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240 AND 260Z R200 HANDLING PROBLEMS
Its common for Datsun 240 and 260Z owners to replace their 3:36 or 3:54 geared R180 rear end units with a 3:90 geared R200 unit. Its a cheap and easy way to get a good ratio that works well with a 5 speed transmission swapped into those early chassis. But, the swap of an R200 in place of an R180 in the 240 and 260Z chassis produces handling problems.
The handling problems are felt as:
1. On hard, drag strip type launches, the car consistently pulls to the left when the rear squats.
2. The rear doesn't take a set, constant steering correction is needed on right turns while racing on an autocross course or a track, and its difficult to put the power down on corner exit.
The R200 is physically wider then the R180 and that width is asymetric - the R200 is wider on the driver's side of the vehicle then it is on the passenger side. This causes a suspension binding problem on the driver's side when the halfshaft bottoms (run out of travel).
All the halfshafts used in the 240, 260, and 280Zs are basically the same, with differences on how the shafts are connected to the differential stub axles (center bolt yoke or four bolt flange). The fully compressed length of the halfshafts, as measured from yoke centerline to yoke centerline, is 12 3/16". The fully extended length of the halfshaft, measured the same way, is 14 3/8". This gives total travel of 2 3/16". I came up with these numbers after measuring four halfshafts, two with the four bolt flange and two with the ceter bolt yoke.
In a R200 installtion, with the lower control arms about 7.5 degrees from parallel to the ground, the driver's side halfshaft's length is 12 3/8" while the passenger side halfshaft's length is 13 1/4". The driver's side halfshaft is almost bottomed out while this coil-over equipped 260Z is sitting at an unladen ride height of 6" at the rear. With the driver in the car and fuel on board, the driver's side halfshaft will be 1/8" from bottoming.
Driver's side halfshaft almost fully compressed at static ride height.
Passenger side halfshaft still has about 7/8" of travel before full compression
At this point, the driver's side rear suspension will go into a bind with any compressive load and the spring rate will skyrocket to some number defined by the flexing of metal parts in the rear suspension and rear housing mounting. In addition, large stresses are being applied to the driver's side companion flange, stub axle, bearings, and bearing housing. These parts tend to fail more frequently in 240 and 260Zs equipped with a R200.
How can the problem be fixed?
1. Disassemble the halfshafts and machine the outer to allow an additional 1" of compression travel. This is a difficult process mainly because the slip joint in the halfshaft is a bear to reassembly properly and the nylon spacers are NLA.
2. Make custom halfshafts of the proper length. This is a common fix and is done as part of a conversion to constant velocity joints.
3. Keep the static rear ride height at a point where the rear lower control arms still point down.
I've had a few folks tell me that some 280Z halfshafts are shorter then the 240/260Z halfshafts. I've traded e-mails with 3 long time Z racers and all of them say the've never come across any shorter halfshafts that fit in the 240/260/280Z chassis. A couple Z parts hoarders that I know checked through their piles of halfshafts and were not able to locate any 240/260/280Z R180 or R200 halfshafts that were shorter. I think the idea of a shorter driver's side halfshaft for the R200 insalls in the 280Z is a myth.