Forums/Z31P/z31-performance-upgrade-forums suspension-chassis-and-brakes/anyone ever shorten and rethread a strut shaft?
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slammedcoupe: (2013-06-24 23:09:48)
the kybs in my car are pretty much brand new, and I don't really want to buy new inserts atm.
i was thinking about getting the shock shaft shortened and rethreaded at a machine shop to gain some travel in the shock while still being low
i have ordered QA1 springs, A1 racing steel sleeves and adjuster nuts.
i also have some upper perches and s13 camber plates from the s13 coilovers.
any input on shortening the shafts? i am planning on sectioning the strut tubes later on but i cant afford new strut inserts for a long while
G-E: (2013-06-24 23:22:04)
You already have s13 coilovers and you want to hack together a ground-control type setup with them and some kyb's ?
slammedcoupe: (2013-06-25 03:33:35)
sold the fronts for the s13 coilovers, just have some pieces left. to bad you didn't come out with your adapters 6 months ago.... the s13 coilovers weren't anything special and the rears are already on the back of the car!
G-E: (2013-06-25 04:07:30)
Sorry, I'll try to be more psychic next time
james: (2013-06-25 09:54:11)
Well in New Zealand people do it all the time, usually done on a screw cutting lathe by an engineer type.
Give him your inserts tell him it needs to be identical but XXmm shorter.
slammedcoupe: (2013-06-25 13:57:59)
you better damn it!
slammedcoupe: (2013-06-25 13:58:29)
awesome thanks james!
jesus94p: (2013-06-25 21:56:14)
I thought about doing this when I built my front setup. Ended up buying shorter inserts. In to see how this ends up
slammedcoupe: (2013-06-26 19:16:08)
in theory it should work.
but we will see
adamvann3: (2013-06-27 00:23:42)
Miata people do this all the time. There are numerous shops that should have this experience. Any local SCCA board should be able to guide you in the correct direction.
slammedcoupe: (2013-06-27 16:16:23)
no doubt, i never thought of that! thanks man!
ps your car is the secks
1sikz: (2013-06-28 01:36:58)
Old school way of lowering without blowing out your shocks. Has been done 1000's of times. Edit: Guess that I should have said it's an old school way of lowering when accompanied by cut springs
G-E: (2013-06-28 02:31:19)
Ground control does this too if you ask…
adroitcaptor: (2013-07-15 15:34:44)
Not trying to thread jack here… I am pretty sure I am trying to do the same thing but with an extra step?
I do not understand how shortening the "shock shaft" (piston rod) would change travel in the shock. Based on function would it not simply adjust the resting height of the shock itself allowing you to lower the car without 'preloading' the shock absorber?
1sikz: (2013-07-15 17:47:27)
That is exactly what it is meant to do. If you lower the car without changing the strut or modifying it, you will greatly reduce the life of it.
Careless: (2013-07-15 17:58:25)
by cutting the shock rod, you move the piston's resting height upward in the shock absorber body, so now you have a greater range of motion within the shock absorber body itself between resting and bottoming out. the part you need to properly gauge is how much of the rod to cut so that you get the maximum effectiveness from both the springs and the shocks because cutting the shock rod requires more compression to fasten the upper mounts to the assembly- thus preloading the springs to a certain degree. it doesn't really change the "travel". it just makes better use of the shock absorber's duty, which is to compress gas/liquid inside the strut tube. if you just dump the car to max low, the liquid inside the shock absorber is compressed almost to its limit, even when the car is just sitting. that is what reduces the overall effectiveness of the shock absorber and ultimately leads to failure.
it's been years since, but a friend and i prepared this for an ae86 by cutting the tube in the middle and sectioning out the strut tube so that we retain the gland nut and threads at the top of the tube. then re-welding it back together and using MR2 shocks. this is a common mod on the ae86's apparently so all the information about how much to cut was already there. this also negates the need to shorten the strut rod since the shock absorber itself is shorter even at full rest height- making the assembly shorter, thus making the car lower.
if you can find a guide that has a detailed explanation of how much is to be cut off the ae86 strut tubes to use the mr2 struts, you might be able to find a way to transfer the ratio to a z31 strut tube and find a shock absorber that works to replace the z31 specific type while retaining maximum shock travel/efficiency.
IMHO, that would be a better way of going about this… because if you shorten the strut shaft i think there will be negative effects in relation to how much dampening the shock absorber should see at rest. but it doesn't sound like you really care about that anyways, so i would just wing it and see what happens.
keep some flat spots on the strut shaft to make taping easier. and don't cut all the way through in one pass. the shaft gets hot very fast and the oil will spew out of the top seal before ya know it.
DeleriousZ: (2013-07-15 18:29:19)
hmm? If you lower the car by 50mm, and shorten the shafts for the struts by 50mm, you'll have the same amount of piston stroke and position within the tube as you would at stock height.
