Reassembling front suspension of BN6

[BN6_2197]

Gents,

I refurbished the swivel pins and the front axles of my BN6. After that I started to reassemble the front suspension according to section L.5 of the workshop manual. After placing the distance peace (see Fig. L.7) I fastened all the screws (see steps 4-7 of page L.5 of the manual). While letting the distance peace in place I refitted the coil spring as documented in step 8. When the coil spring was in place as well I was not able to remove the distance peace since the upper wishbone arms pressed it on the bracket of the shock absorber. This is unexpected from my point of view. Any idea what I did wrong?

Regards,

Volker

 

[Randy Forbes]

I think you should've removed the distance piece after setting & tightening the bushes, but before installing the spring.

Just lower the spring pan again, until the tension on the spring is relieved enough to get the block out.

 

[Randy Forbes]

Yes, I had already removed the block when putting this BJ8 back together:

 

[BN6_2197]

Randy, I tried this. But when removing the distance peace after tightening the srews the intended distance of the upper arms is not kept. The complete setting (upper and lower wishbone arms with the front-axle component) lowers then. Is this expected or did I have to fasten the srews and bearing harder?

 

[John Turney]

I leave the distance piece in until the car's back on it's wheels. Then it falls out. That way, the bushings stay in their neutral position until I'm done.

 

[BN6_2197]

Can I really fix the position of the upper and lower wishbone arms to keep the distance?

 

[Randy Forbes]

The distance piece: it's purpose is to allow you to TIGHTEN the upper and lower pivot points in the middle of their travel (specifically with rubber bushes having steel sleeves; polyurethane bushes may be different, but I still do them all the same).

Allowing the suspension to reach full bump/full bounce is within the expected range of the bushing's flexibility, so it's a personal choice about leaving the piece in until the car's wheels are back on the ground.

Do you insert the distance piece when merely raising a wheel off the ground? Same thing.

In closing, when you remove the distance piece, it's okay if the distance doesn't remain the same__it's suspension travel__and no amount of tightening will "keep" that distance constant (I swear, didn't we all just go through this topic...?). Besides, all the fasteners/cups, etc., should only be tightened to specification anyway.

 

[BN6_2197]

Randy, thank you very much for the explanation. I understood that I cannot keep the distance of the upper wishbone arms and the housing of the shock absorbers by the distance peace. BUT after fitting the coil spring the upper wishbone arms are pressed on the housing of the shock absorbers so there is no distance for bouncing of the shock absorber arms any more. Any idea what I did wrong?

 

[Keoke]

Any idea what I did wrong?

Is there a jack under the spring pan or is the wheel on the ground when this 0ccurs seems strange

 

[Randy Forbes]

A picture might help us understand what is going on...?

 

[steveg]

Yes, I had already removed the block when putting this BJ8 back together:

Interesting - the BJ8 has a slightly different spring tower design than the BN6. I had a problem with my Toyota caliper pipe hitting the flange and had to notch it:

 

[BN6_2197]

Gents, here is the whole story.

The car is put on the frame. I fitted the front axle put in the distance peace and fastened the nuts of the inner bearings of the lower wishbone assembly. Setting shown here


I removed the distance peace. After that the distance is still fine.



In this state I am not able to connect the anti role bar to the lower wishbone arm. Nevertheless I started to fit the coil spring to check how the distance - which was initially kept by the distance peace - behaves. After fitting the coil spring the half way, the upper wishbone arms are pressed on the rubber of the shock absorber housing.







Is it expected that the upper wishbone arms are pressed on the rubber in this state of assembly? Remember, the car is on the frame, no jack under the spring pan. If this is expected, I really do not understand the reason for putting the distance peace.

By the way: please apologize the orientation of the pics. The were well oriented in the preview :-(

Volker

 

[GregW]

In the third picture where you are installing the spring, you haven't put the nut on the Kingpin/shock arm bolt. The rubber bushings there are what need the distance piece when they are tightened into place.

 

[steveg]

Before tightening the spring, you need to run your threaded rods through the holes in the anti-roll bar plate as well as the lower suspension arm.

Expaining the distance piece:
With the stock rubber A-arm bushings, the entire rotation occurs within the rubber of the bushings. The inner metal sleeve remains in a fixed position on the A-arm pin, and the rubber flexes as the suspension arm moves up and down. It's an elegant frictionless, lubricationless design.

Let's say you didn't use the distance piece and tightened your lower suspension pins with the bushings in that position. When you put the car on the road, the rubber would be maximally stressed with the car at rest; when you hit a bump the rubber would be overstressed. The distance piece ensures the rubber bushings are unstressed at the neutral position when the car's at rest on its suspension. On bump, the rubber stretches counter-clockwise from neutral; on rebound the rubber stretches the other way - both stretches are within the capacity of the rubber in the bushing.

