No, longer than that.
I leafed through the maintenance log I keep for my ’76 Trans-Am (I have one for all my vehicles; it’s the only way to keep track of things short of having someone else keep track of them for you) and found the entry: April 7, 1999. Fourteen – almost fifteen – years ago that I last changed the differential fluid (gear lube). That’s too long – even for an antique muscle car that’s not driven regularly. In part, because over that span of time, even a very minor leak (and what 40-year-old car doesn’t leak?) could gradually result in a too-low level that you might not notice until a mechanical failure brings it to your attention. And even if the level is right, contaminants accumulate and the bottom line is it’s just not smart policy to neglect this job, given how easy (and inexpensive) it is vs. how expensive (and difficult) it is to deal with a major rear axle issue.
My car is a Pontiac (and a Trans-Am) but the procedure is pretty much the same for most RWD cars. If you’re working on a ’70-81 Firebird or Camaro, it will be exactly the same because all these cars (with the exception of a few high-performance 1970 models) have the same 10-bolt rear axle. This axle was also used in same-era Chevy Novas (and Pontiac Venturas and Buick Apollos) as well as Malibus and pretty much every other RWD/V-8 car GM made during those years.
Mine takes 4.5 pints of gear lube – plus a bottle of limited slip additive, which you’ll need if your car has a limited slip axle. Most Z28s and Trans-Ams from the ’70s came standard with a limited slip (also known as “posi-traction”) rear end. But it could be ordered with almost any Camaro or Firebird – as well as Novas (and so on). Look for a little metal tag that reads “limited slip only” secured to the rear axle cover via one of the bolts that holds the cover to the axle housing. You can buy the little bottle of additive at any GM dealer; many car parts stores also stock it. The gear lube (be sure to get the right weight; check the manual for your particular year and application) comes in plastic quart bottles. If your car is like mine, you’ll need three. I use synthetic, but regular’s ok to. I prefer synthetic because it flows better at lower temperatures and gives a higher level of protection at higher temperatures/under severe loads/abusive conditions. My Trans-Am, with a street-strip 455 making probably close to 500 lbs.-ft of torque up front and pretty aggressive 3.90 gears in the pumpkin, needs the extra protection. Your car may not.
In addition to the fresh gear lube (and limited slip additive, if applicable) you’ll need the following to do this job:
* Half-inch socket/wrench.
* Gasket scraper.
* 3/8 inch extender bar.
* Catch pan.
* About a foot of old fuel hose, 7/16 in diameter.
* Jack/jack stands.
First, warm the car up – ideally by driving it for about 15 minutes. Then raise and support the back end high enough off the ground to give you room to work around the axle. Loosen but do not remove the 10 bolts holding the pumpkin cover in place. Slide a catch pan underneath and then pry the cover loose. Let all the old lube drain completely. Remove the bolts – being careful to keep track of them – and slide the pumpkin cover away from the axle housing. The ring and pinion are now visible. I use my hand to scoop out any remaining old lube in the bottom of the case. Use a razor blade or scraper to peel off any old gasket material – being careful not to let any fall into the axle housing. Clean it out if some does fall in there.
Use the 3/8 inch extender bar to loose the fill plug, which is typically located on the upper passenger side of the axle housing. Be careful not to lose this plug! Also be careful not to damage it while trying to extract it. If the plug is tight, spray it with some PB-40 or similar penetrating fluid, let it sit then try again. Use leverage (breaker bar, etc.) to ease it out.
Wipe out/clean the pumpkin cover and bolts. If yours has a magnet, be sure to carefully clean and re-install it. Place the fresh gasket on the cover, using one or two of the bolts to hold it in place. Align the cover, being sure the gasket is also lined up correctly, and reinstall the cover. Tighten the bolts in a cross-hatch pattern to avoid warping the cover and to assure a good seal.
Now comes the fun part!
