I’ll start off by saying I know basically zero about the rear end under my 70 351 Eliminator. Axle Code is 6 which is 3.00 Conventional. I’ve got a small leak at the read end. Nothing major but drips a few drops between drivings. I’m going on the longest trip tomorrow since I’ve had the car…about a 200 mile round trip. So, I thought I’d climb under there and add some fluid.
Questions…
I was told 80 or 90 weight fluid from AutoZone is what I need. Is that correct? Is it called differential fluid or gear oil or what? What weight do I get?
Where my finger is appears to be where it’s leaking. Where the front cover bolts on to the housing. 50 years of gunk under there. Do I need to go around that cover and tighten all the bolts or is it just a seal worn out?
It’s the first time I’ve really looked under the car and everything looks a lot better than what I expected. I was pleased. LOL
CRAP!!! I just looked to see what the local AutoZone has and now I’m wondering do I use synthetic??? Is it safe to add it to what I’ve got or do I need to get non-synthetic?
If you’re just adding fluid I’d stick with conventional since that’s probably what’s in there. You might want to change it entirely though since you don’t know how old it is, and it’s probably quite old. If you do that then you might as well step up to synthetic. You can try tightening the nuts to see if that stops the leak but at some point you might just need to take the pumpkin out and re-gasket it. Be advised that the copper crush washers can keep things tightly together so you need to pry them off the studs, and use new ones for reinstallation.
I’m not sure what the best way to drain out the old fluid is, while everything is together. You probably have to use one of those hand pumps with a hose that you can snake in through the fill hole and pump it out.
My experience here is limited… I completely took apart and rebuilt my rear end so it was easy to fill it with new fluid when it was out of the car. Doing all of this while it’s still installed sounds tricky. I’m sure others here will have better tips.
Well I just went and got a quart and YES mfc133, you can NOT hold the bottle at an angle to get it to go in no matter how much you squeeze that stupid bottle. I used something like a giant turkey baster and shot the entire quart in there and it’s still not to the bottom of the hole! How much does that sucker hold and how bad has it been for the rear end to have been ran so low on fluid? It’s never made any noise or acted strange. I’ve got limited miles on it since I’ve only had it about 10 months.
I use two long neck funnels, one into the other that allows me to reach the center diff from the driver’s side wheel well. It takes patience but eludes the mess.
Well it ended up taking about 1 and 1/2 quarts to top it off. I used something like a giant turkey baster and it worked very well. I drove the Cougar 160+ miles today and no issues at all.
That is not a wire but, I believe, an air line for air shocks. Follow the “wire” to its other end and you will probably find a Schrader valve like on your wheel.
I use a length of clear tubing and stick one end on the oil jug and the other end into the filler hole. Then I can sit by the back tire and hold the jug up and squeeze the oil into the diff.
A good winter project would be to remove the rear end.Install new pinion seal, differential gasket, axle seals and axle bearings. Then it would be good for another 50 years.
And if the car does have air shocks, you may want to remove them. They tend to place a lot of pressure on mounting structures and can cause damage. They are often used in place of fixing the real underlying problem with the rear suspension- worn springs.
Hard to tell but it looks to be leaking from both the main housing gasket and the pinion seal. The pinion seal normally goes bad because the pinion bearing is shot. At some point it needs to be taken apart and evaluated.
It wouldn’t surprise me if the leak on the differential isn’t entirely from the gasket between the ‘pumpkin’ and the differential housing. I’ve had this same problem on my T-bird ( 1970 Landau ) and Lincoln Mark III ( 1971 ) - it was the pinion seal. When it leaks ( even if a small amount ) the speed of the rotation combined with air rushing under the car will ‘drive’ the oil all over the third member ( “pumpkin” ) and it may therefore appear to be originating from the gasket. Even the small drip that will be at the lowest point on the differential might be deceiving, as it is actually coming from the seal ( behind the yoke flange ). Worth having a look at - especially if the entire area is cleaned up to confirm your ‘diagnosis’. Best of luck - leaks of any kind are sometimes hard to find their source !
Hmmmm, never thought it could be air shocks. I remember kinda tracing the wire from the passenger side and it went back toward the tag. That was Friday night went I was adding the gear oil. I’ve never had air shocks, so I have no clue. I’m thinking this winter would be a good time to redo the entire front and rear suspension. She’s riding pretty rough after all these years.
I’ll try to trace it down this weekend. Spending time with the kids today.
You MIGHT be able to get away with cutting the hose at the break and pulling some of the extra hose down, and just reattaching it. While you have it off, be sure to clean out the little vent nipple to prevent pressure build up in the axle. You can just run a wire or pin down the nipple vent to make sure it is clear.
While you are fixing that vent tube hose, would be a good time to replace the air shocks and straighten the shock mounting bracket on the drivers side. I’d also check the brake lines as they look kind of sketchy. Most of this stuff is sweat equity other than getting a set of shocks. The brake lines and vent tube hose are pretty reasonable and easy to source. Cleaning up stuff like this gives you some piece of mind as you drive around this summer.
