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Differential Laser Alignment Tool

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Alignment Tool

Here’s info on how to make a Differential Laser Alignment Tool. This tool allows the user to verify that the differential and transmission are in phase. I have used this on my 81 280ZX(LT1/4l60E with R230) and have had no driveline vibrations.


I am posting this info because there have been questions regarding how to align your diff with your tranny. This is a good alternative to the other options.


Special Note

This is Pop N Wood’s idea. He thought of the idea of using lasers and everything. All credit should go to him.


This is NOT my write-up for building the alignment tool. I can’t find the originator and his website is long gone. I merely had a saved copy of his write-up on my computer. Additionally, the Hybrid Z thread discussing this stuff was deleted years ago due to the server changes.



Parts Required

2) 1/4" x 1" tapered head machine screws and nuts (I used 1.25" long screws and shortened them because that's just what was on hand)


2) 9/16" 'ACE' hardware branded sockets, 3/8" drive, 12 point (only use 12 point. other brands may work, but the tolerances may also be different enough that the fit will not be secure or too tight) $2.50 each


2) Model #MP600, Apollo brand laser pointers from office depot. $10 each


1) length of 9/16" brass tube from ACE $2.50


1) length of 19/32" brass tube from ACE $2.50


1) 3.2" diameter lifting magnet [The Magnet Source, model 07223] from ACE (particular magnet for your transmission application may differ. This particular model has a 1.20" diameter hole in the middle of the magnet, which allows the output shaft to fit inside enough for the flat end to seat against the metal shell of the magnet. other applications may need a smaller center hole so the magnet face seats on the output shaft, or a larger hole for a larger shaft. Alternatively, as long as the transmission you will be using does not have some change of output angle built into as some do, you can select a magnet that will fit firmly on the back of your engine's crank.) $7


1) 2 5/8" diameter lifting magnet [The Magnet Source, model 07222] from ACE $5.50


Below is a picture of all the parts required





Attaching 9/16†Socket to the 2 5/8†Magnet

Place one of the sockets on the top of the 2 5/8" magnet shell with the ratchet attachment side down. pass one of the machine screws down through the socket and into the small hole in the magnet shell. Thread one of the nuts down on the other side of the magnet and tighten. The tapered head of the screw should automatically center the socket on the magnet. Example pics show a 1.25" machine screw that has been ground down on the threaded end. A 1" machine screw should not require this, but be sure to check that the magnet seats firmly and that the screw is not high-centering the device against the input flange's nut. If the screws are ground down to perfect length, be sure to tread down one of the nuts past where it will be cut/ground so it can be backed off to realign the threads when done.





Assemble Tools

Read entire step before proceeding


Step 1 Cut a 1.25" length of each end of each of the pieces of brass tubing. You will want the nice flat manufacturer's end of the tubes to be unmolested so they can seat firmly and evenly down in the socket. These two pieces will nest inside each other nicely, but given the short length of the tube that will actually be used, you may find a slight amount of play. In the z car, the short driveshaft length makes angular accuracy critical, so I felt I needed to address this nearly imperceptible tolerance. Your particular tubes may fit more snuggly than mine depending on manufacturer and such. If needed, some silicone gasket sealer or epoxy could be worked inside the 19/32" tube, left to sit for about 5 minutes and then insert the 9/16" tube. If you are going to do this operation, do so before making the 1.25" cuts. With the full length of the tubes nested together, there will be almost 0 angular movement, and this is the best environment in which to allow the gasket sealer or epoxy to set up. I used 'plastic welder' epoxy that has a set time of about 15 minutes and remains slightly pliable after setup so it wouldn’t fracture while I am cutting the tubing. I only applied it inside the last two inches of each end of the 19/32" and then fed the smaller tube inside. most of the epoxy will be pushed out, but that should be okay since only a fine film is necessary to close the gap.


While the epoxy or silicone is setting, move on to the transmission side.


Step 2 For the transmission end, my ford t-5 has a centered machined depression in its output shaft that could be used for centering the magnet with its protruding screw, except that the shaft sits in the inner diameter of the magnet, so the inside part of the metal shell needs to remain flat. What I decided to do here is screw the socket in the same manner as the differential unit and then place four tack welds around the base of the socket, then removed the screw and nut. You could alternatively use epoxy (jb weld) in substitution, just make sure the screw stays unglued so you can later free it once the epoxy has set...and take care to evenly sand the metal magnet 'skin' to give the epoxy something to set into while making sure the 'skin' surface stays flat and true. take care that the metal shell of the magnet does not warp from welding heat. use the lowest temp necessary. I placed my ground clamp on the socket, to keep the current path as far from the magnet itself, just incase that might have caused a problem. be careful to make sure the glue holding the under side magnet is not preventing the output shaft from seating evenly. It could probably be ground down with a dremel if it is.