There are several ways to get the fresh fluid into the housing. Some use hand pumps, some use turkey basters. I like to use the plastic bottles the gear lube comes in – with a length (about 10 inches) of 7/16 fuel hose secure to the nipple on top of the bottle. Using this set-up, you can insert the flexible hose into the fill plug while getting the bottle into position. Now, squeeze! You ought to be able to empty most of the bottle’s contents this way. Do the same with the second bottle. This will get you close to 4 pints (there will still be some left in both bottles). Use the third bottle to get another half-plus pint in to fill to capacity. You’ll know you’re there when the lube level in the case is right at the level of the fill hole and there is some slight seepage. Double check to be sure the level’s right, then re-install the plug.
Hopefully it won’t be another almost fifteen years before I get to this again!
Throw it in the Woods?
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Talking about automatic transmission oil pans, installing drain plugs along with a conversion to a high-quality synthetic ATF was the best bit of maintenance I did for a ’98 Taurus wagon and a ’90 Ranger I once owned. You had to drop the pan to drill the hole for the plug anyway, so changing the filter while in there was a no-brainer. Then you also had to check for the best spot for the plug to keep from interfering with parts projecting from the transmission inside. Overall it was worth it. I could change what was in the pan every, say, 25,000 miles. On the Taurus that was about half the total capacity. Used Amsoil, but Redline or another good synthetic would have been great too.
When I ended up junking that Taurus over an engine failure (cracked head or block from overheating after thermostat failure), it still had its original transaxle after 220,000 miles. And that particular transaxle was known to be troubleprone in earlier Tauruses.
I put a drain plug in the Trans-Am’s tranny pan, too!
It’s about a 5 minute job once you’ve got the pan off.
It’d be really nice if they still put drain plugs in torque converters…
EK, I don’t know if I posted here but my wife’s Cutlass’ tranny started screwing up a year ago. Last couple times I changed oil and filter on it I had left my Amsoil synthetic at home so used regular fluid. This time the fluid looked find, filter had nearly nothing in it so things looked bleak. I did remember my Amsoil though and that’s what it got filled with. There was a big leak near the front, probably an o-ring near the cooler hard lines but I am crippled now and didn’t want to be removing radiator support or something so I just said I’d feed it. After 3 weeks of Amsoil the leak quit entirely, the tranny started shifting correctly again and my only complaint is not being able to drain the torque converter. I noticed about 10 years ago while working on a couple of one ton Fords and GM pickups that Ford still had a drain plug on the converter but GM didn’t damn it. I don’t know if it’s changed for the better for GM but I do know those trucks get much better transmission maintenance now than before with oil drain plugs in the pan and external filters. It should have always been this way.
Oh yeah, I forgot to mention, rear end fluid comes in at a tie with Tranny fluid as the worst smelling stuff, ever.
Ever get it (gear lube) in your hair?
eric, that’s just the bestest place. Talking with old college buddies yesterday remembering the various engines/transmissions built in the dorms. One guy rebuilt his ’57 Chevy’s 283 in his room and then fired it up on Coke crates(the most versatile thing ever invented). I walked into my dorm one day and gagged from exhaust fumes. A guy rebuilt his SBC and then used a run-in stand to break it in…in his room. We were tough back then or just had no sense. I got my room all cleaned up for inspection to get my deposit back but when I checked back on it it smelled highly like 90W gear lube since I rebuilt trannies there, the floor was once again oozing black. I put off the inspection and used a hefty dose of spic and span, got the black up and masked the smell, got it inspected and my money back. I always wondered about the poor soul who inherited that. I remember a GF getting in the car “What’s that smell?” Everybody probably thought I rode a bobtail Harley and caught all that chain oil up my back.
Roth, you have never changed nappies (diapers). Or been around hydrogen sulfide, or tddm ( a mercaptan placed into natural gas). Or an Australian aboriginal woman!!
Baaaddass bird dude! I recently did the front, rear and transfer case on my 2500HD Silverado 4X4. After that expensive (Lucas synthetic), time consuming, messy job it may be 10 years before I do that again. 🙂
I use Lucas also.
I’m gonna do a video walk-around and road test of the old ‘Bird in the near future, too!
There’s a fill plug, but no drain plug? Seems strange that you have to remove the cover in order to drain the lube.
Not on these GM 10 bolts!
