Hereâ€™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.
This is Pop N Woodâ€™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 canâ€™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.
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 9/16â€ Socket to the 2 5/8â€ 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.
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 wouldnâ€™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 centeredâ€¦.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)