Front Axle Seal Still Leaks. 1974 FJ40.

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Apr 30, 2013
Worcester, PA
Haven't posted in a while because I wanted my next post to take place after all the work I did to the truck over the past couple months was done, but here I am posting about an issue that I am having with the driver side leaking gear oil even after doing the knuckle rebuild.

I did the rebuild, drove the truck about five miles, then noticed it was leaking. Realized I forgot to clean the differential breather, so I took care of that, purchased a napa seal which broke, as well as another before getting one from the local dealer and that one leaked after driving it 10 miles. I broke the first two seals because I did not have the right tool. The third one was a smooth install because I used the bearing race/seal tool from Harbor Freight which is great. The only thing I did not do was replace the grease which was replaced during the rebuild. It looked and felt fine. Surfaces looked good as well.

Any ideas other than replacing the seals with the Marlin seal?
Did you use the axle centering tool to recenter or did you just replace the shims?
Is it possible you got the shims reversed or somehow messed up when you put them back?
I made sure the shims were in the same position when they were reinstalled, although the top shims did get a little bit messed up from the constant removal and installation process. I have new shims but didn't install em cuz I didn't want to get the centering tool. I followed the process in the minitruck front axle disc brake thread. Could it be anything other than the shims? If not, I will end up getting the centering tool.
If the sealing surface on the axle is good and there are no gouges in the housing where the seal sits, there aren't many other things it could be. Now that you're a pro at pulling the shaft and replacing the seal :rolleyes:, what I would do is to replace the old "messed up" shims with new shims of the same thickness, AND use a marlin seal. The centering tool is expensive and takes quite a while to figure out how to use.
Try to keep the weight of the axle off the seal as you slide the axle back in. Otherwise the axle can deform the seal. If the knuckle preload measures within spec I wouldn't worry about the shims, although replacing the old shims with new ones, of the same thickness, can't hurt. Definitely use the Marlin seals.
Since I will have to replace the shims, I might as well redo the whole project, including replacing the seals with the marlin ones. In the meantime, I'd really like to take the top off and drive the truck while it's still warm out until the Marlin seals come in.

It took me days to do just one side. I don't have a manual so was going back and fourth to the computer to make sure I was doing everything right. I did mess up a couple of times and end up doing some things over again but now It should take about a full work day to do both sides.

My front Asco hubs did get a little banged up and am thinking about selling em along with three individual Warns I have for a good set to save some time and money. I know some of you like the Ascos since they are not as common as the Warns, so please get in touch with me if you are interested in a trade. At least I think I did a good job on the rear since it doesn't seem to be leaking or vibrating.
Dumb question, but if you didn't change the grease (which was contaminated by the diff fluid), how do you know you've got a leak and it's not the fluid from the first bad seal? And question 2, did you drain and refill the diff each time you did this? I could imagine a bunch of diff fluid gettting by the seal as you slide the axle in. Just thinking through what could have gone wrong.
It's a very good question, actually. I thought about changing the grease but it felt and looked fine. Think I wiped off the parts when they came out, but I'm not positive. Didn't change the diff fluid until I put the second seal in. Was gonna clean it up and drive it for a bit to see what happens. If it continues to leak, I'll just do it again and do it right since the job is now easy to do.
:confused: Confused. The way these things usually leak is the diff fluid gets by the axle seal into the birf grease and turns the grease into a soup that leaks by the felt seals (and anywhere else it can find). How was yours leaking that it left the grease looking ok?
What's the leak look like? Thick gooey grease soup, diff fluid, brake fluid? (Wouldn't it be a killer if it was a something else like brakes or power steering leaking? Ha.)
Take a picture of the leaking axle, and post it up. If you just replaced the diff fluid then it shouldn't be dark at all. Diff fluid is very light when you fill it up with new, and it would take some time to darken up. Sounds to me like something else is going on, maybe a leaking drum brake cylinder. Check the level of your brake fluid reservoir and rule everything else out before dissembling your knuckles again.
I just bought the Marlin Seals. BIG improvement !!! Money well spent, and not a lot of it.
Brake fluid is still at the same level. I checked the color of the oil with a paper towel and it is just about the same color as new gear oil, just slightly darker probably due to dirt. The seal was packed with grease to retain the spring. I will drive it and see if it still leaks. Here are the pics- best I could do:

Users who are viewing this thread

Top Bottom