Hopefully the brass tubes are ready to be cut by now.


Step 3 As stated before, cut 1.25" of each end of the tubes. be sure to use very fine blades. I'd suggest doing it by hand to be safe to make sure they don't deform. clean up the cut ends of the short pieces so they aren't jagged. The lasers have rubber buttons, and could be snagged and torn if the tubes aren't smooth. use some fine sandpaper for this. Be sure there are no burrs or excess globs of glue or silicone inside the tubes because they will be very difficult to extract later.


Step 4 Carefully fit the pieces of each nested tube assembly into each socket. Some pressure may be needed because it is a very snug fit. be sure to apply pressure perpendicular to the face of the magnet. using a vice or press may be a good idea too.


Step 5 Insert each laser into each magnet/brass tube/socket assembly. Sanding the paint off the laser may be necessary to fit it in the tube. Sand up and down the length of the laser to make it easier to slide in. To turn on the laser, simply push it down in the tube far enough to push the red button in [Addition: When you push the button into the tube, this will cause the laser to not be perfectly centered….Meaning if you rotate the magnet, the laser beam will follow a circular path instead of being perfectly stationary]. To turn it off, pull it out of the tube slightly. Optionally, you could pull the button off, drill a hole through the side of the tube and insert a rubber plug or something through the hole into the laser switch area and use a hose clamp to put pressure on the rubber plug.




Using the Tool

Now, make sure the laser assembly is accurate. place each one on the nose of a differential and turn it by hand, taking note of the path the dot takes against a wall or other flat surface. The greater the distance between the laser and the flat surface, the easier it will be to true of course. you can shim in a number of ways to get the laser true...placing slivers of aluminum soda cans, sheet metal, paper, or tape between the magnet and the surface, bending the laser and tube slightly, or placing paper or tape under the socket and re-securing the socket against the magnet. Continue to shim and test until the laser's dot does not trace a circle against the test surface.


This entire calibration could be avoided though if you simply hang a sheet of paper in front of the transmission output shaft and trace the path of the dot to find the center while both are in the car. The same can be done at the diff. However, if the lasers are trued, you can use steam, dust, or a fog machine to very easily determine if the lines from the transmission and the diff are parallel in both dimensions just by eyeing them and moving the drivetrain components around. If a smoky substance is not available, you can insert a piece of paper at different points along the two beams and see if they stay equidistant or not and adjust as necessary.



To obtain the angle of the tranny compared with the differential:


Arc tan(Distance between the two laser beams divided by the distance between the output shaft of the tranny and the input flange of the differential)










Sean :)

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  • 3 months later...

Damn! Such a good idea I decided to do the same




Got two $8.99 keychain laser pointers at PETCO in the cat toy aisle. Ground off the key chain mount, drilled and tapped a hole then mounted to a flat piece of scrap. Three button sized magnets, put the thing on the drill press table and shimmed the pointers until spinning the table scribed a single dot on the ceiling. Only thing left to do is use a small clamp to hold them on.


These and a box of cigars will greatly simplify setting up the motor mounts.

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  • 5 months later...

Sorry to reinvent the wheel, but I had trouble finding the 9/16" and 19/32" brass tubes mentioned in Top Fuel ZX's post, so I thought I'd post how I did it. Basically I used the same magnets that Top Fuel ZX used, with Keychain Laser Pointers from Office Depot placed inside 3/4" copper pipe. They fit inside the pipe very well, and actually hold the button down (to turn it on) when it is inserted into the pipe. I secured the pipe to the magnets by first screwing a 3/4" copper cap to the magnet, and then slid the pipe into the cap. I chose to sweat (or solder) the pipe to the cap, to keep it from moving, but I'm sure epoxy would work also. I had to make 3 stops:



Ace Hardware:

1 - Magnet Source model 07223 magnet

1 - Magnet Source model 07222 magnet



Office Depot:

2 - "Keychain Laser Pointers"




1 (pkg of 2) - 1/4"-20 x 3/4" flat head cap screw #214022



2 - 1/4"-20 lock nuts

2 - 3/4" copper tubing caps (solder type) might want to buy some extras if you dont have a drill press since its a little difficult to drill the exact center by hand.



