Once you have installed a bigger engine in your Datsun, a whole new set of problems come to light. One is the brakes …Datsun’s are not blessed with particularly great stoppers. Another is the differential. Too much abuse and that little R160 will go pop! The R160 Diff is fitted to the 510 and 610 sedans as well as 610 and 710 SSS coupes. This diff is a little weak in stock open form. By open I mean, non-limited slip. The weak link is the small side gears and pinions with the carrier itself. Launch to hard a few times and the teeth will strip from these gears in a moment. The best solution would be to fit a limited slip differential in it’s place. As the LSD had a clutch pack taking the load rather than the gears in question, it is substantially stronger, however, the R160 LSD is not particularly easy to come by, especially in the UK.
For street use, you don’t really need an LSD but you will still need a stronger diff. This is where the R200 comes in. The R200 can be found in many Datsun models including 260Z (S30), Silvia (S12), and 300ZX (Z31). The R200 is a monster in comparison to the R160, which is great if you want to be able to drive the car very hard. This diff is virtually unbreakable! Below you can see an R200 from a 260Z compared to an R160 from a 510. Once you pop the cover off the difference is even more apparent. Not only is the crown wheel considerably bigger, but the entire carrier is too! As you can imagine it would be pretty difficult to break this!
So, what about fitting one to your Datsun? First you need to locate a suitable diff. Donors include the 300ZX, Silvia S12 and late C32 Laurel (other countries may have them on 280ZX and R30 Skylines too). For street use with a fairly powerful engine you will probably want a 3.7:1 ratio. These can be found in Nissan Silvia (S12) manual transmission models. The Automatics have a 3.9:1 as far as I am aware. You can check the ratio once the rear cover is off as it is stamped on the crown wheel. The ratio’s are usually expressed as 37:10 or 37:9, which is the number of teeth on the crown wheel and pinion. To find the ratio, divide the larger number by the small one, hence 37:10 = 3.7:1.
All of these diffs will bolt in but you will need to change the driveshaft arrangement. All of the cars I have just mentioned run constant velocity joints (CV’s) on the rear where as our Datsuns run universal joints (UJ’s). The answer is a 260Z diff. You can use the entire diff from the 260Z as it already comes equipped with flanges to take UJ shafts. However, I found the manual gearbox version I acquired had a ratio of around 3.5:1, which is a little to tall for any kind of performance application. The good news is that you can use the flanges from the 260Z diff to install any other R200 …just pop them out and snap them into the R200 of your choice! As the R200 is wider than the R160 you cannot use R160 flanges. It should also be noted that the R200 flanges are different lengths as the carrier if offset in the casing. Below you can see two R200’s, one from a Silvia and one from a 260Z in comparison. Here you can see that the axle flanges are different lengths.
The axle flanges are held into the R200 in a different way to the R160. The R160 flanges are retained by a single bolt through the center into the side gear but the R200 uses snap rings. When you pull the diff from a Silvia you can just prise the CV shafts out of the sides of the diff. The 260Z flanges just push back in. They should locate solidly once the snap ring has engaged. Remember they are different lengths so the flanges are handed left and right! I chose to use the rear cover from the Silvia rather than the 260Z one. One reason is that it looks better, but apart from that the fins might have some effect on the diffs cooling capabilities and the slightly extended cover will also allow for a little more oil capacity. No bad thing. Below you can see the R200, ready to install, compared to the original R160. There is a bit of a weight penalty for fitting the R200 as it’s 12kg heavier than the R160 but that’s not a big price to pay for reliability.
Now we come to the important bit ..getting the R200 into your Datsun. This is pretty straight forward although it does require some welding and a little grinding.
The first step in doing the R200 swap is to remove the old diff. First you want the rear of the car supported at a decent working height. You need to place the axle stands under the rear end but NOT under the crossmember as it needs to be able to move down to allow the diff to slide out. If your sills are good you might be able to support it under them. Failing that any structurally strong area under the rear of the car will do, just make sure the stand won’t slip or the that the loaded area won’t collapse! It is a very good idea to chock the front wheels to prevent the car from rolling forward or back too.
Before removing the diff take a measurement. You want to make a note of how far the center of the axle flange is away from the floor above vertically. This will help you to get the rear end of the R200 mounted at the right height when installing it. Remember, you will have to fabricate the rear mounting strap so you will need some idea of where the diff should be positioned. The angle at which the diff mounts not only affects the angle of the driveshafts, it also affects the angle of the rear propshaft flange but more importantly the camber of the rear wheels.
Once the car is safely supported, get under and unbolt the propshaft and the two drive shafts from the diff flanges. Remove the left hand shaft completely from the car as this will need shortening (easy job, don’t worry!). It’s not a bad idea to take the right hand one off anyway as it gives you more room to work in. Undo the four 17mm bolts holding the diff to the crossmember and the two holding the diff to the rear support bar. The bar is attached to the diff with two studs and nuts. You need to unscrew the studs out of the diff cover in order to be able to remove the bar from the chassis. This is achieved by locking two nuts together on the stud. Once they are out just unbolt the support bar and drop it down off the mounting spindles. The diff should now be loose and ready to come out. You may have to get some kind of lever in between the crossmember and floor to lever it downward. This makes it easier to slide the diff out past the spare wheel well. Remember to catch the small shims that go between the diff and the bottom of the crossmember around the 17mm mounting bolts!
