Live Axle Mods Thread

[Konakid]

Have wanted to start this for a while, hoping that others more knowledgeable than myself can shed some light on questions i have and make this thread a 'general rear end tech talk thread' where people can post up their ideas/explanations etc.

Firstly. I've heard about the 'drilled out bush' mod to the passenger? upper trailing arm to allow more give as the diff twists when cornering right and it moves upward on an angle. Like most people my car oversteers FAR easier on the limit when turning right than left, i thought that this mod might cure this as it is quite annoying.

Who has done it? Did it work? Why does it work?

Someone posted up some diagrams on the old forums about how the diff moves under compression in relation to the panhard rod and why equal link eliminates most of the arc that the diff travels through under compression.



Thought we could add in explanation and pictures of Equal length setups, watts link setups, lowered shock mounts, traction brackets, pinion angle etc etc, as i think many dont/didnt bother with rear end mods (myself) instead pouring money into the front end.

Hoping guys like SR rolla and others can help out.

Post away.

[bigm]

This will be a good thread.

i am also interested to see if anyone had toyed with the idea of Camber on live axle. me and a friend have toyed with the idea but some more information/experience would be handy.

[Touge Boy]

quite a few IPRA guys have their housings bent in a press by an engineering company... so yeah, you can run camber

I imagine it'd chew shit out pretty regularly.

[bigm]

yea read a big about that,
we were thinking more along the lines of running a uni joint in the housing and cut and shut the housing to suit the angle we want. so a fixed IRS in a sense

[--Redwork--]

I dont understand how bending the housing will result in adding camber the axle is still straight.. Unless you bend the housing where the axle tubes meet the center thus altering the angle at which the axle enterin the center... That would create some camber but I would image it would destroy the bearing in your center awfully fast.

Only reliable way to get camber with live axle is go to fully floating arangment...
Sorta like IRS but solid... you have the center, then the axle, then a hub at the out side wihich the axle runs into.. Axle is splined on both ends..

[fantapants]

usually they heat and bend the housing... gets to about -1.5 camber? or even weld long one side of the housing will allow for bending, but that is a lot less accurate.

a friends dad just forked out for camber stuff for his ipra car... the ducks nuts sorta stuff, ill look into finding the details for you.

samq has a very good explanation of the drilled bushing theory and application on his website. ill let him link if he wishes.

im VERY interested in watts linkage, after i have done my equal length boxs. My personal situation - coilovers - leaves me wandering if i am better off leaving the top arm location, or what the advantages are of moving them directly above the lower arms, or disadvantages ala slydar.

From the little i have looked into it, watts linkages are rarely stiff enough, and its surprisingly easy to make VERY easily adjustable roll centre setups. The ones that mount the pivot on the diff seem to be the worst in terms of stiffness and robustness ( dont think thats even a word )

[Frak]

I think on a very low 86, equal length arm is a MUST, I was luck enough to source a genuine TRD N2 kit out of Japan a while back.

[--Redwork--]

I just did my equal the same as everyone else with it straight above the originals..
I think a watts link would be pointless for our cars.. Nearly everyone hear would have only very minimal suspension travel and no need for it..

As for rear roll centers... I now nothing about this.. I did how ever move my mount lower on the diff when I sapped the brackets over.. To try and help correct it alittle..


I would like to know how raising/lowering roll center effects the handeling of the car..

Think there's a roll center thread on Nissan Silvia they just started the other day..

[keiichi]

drilled out bushing is because when you fit a full unequal length rose joint 4-link setup the axle twists during cornering and tears away at your seams.
so you run a 3.5 link so there's 3 spherical bearings and one rubber bushing which takes up the slack.

if you're going to go spherical bearing links you should go equal length... so, you need to cut holes in the floor of your car to weld in box sections to allow for the extra long upper links. then the links need to be parallel to each other and also the ground. this is so that when your springs compress (and lets hope their not too soft) as the links travel the same radius - the lower ones will pull and the tops will push and visa versa on the opposite side during cornering - the diff wont twist because there is no pivoting at either end (hope that made sense sorry im terrible at explaining things).

live axle roll center is inbetween the panhard mounts put simply - i think! im not 100% on that, just my judgment.

when you lower a car your panhard pushes the diff to one side - hence adjustable panhards - i think offset panhards might be the cause of konakids uneven oversteer? *edit* if the panhard isnt level, the body is going to be shifting left or right over the diff depending on the direction of the corner. so yeh, most of us would get this. i think maybe if you lowered the panhard body mounting point so that the panhard was level with the diff and centered i think you will solve this problem almost and you will lower your roll center aswell. hence why there is watts link.

also i think with a full parallel setup in the rear you will get better effective spring rate. since your diff is traveling perfectly up and down now and not twisting/pivoting the car will be pushing directly down on the spring not offset to one side if that makes sense.

anyone feel like stepping in and correcting me here please do so :)

love these threads

i will be experimenting with all of the above and more on my next project - probobly another corona when i find a decent one. so keep an eye out for a thread by me in the next few months.

