proper u joint greasing method.

i've always pumped enough grease to get the old grease out.

the guys at the shop I go to told me that I put too much grease into the u joints and I'd be breaking the seal at that point.

Does this rule vary depending on the type of u joint? Or are there just way too many contradictory rules out there regarding this?

 

I just pump it until you heard it purge

 

I pump until I see new grease coming out...

 

Everything I've read says to pump until only a little of the old grease starts to come out. I too have thought about forcing all of the old grease out, but I think at the end of the day the intent is to just ensure the bearings are not starved of grease.

 

what is the difference between allowing all the old grease to come out vs just some? I mean, by that point, you've already opened seal...

This answer must be something very black n' white.

 

I think the difference is that you need to push in a lot of new grease to push all of the hold out. The point is not that the seal is broken, which is misleading because it is not really a "seal" because it is not a closed/sealed system...hence why you have to regrease it and know it has received new grease when some old comes out of the seals.

Therefore, you don't need a lot of grease to refill the joint and force just a little out of the seal. However, you likely need much more grease and therefore increased pressure to push all of the old grease out. This increased pressure likely overfills or over stresses the bearigns, joint, and seals. For example, you may want to simply regrease the bearings, but too much pressure may irreversibly break/damage the seals or lodge the bearings with overloaded grease, etc. This is my impression, and everything I've read just says to force a little old grease out.