Differential cover

NJTB

Silver Supporter
All
I tried to change the rear end fluid on my 2004 Trailblazer LS 4WD. Luckily the first thing I did was try to get the filler plug out which was STUCK. Hammered a 3/8 extension into the plug, used lots of PB Blaster, breaker bar, heat (plumbers torch, don't have a oxy/acetaline) then a half inch impact.
So I decided to look for a cover with the plug in it, and spent a few hours on Google. No luck.
Can anyone suggest where to go to get one? Amazon, Rock Auto, Ebay and others don't seem to list the one with the plug that fits the car, without spending $200.
Any help appreciated.
 

HARDTRAILZ

Moderator
Purple Cranium has one for us IIRC
 

TollKeeper

Well-Known Member
Someone on the forum might be willing to sell you there's from a diff sweep they did too.
 

Reprise

Lifetime VIP Supporter
You could use a bolt extractor. Be sure to have a new plug on hand, of course.
Also, there's the matter of filings in the case, so you'll likely need to pull the cover and clean well.

My '03 envoy w/ the 8.6" has the fill plug on the passenger side forward part (just above the halfway point, above the casting line). If yours is the same, you may not want to drill in that area, as it will be hard to access for thorough cleaning, and it's close to the pinion seal, besides. Although if your pinion seal is leaking, it could be an opportunity to replace it, as part of resolving the plug issue.

When I did mine, I didn't have trouble with the plug being stuck. I do seem to recall that the 3/8" extension didn't seat well, and I wound up using the ratchet directly on the plug. There's not enough depth in the plug to seat an extension bar properly. You can take a bar and ground down enough off the top where it will seat better, but I don't think that's your solution, the way you describe it.
 

Mooseman

Moderator
Yeah, the 8.0 diff is an oddball with few, if any, options for them. One possibility is to add a transmission drain plug like this to the cover. If it's too rusty you'll have to get a new regular cover for it.

 
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BrianF

Well-Known Member
Another trick to try, once the plug recess is cleaned out. Tap that 3/8 extension in and then tighten the plug. There should be enough meat still on the bone to torque it backwards to break it free.

At some point in the first 25,000km that the previous owner had my Trailblazer, someone tried to remove that plug and began to strip it out. I was not able to get it done in the most optimum position (Buddy had a pit in his shop so I had ample room and leverage). The local independent mechanic declined to do it as he said to try the tightening method first as he was not going to charge me money for something I can do. Well it worked.
 

Mooseman

Moderator
And also grind down the end of that extension to get a completely flat end so you have more of that meat on it. Just yesterday, I used a 1/2 > 3/8 adapter that I ground flat the end and used my electric impact on it. This was on an '85 S10 diff that I have on a homemade trailer that I hadn't removed the plug in over 25 years. Worked a treat.
 
OP
N

NJTB

Silver Supporter
Thanks, learned members.
Works been real slow with the virus thing, so I've had a little more time to deal with this.
Hardtrails suggestion of ordering from Purple Cranium was great, and I placed the order. With shipping it was $75, not great but doable.
I would have hated taking it to the local shop and asking to heat it up with a oxy/acetaline torch and get it out.
I do appreciate everyones replies, thanks again, I'll post back when I get the cover.
 

Chickenhawk

Well-Known Member
I bought a hex plug from the local Princess Auto to replace that silly 3/8" square hole plug, and a new factory cover. It came with new bolts and gasket, for about $30. WAY less than an aftermarket cover, plus studies have show that factory covers flow fluid way better than aftermarket ones. There is a video somewhere in this site that shows that with clear plastic covers.
 

Mooseman

Moderator
Yes, it was from Gale Banks. Reason I'm not too fussy about those flat ones.


@NJTB , which one did you get? I couldn't find one specifically for the TB. Saw a chrome one for the H3 that might be the same.
 
OP
N

NJTB

Silver Supporter
Mooseman
On Purple Craniums web site, the part number is 6629370, GM 10 bolt rear cover. It appears to be stock shape with the fill plug ($27). Then add $10 for color (gloss black, color was a requirement), $4 for a magnetic fill plug, $8 stainless steel bolts, $5 for a gasket, $13 shipping. There's also an option for a drain plug I didn't get. All added up to around $70.
There's also a space to fill out which vehicle you have to be sure it fits.
To be sure, I called the number on the site to make sure it would fit, and they said it would.
I don't like ordering from the web with pictures, as they arent always accurate, and there are mistakes with the part numbers.
I do know there is a very similar cover but the top bolt holes are just a bit off on it, so I'm hoping.
I'll post back when I get it, in about a week, and let everyone know what happens.
 

HARDTRAILZ

Moderator
Purple Cranium has been used for many years by the offroad crew. More for the half spider protector than covers, but it dates way back to the Roadie era, so you should be good.
 
OP
N

NJTB

Silver Supporter
Well it's a bust. Got an email from Purple Cranium this morning that the cover they thought they had in stock wasn't, their supplier is closed due to the virus so they're not getting any more soon, and they refunded my money.
Gonna spend a bit more time on the web to see if I can find another supplier, and if I can't find one, take it to someone with a torch to get the drain plug out.
 

coolride

Silver Supporter
Had the same problem. Used it as an excuse to buy a 1/2" Bauer impact wrench at HF. I paid 99 bucks. Backed the fill plug out in about 3 seconds. Had to grind the socket extension flat.
 
OP
N

NJTB

Silver Supporter
Yesterday I took it to the local repair shop, he used an inductive? heater on it, damn plug came out. I'm going to change the fluid today.
For a laugh, last weekend I changed the trans fluid, thought it was going to be an hour job, start to finish. The trans gasket was so stuck on to the pan, it took me about an hour to scrape it off.
So I'm a bit apprehensive about the rear end cover gasket.
 

