As many of you know, overgreasing the zirk fitting that feeds the rear shaft spline can lead to the shaft being essentially "hydrolocked" and doing damage to the center diff or rear diff due to enormous force they are not designed to take longitudinally.
The other day, I greased the shafts and again had trouble getting any grease in the rear shaft. Today I was under the vehicle to grease the birfields and noted that no grease had come out the splines in the intervening days. Strange.
So, I pulled the shaft off for the first time ever and had a look. I've always wondered what I'd find. Poor machining in the grease gallery behind the zirk? Dried grease blocking the splines? What?
I cleaned out both halves (male/female) which took an hour and a half and a lot of degreaser. Finished up with brake cleaner. I could see no evidence of ANYTHING amiss. The only thing I did not expect to find was a dust seal on the female end that had an interesting contact area made of fiber. It looks like the non hooking side of velcro and was very tight. I suspect this is the culprit as it provides a surprisingly tight fit once saturated with grease. The fibers may provide an incredible amount of force preventing grease from getting through. So I'm going with this.
On my shaft, I switched to red Mobil 1 grease 5 years ago. So, perhaps 10 consecutive greasings. Wanna know how much of this had made its way through the splines to this seal? Zero! It was all trapped in the end and the splines and this strange seal were full of completely black grease that may have been original. Incredible.
I'll update over the next few weeks to let you know if the purple grease I put in it is able to get past the seal as I'd expect a design like this to allow. Everything was perfectly clean and I hand packed the halves before reassembling, so if the design is going to work properly, I should know soon..
In the mean time, use extreme caution on this as I was struck by how effectively the seal prevents fresh grease from getting where it needs to be, which means the shaft is capable of exerting damaging pressure for a very, very long time after you grease it.
DougM
The other day, I greased the shafts and again had trouble getting any grease in the rear shaft. Today I was under the vehicle to grease the birfields and noted that no grease had come out the splines in the intervening days. Strange.
So, I pulled the shaft off for the first time ever and had a look. I've always wondered what I'd find. Poor machining in the grease gallery behind the zirk? Dried grease blocking the splines? What?
I cleaned out both halves (male/female) which took an hour and a half and a lot of degreaser. Finished up with brake cleaner. I could see no evidence of ANYTHING amiss. The only thing I did not expect to find was a dust seal on the female end that had an interesting contact area made of fiber. It looks like the non hooking side of velcro and was very tight. I suspect this is the culprit as it provides a surprisingly tight fit once saturated with grease. The fibers may provide an incredible amount of force preventing grease from getting through. So I'm going with this.
On my shaft, I switched to red Mobil 1 grease 5 years ago. So, perhaps 10 consecutive greasings. Wanna know how much of this had made its way through the splines to this seal? Zero! It was all trapped in the end and the splines and this strange seal were full of completely black grease that may have been original. Incredible.
I'll update over the next few weeks to let you know if the purple grease I put in it is able to get past the seal as I'd expect a design like this to allow. Everything was perfectly clean and I hand packed the halves before reassembling, so if the design is going to work properly, I should know soon..
In the mean time, use extreme caution on this as I was struck by how effectively the seal prevents fresh grease from getting where it needs to be, which means the shaft is capable of exerting damaging pressure for a very, very long time after you grease it.
DougM