do I need an additive in my 8 3/4 sure grip?

jefframin · Mar 28, 2016

Hi folks.

I have a (very) slow leak from my 8 3/4. I want to top off the fluid.

Question - do I need to worry about the limited slip additive? When I first filled it, I know I used a bottle of the skunk oil, but I've read online that if I find gear lube that states it's good for limited slip diffs that it isn't necessary?

Thoughts?

Bad Sport · Mar 28, 2016

If it's a small amount, you should be fine.

BlueDream · Mar 28, 2016

I'd fix the leak first and then put in the correct oil with the limited slip additive.

Daves69 · Mar 28, 2016

jefframin said:
................. I find gear lube that states it's good for limited slip diffs that it isn't necessary?

Thoughts?

Not necessarily true. At least not true for my '05 Ram 9-1/4" LSD (corporate) when I changed it. Clicked and chattered without the stuff.

charger426 · Mar 28, 2016

Daves69 said:
Not necessarily true. At least not true for my '05 Ram 9-1/4" LSD (corporate) when I changed it. Clicked and chattered without the stuff.

Depends on what oil they used. Generally speaking factory uses crude gear oil and some additive when doing changes. Full synthetic gear lubes (like AMSOIL) generally don't need an additive. With that being said there are some case where a small amount of gear additive is needed even with synthetic lube.

Bad Sport · Mar 28, 2016

BlueDream said:
I'd fix the leak first and then put in the correct oil with the limited slip additive.

Ultimately, this ^^ is the best route.

Jeff, keep in mind that it's a must to have the additive, it lets the suregrip 'slip', if you will, during normal driving conditions, it helps the unit to not wear out prematurely.

jefframin · Mar 28, 2016

Bad Sport said:
Ultimately, this ^^ is the best route.

Jeff, keep in mind that it's a must to have the additive, it lets the suregrip 'slip', if you will, during normal driving conditions, it helps the unit to not wear out prematurely.

Well, I'm not going to remove the chunk. Too much work for such a small problem.

Anybody know what the ratio from oil to additive is, if I was filling one from scratch?

Bad Sport · Mar 28, 2016

jefframin said:
Well, I'm not going to remove the chunk. Too much work for such a small problem.

Anybody know what the ratio from oil to additive is, if I was filling one from scratch?

Where is it leaking? It's quite possible you could fix it without doing that. Is it an axle seal or something?

Secondly, I don't know the exact mix, but I think if you top it off and add just a bit of the additive, it should be fine.

Daves69 · Mar 28, 2016

charger426 said:
................ With that being said there are some case where a small amount of gear additive is needed even with synthetic lube.

Here's one of those then.
Straight Mobil 1 Synthetic LS lube didn't happen for me. Night and day difference with the additive.

SGBARRACUDA · Mar 28, 2016

Simple answer, if it pops and chatters, add some additive. If it doesn't when making turns, your good to go.

jefframin · Mar 28, 2016

Bad Sport said:
Where is it leaking?

The mating surface between the chunk & the axle housing.

Bad Sport · Mar 28, 2016

jefframin said:
The mating surface between the chunk & the axle housing.

Well...that's a bummer.

65 Dartman · Mar 28, 2016

jefframin said:
Anybody know what the ratio from oil to additive is, if I was filling one from scratch?

I bought a bottle from the local dealer and IIRC the instructions say add the bottle then fill it with lube.

jefframin · Mar 28, 2016

65 Dartman said:
I bought a bottle from the local dealer and IIRC the instructions say add the bottle then fill it with lube.

Right...do we know how much lube an 8 3/4 holds?

salinasjoel · Mar 28, 2016

off topic sorry but had to ask, was looking at your restoration page. What size wheels and tires are you using? are they factory 5.5 steel wheels? what size rubber? I am getting ready to put new tires on mine and like the way yours fill the wheel well.

jefframin · Mar 28, 2016

salinasjoel said:
off topic sorry but had to ask, was looking at your restoration page. What size wheels and tires are you using? are they factory 5.5 steel wheels? what size rubber? I am getting ready to put new tires on mine and like the way yours fill the wheel well.

I'll correct this post later if I'm wrong; I need to double-check when I get home.

Fronts are 195/70 on the stock HD wheels (14 x 5.5).

Rears are 235/60 on custom made 14 x 6.

charger426 · Mar 28, 2016

jefframin said:
Right...do we know how much lube an 8 3/4 holds?

Mine took 2 and half quarts no slip diff additive when using AMSOIL Severe Duty Gear Lube. You could try to smear some black RTV to help stop the leak.

charger426 · Mar 28, 2016

Daves69 said:
Here's one of those then.
Straight Mobil 1 Synthetic LS lube didn't happen for me. Night and day difference with the additive.

Yeah I have no idea why some do and some don't and the run it to find out really sucks. Oh and if you have to much it won't lock up....there has to be a better way lol.

EL5DEMON340 · Mar 28, 2016

I would add it if you have a clutch type, the cone is not as critical even though it's recommend. Use the ford stuff it's like $6 for 4 oz.

Marcohotrod · Mar 28, 2016

the 8.75 holds 2.25 quarts. if your just topping it of a little no need to add more additive. I would also try cleaning it very well and smearing some silicone to stop leak

DoctorDiff · Mar 29, 2016

Regardless of what the label on the bottle of lube implies, you must add friction modifier when used with a good limited slip differential.

If gear lube does not smell like friction modifier, it contains very little, if any, additive.

partsmonsta · Mar 30, 2016

Can somebody tell me where I can get this additive? :banghead:

My 98 Dodge Dually is making noise in the rear. Would like to drain current fluid, add some of the Lucas Rear Oil and add the additive.

Rear gets noisy towing in 90+ degree heat in Summer. Has knocking sound when I pull into refuel. I think it is on the DOWNWARD SPIRAL.

I hear the Ford additive is the best, containing whale oil.

BlueDream · Mar 30, 2016

partsmonsta said:
Can somebody tell me where I can get this additive? :banghead:

My 98 Dodge Dually is making noise in the rear. Would like to drain current fluid, add some of the Lucas Rear Oil and add the additive.

Rear gets noisy towing in 90+ degree heat in Summer. Has knocking sound when I pull into refuel. I think it is on the DOWNWARD SPIRAL.

I hear the Ford additive is the best, containing whale oil.

I do believe this is it: http://www.amazon.com/Ford-XL-3-Friction-Modifier-Additive/dp/B000NU5LP6

EL5DEMON340 · Mar 30, 2016

partsmonsta said:
Can somebody tell me where I can get this additive? :banghead:

My 98 Dodge Dually is making noise in the rear. Would like to drain current fluid, add some of the Lucas Rear Oil and add the additive.

Rear gets noisy towing in 90+ degree heat in Summer. Has knocking sound when I pull into refuel. I think it is on the DOWNWARD SPIRAL.

I hear the Ford additive is the best, containing whale oil.

My rear in the dakota was quietest with 75/140 mobil 1 and a bottle of FM that napa sells on the shelf maybe CRC or sta lube??

mguner · Mar 30, 2016

Motorcraft additive is XL-3 $6.23 per 4 OZ bottle.

do I need an additive in my 8 3/4 sure grip?

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