[Sam-Q]

fantapants: thanks

http://s-86.com/s-5linkrear.html


keiichi: great post. People don't realise that an unequal length 4 link has a contradictory movement and something has to flex and give with solid bushes. I did a toymods post about it a long time ago when I realised myself after trying to figure out the geometry.

I still plan on get my housing modded to have -0.5 degrees of camber, its just not a high priority for me right now.

[Konakid]

Some good discussion already, keiichi, nice work, Sam, your article on your website makes a lot of sense!

Ill put a link in my original post if thats ok?

[Sam-Q]

oh sorry I thought thats what you meant, yeah you never need to ask for my permission for things like that

[Tim.duncan]

i am looking at making my own traction brackets. one thing i need to know, am i aiming to get the lower arms horizontal with the ground or on a slight angle leading down towards the diff?

also people talk about pinion angle changing whan you lower the car, and this needs to be rectafied by having adjustable top arms. now my question is when i make the traction brakets if i was to change the position of the mounting hole towards the rear of the car this would be effectively making the lower arms "shorter" bringing the pinion angle back up??? have i got this all wrong or would this work?

[Sam-Q]

moving the mounting point forward or back does nothing but change the diff angle which you just wouldn't do that way. You make traction brackets to make the pivot point lower to the ground, so basically increasing the angle not making it flat. Basicly you want the diff pivot for the lower arm to much lower than the one on the body. I suggest having a look at my guide if you have a moment.

Also if you make any of the bars adjustable I suggest doing it to the bottom, they can be easier to work with

[FAST EDDIE]

i havent done much research as when ive needed more traction on my drift car i just use gripier tyres but ive put in adj upper trailing arms and adjusted them up and got a whole ammount of fark all difference difference so i guess the stock setup is at its best in my situation.

[Konakid]

Same here eddy i got some cheap noltec poly bushed adj upper arms in the corona but havent played with them, they are just as standard length. Did you adjust them longer, to point the diff nose back up?

Would i see any gains in making them longer to point the diff nose back up to horizontal?

When the F series goes in i also got the shock mounts lowered 25mm hoping to get some captivity going on with some slightly taller springs.

[Tim.duncan]

moving the mounting point forward or back does nothing but change the diff angle which you just wouldn't do that way.

isent that changing the pinion angle? which points downwards when you lower the car so needs to be pointed back up which is why people use adjustable arms? why is moving the mounting hole any different than changing the length of the bar?

no worries ill go have a read now

[Sam-Q]

actually it's a bit of a myth that changing pinion angle changes the suspension response. Correcting pinion angle is purely for reducing power loss and wear through the rear uni joint. I need to add this to my guide

Now Tim, you can change the pinion angle by redrilling the bottom hole but really you would be lucky to have 2 different positions with a lot of work. What I mean to say is that geometry wise you won't change anything, only moving the pivot further to the ground changes something

[FAST EDDIE]

actually it's a bit of a myth that changing pinion angle changes the suspension response. Correcting pinion angle is purely for reducing power loss and wear through the rear uni joint. I need to add this to my guide

Now Tim, you can change the pinion angle by redrilling the bottom hole but really you would be lucky to have 2 different positions with a lot of work. What I mean to say is that geometry wise you won't change anything, only moving the pivot further to the ground changes something

i didnt want to say it but i believe the same thing sam how does it realy give you more grip, think aobut it lol

[Sam-Q]

hehehe, hey we all thought it did something at one stage eh?

[keiichi]

the pinion angle itself isn't what gives you grip so much as what direction the diff rotates under throttle/load.

(looking from the side of the car) if you were to have the upper arms pointing upwards from the diff towards the body and the lower arms level, as you accelerate and weight is transferred to the rear of the car the top of the diff is pushed to the rear rotating it backwards. this means your wheels are less likely to spin because effectively the diff is rotating the opposite way the wheels spin, sought of making the axle/wheel/hub stationary in the housing for a fraction and dampening the friction between the tyre and the road..... wow that was hard haha.

now if you're looking from the top of the car, as you go around a left hand corner, the diff rotates clockwise/to the right, sought of making it like all-wheel-steering - again dampening friction.

good for grip, bad for drift.

[driftke70]

fantapants: thanks

http://s-86.com/s-5linkrear.html


keiichi: great post. People don't realise that an unequal length 4 link has a contradictory movement and something has to flex and give with solid bushes. .

Precisely, your tyres, which is what brings in the predictibility and easier sliding.

Changing the pinion angle of your diff only matters if your running un-equal length.

The reason this is has nothing to do with tail shaft angles or anything, but the way that the arms mount to the diff. They arnt directly above and below each other and effectible your changing the fulcrum point of your diff turning through its axis and its lever affect on the spring and bushes ect.

