Jethro-Bilt 14-Bolt Diff Cover Review

By Bill "BillaVista" Ansell
Photography: Bill Ansell
Copyright 2005 - Bill Ansell
(click any pic to enlarge)


Having just invested a substantial amount of cash on new gears and a locker for my trusty 14-Bolt rear axle, it was only natural to want to protect that investment. What I wanted was simply a smash-proof, bomb-proof, diff cover that would protect my axle's guts, stand up to my "driving by brail" technique in the rocks, and fit right the first time. The solution I found was with this handsome unit built by relative newcomer Jethro-Bilt. There are many more heavy duty diff covers available on the market today than there were even just a few years ago, but I chose this one because of several attractive features:

First was its impressively stout construction - built entirely from 3/8" steel plate!
Second was the quality construction that I had noticed in some pictures Joe had posted of his original prototype units.
I am by no means a welding inspector, but the first pictures I saw indicated that the unit was well designed, welded properly, and just generally very well built.

I was also impressed by the available flush-mount bolts. I tend to beat the living daylights out of my axles/diffs/diff covers in the rocks and have had problems in the past with regular hex-head bolts and socket head cap screws (Allen bolts).

The idea of countersinking the heads of the mounting bolts seemed to me to be a great one for protecting the bolt heads so you can get them back out when you need to - no more undoing-the-lowest-cover-bolt-1/64th-at-a-time-with-a-bent-wrench-because-9/10ths-of-the-bolt-head-has-been-ground-away-on-the-rocks for me!

The cover comes complete with all the necessary flush-mount bolts - including two spares - which is a nice touch.

But the feature that sealed it for me was Joe's inclusion of both drain and fill plugs in the cover. Normally you have to completely remove the 14-Bolt cover in order to drain the gear oil. This is fine if you're doing major maintenance anyway, but can be a real PITA sometimes, especially if you're using a good quality RTV compound to seal the cover.

What this inevitable leads to, certainly in my lazy case, is less frequent changes of gear oil than might otherwise be prudent. I wheel in a huge variety of terrain - including plenty of mud and swampy water (I know, I know - I don't really like it myself but my son loves it!). In the past, if I couldn't be bothered to completely pull the cover, the gear oil didn't get changed - and the bearings probably suffered.

Now, with a convenient drain plug, after a wet or muddy run, I can do a quick drain, flush and re-fill and the guts of my axle will be much happier. Long-term maintenance will still require a cover-pull and complete cleaning and inspection - and the drain plug doesn't replace that; but in the meantime - it's nice to have the option to do a quick, convenient oil change.


Installation was a breeze - all the holes were perfectly round and perfectly matched the housing. Whether you're just replacing your cover or doing a complete overhaul like I was, you'll want to install the new cover with a good high-quality RTV compound.

My favourites are the factory GM stuff and Permatex's "The Right Stuff". Not only are they much stronger than the cheap auto-parts store stuff, but no curing is required before placing parts back in service - which means you can slap the cover on, fill it with 90wt right away, and hit the trails - no waiting!

Tech tidbit: by the way - in case you ever wondered - RTV stands for "room temperature vulcanizing". Vulcanizing is, of course, the process by which crude rubber is treated to make it more durable and suitable for different uses - a process normally conducted at very high temperatures. So RTV is a rubber-like compound that works at room temperature.


Cover bolts should be tightened to 35 ft/lbs.

The finished product both looks and feels very beefy - just the ticket for my 14-Bolt and the ideal protection for a locker and new gears.

After installing the cover, all you need to do is add the gear oil. Due to the angle of my pinion, I did find that adding the gear oil through the factory port in the side of the pinion housing allowed me to add just over one litre more gear oil than using the fill port in the Jethro-Bilt cover. Individual results will vary depending on pinion angle. For those with a need, Joe can supply covers with the fill ports raised, or even deleted entirely if that's what the customer wants.
One nice bonus to a heavy-duty diff cover is the fact that it stiffens and strengthens your entire axle assembly. Normally, a thin factory cover is unlikely to offer any decent rigidity. In addition, being that the cover covers the gears, where all the force is applied, if the axle housing were to tweak or creep under load, it would likely be in this area. Now, with a 3/8" thick fabricated steel cover attached with 14 bolts torqued to 35ft/lbs, there's no question my housing is stiffer than it was before.


Stout, good-looking, well built, nice features, and built by a fellow enthusiast and wheeler - what's not to like?

I'm very pleased with my new diff cover - and my gears and locker probably are too!


Jethro-Bilt Differential Covers
Paradise, CA
Joe Rollins
(530) 575-1443



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