Rear Diff Fluid Change

[harriw]

Hey folks,

Just got my "new" '94 inspected today. One of the things the mechanic mentioned was that the rear diff felt significantly hotter than it should when I came in, and recommended changing the fluid.

So - I finally got a Haynes manual, which of course said nothing about oil type or capacity for the rear diff. Guy at Advance Auto said to use GL-5 80W90. So, I got a full gallon of Coastal GL-5, GL-4, GL-3 SAE 80W 90. Will that be OK? I was surprised that I didn't find an SAE certification mark on the jug anywhere though... Is that only for actual MOTOR oil? It was pretty much the only brand of gear oil they had.

Haynes also had nothing to say about torque specs for the rear diff. cover bolts. Anyone know how tight they should go? I'm gonna pull off the cover and re-seal it too - it looks like there might have been a leak at one of the bolts at some point, so I was thinking of doing this anyway. To that end, I also got some Permatex "1 Minute Gasket" - says for Differentials right on it (and thermostats - that's next month's fix). Up to 450 deg. F continuous - that OK for diffs and thermostat housings too?

Thanks a lot guys. And sorry for all the stupid questions - just a newbie trying to get it right the first time (I did do a search first - just want to make sure I get it all right)

 

[WNY964x4]

Hey folks,

Just got my "new" '94 inspected today. One of the things the mechanic mentioned was that the rear diff felt significantly hotter than it should when I came in, and recommended changing the fluid.

So - I finally got a Haynes manual, which of course said nothing about oil type or capacity for the rear diff. Guy at Advance Auto said to use GL-5 80W90. So, I got a full gallon of Coastal GL-5, GL-4, GL-3 SAE 80W 90. Will that be OK? I was surprised that I didn't find an SAE certification mark on the jug anywhere though... Is that only for actual MOTOR oil? It was pretty much the only brand of gear oil they had.

Haynes also had nothing to say about torque specs for the rear diff. cover bolts. Anyone know how tight they should go? I'm gonna pull off the cover and re-seal it too - it looks like there might have been a leak at one of the bolts at some point, so I was thinking of doing this anyway. To that end, I also got some Permatex "1 Minute Gasket" - says for Differentials right on it (and thermostats - that's next month's fix). Up to 450 deg. F continuous - that OK for diffs and thermostat housings too?

Thanks a lot guys. And sorry for all the stupid questions - just a newbie trying to get it right the first time (I did do a search first - just want to make sure I get it all right)

the one minute gasket should work , i used red rtv when i did the one on my 96 , and the api/sae label is for motor oil only , as for the torque specs , i just tightened them until they were pretty snug , kinda like a tranny pan , go snug then about 1/4 turn past that , and the oil should work as long as it is the right weight , and if you have an l/s axle , make sure to get some additive

btw , a little off topic , but where in western ny you from

 

[pacodiablo]

API labels are for motor oil, but Coastal is pretty much the bottom of the barrel. It will be okay to use, but keep an eye on the condition. I'd change it out no later than 30K miles.

80W90 or 75W140 is fine. Full synthetic is ideal. As long as it doesn't get contaminated, it can last 100K miles, so the cost balances out.

I've never used 1 Minute Gasket before, but if Permatex says it's okay to use in both applications, it should be. Personally, I like Ultra Black for diff covers.

 

[harriw]

Alright, thanks guys. I'll take back the coastal and keep looking - as long as I'm doing it, I might as well do it right. I decided I want a different siphon pump anyway. Is there any concern using synthetic in older differentials (165k mi)? I know it's a bad idea to switch over to synthetic engine oil on an older engine.

How aggressive should I be in cleaning out the internals of the differencial? Should I go at it with some brake clean or anything, or just let the old drip out, clean the seal, re-assemble and fill?

I looked at the Ultra black, actually. Decided I wanted a contrasting color to make it easy to inspect the seal.

By the way, in defense of Haynes, they DO list weight and capacity - I just needed to turn the dang page...