When you lower 86/70 they dont actually end up in that bad of a position. You can get minor gains but most are negligible. Other cars this would be of significance, or if you ran a rally setup with higher suspension in the rear.

I have done alot of research on custom rear ends, i was going to run inboard horizontal coil overs at once point with custom alloy triangular arms and stuff, but what I came out with was all you need is the right spring rate and shock, equal length rose jointed, drop mounts, and a well adjusted well bushed panhard. Anything more is really plucking at hairs.

For starters with a watts link you have twice as many bushes, twice as many zones of flex, and twice as many unpredictable adjustments.

Just thought id also mention the reason drag guys are obsessed with their pinion angle in the rear, is because they run pretty high rears to fit their massive tyres in, they run soft springs and their diff starts off in a real bad place because of the height, and gets corrected too far through the squat characteristics of their spring rates.

[Konakid]

Im keen to do it to mine anyway when its driving again and see how it makes a difference if at all.

Edit: Keiichi, thats what i thought, when accelerating, it doesnt try and twist the diff and make it roll forwards, instead backwards. What effect this has when cornering/sliding under power would probably be more rear end grip i would have thought.

[driftke70]

for grip you basically want to point it down till you get axle tramp the go up a bit.

[keiichi]

Im keen to do it to mine anyway when its driving again and see how it makes a difference if at all.

Edit: Keiichi, thats what i thought, when accelerating, it doesnt try and twist the diff and make it roll forwards, instead backwards. What effect this has when cornering/sliding under power would probably be more rear end grip i would have thought.

just thinking out loud here in regards to drifting but - might be good for cars with lots of power i reckon - vehicles with lots of torque or boost. would just bog down 4banger NA cars i think. also the housing twist is the wrong way for drift, is gonna carry the rear around the more throttle you give, counteracting the potential grip you gain on-throttle.

[sundee]

they do make a watts link.. pretty pricy

http://www.rhdjapan.com/jdm-low/SS-Works-Watt-Link-Pro-Rear-Axle-Kit-AE86-Levin-Trueno-60906

[keiichi]

then you still need to make up mounts on the body too... looks pretty straight forward to build. anyone know what kind of bearing is used at the center?

*edit* not that i would bother on a drift car.

[Sam-Q]

Precisely, your tyres, which is what brings in the predictibility and easier sliding.

Changing the pinion angle of your diff only matters if your running un-equal length.

The reason this is has nothing to do with tail shaft angles or anything, but the way that the arms mount to the diff. They arnt directly above and below each other and effectible your changing the fulcrum point of your diff turning through its axis and its lever affect on the spring and bushes ect.

When you lower 86/70 they dont actually end up in that bad of a position. You can get minor gains but most are negligible. Other cars this would be of significance, or if you ran a rally setup with higher suspension in the rear.

I have done alot of research on custom rear ends, i was going to run inboard horizontal coil overs at once point with custom alloy triangular arms and stuff, but what I came out with was all you need is the right spring rate and shock, equal length rose jointed, drop mounts, and a well adjusted well bushed panhard. Anything more is really plucking at hairs.

For starters with a watts link you have twice as many bushes, twice as many zones of flex, and twice as many unpredictable adjustments.

Just thought id also mention the reason drag guys are obsessed with their pinion angle in the rear, is because they run pretty high rears to fit their massive tyres in, they run soft springs and their diff starts off in a real bad place because of the height, and gets corrected too far through the squat characteristics of their spring rates.

your wrong about the tyres taking it up. thats not where the problem is at all and what they do is irrelevant to this problem. Ok look at it this way on a normal diff the top arm is shorter, so when it goes over a bump it tilts the pinion down (I think). However if one side is going up and the other down they are trying to mechanically twist in different directions. That means in pure theory if there was no give or flex in the suspension at all an ae86 would not be able to lean in the back.

I thought the only rear adjustment you do with the watts link is the X and Y axes of the pivot. I don't know if there are many real world gains to be had though.

I could be very wrong here but with the slight changes in pinion angle from raising or lowering it doesn't really have any effect on spring levering and minimal geometry changes.

I didnt modify my diff to have a lower pivot point to correct the car after lowering I did it to further raise the anti-squat angle. I would love to take it much lower again and I might fit rod end joints to clear the road and still have 100mm of clearence.

sundee86: I am wary of that one, it looks creative but I don't think it would be rigid enough.

keiichi, it could have a few things there, idealy a wide needle bearing assembly maybe or a sintered bronze bush?

[sundee]

yeah i do agree.. i just remember seeing it around and thought it would be good for guys to get a visual

[Sam-Q]

yep that it is

[Tim.duncan]

can some one explain to me "roll centre" for the rear end, and the advantages of being able to adjust it?

i have seen the cusco rca for the rear and dont undertand where it goes or what it does?

[sundee]

check out this thread - should sum it all up

http://www.ae86drivingclub.com.au/forums/showthread.php?t=13274