Sparky

Moderator
Rear gasket is (reusable) rubber, or if it had ever been replaced is probably RTV. Very different from and much easier than that awful papery trans pan gasket.
 

Mooseman

Moderator
Putting in a new plug I assume? To keep it from seizing again, you could put some Teflon tape on it and it doesn't need to torque to holy hell. Just a nice snug fit.

Eric O. shows how an inductive heater works but I'm not sure how it would have worked with a recessed plug?

 

BrianF

Well-Known Member
I like that hex head plug. I might look for one next time I am at princess. I have not had mine out since 2012, about 130,000km ago. It's due to at minimum inspect.
 
OP
N

NJTB

Silver Supporter
It's done, shop got the plug loose. Usual aggrivation, took the cover off, wrong gasket, back to Autozone to get the correct gasket, they don't have it, and neither does Advanced Auto or NAPA. Wound up using Permatex form a gasket. No new plug either.
On Thursday scoured the web again for the correct cover, called the suppliers that had a phone number listed. I was pretty surprised to talk to a few that knew Trailblazers and knew what I needed but of course, didn't have the correct part.
 

BrianF

Well-Known Member
Well at least its done and you will have plenty of time to source the new parts if you still wish to pursue that Avenue.
 
OP
N

NJTB

Silver Supporter
Yes, now I'm off to front stabalizer bushings, rear stabalizer links, and figuring out how to do something to get the rust off the frame and paint it while it's on jackstands.. No rust through, but probably 2 years there will be.
 
All
I tried to change the rear end fluid on my 2004 Trailblazer LS 4WD. Luckily the first thing I did was try to get the filler plug out which was STUCK. Hammered a 3/8 extension into the plug, used lots of PB Blaster, breaker bar, heat (plumbers torch, don't have a oxy/acetaline) then a half inch impact.
So I decided to look for a cover with the plug in it, and spent a few hours on Google. No luck.
Can anyone suggest where to go to get one? Amazon, Rock Auto, Ebay and others don't seem to list the one with the plug that fits the car, without spending $200.
Any help appreciated.
I'm a novice at this stuff but here's what I did....I followed MAY03LT'S video on youtube showing how to do a rear diff oil change. My check /fill plug was very rusty and would not budge. My neighbor helped me by bringing his MAP gas tank. Propane wil not get the plug and surrounding area hot enough. He heated the plug and the area around the plug for a few minutes--tried to loosen the plug--no go. He heated it up again and re-tried and it finally cracked. He used his own 1/2" reduced to a 3/8" socket. After that, the fluid change was easy...I carefully cracked all the rusted bolts on the pan, and carefully pulled the pan away and the diff oil drained. replaced it with a little over 2 qts of Mobil1 75W-90 synthetic gear oil. No leaks. Rather than buying a new pan with a plug, I'd get the MAP gas. It will work.
 
I'm a novice at this stuff but here's what I did....I followed MAY03LT'S video on youtube showing how to do a rear diff oil change. My check /fill plug was very rusty and would not budge. My neighbor helped me by bringing his MAP gas tank. Propane wil not get the plug and surrounding area hot enough. He heated the plug and the area around the plug for a few minutes--tried to loosen the plug--no go. He heated it up again and re-tried and it finally cracked. He used his own 1/2" reduced to a 3/8" socket. After that, the fluid change was easy...I carefully cracked all the rusted bolts on the pan, and carefully pulled the pan away and the diff oil drained. replaced it with a little over 2 qts of Mobil1 75W-90 synthetic gear oil. No leaks. Rather than buying a new pan with a plug, I'd get the MAP gas. It will work.
One other thing.....a made up my own penetrating oil--I used a half and half mix of trasmission oil and Acetone mixed it up in a small glass jar.. I took a rag and soaked each of the pan bolts for about 15 minutes before attempting to crack them. Wear safety goggles because you don't want to get that mix in your eyes ! I did that because the rear diff pan bolts on my 2004 were never removed....I didn't want to bust one off. Seemed to work well.
 

MRRSM

Lifetime VIP Supporter
Here is some actual Test Evidence that supports your own Positive Empirical Results:

The “Machinist's Workshop” Magazine actually tested Penetrants for Break Out Torque on Rusted Nuts. Significant results! They arranged a subjective test of all the Popular Penetrants with the control being: The Torque Required to Remove the Nut from a "Scientifically Rusted" environment:

Penetrating Oil ........ Average load

None .................…….. 516 pounds
WD-40 .................…... 238 pounds
PB Blaster ...........…... 214 pounds
Liquid Wrench .......... 127 pounds
Kano Kroil ........…..... 106 pounds
ATF-Acetone Mix ........ 53 pounds

The Automatic Transmission fluid (ATF)-Acetone mix was a "Home Brew" Mix of 50 - 50 Automatic Transmission Fluid and Acetone.

Note:

The "Home Brew" was Better than ANY Commercial Product in this one particular test. A local machinist group mixed up a batch and all now use it with equally good results. Note also that "Liquid Wrench" is about as good as "Kroil" for about 20% of the price.


My own "SWAG here (Scientific Wild Ass Guess) is that since the Acetone and ATF can NEVER actually MIx together... The Rapid Evaporation of the Acetone gets Cold enough to shrink the Metal Fasteners enough to momentarily Break up the Rust Bond ... just long enough to allow the ATF as a Light Oil to work its way around the Thread Lines, making things MUCH EZR to unwind.

Pretty Cool!



Refer to:

 

Mooseman

Moderator
Project Farm did a pretty comprehensive testing of different penetrating fluids. Some results were surprising.

 

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