Got my head in my rear end...

[pasvorto1]

and I am trying to replace the fluid. I bought 2 units of posi fluid and 2 units of diff fluid. I jacked up the left rear and crawled under to have a look. All I saw was spring and skid plate. Above that, after some wiggling around, I saw the inspection /fill hole for the diff. I did not see a drain hole. I made a run to the local Chevy dealer to talk to their mechanics. I was told that there was no drain plug on a 78. My choices were to either siphon the fluid out (not what they would do) or take off the rear cover and drain it (which they would do). I'm thinking maybe loosening up the bolts enough to drain the fluid, rather than remove the whole plate. Since I have no access to a hoist, I would have to drive it up on a set of ramps, and then jack up the back end enough to place some ramps under the tires. I'm not even sure that is possible. I don't know if my jack would get under it, and I'm not sure my jack would get it high enough. Could be a real PITA. Should I just take it somewhere?
Is there an easier way? Any "gotchas" that I need to be prepared for? Is the rear cover just that; a cover? Or is the pumpkin attached to it?

 

[JOE BYRNE]

Jack stands....siphon..I used a siphon attatchment on my drill

 

[curtis]

I used this sucker thing that kindof looks like a grease gun, but no tip on the hose. Cheap.

 

[Dave L.]

Jack up rear. Remove tire carrier. Remove right rear wheel. Use suction gun...you'll have plenty of room to work.

 

[GTR1999]

The only real way to do it without a drain plug is the suction gun. Forget what the Chevy dealer says they probably don't have anyone there who knows these cars anyway. You should ask them how they remove the rear cover-since it's holding up the rear end! You'll get a bill for $450 to do an oil change!

FYI When I rebuild these I always add a drain plug for future service.

 

[pasvorto1]

You guys called it. It took me about 2 hours to do the job. I removed the Right Rear tire and all the spare tire garbage. Probably a good thing because I found out that the spare tire was flat. It took longer for me to find a wrench to fit the fill plug than anything else. I, too , noticed that I couldn't remove the rear cover on the diff. What was that mechanic thinking?

I took it for a spin after I buttoned it back up and the noise only occurred once. That was when I stopped to open the garage door. Then I did a hard left into the driveway (from a dead stop). I got the noise, a bit, then it went away. Before It would have made your teeth hurt and it would 'grind' until I came to a stop in the garage.

I don't want to jinx myself, but I think I may finally have it solved.

 

[lucky76]

Seems like I remember reading somewhere about making so many left and right turns after replacing the differential lub to lubricate the positrac but I don't know where I saw it. I changed mine but I didn't have any noise. Just OLD STINKING grease in it. Boy did it stink.
Changed my 4 speed transmission grease (it has a drain plug) and it looked like mud. The gears shifted a lot better aftwards. I guess the owners before me just check for fullness. I changed it again two weeks later just for the heck of it.
Your lub may be full but it may also be 30 years old.
Lucky76

 

[dk1977]

I had the same "grinding noise on turns" with my '77. I used a siphon gun and replaced the fliud with new and 2 bottles of posi lube. I still had some noise after, so I went to a large empty parking lot and turned circles to the right and left (slowly) for about 5 minutes each way...the noise went away and hasn't been back!! I still do this once a month, just a few times, for good luck.

 

[pasvorto1]

Took a long ride today. Didn't hear the noise once

 

[Dave L.]

Good job! I'm glad your dif' noise is gone.

 

[DarkBlue]

I'm wondering if this is my problem, too. A left or right turn from a stop, for example waiting to make a left turn in an intersection, produces an intermitten whine from the rear end. I had the rear end apart about 15 months ago to replace a leaking seal and replaced all fluids at that time. I've put about 10,000 miles on it since that time. I shouldn't have to siphon and replace again, should I? Can I just put in additive and then top it off with the fluid? Thanks.

 

[gmjunkie]

I'm wondering if this is my problem, too. A left or right turn from a stop, for example waiting to make a left turn in an intersection, produces an intermitten whine from the rear end. I had the rear end apart about 15 months ago to replace a leaking seal and replaced all fluids at that time. I've put about 10,000 miles on it since that time. I shouldn't have to siphon and replace again, should I? Can I just put in additive and then top it off with the fluid? Thanks.

I Take mine out to a large parking Lot and Drive around Backword's in Fig. 8's 6-7 times!! ( scuff's crud of plates in Diff.) Will clean them right up!! junk!!

 

[GaryS]

I Take mine out to a large parking Lot and Drive around Backword's in Fig. 8's 6-7 times!! ( scuff's crud of plates in Diff.) Will clean them right up!! junk!!

This is the gist of what folks are saying to do, AFTER a differential oil change. Of course, that oil change should include one (I use two) containers of GM brand Posi additive. After siphoning off as much diff oil as possible, I put in the two containers of additive and fill to the bottom of the drain hole. Seal it all up, go to Wal Mart and drive tight right and then tight left circles.

Gary

 

[DarkBlue]

I took the car to the chevy dealer and they changed the rear end fluid while I waited. I then went to a parking lot and drove in tight circles left and right. The noise is gone! That's the good news. After driving in circles, however, I now have a low whistle type of noise coming from the power steering, but only when I turn right. I drove to the mechanic. Power steering fluid is ok. He said that the hard turns probably caused a valve to stick and he recommended Seafoam from NAPA, and said to put a little in the power steering reservoir to unstick the valve. Does this sound right? How much should I put in? A couple tablespoons? Gene.

 

[curtis]

Seafoam is for cleaning varnish and gum deposits from things exposed to gasoline (like fuel lines, carburetors and intake valves to some degree). It will most likely destroy the lubricating properties of your power steering fluid. I would probably just use some power steering conditioner.