Adjustable lower trailing arms discussion.

[n00bus m@x1mus 465]

Hence were i get lost with the whole pinion angel science... its supposed to be the opposite to the gearbox right?

Heres a diagram i copied once out of an SM mag....

 

 

So if the box is pointing say 2 degrees down to the rear then that means the pinion angle must point 1-2 degrees up????  but then every trail arm configuration wants to curl the diff forwards as it rises thus pointing it downwards right at the wrong time, when your unis want to give way the most they have more bind introduced into them because of this.

 

Is this anyones elses take on the subject or have i got it completely wrong?

[Crazy2287 1,886]

Under acelleration the pinion gear climbs the crown wheel. Causing your diff to try and twist. This can be anywhere from 0 degrees with a solid 4 link to 6 or more with leaf.

I have laddar bar' I think that's what its called, type whichis similar to a 4 link except uses a whatts link. And am using firm poly bushes. Compliance of the joints won't allow much more than 2 degrees with my range of horsepower, so I have read. Rubber bushes will be higher.

If it truely doer roll foward as the diff rises into the body' this could be a design to keep pinion angle constant uunder acelleration. As weight transfers back compressing the rear suspension due to acelleration the diff is rolled toward to cancel out the effect. Of the loading on the bushes in the trailing arms.

[n00bus m@x1mus 465]

It rolls forward quite a bit.  While you working on your angles pop your springs out and jack your diff up into the body, you will see how much it affects it.  The only benefit i can see is that it keeps the tailshaft from smacking the tunnel as the diff goes up.  If the pinion wants to climb the crown under acceleration then this will force the pinion angle skywards, the top arms prevent this and applies more torque to the wheels and im guessing that by making it squat in the arse it will add to the general rotation of the wheels forward aswell for more launch.  But as i said before this fights against the logic of correct pinion angle as it forces the nose down and induces bind on the unis.

[Thom 6,654]

That's exactly the reason you want to do it, as you accelerate the pinion is forced in the opposite directions from what it is trying to rotate and cause more "bite" into the ashfalt creating more traction

[slydog 7,873]

Victor Bray ran 6 sec's with ladder bars and 3000 hp...logic says they work.

[n00bus m@x1mus 465]

So im guessing that correct pinion angle is only desirable while at cruise so it gets even uni rotation at both ends and aids in wear of the bearings and balance issues of the tailshaft. External to that its not really considered at all... but rather disregaurded entirely to achieve the best senario for launch grip and applied torque to the wheels.

[Thom 6,654]

That's where you have to work out the purpose of the car, or adjust whenever you go racing

[slydog 7,873]

Yeah thats right Thom...TBH I would prefer to see them on the top arm but it is serving the same basic purpose top or bottom.

 

By limiting the amount of pinion angle due to stopping the diff moving around on it's mounts and suspension the pinion will apply more given force to the crown wheel to rotate the axles and propel the car foward not up or down...Well that is the theory anyway.

 

This in theory should allow Q to leave the line HARD at around 4000rpm with limited wheels spin even on street tyres as it should force the tyres into the road harder.Only issue is thats only 1000rpm of his self imposed RPM limit. 

[Thom 6,654]

Cmon q rest you limiter, you know you want to be part of the 6000rpm+ club

[Crazy2287 1,886]

I was just  at 5500rpms testing it out then. Wet n slippery at the moment so there was a bit of skidding going on.  Fell victum to what im gonna assume was axle tramp so im thinking it's a bit too nose up now.

 

This is all with reference to gravity/level with the car jacked to the same position each time.

I checked the gearbox and got: negative 0.5 While on the pinion i got positive 5.5 so i wound the arms in until i got 1.5 on the pinion.

 

So. if the gearbox i -0.5 and the diff is 1.5 = i should have 2 deg downward offset.

Im thinking if axle tramp is gonna be a problem i will bring it to 3 deg down.

 

As for which arm. Lower is easier to get to, but top arm would be better. Shortening the lower arms is going to cause an issue with the sway bar geometries and clearances

[Thom 6,654]

If still suffering axle tramp after getting your pinion settings right I would change to a slower rebound rate shock absorber

[slydog 7,873]

Check out Murray Anderson right here...^^^

 

Q if you can find it research DJR's Greens Tuff XE Falcon suspension mods.It will tell you everything you need to know to help set up Betty.He like you used stock pick-up points but added adjustabiltiy to the arms so he could get his preferred angle.

 

Drag cars run a VERY stiff rear end set up due to having a soft tyre sidewall to take up most of the load which crinkle's up until the wheel speed is up a bit.Your trying to do this with street tyres on a softer set up with harder tyres thru a manual...

 

Id also suggest getting a spare T5...engine and gear box mounts too.

[Crazy2287 1,886]

Good point Thom, I'm just running munros in the rear.

 

Rob, Will look into that prolly when i get back from canberra cheers.

[Crazy2287 1,886]

Home made inclinometer. and a heap of work working out.

 

[Thom 6,654]

Calculating, calculating error does not compute, looks good Q should do the trick

[Crazy2287 1,886]

Yeah the bloody thing had me scratching my head for a bit. Probably didn't help that i was on the ciders. Confused the shit out of me because it wasn't what i was expecting. I was expecting the diff to be lower than gearbox across centerline and the diff angle to be up. But diff is a tiny bit higher than gearbox and pointing down by about 6.5 degrees.

 

Plus all the measurements i needed to hold the protractor the proper way or it would be on the wrong side of 90. and i had to deduct 90 from it to get the total. Duuurrrrrppppp

 

Rob, where did you find info on DJR's Greens Tuff XE Falcon suspension mods i googled it but only found some general tech info about the car nothing focused on the rear end?

[Thom 6,654]

Just be glad your not running leafs<br />

[slydog 7,873]

I read about it all in SM years ago Q but like you can't find jack shit.He did detail all the bits your going thru now though...

 

Wow that vid shows soo much right there.

[n00bus m@x1mus 465]

I want to do the same thing with my leafspring mods si i can convince myself more than anything that it worked. Just need to convince the old man to strap on his go pro lol.. is that the exhaust pipe glowing red right in front of it??