Face-to-face dimension for rear IRS?

[bystickel]

I am hoping someone has a measured width for the rear IRS set-up. I'm looming for outer drum face to outer drum face (wheel-mounting faces). I missed my opportunity when a friend had a complete unit out of a car, which would be the easiest way to check it. Unfortunately, my cars aren't nearby and it'll be difficult for me to check them.

I'd appreciate it if anyone has or can easily get that number for me.

Thanks.

[JordanTr]

I know I measured it. I will dig through my thread and try to find it for ya.

[JordanTr]

Grabbed this from my thread.

So this morning I figured it would be good to measure what the axle length change of a stock 510 half shaft is through the full suspension travel from full droop to the bump stops. I pulled the boot off the half shaft and mounted up a digital caliper to measure the displacement of the outer half shaft relative to the inner side.



After taking a bunch of measurement at different positions in the travel I ended up with this:



Unsurprisingly, the curve is parabolic and you can see that the axle is shortened by 15mm throughout full suspension travel of 7.5" measured at the outer lip of the rim. This suspension curve is set for -1.5* camber at ride height. With more positive camber, I believe the axle would be shortened less than 15mm since the camber gain near the top of the travel would be less severe. For a relatively redneck setup, the R^2 value is pretty good. Better than most of my labs at school

The whole point of this exercise was to determine how much wiggle room I have on the sliding joints on the Z31T outer CVs. After messing around with the sliding CV joint, I determined it can take ~37 mm of sliding in and out before hitting the edges of the joint. This is with the cage flipped, without the cage flipped it would be a little bit more.

As mentioned above, I have to increase the rear track by at least 3.5mm to fit the ebrake assembly into the rear control arms. To be able to pull this off, I'd need to chop the inner fender ledge as well. If I add 2.5mm past the point of extreme wheel fitment on each side it should still be OK once the lip is chopped. Extreme fitment from above was 6.5mm wider drivers side and 1mm passenger side. This would mean that the driver side would receive 6.5+2.5=9mm wider rear track and the passenger side would receive ~1+2.5=3.5mm wider rear track. If this was all done than the wheel fitment would be the same for each side.

Looking below to the picture I made up for this thread you can see how much too long the axles are per side (highlighted yellow). 2.38mm passenger side and 13.5mm drivers side. If we apply the desired increase in track width to each side, you end up with a drivers CV that is 13.5-9=4.5mm too long and a passenger CV that is 2.38-3.5=1.12mm too short. WOW! This actually looks pretty promising without modifications to the Pathfinder CVs.

If we assume Nissan put the CV joint in the middle of the slider at ride height on the z31T, then we have 37/2=18.5mm of slide in and out. As you can tell, both 4.5 and 1.1 are << 18.5mm. Even if this assumption is incorrect, there is a decent amount of wiggle room.



Once I get the control arms made up then I can assemble the whole shebang and see how the CVs are working with real parts (i.e. no calcs!)

Unfortunately, that's not exactly what you needed.

I found the rear track of a late Z31T to be 1455mm. The late turbos used 16x7 +30 rims. So 1455 -2(30) = 1395mm = ~54.9".

Using the above info, you can deduce that a stockish 510 has a rear face:face distance of ~49.6".

I also found this post by Okayfine in Jeffball's thread:

Does anyone have another way to measure for proper wheel fitment and track width? There are a ton of variables that each of us will have, so I'm trying to find some generic methods to get us in the ballpark area without asking "will this wheel fit?" a hundred times on this forum.

"Track width" is generally defined as center-to-center of the tires at each axle. Tough to measure track width without having rims and tires that fit

Stock 510 track is measured at 50.0" front and rear.

As to your "generic method to get us in the ballpark," with regard to wheel fitment, a few millimeters can make all the difference between fitting and rubbing. I don't think a ballpark figure will mean much, especially as most wheels are offered in only a few offsets.

HTH

What is your plan? Z31? S13? Something else?

[bystickel]

Thanks, Jordan! That info will validate an actual measurement, something I usually need to do 8-10 times before I begin to trust my attempts (;

I'm thinking about making a bolt-in subframe to accept NA/NB Miata parts. It's A-arm, pretty simple, with lots of availability and aftermarket support.

A Nissan conversion might have more appeal, but it's more complicated. And any time I've mentioned the idea, the ridicule has far outweighed the encouragement, so it might end up just being a one or two-off for myself.

[Byron510]

Thanks, Jordan! That info will validate an actual measurement, something I usually need to do 8-10 times before I begin to trust my attempts (;

I'm thinking about making a bolt-in subframe to accept NA/NB Miata parts. It's A-arm, pretty simple, with lots of availability and aftermarket support.

A Nissan conversion might have more appeal, but it's more complicated. And any time I've mentioned the idea, the ridicule has far outweighed the encouragement, so it might end up just being a one or two-off for myself.

Certainly keep us posted here of your progress on the project, sounds like a good one.

Byron

[JordanTr]

Awesome. Take a look at 510wizard's wagon thread with Miata IRS.

[bystickel]

I checked out your thread, too. I remember those rear arms, great job on your entire car. It's great you have your Dad to work with you

I was reading the wagon IRS thread...some projects are so ambitious, with owners so detail-oriented, that it's difficult for them to reach completion. I hope it does.

[510wizard]

Look below

[510wizard]

Three problems with the Miata to start with( there's probably more);
1. On the wagon and probably the 2/4 dr, the Miata is 5.5" to wide, so new subframe and/or new "A" arms and new axles.
2. Miata height of assembly is also a problem, if you don't want to go into the cargo/trunk area. This is why Datsun used the trailing arm design in the first place, low assy height. Also the force better to be with you to hope that the coil overs line up with the 510 shock mounting points.
3. Miata lug pattern is wrong at 100mm.
To do this is a very big project with a lot of unforeseen problems( snow ball effect) and even more so if you are detail oriented as you say. Ask me how I know!

[bystickel]

Thanks, Wiz. My car needs new exhaust and a rebuild of the LSD, along with a CV conversion and rear disks, so if I'm going to do those things, I might just do them for the Miata conversion. That's my "logic".
1. I'd like to use a new subframe to reduce the width, as you did.
2.The upper control arm inner locations could be a concern, if they can't be placed high enough. A curved upper arm will be needed to clear the vertical sheetmetal seam, no matter what (on sedans). If I can't get the inner pivot location high enough, I may be able to relocate the outer pivot downward or do a tricky virtual pivot. I was encouraged to see that the shock location on the A/B set-up is just inboard of the wheel and behind the axle, just like the sedans. That's no guarantee, but.
3. I can live with 4 on 100, at least for a while, especially since my 13s aren't likely to fit.
IF I can complete this project, it would have to be far less beautiful than the work you're doing. That was the point I was trying to make.The first would be proof of concept quality.

And when this project fails, I'll have more time for my multi-link front strut conversion...