I'm a long-time lurker on JeepForum and have benefited greatly from reading about others' experiences, but I finally have a question of my own I can't figure out from the archives. I know you folks mostly run heavy-duty rear ends, but hopefully there's somebody familiar with the Dana 35 who can help me out.
I've got a '98 ZJ 4.0 with 134k. The short story is that a pinion bearing went out on the original diff. I didn't feel up to rebuilding it in the vehicle, so I got another 3.73 D35 rear end from a junkyard (unknown history, but it looked clean inside) and installed it last weekend. Now I'm questioning whether it is good or not.
I can feel and see some play in the pinion (input) shaft. With the drive-shaft removed, it's rock solid laterally, but if I push it in or pull it out, it'll move about 1/8" inch axially while simultaneously twisting a few degrees, like it's being "screwed" in and out. The yoke is solid against the shaft - there's no relative motion between them (i.e. the nut is tight), but the entire shaft can move helically.
I'm also hearing a distinct gear noise from the rear end - it's apparent at speeds above about 40 mph and gets fairly prominent at highway speeds. It only happens under load (on the gas, not when coasting or on the brake). It's been a while since my old diff was good (I drove it for months as the bearings disintegrated), so I don't remember how it is "supposed to" sound anymore, but this is definitely extraordinarily loud. I'm fairly sure it's gear noise rather than a bearing or something else.
How concerned should I be about this? Is it in danger of immediately failing, or is this an indicator of a problem that probably won't cause it to fail in 20-50kmiles? Is it likely to fail gradually or should I expect sudden catastropic (i.e. undrivable) failure. My primary use is on-road (with stock tires!) with occasional very light off-roading, with maybe 1000 miles/year of pulling 3000-5000 lb boat trailers.
I'm not entirely sure what's going on, either. Is this just an indication of excess lash between the ring gear and pinion? Would that be caused by improper side-to-side shimming of the carrier or only improper shimming behind the inner pinion bearing? loose u-bolts holding down the carrier? inadequately torqued yoke bolt allowing play between the two pinion bearings? overtighted yoke bolt (at some time in the past) causing overcollapse of the crush spacer and allowing play?
My options at this point are:
- Go back to the junkyard and try to get them to honor their 90-day warranty. They only offer credit, so I'm guessing they'll insist on something ridiculous like me bringing back the axle they sold me before they'll give me another. They don't have a very good reputation locally, and I don't think they have very many Jeeps, so that might end up being a hassle.
- Replace the outer pinion bearing, collapsible spacer, and pinion seal on the axle in the truck. I've already got all the parts and can borrow the 4-foot 3/4" drive torque wrench for setting the pinion preload. Is that likely to fix it or just a waste of time?
- Leave the new axle in, do nothing, and hope it lasts a while, while also attempting to rebuild my original axle so I have a spare available if/when it goes. I'm pretty its inner pinion bearing is shredded, as the oil had some fine metal powder in it. Everything else looks okay though - no apparent damage to the gears (haven't disassembled it yet to look at the shafts). I need to find a case spreader - I think I have the other tools I need available. I don't mind doing another swap, but I'd rather not do it right away if avoidable.