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240Z rack into 280Z


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I know this is not a huge technical challenge but I really like the faster steering ratio of my 240Z. My 280Z feels more like a jet powered chuck-wagon when I come from the 240Z. I am always late entering a corner with the 280Z because of the "slow" in turn in, as compared to the 240Z. The 240Z has significant less steering wheel turn, for the same amount of steer. I have a spare 240Z rack laying around and I am thinking about swapping the sluggish 280Z rack out for the 240Z one. Has anyone done it, and what was your end result like? Is it wiser to just pick up some quick steering arms for the 280Z instead?

Edited by cygnusx1
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Calculate out the total steering ratio (factoring in steering arms) and you should have a valid comparison between the two options.

 

I have not done this but it should be simple enough to do; the overall steering ratio is # turns at steering wheel/# turns at wheel. One turn of the steering wheel translates to a set amount of motion at the tie-rod ends, which would give a certain angle of rotation at the road wheel. All you need to know to do this is the steering rack transfer function and steering arm length.

 

EDIT: If you choose to switch racks, be aware that the 240Z and 280Z rack bushings are different.

Edited by Leon
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EDIT: If you choose to switch racks, be aware that the 240Z and 280Z rack bushings are different.

 

Thanks for the heads up!

 

The cause for my inquiry is that my 240Z has really light and razor sharp steering feel at anything above 5-10 mph. Whereas, my 280Z steering feels heavy "muddy" all the time or until about 45-50 mph. So I am concerned that if I go to the 240Z rack, I will get the quicker ratio but increase the effort and "muddy'ness" over what my 280Z already has.

 

Both cars have nearly equivalent suspension, wheel, tire, toe, setups. I could be barking up the wrong tree too. Maybe my 280Z rack has reached the end of it's life and is just "draggy". Or maybe the cars are just that different from each other. I recently greased it all up to try to get rid of the muddy feeling but it didn't change. With the front up in the air, the rack moves smoothly.

Edited by cygnusx1
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Is it wiser to just pick up some quick steering arms for the 280Z instead?

 

The quick knuckles change the geometry of the steering. Installing them is moving away from Ackermann. It's in ongoing argument, but I think you'll find more knowledgeable people pro-Ackermann than anti. Myself, I would prefer to lengthen the arms, if the option were there, simply because I believe the S30 is lacking in this area (close to parallel steering).

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I am pretty sure that the rack ratios are the same. If you want, you can do one turn of the steering shaft and measure how many inches the rack moves (I've got one sitting on my work bench). Also I think the steer knuckles are the same length as well. I've got 280 knuckles handy if you want to measure your 240 ones, but I'm pretty sure they're dimensionally the same as 240 knuckles.

 

Up until I actually graphed it out, I would have agreed with Ron that longer arms are better. Now that I've done the graphing, I think the difference the shorter arm makes with respect to Ackerman is pretty minimal, so if you want quicker steering that is a reasonable way to go about it, and if the relatively small gain in quickness is worth the relatively small loss in Ackerman and increase in effort, then go for it.

 

Here is a very detailed article on Ackerman that tells you how to graph it out. http://forums.hybridz.org/index.php/topic/97426-ackerman-article-by-erik-zapletal/page__p__914846__hl__ackerman__fromsearch__1?do=findComment&comment=914846

 

If you skip to the end of this thread and read backwards, you'll see some of my calculations for Ackerman and rack position and steer knuckle length: http://forums.hybridz.org/index.php/topic/97092-toe-changes-for-track-use/page__st__80

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The 280Z steering feel is hard and slow and somewhat damped, where the 240 is light and quick. The steering ratios and efforts of my 280Z and 240Z feel totally different. I wonder if the PO had installed shorties on the 240. Hmm, tomorrow if the new snow melts, I'll get a closer look with some measuring tools. I'll check the arms, and the rack ratios. Something strange if both racks are the same. I thought they put in a "slower" rack in the 280Z to offset the steering effort gain due to the added weight of the car. I read all the Ackerman arguments already and I am not too worried about it, since 99% of my driving is on back roads (not on a race track competitively). I run right around zero front toe on both cars.

