Today I re-assembled the rear end, which included replacing the leaf springs, re-attaching the differential, and installing the new shock absorbers.
I am going with a different rear suspension set-up than stock or what came with the car. I bought a new pair of rear leaf springs. After reading the recommendations in the Bob Sharp Competition Manual I decided to swap out the later-style leaf springs for a pair of the early roadster leaf springs that came in the pre 1967.5 1600 and 1500 cars. The early-style springs have the same dimensions as the later ones, but are a bit firmer and maybe a bit lower. The other popular option is to go with a pair of Nissan Competition leaf springs. Although these are more readily available than the early-style stock springs, they are very flat and most people say they ride pretty rough. I am looking for good handling without too much compromise in ride comfort, so the early stock springs are what I chose.
The early-style stock leaf springs are No Longer Available from Nissan in the U.S. (I checked). Using the part number I inquired of a number of custom spring manufacturers to see if I could have a set made to spec. The cheapest I found was $300 per set at an order quantity of five pairs. I figured I could find four other people looking to get these springs but actually could not find enough interest in a timely manner. Additionally, that price did not include the front eyelet bushings, which would have added to the cost somewhat. Ultimately I ended up buying a new pair of Nissan springs (with the front eyelet bushings) from Rallye, which is a roadster parts vendor in Washington state, for $342.43 plus shipping. I also wanted to upgrade my rear spring bushings and sandwich pads at the same time. I also scouted around to see if there was an application from Energy Suspension or another company that would fit the roadster. In the U.S. these companies (in my experience) are fairly reluctant to recommend parts based on dimensions if they were originally intended for a different application, probably due to legal concerns. In Australia, where there are quite a few urethane suspension bushing manufacturers willing to do just that, I did find a couple of matching applications, but they were fairly expensive even before shipping. I found that Dean at datsunparts.com makes and sells urethane leaf spring kits specifically for the roadster. I bought a set of their urethane bushings and sandwich pads for $88.
I also went with new Gas Adjust shocks from KYB which match those I used in the front. The part number is KG5447 and I found a pair in stock at my local Van’s Auto Parts for $95.50. This part was originally for a Nissan pick-up but fits the roadster perfectly. The one exception is the lower tower bushings that come with the shocks are smaller than stock. I found a set of rubber shock tower bushings for $12 in the Help! aisle at Autozone that were nearly a perfect match to the stock ones. Below right is a picture of the new one next to the old one.
I began by lifting up the rear end of the car and supporting it with a pair of jack stands.
The first step was to mount the leaf springs in the rear, which required first bolting on the “scroll” brackets to which the back of the springs mount.
When the frame was powdercoated, some of the coating ended up inside the threaded bolt holes, so I chased them using a 3/8″-24 tap. Then I lined-up the scroll brackets on either side. The brackets are not interchangeable, but it is pretty clear which one goes on which side based on the triangular pattern of bolt holes on each.
Then I threaded on the new mounting hardware, which was part of the Frame Bolt Kit I got from Pat Mahoney. I tightened down the bolts using a 9/16″ socket and a same-sized box wrench when necessary to hold the nuts.
Here are the scrolls installed.
The brackets are oriented such that the spring eyelet floats above the scroll eyelet. The two mount together with a piece that has two threaded studs. I slipped two of the new spring bushings onto the ends of each stud. Then I inserted the studs through the scroll bracket (below) and the rear spring eye (above).
Then I slipped two more of the bushings onto the other ends of the two studs.
Then I slapped the retainer plate over the two studs and added two new nylock nuts. The bolt set actually did not provide these two nuts, but there were four leftover nuts of the correct size from the front end set, which would have been used on the upper A-arm spindle mounting bolts if I could have found a way to get them inside the housing. I couldn’t, and rather than use the old nuts here I used these new spares, which were the same size. I did the same thing on the other side.
I tightened the nuts down using a 9/16″ socket.
Next I hung the shock absorbers in place from their top mounting points. The threads on the studs on which they mount had likewise been covered in powder which made the nuts difficult to thread. I used a wire wheel to remove the coating from the threads.
That cleaned-up the threads and allowed the new shock nuts to thread.
So I pushed the upper shock eyes over the posts. In order to seat them all way down without pushing the shock off the rubber upper eye bushing, I used a 17 mm socket, which had an internal diameter just wider than the post itself, and tapped on the bushing. That moved the shock inward without coming off that bushing.
So then I threaded on the new upper shock nuts and tightened them down (not too tight, the shocks needed to rotate into their final position) using a 1″ socket.
