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R200 Handling Problems BetaMotorsports article


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Here is the text so others don't have to scroll through FB:

 

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.

 

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That question was asked in the comments section of the FB post. The answer - it wasn't. At stock ride height, it wasn't a problem in the 280Z.

A bit sparse on facts and numbers, and there are many lowered 280Z's out there but almost no complaints about binding.  I've never seen any.  Seems like thee would be some 280Z's racing out there who would have felt the pull to the left or the handling problems.

 

Not sure if that's JC commenting as Beta, or if someone else is.  The issue's been discussed before.  A measurement of the axle assemblies might show something.  The 240Z stub and flange, bolted together, should be wider than the 280Z.  If that's the cause.  Easier than measuring distance between flanges, in the car.  Since the track dimensions are the same, it should show up in the axle assemblies  Can't ever seem to find anybody with both axle sets whenever this comes up, so it always remains unresolved.

 

Anybody got both axle sets?

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Also, I think that it's been shown that the axles are most compressed when the wheels are hanging, not when the car is lowered.

 

Here's a thread, look at #18.  My comments are wrong, logic-wise, I figured out later in a different thread.  The arcs are different.  JM, and Ross apparently, took actual measurements.

 

http://forums.hybridz.org/topic/109669-axle-problems/

 

One thing that's often left out of the discussions is the amount of movement all of the stock rubber allows.  Rubber diff mount, rubber suspension mounting.  Maybe there's actually something else going on, not inherent to axle length but caused by too many parts moving under heavy loads.  suggesting that there might be other solutions, beside axle shortening.

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I think this is just in reference to the 240z and 260z swapping in a non native R200. I want to say the 280z since it has a native R200 isn't included in the list, but would suffer the same problem.

 

I've got both sets of rear uprights. My recollection is no difference in the stub axle flange between the 25 and 27 spline, and the axles being the same so any difference would probably be in the angle of the hub housing if there is one. I'll have to pull them out and measure once my car stops blocking the way.

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The strut housings are longer on the 280 and the insulators are taller and the rear strut towers are different. The mustache bars swap, the control arms swap, etc. On the 240 the distance between the diff flange and the companion flange gets shorter when you lift the car up in the air. I think it's pretty safe to say that Nissan wouldn't build a car with bottomed halfshafts from the factory, so there must be a difference. Seems like the relative height of the diff to the companion flange is different, and that must be why it works.  

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But the transverse links (aka control arms) set the arc of the hub and half-shaft end, so the tops of the struts shouldn't come in to play.  Unless deflection of the rubber parts is different.

 

Wish I lived in some cold snowy long winter area, with a big warm garage and one each 240Z and 280Z.  I'd do some comparing.

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I went through this last winter. Replaced R180 with R200 in 240z. I had halfshafts from both and they measured exactly the same, compressed and extended. Ended up using the R180 halfshafts as they were in better shape.

 

Had read about the binding issue so that was thoroughly checked out and halfshafts were compressed most at full droop. The halfshafts got longer as the suspension compessed.

No issues driving.

Edited by BJSZED
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Did you measure the half-shaft length as droop changed, or the distance between the flanges?  The change is not dramatic and the changing angle of the flanges, relative to the axle axis, makes it hard to just eye-ball it.

 

The handling issues are described as happening under somewhat extreme conditions; drag-race type launches and accelerating out of corners in competition.  People generally don't notice anything otherwise, when they swap an R200 in to their 240Z, apparently.

 

A couple of measurements and we'd know if there's less space between the flanges or not.

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With the left halfshaft bolted in place at the wheel side and the suspension at full droop, there is little play when bolting the left inner side up. When the suspension is compressed there is more play on the inner side when bolting them up. Anyone having a hard time getting them in should compress the suspension slightly and in they go.

I was quite worried about it and was going to run the suspension through full travel without the spring but my drag racing buddy came over and showed me how the shaft length got longer as the suspension went up.

 

There is a thread somewhere on here in which someone ran the suspension without a spring and shaft length was shortest at full droop and got longer the more the suspension was compressed.

Edited by BJSZED
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I misread your post, my brain was thinking the car was raised, not the wheel.  You're confirming what JMortensen wrote, I think that his thread is the one you're referring to.  

 

Still don't know if binding happens on the 280Z or if the 240 and 280 are different.  The inner bushings on the transverse link have to compress in a corner.  That shortens the distance from flange to flange.  Who knows.  

 

I wonder what parts contact at full compression in the halfshaft.  They should show some wear or damage if binding happens.

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I changed my descriptions to compressed, less confusion.

 

I don't think a 280z would be any different as far as shaft length changes, as in getting longer under compression. I believe the basic design is the same other than the strut assembly length.

On the 240z the half shafts are really close to fully compressed at full droop, probably not much more than an 1/8" play left. I was pretty worried about it until my friend showed me the light !

 

Could possibly be an issue if lifting the left rear wheel on a road course with the extra side pressure on the other wheel or the weight of the diff moving on the mustache bar bushings....dunno ?

Edited by BJSZED
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Reading this thread makes me wonder if the dynamic camber is different between the 240 and 280 chassis. If the strut mounts are further apart on the 280, it should experience less camber and therefore the axles should be less compressed, correct? This goes out the window with camber plates, of course. Then again, camber plates might be a contributing factor pushing the companion flanges slightly inboard when running more camber.

 

Also related, are series 1 axles also the same? If so, that might also explain the axle length due to the diff mount change.

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