Careless: (2013-07-15 18:42:47)
pretty sure that was the first thing we tried with the ae86 tubes and it rode like shite. i think it had more to do with the springs used which are stiffer in addition to being shorter. which is why it takes a little more math and some guys on other platforms have already figured it out for their application.
in order for it to ride a bit better with stiffer lowering springs, you'd most likely need to cut a bit less than 50mm on the strut shaft (say 45 to 30mm - the less you cut, the longer the shaft is (just to avoid confusion)). ideally, IF you want to lower the car 50mm- keep the shock shaft slightly longer so as to pre-load the damping fluid a bit since the springs are going to get harder wayyyy before the shock absorber has time to make use of the fluid inside the body (being that they lowering springs are most likely stiffer springs- so the same spring compression on lowering springs equates to them being a lot stiffer than the stockers at the same compression).
you WANT a bit of preload… just not the same preload you'd have by just lowering and not cutting the absorber shaft. like I said, if you really care- there is a ratio or some experimenting to be done. I would equate this to being similar in practice to using the adjuster on adjustable shocks. some people find the right setting that makes the car ride how they want- and they use that setting, while others would say it's too soft/too hard.
its not just the shock absorber travel you have to worry about. it's the spring compression in relation to the damper itself. but if "decent" is all you want to achieve, 50/50mm is not a bad place to be, I guess. the shocks will probably just be a bit late on its absorption effects.
it's the same as lowering springs on stock shocks… it rides crappy. they aren't damped accordingly. generally sport damping shocks are a better match to sport springs because they're both stiffer than stock.
coles:
if you don't cut the shaft, you are not making use of the shock absorber's fluid damping.
if you cut the shaft the same length as the drop or more, your springs are going to get really tight/stiff well before the shock can be utilized fully.
if you cut the shaft slightly less than your drop, you will preload the fluid a bit so that you equalize the effects of the spring/shock combo and they will ease into a nice sweet spot that they should be.
it's easy to do because you can just tap the strut rod for like 2 inches, and then just tighten up the bolt at the top to pull the rod up to adjust the rod's length (effectively making it shorter). once you find the sweet spot. cut off the excess… (or leave it there for ghetto adjustability if it doesn't hit the hood).
this is the type of shit we did to make the drift cars 1% better on gymkhana days since we had nothing better to do and no money to do anything better.
slammedcoupe: (2013-07-15 19:10:40)
im trying to find some one local to do this, if not i may just use the regualar lenght of the shock and get some shorter ones for next year and section the struts.
i just wanna drive [archived image: frown.png]
1sikz: (2013-07-15 19:26:47)
This. When you lower the car without modifying the struts, you decrease the available travel length, putting more stress on the valve. This ends up "blowing out" your struts
adamvann3: (2013-07-15 21:41:54)
Not fully reading Careless long drawn out posts, I think he is trying to make the point if you are going to a shorter, stiffer springs the struts would need to be properly valved (along with shortening the rod) to perform at its best.
You know, cars love that full stroke damping for your riding pleasure
DeleriousZ: (2013-07-15 21:51:12)
Did you put a post up on beyond? Someone there should know.
Careless: (2013-07-15 22:20:46)
you just love mentioning that every time, eh jack ass?
DeleriousZ: (2013-07-15 22:30:15)
To be fair, they are long and drawn out. I don't think I've fully read one in a long time.
Careless: (2013-07-15 22:33:12)
they say what they need to say. otherwise you're leaving people in the dark about what they're doing.
not my fault you guys can't keep your eyes peeled for an extra minute.
what are you guys, 11 year olds with ADHD?
i even put "coles" on one of them because I knew it was a bit longer than most of you guys can hold an attention span for.
G-E: (2013-07-15 22:42:32)
It's less about the length and more about the girth? Ladies love girth
slammedcoupe: (2013-07-15 23:13:19)
good idea, I shall try that!
I may just run them and see how it goes, their just kyb inserts anyways.
Rahlude92: (2013-09-05 02:38:49)
I know im thread jacking here, but ground control has gone bat shit crazy with the modification to the front strut. I guess too many people bailed out on them and they have resorted to Z31 rape. I want to also do the strut sectioning and weld on perch goodness. So i've been looking around, not nearly as much as I should since I just thought about doing this yesterday, but would you use the 280zx front coilover kit for the Z31? I tried finding measurements to no avail. Here's the link http://www.ground-control-store.com/…p/II=849/CA=27. I was thinking about using the mr2 rear insert for better performance since to get the full potential out of this setup, everything should be properly fabricated. I got a set of s13 rear coils off of ebay that should do the job. Hopefully they dont cave under the torque.
Rahlude92: (2013-09-05 02:39:40)
s13 rear coilovers*
Rahlude92: (2013-09-05 02:41:28)
also, would these work in NA strut tubes? 89 to be precise
G-E: (2013-09-05 03:29:31)
What did they do?
Rahlude92: (2013-09-05 04:13:16)
To modify the front strut housing $1049 fronts only....for a little bit extra....full set of stance....
G-E: (2013-09-05 04:34:10)
That's madness
707Redz31: (2013-09-05 05:16:01)
I actually called them a couple months ago about this and they said they don't do it. Do you know who talk to there? Cause no one i talked to seemed to know anything about this as a service from them.
G-E: (2013-09-05 10:59:36)
No, I did hear a few people using other cars up here did, but I never had any intention of going gc anyway
… it's beginning to sound like they don't want our business anyway :
Rahlude92: (2013-09-05 12:27:20)
Yup. Do you know of any coil over sleeves that would work? And whether its for the s13 or 280zx?
DeleriousZ: (2013-09-05 14:45:11)
madness?
[archived image: This_is_sparta_This_is_SPARTA-s373x411-14709-580.jpg]
Rahlude92: (2013-09-05 19:58:00)
lol can anyone pitch in the info?