With the leaf springs mounted in the rear and the shocks bolted on top, I rolled the differential into its position. I placed the diff on my dolly and moved it in over top of the fronts of the leaf springs and and positioned the shocks in front of the axle.
Then I raised the differential up by stacking some wood blocks underneath it in the middle. I raised it up higher than it actually sits relative to the frame so that I could attach the leaf springs in the front unencumbered and then later lower the diff down onto the springs. From this point I fully completed one side before working on the other.
In the front, the leaf springs mounted to a bracket and a bolt went through the bracket from the outside and the eyelet bushing with a nut holding everything in place on the inside edge of the frame. I lifted the spring up in the front and positioned it so it lined-up with the mounting holes. Here are some shots of the right (passenger) side.
Then I started the mounting bolt from the outside, re-using the original bolts, lock washers, and nuts. The bolt has a flat spot on its head that matches up against a tab on the frame to prevent it from rotating in place. I used a mallet to tap the bolt through the spring’s eyelet bushing.
With the bolt in place I added the lock washer and nut on the inside and tightened it down with an 11/16″ socket.
With the differential raised up artificially high, I put one of the new sandwich pads onto the spring.
Then I put on one of the retaining plates, which have straight edges in the front and back. I lowered the axle onto the plate.
On top of the axle housing I put the rear bumpstops. I re-used the old bumps, which I had cleaned up and painted. The rubber was still in pretty good condition. I oriented the bumps so that the rubber part was closer to the center of the frame than the outside of the frame, that way they line up more closely with the frame member above. Over the bumpstops and down through the holes in the plate I fed the two U-shaped spring bolts.
Below the axle is a similar set-up, where the inner sandwich pad was covered by the outer plate. I first slid the sandwich pad up onto the spring post from below.
Underneath the sandwich pad plate went the shock-mount plate. These parts are not interchangeable from side-to-side. Facing the side of the car onto which I was installing the shock plate, I knew I had the correct part when the tab that the shock tower mounted to, when facing up to the sky, was tilted towards the rear of the car. Another way to see if I had the right part for that side of the car was that, with the sandwich pad plate lined up on the shock mount plate the shock mount plate’s mounting hole would be pointing in and forward toward the center of the frame. If I tried this orientation with the shock plate from the other side of the car the holes on the two plates would not line up.
So with everything oriented correctly I slid the sandwich plate and shock plate over the spring bolt ends and threaded on the new nylock nuts to hold everything in place.
I tightened the nuts down using a 9/16″ socket.
Then I mounted the lower shock end onto the hole in the tab of the shock plate. I first added the shock washer and a new rubber bushing, then I stood over the shock and pulled the bottom of it upwards, compressing the shock, until I could drop it over the shock plate hole and have it extend down with the shaft going through the hole in the plate.
Then I added the bushing, washer, and retaining nut on the bottom of the plate.
That basically completed the installation of rear end parts. I put both sides together, and then came back to tighten and torque everything down once everything was in place. I tightened down the upper shock nuts down first.
Before tightening down the leaf spring nuts I jacked-up under the shock plate and axle in order to relieve any downward pressure so I could line the springs up under compression. I torqued down the rear mounting nuts to 50 pound-feet, again using an 11/16″ socket.
I torqued down the front leaf spring mounting nut, using an 11/16″ socket, to 50 pound-feet.
The four axle bolt nuts under the shock plate I had to tighten down quite a bit using my 9/16″ socket. Once they threaded down, pulled the sandwich together, and firmly seated the axle in place, I used my torque wrench to tighten them to 35 pound-feet.
I tightened down the lower shock tower nut using a 9/16″ box wrench. When it tightened enough to want to spin the shaft I held the shaft using my vice grips and tightened some more.
Then I added the lock nut onto the shaft. I tightened it against the first nut by holding the upper nut with a wrench and using a 9/16″ socket on the lock nut.
The final thing I did was to re-install the torque strut on the right (passenger) side of the car. It went between to mounting brackets on the frame and its role is to reduce flex in differential relative to the frame as power is sent to the wheels. I dropped the torque strut down onto its mounting brackets from above and fed the original bolts through the brackets and eyelet bushings in the strut. Although the eyelet bushings are in good shape, I would have considered replacing them if I could have found new ones anywhere (but I couldn’t).
I tightened both the front and rear bolts using a 3/4″ socket and wrench. I torqued them down to 75 pound feet.
Here is a picture of the completed right rear end, including the torque strut.
Here are the two suspension assemblies from the front and rear.
And a couple of final pictures from the front and right rear.