• More traction
• If one rear tire goes flat, comes off entirely, or leaves the ground.. The other rear tire will still receive power from the motor.
• It lets you really whip the rear of the car around.. Good for showmanship and to get out of someone's way!

Here's all you need to know if you want to "lock" your rear end. You will need

• A welder; use only with appropriate knowledge, safety gear and attire.
• Jack
• Jack Stands
• 8 Med Sized Bolts
• Basic Hand Tools
• Optional; Impact Wrench (it'll really help!)

Important Notices:

• Follow these instructions at your own risk. We take no responsibility for injury or damage.
• Check your rules before locking your rear. It cannot be undone.
• Use all necessary safety precautions when working under a lifted car. Portions of this process require you to be under the rear axle, which could easily crush you if the vehicle were to fall.
• Use all necessary safety precautions when working with a welder, read and follow the welders instructions.
• Weld in a well ventilated area. There will be fumes!
• This web page is here only as a guide, not all rear ends are the same. The rear depicted in the following pictures is under a 1976 Cordoba.
• Not all rear ends are capable of being locked, the only way to tell is pop it open and find out.
• If you're racing on asphalt, you might want to think twice about locking your rear. Surf to the bottom and read "Now your rear is locked" to see why.

Preliminary work:

• Chock front wheels.
• Place car in Neutral.
• Jack rear of car up. The higher the better -- but KEEP IT SAFE!
• Place jack stands under frame, in front of rear axle.
• Let the car down on the jack stands. This allows the rear to "hang" down from the car, and gives better access for work.

For better detail, click on the pictures for larger versions.

 

	Here's the rear end of our car. This is the rear cover, or access panel. If your rear end does not have a rear cover (some Fords and Chryslers) surf down to the bottom of this page for more info.
	Remove all the bolts.
	You might have to move the rear brake line out of your way. Use caution when moving the line so you don't break it.
	Use a screw driver to pry off the cover. Use care and you'll be able to re-use the gasket.
	Make sure you use something big enough to catch the oil. It's not necessarily a lot of oil, its just that it comes out the entire width of the differential. Also, if you use a clean catch pan, you can re-use the old oil.
	Reach in there and remove the remaining oil. The more you get out, the less chance you'll have a fire... and the more clean oil you'll be able to put back in.
	Ok.. Here's what a differential looks like. The big gear on the left is called the "ring". The four gears in the box formation are the spider gears. The box that holds the 4 spider gears is called the "carrier". Finally, there is a gear all the way in the back that receives the power from the drive shaft, it's name is the "pinion". Power comes in from the pinion (connected to the drive shaft) and is transmitted to the ring (during this transmission, the power makes a 90 degree turn, and is also geared). The ring transmits the power to the carrier, which in turn transmit the power to the top and bottom spider gears (they are pinned to the carrier). The top and bottom spiders transmit the power to the left and right spiders, which are attached to the left and right axles. The axles run out to the wheels and tires. Our job here is to lock the 4 spider gears together. When you hear someone talking about a "spool", they are referring to a solid machined piece of steel that replaces the carrier and spider gears. This is the "rich man's" way of locking a rear. If you open up your rear and don't see any spider gears, just a big metal thing on the right of the ring gear -- then your can't lock your rear. You have a solid carrier with the spiders inside. There is no way to get in there and lock'm together.
	Select a bolt from your personal can-o-bolts. Pick a bolt that is about as long as the spider gears are thick. Another way of looking at it is to pick a bolt that is as long as the area 2 spider gears mesh together. If you're still not sure what I mean, read on and you'll probably get the picture. Dark colored bolts work much better then silver looking ones. Place the bolt in between the left and bottom spider gears, thus "jamming" the gears from meshing.
	Use a straight screw driver and a hammer to really JAM that bolt in between those gears!
	Now, weld the bolt to the two spider gears. MAKE SURE THAT BOLT ISN'T GOING ANYWHERE! When I'm done welding, you cannot tell that was originally a bolt.. It's a big gob of molten metal.
	Once your done, let it cool a little.
	See how the bolt's melted in between the teeth of the spider gears.
	Jam another bolt in between the bottom and right spider gears.
	And weld it in!
	Jam another bolt in between the left and top gears. At this point, you're probably going to need to use a pair of pliers to get the bolt in the differential because of the heat. You also might need to vary the thickness of the bolts to get them to fit in between the gears. You want the bolts to be SNUG. To big, and they won't fit in between the teeth, to small, and they won't say put long enough for you to weld them there.
	Welding done there..
	Finally, jam a bolt in between the top and right gears.
	Here's a good look at what the jammed bolt (prior to welding) looks like. I prefer to have the head of the bolt sticking UP.. That way I can melt the head INTO the gear mesh. But... you can't always get that to work, as in this instance.
	That weld is done.
	Flip the rear over (this is why you put the car in neutral)
	And do it all again on the other side.
	Weld the bottom left....
	bottom right.....
	top left....
	and top right.
	I also like to weld the centers of the spiders to the carrier. It's kind of an insurance policy. Here's the aftermath of my welding the bottom spider to the carrier.
	Aftermath of me welding the right spider to the carrier. The bottom spider is the easiest to weld, the right is not much harder.. The top is a pain because you're working against gravity, and the left is usually tucked inside the ring gear and is REAL hard to get to. If you choose to weld the spiders to the carrier, don't forget to do both sides.
	Walk away and let it cool down for at least a half of an hour! Even after a half an hour, the rear might still be too hot to stick your hand into.
	DO NOT PROCEED UNTIL THE REAR HAS COOLED ENOUGH SO THAT YOU CAN TOUCH THE INSIDE OF IT! Once it's cooled enough, use your screw driver to scrape away any loose crap from your welds. Someone told me that they suggested to use a 2 inch wire brush on a drill and clean all the slag off of the welds. It's up to you.
	Stick your hand in there and scrape out all the junk as best you can.
	You can use your screw driver to scrape off some of the more stubborn globs from the bottom of the rear. If the globs feel permanent, then leave them alone. Someone told me that they also use a garden hose, followed by the air compressor to clean out the slag in the bottom. Again, it's up to you.
	Time to put the oil back in. Search around the front of the rear for a plug. Generally, this plug is half way up or higher, and requires a 3/8" or 1/2" ratchet extension to be inserted into it for removal. On this particular vehicle, we needed a 1/2" drive extension. Remove the plug. ** Using an impact wrench for this procedure makes life much easier! If the plug is frozen or stripped (in my experience 1 out of 10 are), start looking for the rear's "vent". Usually this is a little plastic nipple about 1/4" in diameter, and about an inch high. Once you find it, take a pair of pliers and gently attempt to remove the vent. If you cannot find or remove the vent you'll have to make your own fill hole. Drill a hole in the differential cover ** in such a location so that when you screw a sheet metal screw in to plug the hole, it will not interfere with the internals of the differential. It would also be a good idea to drill the hole at the same level as the stock fill plug. This way you'll be able to get the oil level close to where it's supposed to be. Make the hole big enough to allow you use whatever method you've chosen to fill the rear. Once the rear is full, screw a sheet metal screw in the hole to plug it up.
	Here's the removed plug on my extension, on my impact wrench.
	A better look at what the stock plug looks like. Don't forget to put this back in when you're done!
	Reposition the cover, taking care to install the gasket as best you can. Hand tighten the bolts.
	If you use air tools to snug the bolts, I suggest using a hand ratchet to do the final tightening, I like to feel each one by hand. I also suggest tightening in a cris-cross pattern for an even seal.
	This is what I use to replace my oil, it's the container NEW gear oil comes in. You can probably make due with a turkey baster or something. Once you get all the oil back in, plug the fill hole.. and you're done... except...
	for cleanup!

