[minkus316]

I've got a '75 4 speed with (as far as I know) a stock rear end. I see a leak that has the majority of the underside of the pumpkin wet. I'm not sure if the previous owner had the rear end apart or not, but he mentioned replacing the drive lines, so I'm thinking he may have done a diff rebuild kit. The seal between the 2 diff casing half's appears to be a red form-a-gasket material. Wet up to the fill hole and worse on the fill hole side.

Questions:
1) What are the easy things to check first?
2) The red fluid tag spins loosely. Is this normal?
3a) If you were tearing the rear differential apart what would you replace if all parts are original
3b) If you were tearing the rear differential apart what would you replace if all parts were replaced 10 years ago?

[minkus316]

Uploading pictures didn't work for me for some reason, but here are links to a few.

Bottom, passenger and driver sides views...

https://docs.google.com/open?id=0B9o...i1ZVDVxMS1QUmM


https://docs.google.com/open?id=0B9o...HEwNzdMQjF3bFE



https://docs.google.com/open?id=0B9o...HBGeWltZUEteGs

[toobroketoretire]

Originally Posted by minkus316

I've got a '75 4 speed with (as far as I know) a stock rear end. I see a leak that has the majority of the underside of the pumpkin wet. I'm not sure if the previous owner had the rear end apart or not, but he mentioned replacing the drive lines, so I'm thinking he may have done a diff rebuild kit. The seal between the 2 diff casing half's appears to be a red form-a-gasket material. Wet up to the fill hole and worse on the fill hole side.

Questions:
1) What are the easy things to check first?
2) The red fluid tag spins loosely. Is this normal?
3a) If you were tearing the rear differential apart what would you replace if all parts are original
3b) If you were tearing the rear differential apart what would you replace if all parts were replaced 10 years ago?

Not all RTV's (silicon) are compatible with oil and I would guess the previous owner used a wrong kind between the rear cover and the differential housing. All of the Permatex "Ultra" silicon is compatible with oil. I usually use Ultra Black for oil jobs.

The most common point of wear is the ends of the side yokes where they bear against the spider gear shaft. The factory yokes were pretty soft and easily mushroomed. But the new yokes are much harder and will last a lot longer.

[minkus316]

Any other thoughts?

[duane4238]

From the looks of the second picture, your problem may just be a leak at the fill plug, and as you drive the oil migrates around the rearend. Hope that's all it is.
Duane