How do I change diff fluid when...

[wal280z]

Matt - unless you have some strange configuration in there, a open end (17mm if I recall correctly) wrench will do the trick - you may have to play 'flip-flop' with the wrench, but it *should* be able to be inserted from the bottom and turned CCW. Once it is loose enough to turn by hand, reach above the bar and remove the fill plug.

Unless someone has changed the fill plug with the drain plug.....

(PS - while you are down there, change that fuel filter)

[sblake01]

Maybe I'm getting old and my memory is failing me but I don't recall have any real problem removing the fill or plug on my 78. The fill plug is a 17mm and I remember alternating between a regular open end and an offset open end but I got it out.

[Jeff G 78]

I am in the same boat. I bought new Redline gear oil and tried to remove the fill plug. With the car on jackstands, there was no way I could get enough leverage to remove the plug. The 17mm wrench wasn't long enough to loosen it while laying on my back. I tried to use an adjustable wrench that was longer, but it was too thick to sit completely square on the plug and wanted to slip. Since the wrench had to be pointed downward, I couldn't add a cheater as there wasn't enough clearance to the ground.

I posted the question on another forum and Tony D replied that HEAT is the answer. The plug is coated with thread sealer from the factory which bonds it together making it hard to break loose. I haven't had the time to try it yet, but he said to heat it with MAPP gas to break the sealer down. He also suggested to replace the fill plug with another female drive plug like the drain plug for easier removal in the future. Teflon tape should be used to reseal the threads of both plugs.

As soon as I get some free time, I will try heat and see if I can get it off. If I still can't get it, I will take it to my friend's house and put the car on his hoist. That will give me the height for a cheater to be used.

[sblake01]

Actually, it's not a 17mm. I just went through my wrenches and, if you want to get really technical, a 21/32" open end fits it best. Not normally found in most people's toolbox, I must have purchased that one especially for removing that plug back in my 510 days.

[beandip]

If by chance you have a R-200 , you can pull one of the half shafts loose from the wheel end and give it a jerk and the stub will pop out of the pumpkin and you can fill it from there. I haven't needed to try this but have seen it posted several times. One thing if you do remove the transverse link that is blocking your access to the fill plug. don't torque down the bolts for the bushings with the car off the ground. there should be a load in the car of a couple of hundred pounds and the Z resting on the wheels . Then torque it down. Otherwise you will be putting a twist in the bushings . It's in the service manual . Gary

[KDMatt]

Hey guys, thanks for all of your help and experience.

I ended up taking the car to a shop a while ago, and they couldn't get the fill plug out because this link (?) is in the way, they told me that the plug would only thread out a turn or two before the link completely prevents it from being able to come out any further.

I also have a maintenance record somewhere that, IIRC said something about the diff not being the stock diff... has anyone ever had this issue with swapped diffs?

On that note though, I will try to see if what my shop told me was true or if its theoretically possible to get the fill plug out... or maybe I could loosen up that link without completely removing it? ... just enough to slide that fill plug out? We shall see...

Also, yes, the fuel filter I added last year, lookin' a little on the clogged side! I can feel it when I drive too, so I want to get on that soon also, just gotta use up some gas, I guess I've got the 4th of July weekend coming up, though somehow I suspect a weekend of gasoline and fireworks aren't going to mix too favorably...

[jthill3]

Two shops have tried and can not get it out.

This car sat in the garage for 7 years before I bought it last month.

Assumig I can't get anyone to get this out, what should I be looking or listening for to see if I have trouble?

Thanks

[DeesZ]

The "hot - cold" method may assist.... Try heating the surrounding area moderately (not enough to burn anything or get anything even near 'red') with a torch and putting some ice on the plug. Expansion and contraction action should assist in the effort to loosen it up. I've had luck with this method with other applications and problems.

[blue 72]

If it was me I already would have given in and done things the hard way. I'd go ahead and unbolt the curved hanger from its support bars and unbolt the lower control arms to get at the thing. You might also try a brass hammer or something of the like to try and "jar" the plug loose. I guess I got lucky I drained and refilled my R-200 before I put it in the car. I did almost take the whole thing out again later because I had installed the mustache bar backward, so I can feel your pain.

[HKSZ]

There is a simple way.

Remove breather cap, use a zip tie as a dip stick and add oil thru breather hole, or to be totally safe drain oil and add 1.1 ltr of oil thru the breather hole.

[sblake01]

I've been watching this thread and either a 78 is different or my car is special because I've never had a problem getting that plug out. This isn't the greatest picture but you can see that, at least on my car, threre is enough room between the plug and the link to get it out:

[Jeff G 78]

Stephen,

That might just be the worst picture I've ever seen.

Any chance of getting a clearer one? On my '78, I have just enough room to fit an open end wrench on the plug, but with the car on jackstands, I don't have enough height to fit a cheater bar. I think it would be easy with the car on a hoist.

I still haven't had the time to apply heat like Tony suggested. One of these days...