The size or series is where everything starts in the repair, fabrication of new, or design of a driveline. A caliper is, of course, the best and most accurate of all methods. But face it, most of us don't have one because of the cost and the amount of times we'd actually use it, not to mention, we might not even know how to use it. So here is my attempt to simplify the whole ordeal.

I have seen more gadgets, measuring sticks, and devices made by every manufacturer trying to sell a driveline or a driveline componant, that it almost makes me more confused than I was in the beginning. All they are trying to do is make a nice simple way to identify a u-joint size.

American cars and light duty trucks deal with the most common series, or size, of U-joint. I have no clue how it got started, probably because they needed some industry standard. So here are a bunch of numbers to confuse you and later we’ll simplify it for you.

Dimensions = cap size X lockup dimensions. The lockup dimension is the measurement where the clip seats. They are either inside clip or outside clip.

Lockups are simple. Does it have a clip on the outside of the cap that holds it in? The clip and the cap looks like this on an outside clip. So on your yoke there’s a grove for this snap ring, or clip.The cap has a smooth machined surface all the way to the seal.

Inside clips, or inside lockups, have a groove for the snap ring to seat in machined into the cap itself and the yoke has no groove, just a flat machined surface for the clip to lay against, keeping it centered. They look like this:

N3R, 7260, and 7290 are the 3 major inside clip U joints.

For the most part N3R, or S44, is Chevy. 7260 and 7290 are Dodge. Notice a N3R and 7290 are only .066 difference in their lockup. So instead of trying to measure these, just look at your truck and ask yourself, Dodge or Chevy? Simple.

7260 is the smaller of the Dodge U joints. Even with a tape measure, we can measure the difference between 2.125 or 2 1/8, and 2.622 or 2 5/8. So is it a big Dodge U-joint or a little Dodge U-joint? Measure the lockup.

MEASURING CAP & LOCKUP 1310 & 1330 SERIES

The hard part always seems to be the cap size. Those fancy sticks that everyone makes always confuse me, so I started looking for a nice common object that most people have in their basic tool chest. I discovered that a 3/4 inch, 1/2 inch drive socket fits into the hole on a yoke that holds the cap of a 1.063 cap. A 13/16 socket does not. So, if your 3/4 inch, 1/2 inch drive socket fits into the hole above the clip of your outside clip driveline and a 13/16 doesn’t, it’s 1.063.

Take your tape measure and eyeball the lockup. If it measures a little less than 3 1/4 it’s 1310. If it measures a little more than 3 1/2 inches it’s 1330.

MEASURING CAP & LOCKUP 1350 & 1410 SERIES

Great, but what about 1350? For the cap, take a 7/8-inch, 1/2 inch drive socket and see if it fits. Eyeball the lockup with a tape. 3 1/2 +? 1350.

For the cap on a 1410, use a 7/8” 1/2” drive socket and a tape measure on the lockup. The lockup should measure just short of 4 1/4".

So the caps are the same, only the lockups differ.

MEASURING CAP & LOCKUP N3R & 7960 SERIES

The caps on the N3R and 7960 are about the size of a 13/16 inch 1/2 inch drive socket. inside clip, of course.

For the lockup, as stated earlier, for the most part N3R, or S44, is Chevy. 7260 and 7290 are Dodge. Notice a N3R and 7290 are only .066 difference in their lockup. So instead of trying to measure these, just look at your truck and ask yourself, Dodge or Chevy? Simple.

MEASURING CAP & LOCKUP 1480 SERIES

The cap on a 1480 is an easy measure with a tape at 1.375 or 1 3/8" and looks just plain huge compared to all these others. Use a tape on the lockup as well.

The light duty truck people have just recently started using these 1480's.

AL'S SIMPLIFIED

SOCKET/CAP DIMENSIONS BREAKDOWN

I have gone to various auto part stores, and it seems that even if it is an inexpensive foreign set with thin walls on the socket, it will still get you in the ballpark. So here’s my Dimensions Breakdown:

Now if this is too Neanderthal for you, then buy a silly caliper and ride on. This is the easiest I’ve seen. Don’t knock it till you’ve tried it. Driveline shops speak a different language than normal people, and it helps when you call them to speak it also. Once that barrier is overcome, everything gets easier.

MEASURING DRIVELINE LENGTH

As far as measuring the driveline length itself, the industry standard is the center of the cap of the U joint on the end yoke of the differential (arrow 3), to the center of the cap of the U joint on the transmission or transfer case (arrow 1). If you have 2 end yokes on your rig, try to point them both up before measuring (like the diagram). Measure from the top center of one to top center of the other one.

In the case of a transmission slip yoke, measure from the center of the differential (arrow 2) to the seal of the transmission (arrow 1) and then the length of the stub that generally sticks out, usually 3/4”.

TWO PIECE DRIVELINES

2 piece drivelines are composed of a driveline with a carrier bearing on it, which is then joined to another driveline with a slip yoke on it. These are used when the length of the driveline becomes too great to span the distance (see Maximum Length Diagram above). There is a limit to how long you can make a driveline, thus the 2 to 3 piece driveline (AKA center, or carrier bearing style).

These are measured from end yoke (1) or seal of the transmission/transfer case to the center of the holes for the bolts of the carrier bearing on the vehicle (which is the same as the center of the carrier bearing, see 2). This would result in measurement A. Then the other half of the driveline is measured from the center of the holes for the bolts of the carrier bearing on the vehicle (which is the same as the center of the carrier bearing, see 2), to the center of the cap on the differential (3). This results in measurement B. These are best measured on the rig.

Most people don’t deal with drivelines that often. It’s ok if you get confused. It’s the guys job on the phone to help walk you thru it and try to steer you in the right direction. 1-800-856-7802 Ask for Al