Sierra Differential Venting

[Klasik-69]

I noticed my Sierra Diff blowing some oil out of the upper vent hose, which is just resting against the upper aluminum panel at this time. I had never noticed any oil puddling or dripping until the other day when I took it around the block twice to test a new microphone placement in the engine compartment (a whole other issue in itself). When I got back in and backed up the gar in my shop, oil was coming out in small drips. At first I wasn't sure where the oil was coming out of. I put the car on the lift and ran it but nothing further came out. But when I looked up above the differential, I noticed wet oily areas on the right upper side from this time and likely other prior times too.

 

I drained the oil from the differential and measured that I had 36 ounces of gear lube, which appears to be correct. No oil came out of the rear plug when I openned it up to stick my oil sucker in the diff. so I assume it wasn't over-filled. I have no issues with the differential, quiet as a church mouse and silky smooth.

 

Has anyone else experienced this ? I was thinking of adding a vented catch can in the rear storage compartment and running a hose extension from the diff. vent hose. Necessary ? Don't know.

[Croc]

Yep - have had that happen to my current seven (sierra diff LSD internal)first time I put it on track. Was not overfilled but was still dropping a bit out the vent tube. Seems to be more common the hotter the ambient temps got. I ended up installing a catch tank around the side of the fuel tank. A little bit collects but not a lot - I empty it once a year and top up levels same time. I did top up once when a little more than average was observed. Never had an dribbling issue since.

[Klasik-69]

Thanks. I'll install the catch can. I'm going to put it in the storage area, easier to monitor & empty from there.

[Klasik-69]

While messing around with the vent tube issue, I noticed that my de dion suspension tube has been hitting/rubbing the cover plate of the Sierra differential. In fact, it even broke off a piece of the reinforcing web about midway up the case cover, just above the fill plug.

 

I asked Jon @ CaterhamUSA about this and he suggested I take a look at the Watts links and their bushings. According to the assembly manual, the front link is supposed to measure 475 mm (18.70") center to center, and the smaller rear link 244 mm (9.60") center to center. I measured from the outside and it appeared to be off so I took off all 4 links to accurately measure them. Front links were 18.5", rear links at 9.5".

 

If any of you have any interference along the back of the differential, I would check the links, and as Jon pointed out also, the condition of the bushings. I bought my car from the original owner so I assumed he had the suspension correctly set up. Maybe he thought he did. I used center point punches through the holes to get an accurate reading on the center of the mount.

[yellowss7]

When I assembled mine, the build manual had a section that showed that you had to saw or grind off a piece of the diff that would hit the deDion tube if you didn't.

 

I remember that the measurement of the amount of material to take off was critical as if you didn't take enough off it would still hit the deDion tube but if you took too much off it would hole the diff casing.

 

that was early in the build process as the diff is one of the first things that went on the car.

 

If needed I can probably dig up the build manual and post the diagram.

 

Tom

[bsimon]

if you took too much off it would hole the diff casing.

 

:(Very true. I discovered this the hard way.

[Klasik-69]

Yes, I saw the reference to machining the top boss to 38 mm from the face. However, the tube was hitting the case about 3" below that. Incidentally, my upper boss appears to have been machined.

 

For the life of me, I can't see how the rear suspension can compress enough to bring the de dion tube anywhere near the upper boss on the diff cover plate.