34 replies to this topic

[StephenSLR]

I was recommended to install adjustable upper trailing arms as my diff yolk points south of horizontal.

McDonald Brothers Racing have them ~ $300

I remember reading on the old forum years back of some good GM (imported from USA) ones that can suit, I'm not sure if they needed some mods.

TSS (Tubular Suspension Systems) make spherical bearing arms, I can't remember if they were adjustable - their site is under construction atm.

A friend says he's been in a car with the spherical bearing trailing arms and noticed they make a hell of a lot of noise.

What are your experiences/recommendations?

s

[StephenSLR]

I have the mcdonald bros ones in mine to twist the pinion angle down as it was too horizontal.

I will have to check it on a level surface sometime. I just had my diff serviced, the mechanic told me there seemed to be a bit of vibration and I guess he assumed it was the pinion angle.

He said my gearbox (Supra) was higher than the diff so maybe he thought the diff is too low? Of course he could be wrong.

Maybe this topic needs to be moved to 'suspension & steering'.

s

[A9X]

read this,

http://www.gmh-toran.......220&hl=arms

and when you get to it, there are some adjustable arms there for sale.

Welby

[TerrA LX]

Pinion angle is the difference between the tailshaft angle and the pinion angle on the differential.

In your case stephen you first need to ensure the "entry" and "exit" angles are equal on the tailshaft, then measure the pinion angle.

[StephenSLR]

In your case stephen you first need to ensure the "entry" and "exit" angles are equal on the tailshaft, then measure the pinion angle.

Is the exit angle the pinion angle? If not please explain.

Who can I take my car to to measure these things?

when you get to it, there are some adjustable arms there for sale.

Thanks Welby, I just want to make sure the arms are the issue.

Didn't you say those arms were what was causing your vibration?

s

[A9X]

No, i said we removed them as part of our chase to find the vibration.

As part of that chase, i didn't find any difference in handling with putting the factory ones back in, so they stayed in.

We ended up raising the gearbox at the rear mount to fix the issue.

Welby

[ls2lxhatch]

This article explains the problem
http://www.streetrod...gles/index.html

The McDonald Bros upper adjustable trailing arms will not fit a standard Torana banjo housing or a 9" that has used the upper mounts from a Torana housing. The Whiteline upper adjustable trailing arms will fit with a standard Torana upper mount. If your 9" was built using HQ trailing arms as the upper mounts (This is a common method) then the McDonald Bros arms will fit.

McDonald Bros


McDonald Bros


Whiteline

Edited by ls2lxhatch, 20 November 2008 - 04:20 PM.

[TerrA LX]

Is the exit angle the pinion angle? If not please explain.

Who can I take my car to to measure these things?

If you were to put the rear of the car on ramps and then jack the front up and support with stands till the car was level you could then get under the car with some coat hanger wire and check the angles for yourself, at this time the numerical value of the angles is not important, you are just checking if everything is satisfactory at this stage, so bend your wire to suite the "entry" angle, the angle of the gearbox plane and the front of the tailshaft, then compare this angle to the "exit" angle, the angle of the tailshaft to the centreline of the yoke/diff.
These angles, regardless of their value, should be equal.
Now, the included angle of both the tailshaft, and the degree of which the diff is pointing, wether up or down etc, is your pinion angle.

[StephenSLR]

I have a Supra 5 speed g'box and Borg Warner LSD.

The BW was built and fits the original Torana trailing arms so I assume they would have made the mounts the same as banjo diff, would this be the case?

I am just going off what the diff guy said recently - that the yolk/pinion looked like it was pointing down too low.

These angles, regardless of their value, should be equal.

Is the idea to have the pinion angle = 0 degrees under load?

Does anyone know a professional in Sydney that can measure the angles, I'm short of time and don't have ramps/stands.

If I do need to change the angle will those Edelbrock arms fit my set up?

s

[TerrA LX]

Is the idea to have the pinion angle = 0 degrees under load?

Pretty much yes, can't help with the rest sorry, maybe try the yellow pages.

IMO, I would be more worried about the entry/exit angles being the same that the pinion angle if your getting vibration.

[76lxhatch]

Yes I have same problem and have come to the conclusion that the gearbox needs to go up, but that's easier said than done. For the moment keeping to tall diff ratios makes a big difference.

[76lxhatch]

If you go Torana engine mounts that will raise the engine and thus point the trans down, which is the wrong way, isn't it? Trans points up, diff points down on same angle.

I'm no expert but I would imagine that you may want to try 3 or possibly even 4 degrees (depending on how stiff the suspension bushes are), assuming of course you can get the same angle at the trans and diff.

[wot179]

As far as I know,the engine should sit level in the car.That makes the centerline of the gearbox level with the ground.
Opinions vary,but pinion angle should be between 1 and 4 degrees.
To achieve this,put your car on 4 jackstands,with the rear ones under the diff.
Level up your car,from side to side and front to rear.
Across the rails in the front and rear are good places to sit your level,and along the sills under your scratch plates is good for front to rear.
Drop your taishaft and sit your magnetic protractor(cheap) or electronic angle finder(not so cheap)vertically across the pinion on the diff.
That is your pinion angle.
When setting up a gearbox crossmember,level up your engine front to rear and measure for your new crossmember.
Just jacking it up till it hits the floor and dropping it down a bit is not the way to go.

This is the way I have been taught and the way I have always done it.
Ive never had a problem.

http://roofgenius.com/roofangle.htm

[76lxhatch]

Basically why i mentioned the engine mounts because i thought the gearbox should be straight rather than pointing slightly up. I realise what your saying 76LX but you can still have the angle at the front if the gearbox sits level because the diff is slightly lower.

You must have a lot more room in the tunnel to move the gearbox up than I do, good luck and very keen to hear whether you can dial out the vibration completely

[ls2lxhatch]

You could try putting some weight in the back of the car, the diff will point down as the car gets lower. If the vibration disappears then you can modify the arms to achieve the same angle at normal ride height. Raising the gearbox will also have the same effect as pointing the diff down.

This article explains what you are trying to achieve and how to measure the angles.