WNY - originally from Hamburg, out by your neck of the woods. My parents still live there, at least until they sell the house this summer. Settled in the Rochester area now, in Penfield. Can't say I recall ever going to Pembroke, but have been through there on the thruway a few zillion times How much snow you guys have so far this year? I thought leaving the Buffalo area might give me a break, but we get blasted with just as much lake effect off Lake Ontario out here.

Thanks again guys!

-Bill

 

[BeaterMan]

there would be no problem switching to synthedic in the diff. same goes for putting it in the engine, just be aware that if you have an oil leak, with synthedic you will leak more since synthedic is a heavier. when you pull the diff cover, i'd spray it out with brake clean and pay attention to any excessive metal flakes/chunks in the diff.

 

[WNY964x4]

WNY - originally from Hamburg, out by your neck of the woods. My parents still live there, at least until they sell the house this summer. Settled in the Rochester area now, in Penfield. Can't say I recall ever going to Pembroke, but have been through there on the thruway a few zillion times How much snow you guys have so far this year? I thought leaving the Buffalo area might give me a break, but we get blasted with just as much lake effect off Lake Ontario out here.

Thanks again guys!

-Bill

we got at least 2 to 3 feet the couple days before christmas , we were out plowing constantly , broke the plow twice , but then we got some off and on , and now it is starting to clear up

 

[harriw]

Well what do you know!? I checked the axle code on the door sticker, and sure enough it's a limited slip 8.8 (3.73 gears) - assuming it hasn't been swapped out. I imagine the L/S will be obvious once the cover is off (are the ford 8.8 L/S's viscous coupling or some other contraption)? Regardless, there's lots more "stuff" in a L/S than just the ring gear, axle gears, and spider gear(s) you'd find in an open diff, right?

SO, any recommendations on what L/S additive to use?

Thanks again guys!

 

[KELLY88]

Not sure of the brand but like the gear oil there aren't many choices as far as limited slip additive goes. Pretty much whatever the auto parts store carries will work. Sometimes however some gear oils will already have the limited slip additive in them so check the label.

 

[Crunchy]

Just get some 80w90 with the additive in it already. Try valvoline, I use it.

If you really want, you can get the additive at any Ford dealer for $5, you get enough for one diffy change.

Most good brands of 80w90 come with it in it already, read the bottle.

 

[WNY964x4]

there is stuff that you can get at auto zone , called k&w posi-trac , it is what i used , you get enough for one fluid change , ut you still have to put regular gear oil in it

 

[harriw]

Ok, I got some better stuff - valvoline synthetic blend 80W90 (looked for Mobil1, but they only had it in odd weights). Says on the bottle it's for both conventional and limited slip differentials - I assume that means it has the correct additive and is good-to-go right out of the bottle?

Regarding the cover bolts - is it really as simple as cinching them up snug and going 1/4 turn further? Never done any covers before and I'm nervous about leaks. Is the RTV gasket stuff tough enough to make up the difference if you snug it down a bit more/less than you should?

Thanks again guys.

-Bill

 

[kevinsranger]

yea the rtv will be fine. its like tightening a valve cover or installing a spark plug, you want the bolts snug, not torqued down.

 

[martin]

The ford manual lists the torque for the cover bolts as 25 to 35lbs-ft. Sounds too much to me and I certainly did not do mine that tight.

 

[JohnnyO]

Ok, I got some better stuff - valvoline synthetic blend 80W90 (looked for Mobil1, but they only had it in odd weights). Says on the bottle it's for both conventional and limited slip differentials - I assume that means it has the correct additive and is good-to-go right out of the bottle?

I put Mobil 1 in the axles of my previous Sport Trac with limited-slip, I did not put in an additive and never had any issues.

 

[FL_forlife33]

non L/S rear

I did my rear diff. service not too long ago, thinking i had a limited slip, but i don't! i put the additive in there, should I drain it to get rid of it, and get just the gear oil in there? will the additive damage anything since i don't need it?