Rear Axle Housing, Fluid, and Fluid Changing Information for Imperials

Imperial Home Page -> Repair -> Rear Axle -> Housing and Fluid

Question from Steve (1959):

What do the rest of you do about changing the fluid in the rearend of these old Imperials? I am worried that the lube in ours has probably turned to tar in the 40+ years that it has been in there.

I took Tom's Imperial to the rearend shop today to see about having the fluid changed. They told me that we need to pull the axles then pull the front of the pumpkin off to replace the seals and clean everything out good. Cost estimated at $150.00

Should I have it changed? Should I just top it off with new lube?


From Dick:

Assuming you have the correct lube in there, and that it doesn't leak, I see no reason to disturb it. There is no contamination or reason for deterioration other than the minor erosion of metal from wear, and those particle lay in the bottom of the case. You're more likely to stir up trouble by fiddling with it than you are to avoid some future problem by changing the fluid. If you have posi-traction, there might be slightly more reason to drain it and refill, but still I wouldn't do anything other than that.

If you can find the level of grease with your finger tip or a small probe, and it is within 3/4 inch of the bottom of the fill plug, just cap it and leave it be. If it is lower than that, you'll have to add some grease to it. The level will take a while to stabilize after the car is driven, since the ring gear picks up the grease and slings it all around. It takes about 15 minutes to approach the final level after driving, if it is SAE 140, a little less with SAE 90.

For "topping up", be very sure you use the right product. The modern GL-5 grease is not the right stuff, buy the old GL-4 unless you have posi-traction. If you buy the jug with the built in pump, you can do this all yourself very easily. Then you'll know what we're talking about when we mention the lovely smell of rear end grease! If you have posi-traction, you'll have to research further, I don't know what is correct for those.

From Jim:

I don't see any reason not to service your differential, and the cost of $150.00 seems to be fair, considering the disassembling they are going to perform. With this method, all of the gunk will be cleaned out, and you will have nothing but fresh lubricant hitting your bearings & gears. Consider the potential cost of replacement (ask the rear-end shop), and you might find it a wise investment. We use 80w-90 lube, with a sure-grip additive if it is 'posi' (called Sure-Grip by Chrysler). Many years ago, I remember that 140w or 80w-140 was used on Sure-Grip units, or something like that. Newer differentials (9-1/4, 8-1/4,7-1/4, and Dana) have a removable cover on the back - easier for maintenance, harder for gear replacement. For my money, I'd spend the $150. and have it done right!

From Bob:

I wonder if the shop that will pull the axles knows about the effort required to remove the tapered axles?

I thought suction hoses to get old lube out are widely used when there is no drain plug. Or have I assumed wrong? I had EZ-Lube change my differential oil/grease last April on my '66 (at least they charged me for it after I requested it!)

From Bob D.:

I took my '58 for a run to warm it up, then let it drain all night. I re-filled it the next day. There is no need to dismantle the axle and replace the seals unless the axle has some sort of problem with it.

On my 1958 LeBaron, the drain plug is very hard to spot, but it is there. It is located on the lower right of the pumpkin housing. It is a flat plug and it takes an Allen key to remove it. Inspect the area very closely and you will find it. It does not protrude from the cast iron housing, so that is why some of you think it does not exist. You may have to scrape greasy road grime away from the area to un-cover it.

From Kerry:

I'd drain it and put a couple refill it with new lube. Cost about 3 bucks.

From Steve:

Changing the fluid is a good idea. There is a suction gun-device that looks like a grease gun with a 3/8ths hose that is used to suck out the old fluid. Once you are done removing the old fluid, suck the new fluid out of the bottle and squirt it in the rear axle housing. I don't think your housing has a drain-plug. I can't see the point of tearing everything apart to "clean everything out" and replace the seals as the rear end shop suggested, if the rear just needs a fluid change. The rear end in my '75 Imp, which is a 9 1/4 sure grip "posi" unit, was shuddering when starting off in a tight turn. It had 55,000 miles at the time. After changing the fluid, the rear end operates like it should. Mine is changed totally different though, as I have a cover that faces the rear of the car. Yours is known as a "front loader" unit....most likely an 8 3/4. I'd change the fluid and leave the rest alone. Don't forget to grease the u-joints.

Question from Kenyon (1960):

I lost some of the rear diff lubricant as a result of doing the brakes, and I'd like to drain the rest of the fluid and then replace it.

1. I see a bolt that is 3/4 of the way up from the bottom and is pointing at the passenger side wheel, and presume that this is the fill-er-up hole.

The FSM does not detail this procedure, probably because everybody was presumed to know this or something. I am inclined to put new oil in through the plug hole on the passenger side of the differential, and keep going until the oil level reaches the bottom of the bolt hole and starts to come back out. Is this correct?

2. There is what I presume is a drain plug at the bottom. Would be nice to drain the remaining old oil out first, I thought. The problem is that the bolt has a square recess in it that is smaller than a standard drive wratchet extension. I sacrificed an extension and ground it down to fit, but the new "tool" deforms rather than turning the petrified drain plug. What kind of tool goes in there, and where would one aquire such a thing - the local made-in-china tool emporium looked at the grease-smudged paper that I pressed against the plug for an impression and their eyes glazed over and they shrugged.


From John S.:

The filler plug is on the passenger side of the differential. You also drain it there. They usually use a suction pump for this. I donít have one, but have seen them at Pep Boys. Thereís also a breather on top of the axel you should check to be sure is open or it can cause fluid loss.

From Kle:

How easy is it to take the access cover off on the 1960? You could get pretty much all the old gear oil out with that off and a suction pump.

From Kenyon:

There is no access cover - 1960 is an interesting hybrid between 1950's tech and 1960's tech. They didn't really get super-standardized on stuff until the 1963-1975 cars.

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