Differentials

[Rick]

I have owned my 71 240Z now for 18months and probably done about 10 race events consisting of 1 km sprints on street circuits, 20 km sprints on race tracks and various hill climbs.

The cars suspension was set up to try and cater for all types of on road conditions and has proved to be very good.

The engine is basically standard with mild cam, extractors, electronic distributor and N42 head giving 134BHP on the Dyno at the rear wheels. Wheels are 16" x 7" with 205 x 50 series Falken ZE 326 tyres. Doing the 1km sprints I have had difficulties with the huge gap between 2nd and 3rd gear and was 1 - 2 secs slower than other guys in my class. Investigation showed that my 240Z was originally an automatic with a 3.5 to 1 diff.

The guys at the local Z Club advised me to source a higher ratio.

I recently sourced a 4.6 to 1 front diff from a Nissan 720 4 wheel drive ute. The problem I have is that the flanged drive shafts into the diff are different to the standard flanges on the diff in my 240Z. I took off the back cover on the new diff to see how these flanges come off but cannot work out how you remove them.

Does anybody out there know how I can remove them to replace with my existing type flange assembly?

[PrOxLaMuS©]

4.6 damn! talk about some high RPM's at high speeds..

i would say for everyday driving with your automatic...

get a 3.7 or 3.9....

.. sorry kidna pointless

[jmortensen]

My buddy and I were at the Streets of Willow running a POC slalom, and he was having the same problem in his 510. Our cars post times at autox that are within a second of each other, and since he has changed his transmission he has come within 2 seconds of my Z on the big tracks.

His problem was using the 280Z five speed. There is a BIG gap between 2nd and 3rd. When we came onto the straight, he'd stick right with me until he shifted into 3rd, then I'd drop him like a bad habit. He'd drop right out of the power band and the car would lug along until he hit 4000 rpm or so and his 44 Mikunis started to work again, but by that time I was gone!

Your diff ratio seems really extreme, if you are concerned about the 2-3 shift I'd suggest a 280ZX transmission, as it has tighter ratios. I think you might find your top speed really limited by such a low gear.

On my friend's car we installed a Roadster tranny which has ratios similar to the ZX tranny with the comp synchros, and that allowed him to catch me again.

Jon

[biker]

Rick

If you are going to try and catch me go for the 4.6. Not sure how you are going to get it in there though..

Your experiences may assist me as I want to upgrade my diff aw well to keep up the revs through some of the corners.

Hope all goes well

Biker

[texasz]

Not sure about the overseas models but you probably have found an R200 and not an R180. The R180 is stock in a 240Z (US market at least) and to go to an R200 you must also change the stub axles to the ones used in a 280Z which had the R200 in them stock.

Hope this helps...that is if things are not completely different for the cars you got over there.

[Rick]

Some say the 4.6 ratio is too low, others say it will be OK for sprints but too low for the track. The only way to find out is to try it. Had to take the diff to a diff shop to change over the halfshafts form the 240Z to the 720 diff. Also had to change planetories.

Next event is a hillclimb so it should be beneficial in this event.

And biker you will know whether the change over is beneficial as I will be right up your---------.

Have picture of your car at Leyburn but lost your email address.

Rick