You drain by loosening/removing the cover….
eric, they almost give away after-market covers with drain holes, not much over $100. So how to have a drain plug without drilling a hole, welding a nut and so forth? Finally it hit me one day(never said I was smart). Just get a bit and a after-market self-tapping oil pan plug, easy peasy. I realize they want you to inspect the insides but this can get old if you have just changed brakes or any component and then need to change another. Hell, you just saw the gears and don’t need to dump all that expensive synthetic fluid you just installed. Many rear-ends don’t have plugs for drains but require the synthetic lube and it’s a pain to clean to the nth degree a pan to hold it and then wait forever for it to flow through a paint filter when installing it. I know lots of people don’t go to that trouble but my stuff gets treated like the space shuttle. I know what just a little crud can do to a bearing and then seal and then everything else. I’ve griped about GM doing this with all their rear-ends for 50 years but while some say they don’t make THE strongest rear-ends, I’ll say they make plenty strong enough that will hold with double the HP they came with and on a one ton pickup, the 10.5″ ring gear fourteen bolt rear-end is considered the elite of the industry….even though it has no drain plug. Well, there’s my bitch. Guess I’m just mad after just changing the old belt tensioner on my wife’s Cutlass that only has 236,000+ miles and then the new tensioner was very little smoother. I’d put the old one back on if it was the vehicle I drove.It has bearings in it you can pack which I did just a year ago or less and it was mighty slick but had more bounce than I like although it was right on the marks it should be.
“posi-traction” – I Do Sooo like that freaking word. It has such a delightful connotation to it. Pure joy.
I wish I could remember the contents of the homemade solution for that stuff. I’d post it now.
Myles asked, “Seems strange that you have to remove the cover in order to drain the lube.”
eric wrote, “Not on these GM 10 bolts! You drain by loosening/removing the cover….”
Ya, It’s that way on a whole lotta (if not all?) Toyota 4×4’s too.
And all the Ford’s I’ve worked on.
Eightsouthman wrote, “they almost give away after-market covers with drain holes, not much over $100.”
I think maybe the words, “give away” mean something different to some people?
Once again I’m remembering a title to a book I once read, I think it was, ‘Habits of the Wealthy’ or some such.
Anyway, to be fair, I like Eightsouthman’s idea of a drain plug. How-freaking-ever; due to the shape of the rear end cover, with such a drain plug, it seems to me you’d not be draining All the fluid out of it.
Could be I’m wrong.
Could be it don’t matter.
Could be drilling a hold while laying on my back is not my idea of a fun time.
I still like the idea.
I just won’t be doing it.
Well, really, I may not even be doing the fluid change, I’ll just wait til the thing goes bad.
Fuck. Just one more thing I gotta do. …Er, pardon me, I mean, just one more thing I have to add to my list of things to do. …Crap, I still haven’t changed out my clutch reservoir.
Roth, if I went to the salvage yard and they wanted $10 for a diff cover I’d have to think long and hard over that. Of course I could buy 15 of them for the price of one with a plug in it(and some neat lines and such so you could see it’s trick((sic)) ) just to mess around with if I somehow didn’t have the aptitude to drill a single hole at the bottom of a cover and screw a self-tapping bolt into it. I’m old but not that old. It’s so complicated. Go to any auto parts dealer and get a “kit”(drill bit and plug to match, very complicated) if that’s the only way you can do it, and install a drain plug into the cover. Yes, it drains all the lube if you can even feel how far away you are from the edge of the cover or even better yet, if you have vision, something I’m learning to do without.
And the old lady is right. Me and the old tomcat are two of a kind. He was in this eve just kicking ass and taking names and generally giving anything and everything holy hell. I think he’s lost his patience and the old lady thinks I’ve lost mine. I think she’s right.
Eightsouthman wrote, “Yes, it drains all the lube”
How do you know this thing?
Also, I’m certain of one thing, All ornery old guys Have lost their patience.
As an experienced tester of such, I know.
…Did they ever have it in the first place? I sometimes wonder that.
Anyway, even-though my 4×4 ain’t a classic racer, I still try to keep it stock lookin’, and a drain plug ain’t that.
…But like I said, I like your idea.
Roth, you pull the plug and after it quits, you pull the cover which you will find is dry. But you knew it would be since the bottom of the hole is below the top of the inside of the case of the rear-end.