Before you can get the R200 in you will have to grind a little clearance on the cross member. As you can see in the picture below the bottom of the diff casing hits the lip at the bottom of the hole in the cross member. A few minutes work with a small angle grinder or die grinder will cure this.
Once this clearance is made you can slide the diff into the crossmember and bolt it in. You will probably have to lever the crossmember down away from the floor to gain clearance to get the diff in place. It may help to slacken the mounting nut at either end or the crossmember to allow it a little more movement. Once you have the diff bolted into the cross member use a floor lack to support the rear end of it at the desired height using the measurement you took earlier.
The R200 is slightly longer than the R160 so a custom rear mounting bar is required. There are several ways of doing this, ranging from modifying the R160 mount to fabricating an entirely new one. I chose to make a mounting out of the original 260Z one combined with the R160 bar. The two rear mounting studs on the R200 are larger and further apart than the ones on the R160 so I used the center section of the R200 bar and the end mounts of the R160. Below you can see the two mounts side by side. The 260Z one is at the top.
I cut the R160 mount either side of the center mounting face as shown in the picture below left. Measurements are not crucial here but try to cut it neatly and straight. This gives you the two end mounts you need. Grind off any paint and bolt them loosely to their mounting pins under the car. I cut the center from the 260Z mount by cutting three inches outside of the mounting holes as shown below right. This gives a nice amount of material to overlap the outside pieces for a stronger join. Once cut, grind off any rust and paint then bolt this piece to the diff. It is advantageous to bend the ends of it forward slight to make then align a little better with the end mounts. This needs to be done in a bench mounted vice with a big hammer.
Once the parts are in place under the car, double check the diff is at the correct height and angle then clamp the parts of the mounting strap together with Vise Grips or a G-clamp and weld it all together. It is best to runs a weld all the way around the edge of the mounting bar sections as the steel is spring steel and smaller welds may break. I ran a continuous weld around three sides of the overlapping sections and after much abuse it shows no signs of failure yet.
At this stage you should have the diff installed under the car with the crossmember and rear mounting bar all bolted up. You can refit the propshaft to the front of the diff and connect the right hand drive shaft back up. But there is one more piece of fiddling to do yet. Shortening the left driveshaft.
The R200 is somewhat wider than the R160 and most of this extra width is offset to the left. This means that as the left driveshaft swings through the center of it’s travel, the point at which it is most compressed, it will lock up solid as there is not enough sliding movement in it any more. This is obviously undesirable but it is surprisingly easy to cure. The answer is to shorten the internal section of the shaft to allow more compression.
The first thing to do is dismantle the driveshaft. To do this you need to remove the clips holding the bubber boot in place. Pull back the boot and you will find the internals if the shaft are held in by a big C-clip and a washer behind it. Pop this C-clip off and the whole joint will easily slide apart. The internals of the shaft are shown below (except the C-clip and washer which are still tucked inside the rubber boot in this shot)
In the picture above you can see another funny shaped washer and C-clip. This assembly is attached to the inner end of the inner shaft and is there to stop all those ball bearings and spacers dropping into the hollow outer shaft. You need to remove them as well as all the ball bearings and spacers. Give them a clean and put them in a safe place. Make a note of how they are assembled too. Now you can get your angle grinder with a cutting disc and cut a bit off the end of the shaft. Half to three quarters of an inch should do it. Try to cut the end as square as you can although it isn’t vital.
Now you have cut the end of you have lost the circlip groove. No problem. Just hold the funny shaped washer on the end of the shaft and weld around the hole in it’s center to re-attach it. The washer doesn’t rotate or need to move once the shaft is assembled so this is not a problem. Once you have done this clean all the grinding dust etc away and reassemble the bearings and spacers, thoroughly greasing everything. Then you can slide the assembly back into the outer shaft and refit the washer, C-clip and boot. Make sure you get the orientation of the two UJ’s correct…compare with the other shaft to be sure.
Now you can bolt the shaft in and fill the diff up with oil. On my car I had to re-fit the rear anti-roll bar as well. Now you have a virtually bullet proof diff, which will take whatever you can throw at it. Hard launches and burnouts are no longer a problem!
Want to go a step further? It is possible to fit a limited slip R200 differential but sourcing a used one can be tricky and new they are very expensive. You’re looking at a minimum of £500 going uo in excess of £1000 for a Nismo LSD. A plate type LSD was fitted to facelifted 300ZX turbo but it’s not clear whether all of them have it. It is possible to build the diff center from an S13 into an S12 housing too. This, however, is a viscous diff and requires special driveshafts …which on the S13 are CV joints. Much engineering would be required to do this swap I think although it may be possible utilising a mixture of S13 and S130 parts with specially shortened shafts.