4 link adjustment

[--Redwork--]

Aaron...I was under the impression you should set it down a coupl of deggre too...
But up thinking about it i can understand the idea...

With the pinion angled slightly up.. as the car squats (get lower) yje diff will rotate forward because of the top trailing arms being shorter than the bottom ones hence, scribing a shorter arc and pulling the top of the diff over..

Now.. with an equall length trailing arm you don;t get the diff tilt.. Only a difference in the angle if the tail shaft, As the duff travels up the front of the tail shaft stays fixed..
So in theory if your diff travlled far enough you could set it at 2 degree down and at full drop end up with it 2 degrees up...

This all how ever relates in no way to us due to the fact 99% of us run super stiff springs and would be lucky if our diff moved up anymore than 40mm from a static height..

One thing I haven't touched on is deflection...
Say for instance you had no suspension travel at all. Was 100% solid.. You would using the theories explained above set your pinion angle pefectly straight.. yes.??

WRONG!!!!...

Whether your running stock bushed urethan ones or rose joints, you will still have some amount of deflection in the trailing arm bushes. In the case or those running rod ends the defletion will come from the car its self..

So... Me personally.. I would set the pinion angle down just a little reguardless.
But the only way to find the best setup is to experiment with it...


Also note that raising the pinion angle brings the front of the diff up, and you may find if your car is low enough the nose of the diff will hit the floor one occasion..

Perfect example is a freinds car... was supper low. didn't have adjustable trailing arms so the diff was pointing down due to the top arms pulling it over as I explained above..
But nearly ever time he dipped the clutch or smahed threw a gear the diff would twist up and violently smash the floor... Sounded terrible..

Hope that helps...

[RobertoX]

errr... as pointed out by --Redwork-- the following is wrong, sorry:


Depends on which way your tailshaft is spinning, I'm not sure but it might be different between cars.
If it is spinning anticlock wise looking from the rear of the car then your ring gear will need to be on the passengers side and the nose will point down as you load it up (therefore you need the nose pointing slightly up in the static/unloaded position)
If the tailshaft is spinning clockwise when looking from the rear then the ring gear is on the driver's side, the reaction of the nose will be up so the nose has to point down in the unloaded position.

Anybody knows which way the tailshaft spinns in an 80's Toyota? Or what side is the ring gear on?
Also what cars were those links in reference to?

[Mr Fujiwara]

i aimed mine down and it made a filthy noise, a wurring under accel.
my car is very low and i aimed it down when i put the 4link in because orginally the diff nose was hitting the floor, when i set it back close to where it was level the car felt heaps better, i havnt yet had time to work out other good setups, such as aimed up, or even 100% straight in terms of getting links equal links etc.
i was under the impression aimed down gives better propperties for drifting, but i never really did any research.
But the solid mounts seem to give me heaps of traction in any conditions and i would definately say it makes the car more stable. the car is daily driven 2-3 times a week i still dont find it overly uncomfortable.
solid mounts

[--Redwork--]

RebertoX..... which way the tail shaft spins has nothin to do with it...

The diff will always twist up under load... T
he only tme a diff will swist down is when you reverse...

[Jonny Rochester]

For every engine anyone on this forum is going to play with, the crank spins clockwise when looking from the front. And with all the gearboxes we use, they are such that the tailshaft will spin the same way. And in 4th gear the crank is locked to the tailshaft 1:1. And for every finaldrive anyone on here is using, the crownwheel is on the left side and the pinion is mounted below the centre line, and uses a hypoid gear (to reduce noise).

But knowing this, it makes no difference anyhow to what dirrection the tailshaft spins. When the rear axle is loaded, (driving forwards), the front of the diff housing will want to rise. This is why you set it up to point down a little in static position (in relation to the gearbox output shaft, which often is not horizontal).

Whole books are written about this, and the lengths and angles of a 4 link system. For drag racing, you don't just have 4 equal length arms that are parallel and horizontal, there is much more to it than that.

Thankfully, for most of us that just do casual laps and some drift, it makes little difference.

[--Redwork--]

^^^^^^ Your right about the equal 4 link Jonny...
Was just useing a parrallel setup to help explain the effect enequal length arms have on effecting the angle when under compression...
The stock setup when lowered, has vary substainial effect of the pinion angle under suspension compression due to the top arm being already alot shorter and it on nearly a30 degree angle when car is static...

Seting up a proper drag style 4 link is a fairly tricky process..
Changine the angles of the bars has massive effects on line of force.. Altering whether the car squats or lifts or stays in the same possition..

[RobertoX]

Yeah, lol you are absolutely right! That's what I get for posting at 7 in the morning, I'm an idiot