What gear oil??

Rockin302 · Nov 10, 2004

I have a 1990 lx 5.0 notchback 5-speed and I'm planning on having the differential fluid changed out.

Question I have is:

-Does anyone know if my car came equiped with a limited slip? I checked for tags near the fill plug and differential housing and found these #'s (S217A , 3L08 88 OC20) Do they mean anything?

-I've heard of people siphoning the old fluid out from the fill plug instead of removing the cover. The housing doesn't leak right now so I want to keep it that way. Siphoning a good idea??

-What's the correct gear oil? I plan to use a synthetic like Redline or Royal Purple. I've also been told that some already have the friction modifier mixed in. Can anyone confirm?

Thanks for any help!!!

HISSIN50 · Nov 10, 2004

IIRC, all 8.8's came with trac lok. if the rear end is securely in the air, if you turn one wheel and the other turns the same direction, that means you got trac lok. i might check the condition of the clutches before swapping oil (if one needs a rebuild, it all comes out anyhow).

the stinkier the gear oil, the better.

seriously, i like synthetics too. i would drop the cover and check things out and all that - syphoning can leave sediment in the bottom.

as for whether one needs the friction modifier, it depends oil to oil. i would consult with the manufacturer (and/or their site) to see. if in doubt, i would add some anyhow.
when you do it, be sure you can get the fill plug out FIRST. if you cant and drain the fluid (if you remove the cover), you could be up a creek.

good luck.

Rockin302 · Nov 10, 2004

Good point Hissin, I will make sure I can unscrew the fill plug before I take the cover off or else I'll really be screwed!

Oh yeah, I've heard about this ford gasket maker RTV stuff. So I won't need an additional gasket, right? Also, how long does it take for the RTV to set. I want to make sure I have enough time to get the cover back on.

thanks!

HISSIN50 · Nov 10, 2004

Rockin302 said:
Good point Hissin, I will make sure I can unscrew the fill plug before I take the cover off or else I'll really be screwed!

Oh yeah, I've heard about this ford gasket maker RTV stuff. So I won't need an additional gasket, right? Also, how long does it take for the RTV to set. I want to make sure I have enough time to get the cover back on.

thanks!

what i do: i get a gasket (few bucks at parts stores). i apply a thin bead of gasket maker on each side of the gasket and install it. others in here will not use a gasket - they simply use RTV type products. to each his own.

BTW, just in case: the fill plug can be removed with a 3/8" ratchet. i put a short extension on it to get clearance from the pumpkin.

I'm not familiar with that gasket product, so i dont have an idea for ya. i would simpy follow the instructions. they usually list times for skim and functional curing.

good luck.

Rockin302 · Nov 10, 2004

Thanks Hissin, I just hope the fill plug isn't frozen or else I'm up a creek.

Michael Yount · Nov 10, 2004

I'm with Hissin' on the gasket - I prefer to use one lightly coated with RTV (any silicone based, automotive intended gasket maker/sealer - Permatex Copper works fine). Be sure everything is clean and dry. Especially at the bottom of the case - I've used rags and brake cleaner to get the last bit of fluid out of the bottom of the case so it doesn't continue to drip down the bottom of the casing while you're trying to seal it. The cover and casing surfaces must be completely clean and dry. Bolt the cover on - evenly snug up the bolts. My preference is to do this job late in the day, and let the cover sit overnight filling it the next morning. That way I'm sure it set up before I ask it to seal.

89MustangGX · Nov 10, 2004

All MUSTANGS with 8.8's have limited slip (a little correction from earlier).

I've never siphoned out fluid -- always popped the cover, but I agree -- it doesn't sound like a good idea regardless. As for the gasket -- I've used them and they worked fine -- doing the same thing these guys did. Only reason I stopped using them is that I found it could be more of a mess to clean up afterwards for me -- and just using RTV sealed (seals) fine. RTV is standard thing -- can find it at any autoparts store. Comes in different colors for different applications.

