier to mine. The oil did not come with it.

Am I correct in assuming that there are no gaskets for the dif covers?

I used RTV sealant, I think Great Stuff. The darn stuff was so sticky when I placed the cover in position it stayed there when I had to let go of it momentarily. It actually dd not move for about 45 seconds, just got tired of waiting for to move. Mike tells me the stuff I used will be a PTA to remove when I change it again, I guess time will tell. Any good sealant should do the job though. Be sure and clean the old sealant off completely. A razor blade and a scotch brite work very well.

Edited January 12, 201411 yr by dripley

That would be "Right Stuff" I assume. Thanks!

I believe you are correct. Great Stuff is spray foam insulation.

No gasket for the covers. Just sealant. IIRC, I believe in this instance it should be the orange RTV. If not, black should do fine. I usually stuff a rag over things and use a wire wheel to clean things up.

I believe you are correct. Great Stuff is spray foam insulation.

Spray foam might work too ;-)

let me know how that one works out for you.

If we're not careful, this will become a subscribed forum too. Lol.

I normally use just plain old clear silicone in a caulking gun. (RTV) stands for Room Temperature Vulcanization...

 

RTV Silicone (Room Temperature Vulcanizing silicone) is a type of silicone rubber made from a two-component system (base plus curative; A+B) available in a hardness range of very soft to medium - usually from 15 Shore A to 40 Shore. RTV Silicones can be cured with either a platinum catalyst or a tin catalyst. Applications include low temperature overmolding, making molds for reproducing, and some optically clear grades have lens applications.

 

Gaskets are available for a few bucks if you ask for them, a little less messy compared to silicone but either will work. I use synthetic in the rear as the higher 3.54 gears tend to generate alot of heat in the hot summer months when towing. Its pretty much standard on all new OEM vehicles.

Personally I don't see any reason for synthetics lubes but use standard 80w-90 GL-5 gear lube for my standard open differential axles. If you have a Limited Slip then you have to consider lube with the friction modifier or get buy the friction modifier separately. Being that petroleum lubes have done a excellent job up to 224k miles and no failures and excellent MPG's (Highmark at 27.2 MPG last summer).

If you are in extreme cold you will see a huge difference. A guy I know had the same truck as me (F-150 4wd 4spd) and was parked on a slight hill. I parked next to him and we both left at the same time a couple of hours later. I pushed the clutch in and my truck did not move. His truck rolled just as soon as he pushed the clutch in. He had synthetic through out and I didn't. The cold flow capabilities and higher heat tolerances make synthetic better in my book.

Is there a downside to synthetic besides cost? Is it necessary to get all residual old oil out of the axles? Can't imagine it all coming out by draining.

I cant speak for or against synthetic, but when you open it up, its all going to drain other than what sticks to the gears. Make sure you have a good size drain pan in case the cover pops off quickly.

When I go from driving forward to coasting I can feel a bit of a lag on a big hill at hiway speeds. Is this a sign of wear in the rear axle gears? I realize that changing fluid won't solve that. And with one rear wheel on the ground, there is a bit if slop being able to turn the lifted wheel back and forth a bit.

Edited January 12, 201411 yr by joecool911

There is a allowable amount of play. Mine has it and I dont notice that it is any different than when it was new. That was 12 years ago however. I am sure someone will tell us what is normal.

I honestly cant think of one drawback to synthetic diff oil including cost when looking at the big picture. Some synthetic oil manufacturers recomend up to 100k mile service intervals compared to 30k intervals of the traditional mineral oils. They also offer more protection at both ends of the temperature range and will not break down as quickly (hence the extended intervals) Most if not all passenger vehicles these days factory fill with synthetic and is considered a "lifetime fill", meaning the oil is fine until service of the gear sets or seal replacement is needed (or contamination is suspected). Essentially all of the service intervals in the service manuals of our trucks are based off of the oils capabilities at the time. Oils are much more advanced these days and there is really no reason to not take advantage of them and enjoy the added protection and extended service intervals.

Edited January 12, 201411 yr by diesel4life

I cant speak for or against synthetic, but when you open it up, its all going to drain other than what sticks to the gears. Make sure you have a good size drain pan in case the cover pops off quickly.

 

Take off all of the bolts except a few at the top. Loosen them a little and pry the bottom. This will contain the fluid to drain at the bottom and limit flow.