Capacity for '94 C2500 14 Bolt Rear Differential?

[fennell19...@charter.net]

Just bought a used C2500 and plan to pull my 7,000 lb. boat with it.
I'd like to swap out the gear lube in the rear differential with
synthetic SAE 75W-140. I'm not sure how much I'll need on hand for
the refill and can't find the capacity in the owners manual. Can
anyone tell me how much it will take to refill it?

Also, when reinstalling the differential cover, should I:

a. clean mating surfaces and install a new gasket
b. clean mating surfaces and install a new gasket with silicone
sealant
c. skip the new gasket, but clean mating surfaces an install with
silicone sealant.
d. something other than the above.

Thank you.

[Bret Chase]

I'd do either a. or c. depending if I had the gasket on hand. not knowing
which 14 bolt you have makes answering your question difficult, but 3 quarts
is more than enough for the 9.5" 14 bolt (semi floater) and *should* (aka
don't hold me to it) be plenty for the 10.5" 14 bolt (full floater).
75w-140 is waaaaaaaaay too heavy for your rear-end, use 80W-90 GL5 like GM
specs. the 140 is damn near impossible to turn when it's cold out (below
32F, it gets more wax-like than oil like)

hth, and ymmv
Bret

<fennell19...@charter.net> wrote in message
news:5k4u8v8a656v0hmas...@4ax.com...

[Joe F.]

Bret, my owner's manual states the following (p. 7-22):

"3500HD Models with applications requiring extreme overload/trailer
tow conditions and high speed conditions (above 45 mp) for extended
periods of time must change drive axle fluid every 3,000 miles or 3
months, whichever comes first, OR must use 75W - 140 synthetic fluid
meeting GM specifications."

Now granted, my truck is a 2500, but it's a 10.5" ring, 4.10 rear end,
which I believe is the same ring and pinion as many 3500's. Since I
will be towing a moderately heavy load at highway speeds, it seemed
reasonable to use the same lubricant as the 1 tons. Are you sure the
75W-140 synthetic is too thick?

Thanks for your reply. I'll make sure I have a new gasket and 3 qts.
on hand before I do the job.

["Doc"]

"Joe F." <fennell19...@charter.net> wrote in message
news:qfju8vkdf3da0d379...@4ax.com...

> Bret, my owner's manual states the following (p. 7-22):
>
> "3500HD Models with applications requiring extreme overload/trailer
> tow conditions and high speed conditions (above 45 mp) for extended
> periods of time must change drive axle fluid every 3,000 miles or 3
> months, whichever comes first, OR must use 75W - 140 synthetic fluid
> meeting GM specifications."
>
> Now granted, my truck is a 2500, but it's a 10.5" ring, 4.10 rear end,
> which I believe is the same ring and pinion as many 3500's. Since I
> will be towing a moderately heavy load at highway speeds, it seemed
> reasonable to use the same lubricant as the 1 tons. Are you sure the
> 75W-140 synthetic is too thick?
>
> Thanks for your reply. I'll make sure I have a new gasket and 3 qts.
> on hand before I do the job.

Joe,

The 75W-140 will be fine during the spring, summer and fall, but you damned
well better switch it over to 75W-90 when it starts to get cold out! If it
were my truck, I'd stick with 75W-90 Mobil 1 Synthetic and change er' every
3k with the oil. Also, install the meatiest ATF cooler you can get yer'
mits on and install an ATF temp gauge on the HOT cooler line. Regarding the
gasket, don't matter which you choose so long as it seals up. I use some
hi-tak to stick the gasket to the diff. cover, then mate it to the diff with
a thin layer of grease between the gasket and the diff.. This way the
gasket can be reused a few times.

Regards,

Doc

[Bret Chase]

back in '94 the 3500HD shared nothing with the smaller pickups other than
the body sheet metal and interior. it was a medium duty chassis, you can't
really directly compare them, as they used Dana and Rockwell axles. most
likely talking about towing in the 10,000+lbs range.
stick with the 80W-90 (or similar) synthetic, if you live somewhere where it
gets cold, otherwise you're going to have somethings that is seriously
undriveable when it gets close to and below freezing. but if you live in
the deep south, you should be fine with the 75W-140.

"Joe F." <fennell19...@charter.net> wrote in message
news:qfju8vkdf3da0d379...@4ax.com...

[Joe F.]

Bret, Doc, thanks for your input.

I live in Atlanta but will trailer from Spring through Fall along the
gulf coast (Mexico Beach, FL to Venice, LA), and possible to the
Keys. So maybe I'll just changethe lube out twice a year.

Doc, usefule tip on greasing the gasket.