TL;DR: Seal your Dana 35 correctly: Clean mating surfaces, inspect C-clips, use RTV, and torque bolts to 30-35 ft-lbs. For better cooling and easier maintenance, upgrade the stock steel cover to a SPELAB aluminum unit with a magnetic drain plug and sight glass.
In my years of engineering automotive components, I’ve found that the rear differential is often the most neglected part of the drivetrain—until it fails. When changing your gear oil, properly sealing the differential cover isn't just about keeping the driveway clean; it's critical to ensure proper hydrostatic pressure and lubrication for your ring and pinion gears.
Used gear oil contains heavy metals and toxic additives. Always wear nitrile gloves and safety glasses. Dispose of old oil at a certified recycling center. Crucial: Never work under a vehicle supported only by a jack—always use jack stands rated for your Jeep's weight.
This guide is based on a real-life demonstration using a Jeep Cherokee XJ, featuring the ubiquitous Dana 35 rear axle with a 10-bolt cover. While we are using an XJ, the mechanical principles here apply to any Jeep running a Dana 35.
Diagnosis: What is Your Differential Trying to Tell You?
Before we drain the oil, stop and listen to your axle. As an engineer, I diagnose failure through sound and fluid condition. A Dana 35 is notorious for specific noises that indicate wear:
- Whining while accelerating: Usually indicates worn ring and pinion gears or improper backlash.
- Rumbling or growling at any speed: Often points to worn carrier bearings.
- Clunking when shifting from Drive to Reverse: Excessive play in the spider gears or U-joints.
Pro Tip: When you drain the old oil, don't just throw it away. Inspect it. Milky oil means water intrusion (check your breather hose). Glittery/Metallic oil means bearing or gear failure is imminent.
Dana 35 Differential Cover Fitment
The SPELAB Dana 35 10 Bolts Rear Axle Differential Cover is engineered for the following chassis:
- 1984–1997 Jeep Wagoneer
- 1984–2001 Jeep Cherokee (XJ)
- 1993–2004 Jeep Grand Cherokee (ZJ/WJ)
- 1986–1992 Jeep Comanche (MJ)
- 1987–Present Jeep Wrangler (YJ/TJ)
- 2001–2007 Jeep Liberty (KJ)
How to Seal a Differential Cover and Change Gear Oil (The Engineer's Way)
The factory process is messy, but if you follow these steps precisely, you’ll ensure a leak-free seal. Precision is key here.
1. Removing the Differential Cover Bolts & Prep Work
1.1 Preparation & Tools
Make sure your vehicle is safely chocked on level ground. You will need:
- Socket Set: Typically a 1/2 inch or 13mm socket.
- Oil Catch Pan: At least 4-quart capacity.
- Scraper/Razor Blade: To remove old RTV.
- Brake Cleaner: To degrease the mating surface.
- Fresh Gear Oil: Usually 75W-90 or 80W-90 (Check your specific manual).
1.2 Controlled Drain
Loosen all bolts securing the differential cover. Crucial Tip: Remove the bottom bolts but leave the top bolt loosely threaded in. Pry the cover open slightly at the bottom. The top bolt acts as a hinge, preventing the heavy steel cover from splashing into your drain pan.
1.3 Cleaning the Mating Surface
Use a scraper or nylon bristle brush to remove every trace of old gasket material. Wipe down the housing and cover surface with brake cleaner. The surface must be bone dry and oil-free for the sealant to bond.
1.3.5 The "C-Clip" Check (Exclusive to Dana 35)
Since you have the cover open, take 30 seconds to inspect the C-Clips located in the center of the differential carrier. These small clips are the only thing holding your axles in the housing on a Dana 35.
What to look for: Check for any cracks or excessive play. If you see metal shavings at the bottom of the housing that look like fingernail clippings, your C-Clips may be failing. Catching this now prevents a wheel from separating on the highway.
1.4 Choosing the Right Sealant
I recommend a high-quality RTV Silicone meant for gear oil resistance (often labeled "Gear Oil Safe" or Grey/Black RTV). These are formulated to resist the friction modifiers found in modern gear oils.
2. How to Apply the Sealant
The Loop: Draw a continuous bead (approx. 1/8" to 1/4" thick) around the entire perimeter. Important: Ensure the bead runs on the inside of the bolt holes. If you go outside, oil can seep through the bolt threads.