Edited by cygnusx1
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My understanding is that there is a discrepancy in the FSM which contributes to the debate about which is the faster rack. I think the FSM is showing data for what may have been used in Japan or Europe and that we got the same racks in all the Z's, but it will be interesting to see what you come up with and how it compares. I did look up my spec from another thread: "I just went and measured the Z rack at 1.8125 inches per turn of the wheel." This was eyeballing the pinion, so it isn't necessarily right down to the 4th decimal place, but it did look like 1 13/16.

 

Maybe that will save you from crawling under 2 cars...

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Thanks, it looks like I'll get the 280Z on stands in the AM tomorrow and get a count. The answer will also answer my question about my 240Z possibly having shorty knuckles too. Jon, did you measure a 240Z aluminum, or 280Z iron rack? Ineed to know which car not to crawl under ;)

Edited by cygnusx1
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Dave, are the 280Z rack bushings in good condition? If they are soft, it definitely gives the car the "muddy" feeling. The rack moves some before the wheels do, and the more grip you have the worse the muddy feeling gets.

 

It took me a while to figure out why better tires made my car seem worse.

 

jt

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I would have to go with the comment regarding the "feel" being due to difference in steering couple & rack bushings (worn out/replaced/upgraded).

 

As for the steering racks, they 240 rack does have a quicker ratio, but can't remember exactly the number. I think it's something like half or 3/4 of a turn quicker. From what I've seen, steering knuckles are the same.

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Both cars are in tip top shape with excellent poly bushings on the rack. I run a rubber steering coupler on BOTH cars. It's just my preference. I am still cleaning up my garage so I can get the 280Z up on the stands. I did clean up the spare 240Z rack that I intend to install in the 280Z. The 240Z rack I have on my garage floor travels roughly 1.81" for every turn of the input. I'll have the 280Z rack info later on.

Edited by cygnusx1
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OK The 76 280Z rack travels roughly 1.5" per turn of the input shaft. There are 3 full turns lock to lock on the 280Z. There you have it. Pretty significant difference that can easily be felt. The 240Z is much closer to what a modern car with power steering has. The 280Z just feels "off the mark" after coming from a modern car, or a 240Z. I shall proceed with the 240Z rack swap into the 280Z.

 

 

 

 

Rough Measurements:

 

240Z (1972) - 1.81" of travel per 360 deg of steering.

 

280Z (1976) - 1.5" of travel per 360 deg of steering

Edited by cygnusx1
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Well, I got the 240Z rack in place in the 280Z today. I need to button up the engine mounts, sway bar, and do an alignment before I test it out. I must say that the 240Z rack seems quite a bit less beefy than the 280Z one.

 

To pull out the rack you need to drop the front of the sway bar, loosen the engine mount bolts and raise the engine about 1". Then disconnect the steering shaft, and the outer tie rods. I chose to disconnect at the steering coupler. The whole assembly works its way out the front.

 

 

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So I finished the install and did a rough alignment with some strings from the rear wheels to the front wheels, and a tape measure. I drove it, and it still felt muddy but the ratio was definitely better. Obviously, I hadn't really improved the situation much. So I read up on Ackerman and Z alignments again.

 

I decided my tires might just have soft walls, and could be the cause of the muddy feeling. An easy test was to bring them up to 40psi and test drive. This helped a little but not as much as I thought it should.

 

So I decided to take out the 1/8" of toe-in I had. With zero toe and 40psi it was much closer to what I wanted. I decided to go even further. Since I have about -1.5 deg of camber, I thought I could get away with some additional toe-out without getting too "wander-ish" up front. I had gotten the steering wheel on dead center, with the rack on dead center, with zero toe. All I did now was turn the tie rods out equal amounts on each side to get about 1/8" of toe out, and that really woke up the car.

 

Now the steering is much lighter on turn entry, and holds it's course with a linear feel to the steering wheel. Course corrections are quick and easy in mid corner. I may try a tad bit more toe out just to explore the ranges.

 

In conclusion, the 240Z rack does feel really good in the 280Z once you get the front end dialed in. I don't think the improvement is worth spending the money on a new rack, but since my red 240Z came with a spare one, it was worth throwing into the 280Z for a nice quick steering mod. If you haven't tried toe-out in your Z...go do it! ;)

 

It's still not as snappy as the 240Z but I think the 300-400 pounds of the 280Z makes that difference.

 

 

 

Edited by cygnusx1
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