Rears w/o rear access panels:

Not all rears have rear access panels (see pict 1). Some Fords and Chryslers have a removable differential, referred to as a boar's head (when you see one out, you'll see where it get's it's name from). If you've got one of these rears, I've got good news and bad news. Good News: 1) Most people agree that rears like these are some of the strongest rears made, and 2) This type of rear is a lot easier to weld. Why? Well that's because of the bad news.. the differential has to come OUT from under the car to be worked on, and that's a pain.

In order to remove one of these differentials, you've got some work ahead of you. First you have to drop the drive shaft. Then remove both rear wheels, and both rear drums. Behind the plate that holds your rear studs you'll see some bolts (usually 4, see pict 2). These bolts secure the a plate that holds the rear bearings to the rear end. There should be a hole in the stud plate (see pict 2) for you to get your socket in and remove the nuts on the bearing plate. Once you have the bearing plate unbolted, take the drum and mount in on "backwards" (so that the inside of the drum is facing you). Put the lug nuts on, but only 1/4 of the way. Push the backwards drum into the axle, and with a snap, yank it towards you, hitting the lug nuts. This should pop the axle out of the differential. Take the drum off, and pull the axle out about 3-4 inches (no need to remove it all the way). Repeat this process on the other side.

Place a rolling floor jack under the center of the differential. Jack it up so that it's JUST touching the differential. Climb under the car and remove all the bolts (see pict 1) around the differential (these bolts face forward). BE CAREFUL HERE! The differential is VERY HEAVY. I've only done this once, and the differential had to be pried away from the rear end. HOWEVER, I imagine that it's very possible for the differential to fall off under its own weight. Once all the bolts are off, you're either going to have to pry the differential off the rear, or it will fall out on its own. Guide the differential out onto your jack. Once it's off and away from the studs, lower the jack and pull the differential out from under the car. If you have problems getting the rear out, you might not have pulled your axles out enough.

Now that the rear's out, the welding goes as described above. Replacing the differential back into the rear goes exactly opposite as it's removal. You might want some help getting the differential up and in (they are heavy). Reinstalling the axles might take some finagling, but they should pop right back in.

 

Now your rear is locked:

• Make *SURE* both rear tires are the *EXACT* same size. Do not use one American sized tire and one metric sized tire that someone told you are the same size... their NOT. Tires of different sizes will place a tremendous strain on the entire rear end assembly and could easily break something.
• Try not to turn your car on asphalt too much. Turning on solid ground also puts the entire rear end under high strain. This is why you'll want to think twice about locking the rear in a car that will race on asphalt. If something snaps, you'll be VERY lucky if your rear returns to one wheel drive. Most likely, the rear will turn into no wheel drive!
• When turning the car, you will hear a barking sound from the rear tires. This is normal. When making a turn, the outside rear tire has to spin faster (it's got further to go). That's why your car had a differential in the first place. Now that you've locked the rear, that tire cannot spin any faster then the inside tire. Something has to give, so the tire barks.
• Be aware. Now that the rear end is locked, the rear of the car will easily slide when you're on the throttle and turning.