Questions about Adjustable Trailing arm and Traction bracket

[Tom86]

Hi everyone,

I'm looking to buy some adjustable trailing arms for my AE86 so I can adjust the pinion angle to its proper position. Question is do I need both the upper and lower arms to be adjustable? or just the upper one? coz doesn't lengthening the upper arms have the same affect as shortening the lower arms?

Also can someone explain to me the theory behind Traction Brackets and why you need it.

Thanks

Tom

[auto351]

Hi, thinking about the pinion angle adjustment you would only need one set of the arms to be adjustable,

[Tom86]

ahh cool thanks for confirming that

[ddeane]

Tom

Someone will correct me if I am wrong, but my understanding is that the traction brackets are the rear suspension equivalents of the RCAs in the front, in that they give you back (which is a good thing) the factory roll centre through restoring the relative positions and angles that the upper and lower (trailing) control arms work through.

And yes you only really need the adjustable (upper) trailing arms.

Craig

[auto351]

Correcting the angle will reduce power loss through the system,

When Toyota design the swinging arm system for a car, I would think they take into consideration these angle over the full length of travel; and this angle would not exceed the working limits of the universal joints
So I don’t see the need for adjustable arms unless the travel range of the diff has been modified beyond the factory range

Correct me if I’m wrong also

[ddeane]

No you are not wrong.

However toyota did not take into account the effect of a more powerfull engine twisting the rear axle assembly further than their design limits as well as the capability of the uni joints to take the increased power through this greater deviation. The effects being the tendency of the power to lift the diff housing and to damage unis.

Do a search on google on pinion angle and they do a far better job of explaining than me.

Craig

[Tom86]

When Toyota design the swinging arm system for a car, I would think they take into consideration these angle over the full length of travel; and this angle would not exceed the working limits of the universal joints
So I don’t see the need for adjustable arms unless the travel range of the diff has been modified beyond the factory range

My reason for wanting the ability to change the pinion angle is ever since I lowered the rear suspension I get this whirling/vibration noise at certain speed from the tailshaft presumably from the change in angle of the diff.

In order to fix this I tried spacing out the tailshaft center bearing so the angle of the tailshaft is closer to that of the diff. This has somewhat fix the noise problem, but not completely so I thought if I can adjust the pinion angle via other means ie adjustable arms I can tune out the vibration completely.

Someone will correct me if I am wrong, but my understanding is that the traction brackets are the rear suspension equivalents of the RCAs in the front, in that they give you back (which is a good thing) the factory roll centre through restoring the relative positions and angles that the upper and lower (trailing) control arms work through.

ddeane, so how would you know if you need a traction brackets? as with front you know you need RCAs because you get bumpsteer. But with the rear is there any obvious telltale sign to tell me I need traction brackets?

[fergo308]

IIRC,traction brackets are used to give more squat,and to correct the pinion angle when the car has been heavily lowered. more weight transfer under acceleration = better traction. more squat = more weight transfer = more traction.

ideally,you'd fit adjustable lower AND upper arms if you want adjust pinion angle only,as only one pair will not only adjust pinion angle,but also wheelbase to a very small extent.

there isn't really an adjustment for rear roll centre on a live axle car,it's infinite- the axle angle doesn't change regardless of ride height. all you can alter is squat.

cusco do make what they call a roll centre adjuster for the rear of an AE86,which is just a lower mounting point for the panhard rod on the diff end. I haven't worked out if that's worthwhile or not yet. a shorter rod will maintain a normal angle and won't need relocation of it's mounting point.


hope this helps some. (and is accurate,my brain is pretty fuzzy this late in the week and evening.)


Justin...

[auto351]

Tom,

Have you checked your universal joints for wear & also your control arm bushes?
How much did you lower the rear & did you remove the bottoming out bushes?

Manuel

[ddeane]

Ouch! You have exceeded my very limited knowledge on the subject. So have done a little search and found:

'Lower control arm relocation brackets reposition your instant center by changing your lower control arm angle for improved traction. Relocation brackets lower the rear of the control arm up to 3", a must for all lowered vehicles to correct lost suspension geometry. By lowering your vehicle, you are changing the lower control arm angle allowing the rear mounting point to sit higher than the front. This will, in return, cause wheel hop and a great deal of traction loss. Lower control arm relocation brackets allow you to correct this angle and gain back much needed traction. On a stock height vehicle relocation brackets will also work excellent to eliminate tire spin and wheel hop by changing the vehicles instant center point.'
I do not have traction Brackets fitted (although I have some waiting in the wings) but do not have axle hop. I do have traction issues but this might be more the result of 220+ rwkw - but maybe the brackets will help getting power better to the ground coming out of corners.

As to the cause of your specific problem I think I agree with Manuel that it seems to be more than tailshaft alignment. You might have a talk to Rod Try as he seemed to solve some problems with this several years ago.

Craig

[Tom86]

Tom,

Have you checked your universal joints for wear & also your control arm bushes?
How much did you lower the rear & did you remove the bottoming out bushes?

Manuel

The universal joints are fine except for the one near the diff that one is a little bit notchy. The tailshaft has been re-balanced about 6months ago.

The car is not extremely low as it sits now there is a ~1cm gap between the rear tyres and the wheel arch. As for the rubber bump stop I only cut the first notch off.

["Z" UTE]

The universal joints are fine except for the one near the diff that one is a little bit notchy. .

The above statement confirms that the unijoint is shagged. Reading this thread from the beginning, it occurred to me that the uni could be at fault. The first pointer was when you said you had changed the incline angle by spacing down the centre bearing, which made a slight noise difference. This last statement purely confirms that the uni is shagged, as all uni joints should have a smooth motion through their entire range of movement. Change the uni.

cheers Chuck.

[Celica RA45]

gone through this with my suspension guy and he has said if you use the kelway traction brackets as you lower the car then you need the same brackets for the top arms .since this cant be done .he suggests that you keep the 2 peice tail shaft lower the car and soften the rear springs if they are to hard and run some good shockers like bilstein /koni etc
also you change the rear roll center by lowering the panhard bar this has the same effect ,but it must be the same ammount both ends
a ipra car that weighs about 1000 kg will have 300lbs on the front and about 150 to 200 lbs rear spring
this mac struts up front and also live axle rear