3. Reinstallation & Refilling (Technical Specs)
3.1 Installation and Torque Sequence
Carefully place the cover back onto the housing. Hand-thread the bolts to hold it in place.
Torque Specification: Tighten bolts to 30 to 35 ft-lbs. Do not overtighten, or you will warp the flange.
The Star Pattern: To ensure the gasket compresses evenly, follow this tightening sequence. Do not tighten in a circle.
3.2 Refilling Gear Oil
Remove the fill plug. Fill with approximately 1.75 Quarts (3.5 Pints) of 75W-90 oil until it weeps out of the fill hole. If you have a Limited Slip Differential (LSD), ensure your oil contains friction modifiers.
Why I Recommend Upgrading the Stock Cover
Stock vs. SPELAB: The Engineering Data
Why upgrade? It comes down to thermal management and structural rigidity. Here is the data:
| Feature | OEM Stamped Steel Cover | SPELAB Cast Aluminum Cover |
|---|---|---|
| Material Rigidity | Low (Flexes under load, causing leaks) | High (Reinforces the axle housing) |
| Heat Dissipation | Poor (Steel retains heat) | Excellent (Aluminum fins dissipate heat 2x faster) |
| Maintenance | Must remove cover to drain (1 hr+) | Magnetic Drain Plug (10 mins) |
| Inspection | Impossible without disassembly | Sight Glass (Instant visual check) |
With the SPELAB aftermarket Dana 35 differential cover, you solve the maintenance headache and strengthen your axle in one go.
$199.98
Buy NowConclusion
Maintaining your axle shouldn't be a headache. Whether you stick with the stock stamped steel or upgrade to the SPELAB cover for better thermal management, doing it right means no leaks and a longer lifespan for your Jeep.
FAQ
Q1: How do I identify if my Jeep has a Dana 35 rear axle?
A1: The Dana 35 is easily identifiable by its cover. It has an oval shape with 10 bolt holes and measures approximately 9 inches wide by 7.5 inches tall. Unlike the Dana 44 (which is shaped like a stop sign) or the Chrysler 8.25 (which has a flat bottom lip), the Dana 35 is perfectly rounded.
Q2: Is sealant necessary, or can I use a gasket?
A2: A high-quality RTV sealant is superior to paper gaskets on stamped steel covers because it fills surface irregularities. However, SPELAB’s machined covers work excellently with reusable gaskets like LubeLockers, which allow for quicker changes in the future.
Q3: What causes the differential to leak after changing the oil?
A3: The most common cause is dirty mating surfaces—even a small amount of old oil or gasket material can break the seal. Another common issue is overtightening the bolts, which warps the flange. Always torque to 30-35 ft-lbs only.
Q4: How long does the sealant need to cure?
A4: Patience is key. Let the RTV "skin over" for about 15 minutes before bolting the cover on. Once installed, wait at least 1 hour (preferably 24 hours for full cure) before filling it with gear oil to ensure a permanent seal.
Q5: Can the SPELAB Dana 35 differential cover be reused?
A5: Absolutely. Unlike the factory stamped steel cover, which can bend during removal, the SPELAB cast aluminum cover is rigid and durable. It is designed to be a permanent upgrade for the life of your Jeep.
Q6: What is the fluid capacity of a Dana 35 rear differential?
A6: A stock Dana 35 typically holds about 1.75 quarts (3.5 pints). However, because SPELAB covers are designed with cooling fins and a slightly different internal profile, you should always fill until the fluid begins to weep out of the fill hole.
Q7: Do I need to add a friction modifier to my gear oil?
A7: This depends on your differential carrier. If you have a factory Limited Slip Differential (LSD), often called "Trac-Lok," you must add a friction modifier (or use oil with it pre-mixed) to prevent the clutches from chattering. Open differentials do not require it.
Q8: How often should I change my differential gear oil?
A8: For normal highway driving, every 30,000 to 50,000 miles is standard. However, if you tow heavy loads, drive off-road frequently, or submerge your axle in water, you should inspect and change the fluid every 15,000 miles to prevent premature wear.
John Lee
Mechanical Engineer | 10+ Years Experience
John has spent the last decade engineering and testing high-performance automotive components. Specializing in drivetrain durability and thermal management across Powerstroke, Cummins, and Duramax applications, he bridges the gap between OEM limitations and aftermarket performance. His philosophy: "Factory parts are just a starting point."
