71's Rear End Leaking

[Jim and Jutta]

Yesterday was a sunny Northwest day so for the first time in two months I took the Mustang out for a drive. I found a puddle of fluid under the rear end where it had been sitting in the garage. I'd never noticed a leak before, any guesses at what may be causing the leak if so how big a job is it to repair?

The pictures were taken before I drove it so that's where the fluid flowed through gravity, not thrown there.

Jim



You can see the drops of fluid

 

[Mesozoic]

It's usually the main diff seal... a lot of folks use silicone, but I recently purchased a Cometic MLS gasket and it seems to be working very well. The other location it could potentially leak from is the pinion seal, but that's slightly more rare of a situation and often caused by driveline misalignment and other mechanical problems.

 

[Don C]

I see some oil on the tailpipe, so I'm guessing that it's the pinion seal and was flung around when you were driving. Probably been seeping for a while.

I agree with Mesozoic, a leaking pinion seal is often caused by other things going on in the differential, like the pinion bearings. But many of our cars set around so much the seal dries out.

 

[72HCODE]

the oil by the driveshaft that sprayed the exhaust pipes could be from the Zurk fittings for the universals. you need to oil them but the extra always sprays the exhaust pipes.

now you could have a leaking front seal where the yoke goes in.

there could be a leak from the fill plug on the drivers side front of the 3rd member.

you could have a leak between the nose of the 3rd member and the front housing, or a leak from the front housing the to the rear housing.

i have also seen leaks form at the weld seams for the axle body.

first you will need to jack up the car and see where it is dry and where the wetness starts.

check your axle breather on the drivers side to see if it is clogged up. there is a hose that comes off the drivers side of the axle body and goes into the chassis pull it down, and pop the hose off the fitting try to blow air through it.

attach a fresh hose to the axle fitting and try to blow air into it, it should move air easy unless it is clogged.

a clogged breather causes the expansion of air inside the axle to have no escape and it leads to leaks.

good chance the 3rd member will need to come out for servicing and resealing.

if the leak is between the rear axle half and the front body then you can pop off the 3rd member with 2 people and a floor jack clean up the mounting surface get a new gasket and copper washers and nuts, use RTV and reseal. if the leak is from the nose and or the yoke then the 3rd member has to come out to be rebuilt or replace the seals.

once assembled then you refill from the plug on the drivers side. fill it until fluid comes out of the plug then stop.

 

[Don C]

the oil by the driveshaft that sprayed the exhaust pipes could be from the Zurk fittings for the universals. you need to oil them but the extra always sprays the exhaust pipes.

That's a good point and possibility. I looked at the picture and the u-joint looks dry and the tailpipe looks wet, any driving at all usually heats up the tailpipe enough to bake on the grease.

 

[Jeff73Mach1]

I would suggest you start by checking the fluid level in the rear end. If it was overfilled, it may be the pinion seal leaking and draining the excess might stop it. You'll have to pump out any excess if you don't want to remove the 3rd member.

 

[BOSS 351]

Sure looks like a pinion seal leak from your pictures An easy and inexpensive fix.

 

[72HCODE]

problem is the crush sleeve, early mustangs the yoke seal is really easy to replace.

you mark the position of the yoke nut and then pop it off count the number of turns and then remove it and the yoke. reassemble count the turns then turn until the marks line up again. this is with a solid sleeve. it works because you get back to the same preload on the bearings.

unless the rear was converted to a solid sleeve then dealing with the correct bearing preload on the yoke when you reassemble is a REAL pain because it is a crush sleeve. the crush sleeve, crushes down so when you attempt to mark a start point and go to retorque you will be too loose. and it will be impossible to check the preload torque correctly so you can over torque it really easy, you wouldn't know till the rear end starts making noises that are bad, then you have to pull everything apart and rebuilt the bearing chases and again change the crush sleeve.

You are better off pulling the 3rd member or attempting to pull the nose of the 3rd member usually you can't reach all the bolts. so you have to pop the 3rd member off. this is because when you go to retorque the yoke nut the preload will be totally out.

the manuals all cover solid sleeves and leave out the crush sleeve issue. basically you need the nose pulled off the 3rd member (careful to take note of the spacers. then you pull the nut, pop the yoke, take the assembly apart, change the seal install a new crush sleeve and reassemble then you need to clamp the entire nose assembly in a vice and torque to spec, do not over shoot or you get to start all over.

to do this at home will require some expensive tools, so it is best to go to mechanic or a trans rebuilder that has everything to rebuild it for you.

here you can see me rebuild my 3rd member.

http://www.7173mustangs.com/thread-how-to-rebuild-a-ford-9-inch

http://www.7173mustangs.com/thread-how-to-rebuild-a-ford-9-inch-part-2

i had to use a 6 foot breaker bar extension to get the preload i needed on the yoke. to crush the sleeve down.

this all assumes the leak is the pinion yoke seal. so you need to see if it is wet behind the water shield behind the yoke.

if the leak is from the housing then you will need to pop the 3rd member but it will be repairable easier at home

 

[Jim and Jutta]

Thanks for all the great advice and hints. I'll check to make sure it's not over filled and insure the axle breather isn't clogged, clean it up real good then see if I can identify where the leak (s) are coming from. The crush sleeve is more than I want to tackle in my garage so I'll take it to a transmission shop, at least now I'm informed and will know if the mechanic knows what he's talking about when he tells me what it needs or if I need to take it to another shop. Thanks again guys, I'll follow up with what the findings are after the repairs are made.

 

[Jim and Jutta]

Just an update. Degreased the rear end, checked the axle breather hose, it wasn't stopped up, there was a lot of crud in the nipple the hose slid over so I cleaned it out. Open the drain plug, added 80-140 non synthetic gear oil, it took 10 ounces before it was full to the point of over flowing, which means it still had 70 ounces since it holds 2 1/2 quarts. Drove it about 40 miles pulled it back into the garage couldn't find any leaks, it's been sitting now for 4 days after driving it and still no signs of a leak, not a drop on the rear end or floor, so at least I know it's slow leak. I'll be watching to determine where the leak(s) originates from.