F5C71B Gearbox 240RS

F5C71B Gearbox 240RS

Joined: May 19th, 2006, 8:17 pm

August 12th, 2007, 7:53 pm #1

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
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Joined: May 1st, 2004, 7:57 am

August 23rd, 2007, 10:37 am #2

There were a couple of versions of the boxes used in 240RS's , depending on what it was used for .
From memory the Safari box was a direct 5th 5 spd and 5th became 1st followed by the other 3 intermediates . All the rods and forks were different and the conversion kit cost virtually as much as the gearset/shafts . BTW the shift pattern was the Porsche style rather than 5th over to the right in front of reverse like the road boxes .

The Safari box was good because the cars could use 3.9 or 4.1 final drives because 1st was ~ 3.2:1 and the rest reasonably close through to the 1:1 5th . Anyone who's ever given a diff serious curry knows that the competition type ratios have a low pinion tooth count and the fatigue on the steel is huge . Production like ratios have more pinion teeth so share the load more easily .

Cheers .
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260DET
260DET

August 24th, 2007, 7:13 am #3

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
Check out the various Option specs, there were three or four different setups available from Nissan competition. The bog standard FJ20 Nissan box was not a 'C' box though, C standing for close ratio. It was the middle ratio spec from memory, not the 'W' standing for wide ratio.
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daz
daz

August 24th, 2007, 11:45 pm #4

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
The works teams used the close ratio option 1 box which that had been using since the 1970's 240z days. They also used the close ratio option 2 box which had a significantly taller 1st gear. Both were 5 speed 1:1 5th gear boxes.

The option 4 box was known as a rally box with a very short 1st gear (almost unusable really) but I don't think it was used in the 240rs. I do not have enought knowledge on the option 3 to comment.

These cars almost exclusively ran the H190 5.1:1 ratio diff.


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Anonymous
Anonymous

August 26th, 2007, 12:07 am #5

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
No its not unusable at all . Virtualy ALL the close ratio boxes were used with short final drives ie 4.8/5.1/5.3 and some had overdrive 5th ratios .
If you calculate what you are calling the "wide" box ratios with tall final drives ie 3.9/4.1/4.375 you'll see that the ratios and rev drops between the gears is not as much as you may think . Remember in this case 5th ratio is direct or 1 to 1 along the mainshaft so the final drive can be taller (numerically shorter) for constant high speed use such as the Safari .
Generally getting the diffs to hang together was harder than the gearboxes in that era so they went for direct top ratios and higher count diff pinions for durability and reliability .
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Anonymous
Anonymous

August 27th, 2007, 10:16 am #6

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
there was also a box used buy some 240rs (mainly works cars i think) that had an underdriven 5th. this employed the 3.9/4.1 diff ratios. this was done to help with diff life. I think they were made by wisman in the usa.
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Anonymous
Anonymous

August 27th, 2007, 11:05 pm #7

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
the stanza works cars used a hollenger with a 1:1 final ratio
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Joined: May 19th, 2006, 8:17 pm

September 12th, 2007, 6:15 pm #8

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
Did the gear options for the 240RS originate with the 240Z? Also when did the straight cut box make an appearance? Keen to know as it'll mean potentially spares will be more readily available than I first envisaged.
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Tim
Tim

September 28th, 2007, 12:08 am #9

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
Hey Guys

There were early and late 240 boxes.the early boxes were also fitted to the GpA bluebirds and probably some violets. The early ones are pretty fragile and used the porsche type synchros. Both are dogleg first and 1:1 5th

I dont know much about the early boxes, but they may be similar to the early Z box for all I know. They break, so I avoid them.!

The closest production box to the late 240 was the US12 Turbo box. The S12 box had the standard production ratios, but run the wide gears like the 240 and RB20T boxes. The US12 and 240 synchros are the same for 2/3 (production 1/2) and 4/5 (production 3/4) gears, although the synchro cone and dogs that press fit on the side of the gears is different. I have had US12 ones modded to suit my option1 box.

The competition box 1st/rev synchro setup is all different, and fairly fragile. If anyone has any parts for the 1st/rev syncho available, drop me a line tsillay@gmail.com

The 240 box sadly used the smaller striker arm (gear lever to shift rods), (same as early 71 boxes) and these break pretty regularly. You can mod the 240 box to take the later model arms.

Tom, I put my option 1 box on the shelf, and modified a 92 box (S15 6 speed) to fit. These are just fine for 2.4 NA work, and are relatively cheap and available. I will probably get a new ratio for 1st gear cut. I generally run the 5.4 diffs for sprint work, and just start in 2nd (2.1ish:1)


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Joined: May 19th, 2006, 8:17 pm

September 28th, 2007, 4:44 am #10

Hi All,

Have discovered something whilst rebuilding my gearbox - thought I'd share it. It appears there is some difference is size between the standard F5C71B internals and those that were prepared for competition. If you therefore have a competition box that needs new cogs, etc you will struggle to get replacement parts. Chatting with my local Nissan dealership, it transpires that there are no seperate part numbers to differentiate between the internals of a standard box and a competition one. I scoured through some of the period sales literature and the part numbers listed are those for the standard box.
I have identified three types of gearbox -
the standard one, factory special - with thicker laygear, drive gears but standard reverse and idler, and the good old straight cut dog box. Interested if others have anything to add on this.
Tim,

I might be able to help you out with gears for your option one box. I have bought a job lot of spares for the F5C71B - this prompted me to rebuild the one I had!
I just need clarification of the gear you are after - tooth count should suffice.

I am stripping down an S12 box at the moment and I have noticed that the gears are considerably thicker than the 240RS ones. The main drive gear especially. I assume that meshing to a narrower idler hasn't caused you any problems?

Also how the hell do you get the lock pin out from the selector rod?

Good to hear from you by the way.
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