Of course a first class 4X4 racer is tops on my list since I generally want to look sharp, and stock, when I’m dragging a 30′ swather down the road or hauling a load of cattle…..with my one ton rear-end having about 5-6″ of ground clearance. Now I COULD cut a couple inches of bottom diff. housing off straight with level and replace with a 3/8″ plate about 1/8″ from my ring gear but that’s a hell of a lot of work for a farm truck….and while I’m at it, install a propane/nitrous injection on the old diesel so I could show those cows who’s boss. Now that’s kicking ass the way my old tom would. And you wonder if old guys ever had patience? How else to lose it? Hell, I was even a baby once, hard it is to believe.
The last old guy who I worked with was nearing the end of his useful service life.
I think maybe he shifted me into the old man camp. It was a horrible experience.
I think I may have lost my patience a bit.
As we were cutting up this Toyota 4×4 into tiny bits. (doing so, seemed soo wrong) he handed me the cutting torch and at the very last second he unknowingly flipped it up so it kind of burned my eyebrows.
Then when he ran the cutting wheel in a such a way that the sparks rained down upon my head and up my nose I said, “That’s it!”
I felt bad for him, I felt bad for me. And he was clueless.
I think that’s what it must be like for cooks who loose their ability to taste salt.
..Now let me tell you about the man who waited two years before he put oil in the cylinder of the generator when he stored it away for two years. .. Well, I can’t. Because I still have yet to find out how that story unfolds.
Getting old’s such a drag.
Eightsouthman wrote, “Hell, I was even a baby once, hard it is to believe.”
Ha! Yes it is.
Just kidding,.. kind of.
And umm, I hope I didn’t piss you off or anything.
Twas not my intent.
I don’t hate cats.
..In the background, I remember this argument I heard between this old man and this younger guy who worked together frequently.
The younger guy said, ” I know people that can make you disappear.”
I thought it was a joke at the time.
Local ways, are funny that way.
I kinda felt good about not being That local and That Backwoods.
I’ve thought about putting in a drain plug, but it didn’t seem worth the effort (removing the cover is very easy) and more importantly, you’re right that doing it this way would probably leave a fair amount of old lube in the case, because of the way the cover/case are designed; the drain plug would have to be installed about 2 inches or so higher than the lowest part of the sump. I mentioned scooping out the last portion of the old lube bu hand int he video. If you had a drain plug, this portion would remain inside.
The ideal thing would be a drain plug installed in the bottom of the axle housing itself.
As I recall old Ford pickups had the drain plug at the bottom of the housing, below the cover. Ah, the good old days. 🙂
Yup – same goes for automatic transmission pans. They eliminated them decades ago – though at least there was a semi-plausible reason for it: They wanted to encourage people to change the filter and not just the fluid. But damn, it makes the job messy!
eric, it’s probably best to have to remove the cover but I tend to keep things from being “gunky” in my diffs. I have had a few housings with a drain plug in the bottom but if there’s gunk there it stays there. I’ve pulled plugs that had a big build up on them that screwed right out with them and you know the rest stayed in there. I do the same thing on axle housings as I do on anything I intend to drain, get them as hot as possible(normal hot)before draining. I have used my pump up sprayer many times to spray diesel or kerosene into the entire thing to run all the old stuff out. No need to spray down the 3rd member though. I used to use GM posi additive but changed to Amsoil synthetic additive and had it “smooth out” those little sounds and jiggles. I’d really recommend it for people with Trac-Loc since it tends to slip a few times and then eats the ring and pinion, POW as it were going around a corner….damn, what was that? POW, around the next corner. Oh no.
eric, I bought an aftermarket pan that holds an extra quart as well as having holes with widgets that are heat sinks for dumping heat and a drain plug. I guess they think if you’re willing to go to that trouble you’ll replace the filter too. I never saw anything with too much fluid and have used 8 quart oil pans on engines too. Moroso makes one that widens out instead of being deep that’s a really strong pan and gives you that added sense of having plenty oil as well as more cooling. I know I go off the deep end with coolers but then again, I never have anything burn up.