1 - stick of 3/4" Type M copper pipe. There are 2 types of copper pipe....Type L and Type M. The outside diameter is the same, but they have a different wall thickness (I'm pretty sure Type M is the thicker of the two). So the different wall thickness translates to slightly different inside diameters. I would recommend taking the lasers with you, and test fit them to get the fit you want.




I started by center punching the 3/4" copper caps, then drilled a pilot hole. I increased about 2 drill sizes each time until I got a 1/4" hole in the caps.



Next I used a 7/16" nut driver and an allen wrench to secure the caps to the magnets.



After that, I cut a 4" piece of 3/4" copper pipe (using a pipe cutter)


and slid it into the cap.


Epoxy could be used before sliding the pipe into the cap, but I chose to submerge the magnets in water (to prevent heating the glue that holds the magnets to the frame) and solder them.



Laser placed halfway into the pipe:



Laser placed all the way into the pipe:



To make them "true" I placed them on a LEVELED wood table, then drew an outline of the magnet on the table (to keep it in the same spot as I rotate it). I marked the laser dot on the ceiling, then turned the magnet 90 degrees, 180 degrees, 270 degrees etc. and noticed the movement of the dot on the ceiling. There is a little room between the laser and the inside of the pipe to shim the laser until it is true (I used aluminum foil). The reason I made the pipe a little long (4") was to give me more leverage in case I needed to bend the pipe to make it true (but it wasn't needed).









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  • 6 years later...

How accurate does this need to be? I'm spinning my laser and drawing about a 1/2" circle on a 10' ceiling and I can't seem to dial it in much more than that. Good enough?


Also, for someone math challenged, I figured I'd take my digital angle finder and check the angles on the trans and diff yoke, then use the distance between the laser points on a piece of paper at the trans and at the diff to square it up side to side.


Sound reasonable?

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I put the lasers on the diff and driveshaft today. An immediate problem was that I couldn't get the diff centered because the pinion nut sticks out farther than the flange, but I kinda figured I wanted the relationship of the flat part to the flat part, so having it perfectly centered isn't that important. So I positioned both lasers so they were sitting flush on their respective pieces and ran a piece of paper back and forth. I know with the angle finder that there is a 2 degree angle difference between the two, so that was going to make the gap grow vertically, but I wasn't able to detect any horizontal movement at all, so I marked the position of the motor mounts on the frame. I'm going to cut a bit out of the tunnel for trans clearance and then I should be able to get the trans jacked up and fix the angle problem, then I can just double check to make sure that I'm square left to right, and I'm hoping it will be good to go.

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  • 3 months later...

Found the flaw in my procedure with the help of Facebook and another forum. It is possible to have the angles of the trans output shaft and diff flange correct, but still have too much U-joint angle if the trans and diff are too far out of line from each other. So I went back and measured and found that the trans and diff are about 13/16" apart, and the distance from the trans output shaft to the diff flange is 23 3/4". Looked at an old Datsun driveshaft and it looks like about 3 3/4" is taken up to get to the center of the U-joints. Just went ahead and guessed at the CTC of the driveshaft U-joints will be something like 19".


Plugged the math into Google: arctan(.8125/19) and got .0359 radians. Converted to angle and got 2.05. I believe each U-joint takes 1/2 of that, so I'm right at about 1 degree, or just about perfect. Does that sound right?

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  • 8 months later...
  • 10 months later...
I made my own using this post as a guide. Instead of laser pointers (which I found to usually be misaligned) I opted to use laser bore sighters made for sighting in scopes on rifles. I purchased this 20 ga brass bore sighter for $10 on amazon (http://amzn.com/B002OPC7GE) and used the magnet bases 7222 and 7223 listed above.
Magnet, boresighter, and batteries:

boresighter brass base. Remove plastic cap and spring that's normally attached to it:
Drilled through (use aluminum an blocks or similar to prevent damage and warping to brass)
Tapped for M8x1.25:
Attached to base with an m8 x1.25 bolt:


Then just put batteries in, twist until it's on, and voila:
Crappy test run:
Edited by auxilary
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