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What viscosity should I use for my 9 1/4" differential

Billy Lo

Billy Lo

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Auto parts guy gave me two different grades...what should I actually use? The kid didn't seem to sure so I am asking you guys. Its for a 78 Monaco with a 12 bolt 9 1/4 rear, not a suregrip. Thanks, I want to knock this out tomorrow morning.
 
You can use 90W-140 also. Heavier weight might cost a couple horsepower but also can help keep gears a bit quieter and deal with heavier loads. I've tried some Lucas dino gear lube lately and it seems to be really slippery compared to the Valvoline I had used earlier.
 
A little bit of STP will add some slickness too. Heck, I'm using a half a can in a 9 1/4 in a 2000 Durango with a limited slip (Track Lok) because it works better than the regular Sure Grip additive did. Been in it for over 50k miles while the SG additive lasted for less than 10k miles after a fluid change. I guess the SG additive doesn't work as well in this design limited slip? I'm also using 100% STP in a Dana 70 with a set of well worn out gears and it reduced the noise by half or more. That's been in there 2 years but I drive it less than 5k miles a year for the last several years. ....
 
Cranky said:
A little bit of STP will add some slickness too. Heck, I'm using a half a can in a 9 1/4 in a 2000 Durango with a limited slip (Track Lok) because it works better than the regular Sure Grip additive did. Been in it for over 50k miles while the SG additive lasted for less than 10k miles after a fluid change. I guess the SG additive doesn't work as well in this design limited slip? I'm also using 100% STP in a Dana 70 with a set of well worn out gears and it reduced the noise by half or more. That's been in there 2 years but I drive it less than 5k miles a year for the last several years. ....
Click to expand...
your talking regular STP for engines?
 
Billy Lo said:
................... not a suregrip. .................
Click to expand...
Just by chance, do you want it to be?
925ChrysLS0.gif
 
318willrun said:
your talking regular STP for engines?
Click to expand...
Yup. Been 'experimenting' with this stuff for nearly 40 years now lol. At first I just thought it was snake oil but it's not. I also learned a lot about additives after spending 26 years working in a refinery. Now I do go to the extremes at times with it but it seems to still do what I want :)
 
Cranky said:
Yup. Been 'experimenting' with this stuff for nearly 40 years now lol. At first I just thought it was snake oil but it's not. I also learned a lot about additives after spending 26 years working in a refinery. Now I do go to the extremes at times with it but it seems to still do what I want :)
Click to expand...
Just to be sure I have this straight: Go to Walmart and buy STP. Put a 1/2 bottle in the rear to help protect the sure grip (or any rear to protect the gears)? I've always used the sure - grip additive from MOPAR. thanks
 
318willrun said:
Just to be sure I have this straight: Go to Walmart and buy STP. Put a 1/2 bottle in the rear to help protect the sure grip (or any rear to protect the gears)? I've always used the sure - grip additive from MOPAR. thanks
Click to expand...
If the Mopar SG additive works for you, continue to use it. I never tried using STP in either of the two types of limited slip units that were available for the 8 3/4 but the factory SG additive did not work for my 9 1/4 where as the STP does work for that Track Lock POS. It still has clutches but they are out board of the side gears. It's a totally different design vs the Borg Warner anti spin (cone type) or the Power Lock clutch type units that came in the 8 3/4. The Mopar additive always worked well for all of my SG units in the 8 3/4 so I never had any reason to try using STP in them.....
 
Cranky said:
Is that a 9 1/4? If so, it sure doesn't look like the one in my Durango....
Click to expand...
Out of my old Trailduster. Think they changed up around '82 or so.

Page 3-19 thru 3-24 of the '77 Ramcharger Trailduster service manual.
 
Last edited:
Daves69 said:
Out of my old Trailduster. Think they changed up around '82 or so.

Page 3-19 thru 3-24 of the '77 Ramcharger Trailduster service manual.
Click to expand...
Looks like a 2 piece carrier/case in the pic. Never worked on the early 9 1/4 but the newer ones use a 1 piece case and it's a pita to put new clutches in them unless you have the right tools...
 
Billy Lo said:
Gotta ask what is that Dave, a sure grip?? If so how much and would it be a big deal to install in the current axle?
Click to expand...
Sorry for the late reply. Busier than a cat coverin' up the mess lately.
Yeah Bill, it's a 9-1/4" LS out of my old Trailduster that I had a short while. Picked the truck up with a wasted 440 for parts from a good friend. He told me the LS had 2 years on the dealer rebuild.
Asking 80 plus shipping from 60506 (paypal). If one has a service manual, possibly some proficient online coaching help, and some good mechanical ability, I'm sure one could handle it.
 
Cranky said:
Looks like a 2 piece carrier/case in the pic. Never worked on the early 9 1/4 but the newer ones use a 1 piece case and it's a pita to put new clutches in them unless you have the right tools...
Click to expand...

My '05 has the corporate LS with the clutches in it. Evidently there has been problems with the clutch pack retaining clips breaking up and locking the gears in these. They have not recalled them for this as far as I know but have recalled for loose pinion nut. Took it in earlier this year for the nut.
Here is a sketch from the SM of the older one........
9_25LS.gif
 
Daves69 said:
My '05 has the corporate LS with the clutches in it. Evidently there has been problems with the clutch pack retaining clips breaking up and locking the gears in these. They have not recalled them for this as far as I know but have recalled for loose pinion nut. Took it in earlier this year for the nut.
Here is a sketch from the SM of the older one........
View attachment 357365
Click to expand...
The 9 1/4 in my Durango has clutch packs outboard of the side gears....and no springs. It looks just like an open unit until you look for the clutches.
 
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