I like synthetics myself as well. Check with the manufacturer to see if the additive is included. It's probably a safe bet if it doesn't say it on the bottle, it's not in there.

90NotchBack · Nov 10, 2004

I use 75W-140 synthetics

HISSIN50 · Nov 10, 2004

89MustangGX said:
All MUSTANGS with 8.8's have limited slip (a little correction from earlier).

Adam thanks for the correction. i figured we were talking stangs, but that is a very good point to make, with people doing conversions and what not.

i use the same stuff as Michael (Copper). everyone is right on.
good luck.
Adam, for some reason i thought you had a girdle (with drain plug)?

89MustangGX · Nov 10, 2004

HISSIN50 said:
Adam, for some reason i thought you had a girdle (with drain plug)?

I do, but 8.8's don't come with them. At some point I've had standard covers.

Besides, I change gear oil in other vehicles too.

HISSIN50 · Nov 10, 2004

89MustangGX said:
I do, but 8.8's don't come with them. At some point I've had standard covers.

Besides, I change gear oil in other vehicles too.

yep, knew that they are not OEM. i was mainly asking out of jealousy. i like them but dont have the money for one.

90NotchBack · Nov 10, 2004

Girdles make it much easier to change rear end fluid and helps gears life span.

PhLoBuS · Nov 10, 2004

royal purple is good...

Mavrick · Nov 10, 2004

90NotchBack said:
Girdles make it much easier to change rear end fluid and helps gears life span.

Exactly how does it help the life span of a set of gears??

90NotchBack · Nov 10, 2004

The load bolts provide support for the differential bearing caps. The girdle keep the main caps from walking. Just extra insurance. Since the girdle is stronger then the stock cover it helps keep the housing from flexing.

Mavrick · Nov 10, 2004

So less stress on the main bearing caps is the big issue here?

The housing is such thick cast metal, i never even thought of it flexing. Good info though, i'm in the market for one.. not too concerned with the integrity as im not making much power, but more for the convenience as ill want to change fluid once in a while.. due to new gears, and maintenance.

HISSIN50 · Nov 10, 2004

yep, the housing is alright, but the flimsy cover can flex (it is kind of like a load-bearing wall with a large door in the middle. in a quake, the door is what compromises the structural integrity).

plus, as said, the bolstering for the caps. good stuff.

Michael Yount · Nov 10, 2004

Remember, gearing multiplies torque. With a 3.35:1 low gear, and a 3.55 rear gear, the engine's 300 lb-ft of torque becomes almost 3600 lb-ft once it gets transmitted to the axles. With traction - you can see that the housing has to subdue quite a bit of twisting force. In the extreme case, cars are able to pull the front wheels off the ground - all the force to do that gets transmitted through the diff housing; it's sees significant load. My Volvo's stock Dana30 (7 3/4" ring gear) rear end is only rated to about 2600 lb-ft. Since my tires spin and all the torque can't be put to the ground, the rear end lives. But my cover seems to continually seep. Not enough to drip on the ground, but enough to have me wiping it down once a month or so so it doesn't get to looking messy. I'm pretty sure the cast iron housing is flexing enough that the integrity of the gasket seal gets slightly compromised.

Stang8URMPRT · Nov 10, 2004

Take HISSIN' word on making sure you get the fill plug out. I've done many rear end services and I would say 50% of the older (More the 5 years old) vehicles, the fill plug needs to be heated with a torch to break apart the rust. These things basically weld themselves onto the housing and never come out. Get them cherry red with a torch and they come out like budda!

89MustangGX · Nov 10, 2004

HISSIN50 said:
yep, knew that they are not OEM. i was mainly asking out of jealousy. i like them but dont have the money for one.

But I thought all race cars had them?

This is the first car that I really plan to make enough power and stick it hard enough to want one. Besides, with all the parts/work I put in the rear, what's another few bucks to make sure it stays in one piece...

It's only money, right?

What gear oil??

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