Any harm if differentials are overfilled a little?

400Magnum

Original poster
Member
Dec 23, 2011
49
I just drained and replaced the gear oil in the front differential this weekend and I put in a full quart and a few ounces more. Should I try to siphon some out to get it to the 1/2" below plug level, or will it be okay to leave it as is?
 

jrSS

Member
Dec 4, 2011
3,950
I fiiled mine till fluid started coming out of fill plug. You'll be fine.
 

ScarabEpic22

Member
Nov 20, 2011
728
silvernclean said:
I fiiled mine till fluid started coming out of fill plug. You'll be fine.

Thats how you're supposed to do the front according to GM's own TechLine, and Ive done it the same way to the rear in my 02 two or three times now. Going to do the SS in the next few weeks for the first time, just rolled 32,3xx when I got home from my 1,200mi weekend trip (since Thurs actually)!
 

03envoy

Member
Dec 25, 2011
537
ScarabEpic22 said:
Thats how you're supposed to do the front according to GM's own TechLine, and Ive done it the same way to the rear in my 02 two or three times now. Going to do the SS in the next few weeks for the first time, just rolled 32,3xx when I got home from my 1,200mi weekend trip (since Thurs actually)!



How Did you get the fill plug out? I cannot get that freaking thing out.... Also The Gasket is reuseable right? Sorry didnt mean to hijack:redface:
 

400Magnum

Original poster
Member
Dec 23, 2011
49
I had minor headaches getting the front plugs out, they were tight, but eventually came out. The transfer case was another story, they were in there TIGHT and did not want to budge, plus, they take a very large Allen wrench instead of something normal like a regular 3/8" rachet, or at least mine were Allen head. And there's no way they were coming loose just by using the Allen wrench, I had to get a short piece of copper pipe on the Allen wrench to break them loose.

After reading this thread, I'm even more fearful of the rear differential... http://gmtnation.com/f79/trailblazer-throttle-body-rear-diff-drain-fill-without-drain-plug-pics-1179/
There's some good tips in this thread on things that might help. As for myself, I'm going to spray the rear differential fill plug with penetrating fluid a few times before I try to break it loose.
 

03envoy

Member
Dec 25, 2011
537
400Magnum said:
I had minor headaches getting the front plugs out, they were tight, but eventually came out. The transfer case was another story, they were in there TIGHT and did not want to budge, plus, they take a very large Allen wrench instead of something normal like a regular 3/8" rachet, or at least mine were Allen head. And there's no way they were coming loose just by using the Allen wrench, I had to get a short piece of copper pipe on the Allen wrench to break them loose.

After reading this thread, I'm even more fearful of the rear differential... http://gmtnation.com/f79/trailblazer-throttle-body-rear-diff-drain-fill-without-drain-plug-pics-1179/
There's some good tips in this thread on things that might help. As for myself, I'm going to spray the rear differential fill plug with penetrating fluid a few times before I try to break it loose.



Thanks man! Didn't see that thread for some reason lol
 

seanpooh

Member
Jan 24, 2012
461
In the front differential, the fill plug is 18mm and the drain plug is 13mm. I used a impact wrench to remove the fill plug with an extension bar.

The rear end isn't hard, an actual 3/8" socket wrench with no socket fits into both the drain and fill plugs. I used a torque wrench with a size reducer to remove them.

Make sure to get a flat head and scrape out the gunk inside the plugs so the wrench doesn't slip.

As for your actual question, there is enough room inside the differentials for aeration. Overfilling not a problem.
 

Wooluf1952

Member
Nov 20, 2011
2,663
Milwaukee, Wisconsin
I only needed a 3/8" breaker bar for the rear diff drain and fill plugs.
 

seanpooh

Member
Jan 24, 2012
461
Yeah, that's the size. So I used a 1/2" torque wrench with an size down adapter to 3/8" that fits in the drain plugs. Thanks.
 

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