Ford 80W 90 Differential Fluid & Friction Modifier mixture ratio?

KINGPIN33

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#1
Hello, Does anyone know how much of the Ford 80w 90 differential fluid you need to mix with the Ford friction modifier? Do I just toss the entire bottle of the friction modifier into the differential and then add the regular differential fluid?

Thanks in advance.
 

Piratetip

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#2
Start with 1-2 oz. of the Friction modifier.
PN: XL-3

Diff Oil PN:
XY-80W90-QL

Run it for awhile and see if there is any chattering/groaning in the LSD.
If there is and you don't like it, add more friction modifier.

Really depends on your level of acceptance for LSD lockup on cornering.

Chances are if your LSD core is not upgraded, you won't experience any groaning or chattering.
The spring rate and breakaway ft/lbs is low in stock form ~25ft/lbs I usually measure prior rebuilding / upgrading.
 
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KINGPIN33

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#3
Thanks for your response,

My pinion front oil seal of the diff is leaking. It seems like a daunting task to install a new seal there on the car!

1. While replacing the front oil seal, would it also make sense to install a new spacer, bearing and oil slinger?

2. Is it okay to use aftermarket oil seals, spacer, bearing? Rockauto.com has alot of selection!

3. For measuring "back-lash" when tightening the pinion nut on the companion flange, does that just simply mean setting your torque wrench to specified trq as per tsrm and seeing if your rear wheels turn a bit at that trq setting? So essentially, if the wheels turn before your torque wrench clicks, it means you need to tighten that pinion nut more , correct?

Thanks
 

Piratetip

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#4
New seal install should not be that hard if you have the correct tools.
If you also want to do the bearing and crush sleeve, that is more involved.

- You could install a new outer pinion bearing, but you will need a slide hammer and appropriate adapters to pull the bearing race from the diff case.
- Yes definitely replace the pinion crush sleeve with a new one, preferably an OEM one, some of the aftermarket ones I have seen are really poor quality. Timken aftermarket bearing and oil seal should be ok.
- The oil slinger just re-use, there is literally nothing to wear out on it, its just a flat piece of steel.
- The trickiest part of doing this on vehicle will be the removal and re-insall of the outer bearing to the pinion shaft. Its a press fit, so you will need the appropriate puller and installer for this.

- If you go all the way to replacement of the crush sleeve, this is the order of reinstalling the parts.
1. Press in new outer bearing race to case
2. Slide on new crush sleeve over pinion shaft
3. Press new bearing cone to pinion shaft
4. Re-Install oil slinger
5. Press in new oil seal to case
6. Press in pinion flange
7. Tighten pinion nut until factory spec bearing preload settings are reached

To properly set the new pinion bearing preload I would do the following.
- Remove both CV half shafts from differential.
- Remove driveshaft from pinion flange.
- Purchase a bar type in/lb wrench
- Measure the existing start / rolling preload of the entire differential before any work is done
- Remove pinion flange and all preload on the pinion bearings
- Re-Measure start / rolling preload - Subtract this from the first preload measurement.
This gives you the preload on the carrier bearings alone. (Carrier bearings should be around ~5in/lbs if they are used)
- Install the parts as shown above in steps 1-7.
- If you re-use the outer pinion bearing set ONLY pinion preload to 4.3-6.9 in/lbs (you have to subtract carrier bearing preload from the measurement)
- If you install a new outer bearing its a bit trickier since you now have 1 new outer and 1 old inner.
But I would set preload to ~10 in/lbs
Specs are here: http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?S=RA&P=25

Backlash is totally different, it is done by removing the rear cover and using a dial indicator perpendicular to 1 of the ring gear teeth.
Holding the pinion stationary and moving the ring gear back and fourth.
Backlash is adjusted by changing the carrier bearing side washers, has nothing to do with the pinion bearings or preload.
Spec here: http://www.cygnusx1.net/supra/Library/TSRM/MK3/manual.aspx?S=RA&P=36

Your #3 note above is all wrong.
 
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Piratetip

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#5
One other very important thing I did not mention.

Note the depth the OEM pinion seal is installed to, measure it, write it down.

There will be a worn groove into the pinion flange where the positive lip seal has been riding for the last 30 years.

Install the new pinion seal slightly deeper or shallower than the OEM, otherwise it is going to ride in that same groove and probably leak oil again.
 

KINGPIN33

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#6
Piratetip, you speak from a lot of experience! Thank you for that valuable information. I'm sure others will find it very useful aswell!
 

plaaya69

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#8
I only add 1oz of the modifier additive on mine and Yes Piratetip knows what he is talking about, he rebuilt my diff :)
 

Kine

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#9
Start with 1-2 oz. of the Friction modifier.
PN: XL-3

Diff Oil PN:
XY-80W90-QL
Is this the go-to recommended combo right now? Gonna be refilling mine soon as well.
 

Piratetip

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#10
It's been a good known oil since SOGI days.
Plus it's very inexpensive, go to the local Ford parts counter.
Costs more to buy it online vs. in person.
 
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Kine

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#11
It's been a good known oil since SOGI days.
Plus it's very inexpensive, go to the local Ford parts counter.
Costs more to buy it online vs. in person.
Awesome, thanks for the tip about going in person!
 

loc182

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#12
+1 on the buying it in person. That Ford friction modifier is a godsend.

Plus it is always fun to tell the counter person it is for a Toyota Supra. Some are shocked, others are like "We sell more of this to Toyota owners than Ford owners."