 

[Randy Forbes]

Before tightening the spring, you need to run your threaded rods through the holes in the anti-roll bar plate as well as the lower suspension arm.

Expaining the distance piece:
With the stock rubber A-arm bushings, the entire rotation occurs within the rubber of the bushings. The inner metal sleeve remains in a fixed position on the A-arm pin, and the rubber flexes as the suspension arm moves up and down. It's an elegant frictionless, lubricationless design.

Let's say you didn't use the distance piece and tightened your lower suspension pins with the bushings in that position. When you put the car on the road, the rubber would be maximally stressed with the car at rest; when you hit a bump the rubber would be overstressed. The distance piece ensures the rubber bushings are unstressed at the neutral position when the car's at rest on its suspension. On bump, the rubber stretches counter-clockwise from neutral; on rebound the rubber stretches the other way - both stretches are within the capacity of the rubber in the bushing.

Such a simple concept, yet so hard for so many to grasp (no offense to BN6__2197); I still have to make this identical statement__if not word for word__to members of the BMW community too. It's no more understood today, than sixty (>60) years ago when the Healeys were built**





** no doubt, in practice for perhaps sixty (60+) years before then even.

 

[BN6_2197]

In the third picture where you are installing the spring, you haven't put the nut on the Kingpin/shock arm bolt. The rubber bushings there are what need the distance piece when they are tightened into place.

I haven't put the nut on the kingpin/shock arm bolt since I am still "experimenting". When you are talking about the "rubber bushings", I assume that you mean the ones of the inner bearings of the lower wishbone, isn't it?

 

[BN6_2197]

Gents,

I understood the concept of the distance peace: it is to bring the bushings of inner bearings of the lower wishbone arms in neutral position when assembling the front suspension. Fine so far.

As said in an earlier post of this thread it is hard to fit the plates of the anti role bar to the lower wishbone arms. After doing it looks like this:



The rod going from the anti role bar to the plate is not really in a vertical orientation, it is sloped instead. Is this ok?

By the way: does anybody know the correct height of the coil spring of a BN6? My spring is about 10,35 inches high.

Volker

 

[steveg]

Gents,

I understood the concept of the distance peace: it is to bring the bushings of inner bearings of the lower wishbone arms in neutral position when assembling the front suspension. Fine so far.

As said in an earlier post of this thread it is hard to fit the plates of the anti role bar to the lower wishbone arms. After doing it looks like this:

View attachment 37170

The rod going from the anti role bar to the plate is not really in a vertical orientation, it is sloped instead. Is this ok?

By the way: does anybody know the correct height of the coil spring of a BN6? My spring is about 10,35 inches high.

Volker

I have one of my BN6 springs out on the floor right now - it is exactly 12 inches.


Your anti-roll bar setup as shown in the picture is correct. I don't believe it can be assembled incorrectly. If you try to swap the plates from side to side the link won't connect from the a-r bar to the plate. If you try to invert the plate it won't bolt properly to the A-arm.

 

[BN6_2197]

I don't believe it can be assembled incorrectly. If you try to swap the plates from side to side the link won't connect from the a-r bar to the plate. If you try to invert the plate it won't bolt properly to the A-arm.

From the plate point of view you cannot assemble it incorrectly.But I thought that the bar crossing the frame is too much in the front. By the way: thanks for the spring information. I am wondering if mine is too small.

 

[CraigC]

I haven't put the nut on the kingpin/shock arm bolt since I am still "experimenting". When you are talking about the "rubber bushings", I assume that you mean the ones of the inner bearings of the lower wishbone, isn't it?

Gents,

I understood the concept of the distance peace: it is to bring the bushings of inner bearings of the lower wishbone arms in neutral position when assembling the front suspension. Fine so far.

Volker

You must tighten the upper trunnion bolt and the kingpin upper nut while the distance piece is in place and before spring installation.. The upper trunnion pivots in relation to the shock arm by way of the same type of rubber bush as the lower arm pivots on at the frame end. They need to be tightened with the suspension in the same "neutral" position as established with the distance piece. This is all stated clearly in the 100 factory service manual.

As for your concern that the shock arm is pulled down against the rubber bump stop when compressing the spring into place, that is entirely normal. Remember, as you pull the spring pan up to the lower arm, you are compressing the spring. The spring is now applying considerable force on the lower arm, forcing it downward. As it moves down it pulls the shock arms down by way of the kingpin and upper trunnion. If this did not occur it would be an indication of something being terribly wrong. You simply cannot expect the "neutral" position established with the distance piece to remain once it is removed and you begin spring installation.