Castor Trouble

[Pawel66]

I cannot get the castor anywhere near specs. The specs say 4deg +/-15'. All I can get it to is 1 deg 30'. This is maximum to the front on both sides on cam screws holding the leaf spring.

I spent several hours on it today, we could not figure out what may be the reason. All other parameters could be adjusted just fine, the car drives straight, sticks to the direction, etc.

One thing I could notice was that the castor fine-tuning plates were placed: one in front, on the other side in the back of the kingpin upper pivot. I had no means today to dismantle this pivot and check if all the plates and washers are in the proper place (I think dismantling this pivot needs spring compression, a bigger job for me).

But I am not sure if the issue could be this. The whole travel of the spring leaf bolt cam from most rear to most front produced change of castor of -30' to +1deg30' and this travel is a good 10mm. I am still missing 3 degrees - I do not think washers could make 3 degrees difference. Or can they? Please advise.

I also thought that, as the car was on a very modern machine for geometry adjustments - maybe these days this angle is measured in a different way somehow?

The subframe with engine was moving front and aft as I turned the cam (strut, rear engine mount, drive shaft were loosened), but all the movement was from -30' to +1deg30' - nowhere near 4 degrees.

Shall my upper kingpin pivots be screwed to chassis more to the back - with all the washers moved where they are supposed to belong? Will I find 3 degrees this way?

[stickandrudderman]

Most common reason is the car having a front end shunt at some point in its life and the front chassis rails, due to the large bend in them already, are the weakest point and will bend backwards.
A measurement from the central datum hole to the fixed caster mounting will confirm it.
The top of the king pins is for fine tuning only and should not be relied upon for large corrections.

[Benz Dr.]

The upper pivot adjuster is for fine-tuning. Castor is adjusted on the subframe where those flat straps bolt onto the body. Undo the two nuts and turn the screw that sticks out on the front one. There's a cam inside of the frame that will move the subframe around enough to adjust castor. 

[Pawel66]

This is exactly what I was doing. Got as far as 1deg 30'. Missing 3 degrees to specs.

Where those 3 degrees may be?

[Benz Dr.]

The frame could be bent. It happens.

[Pawel66]

Thank you, we had dimensions in the post recently, I will check it.

I wonder if the upper king pin pivot washer and plates arrangement could be the reason as well...

[Pawel66]

May I also ask: how do I measure the length of the leaf spring to check if I have correct ones?

Hans was writing about it many times: for power steering the length is 243mm, for regular steering it is 248mm.

Is it the distance between the front tip of the spring to the center of the bolt that holds it?

Also: I see just one part number: A 111 331 11 12, not sure if it is for power steering, although PN for rubber bushing is for power steering version (
A 110 322 15 85).

Is A 111 331 11 12 correct for power steering?

[Pawel66]

I think I will start with:

1. Making sure the upper king pin pivots are assembled properly on both sides (adjustment plate, washers, etc. in the right places, the tooth engaging in the slot in threaded bushing).
2. Measure length of the leaf springs (here the info between which points it has to have 243mm would be useful); wonder if both are the same...
3. Check off-set 15mm in rubber bushings
4. Check the frame (tricky one, no traces of any repairs, but we will see)

I will see if that helps find the answers.

[PeterPortugal]

Hi Pawel,

this is from my W111 BBB and it includes the data for 230SL and 250SL but not your 280.

It does show you however how to measure the leaf spring.

Regards

Peter

[PeterPortugal]

Pawel,

Have a look at the note too. It also allows use of alternative springs and rubbers to get the correct castor.....possibly not the best option but certainly cheaper than having your frame pulled !

Regards

Peter

[PeterPortugal]

As there are alternatives check that the rubber mountings fitted have the correct eccentricity for your car.

[Pawel66]

Peter,

Great help, thank you!

Yes, I have read through the notes as well. I will do the checks.

I really doubt it is the frame bent, there was nothing that would indicate it was damaged and repaired... we will see.

I wonder if I missed this drawing in my BBB, or it is just not there...

[Pawel66]

As there are alternatives check that the rubber mountings fitted have the correct eccentricity for your car.

yes, exactly, got the point too. Hans was writing about a different offset - I need to check it too again, maybe I just remember the wrong number.

Thank you!

[Pawel66]

I found Hans' post.

He says 1.5mm offset for SL, as in your table, I think. (not 15mm, of course)

If I have more, that is where my 3 degrees can be lost.

[PeterPortugal]

Pawel,

Good luck. If a 280SL is the same as a 250SL in this regard and you have power steering then you should habve 243mm between hole centres in the leaf sprring and a 1.5mm offset in the bushing.

It is fairly obvious how the rubber bushing should fit into the leaf spring but make sure this is correct also. If someone had managed to fit it wrongly it would also have an impact.

Regards

Peter

[Pawel66]

Thank you again!

I do have this table and drawings in my BBB, section 33, where it belongs. I am a bit clumsy with BBB, sorry. I was in Alignment, section 40.

Yes, these are the parameters - 243mm and 1.5mm offset on bushings for 280SL. The drawings on how it should be put together are there.

I am afraid dismantling the king pin pivot, stabilizer and leaf springs will require work with springs (pivot), so I need to take the car to the shop to clean this up.

I already see that at MB leaf spring 248mm (non power steering, A 112 331 11 12) is available, but 243mm for power steering, A 112 331 00 12, is not...

Some vendors, e.g. SLS have one part number for bushings for 113, 108, 111 etc. No idea what the offset is there...

[Pawel66]

Please kindly help me with two questions:

1. Can I dismantle the leaf springs and put them back together with the car standing or with front lifted or lifted by the body? Is there a tension there that I will not be able to cope with in my garage? Looks to me they mainly hold the subframe in place, it is not "hanging on them" like on mounts and springs...

This would allow me to check what length I have and look for shorter ones if need be.

2. From the drawing I see that the leaf spring rubber bushings eccentricity is up/down rather than front/back - am I correct?

[PeterPortugal]

Hi Pawel,

There is no stress in the springs and you can just undo them without anything "flying apart"

The rubbers on the outside have a slight "egg shape" and the tip is located in the opening where the flange bolts together. This means the hole is located towards the front of the car. So I would say front/back rather than up/down.

If you want a picture I can do it later. Mine are still off the car.

Regards

Peter

[Pawel66]

Peter,

Thank you!

I think I will figure it out now, after your post. I saw on the BBB technical drawing the distance was shown in up/down direction (counter-intuitive for me), that is why I asked the question.

I need to check both the bushings and leaf springs.

Thank you!

[Pawel66]

I understand that dismantling upper king pin pivot is related to work with suspension springs. Is it correct?

That is a different story, I would be afraid to touch it myself...

Or, as the spring rests against upper subframe seats and bottom control arms, the upper control arm would have no stress when I lift the car, as shock absorbers will limit bottom arm travel down?

[PeterPortugal]

Pawel,

You don't have to touch the kingpins to remove the front leaf springs.

Picture attached showing the orientation of the offset of the bushing.

Remember when you measure the length don't use the centre of the hole in the bushing. Use the centre of the opening in the leaf spring.

Peter

[Pawel66]

Peter,

Thank you - all clear!

As for the upper king pin pivot - it is a separate job. I see there is a mess in how plate with tooth, washer, seals, threaded bushing are arranged on both sides -  differently, I do not know if someone who put it together knew how they should be assembled. I need to dismantle them and put back in order.

it is related to castor, but nor related to spring leafs.

[garymand]

Pawel,  I had the same caster issue.  My problem was the slip joint on the tail shaft lock nut.  The BBB doesn't tell you to loosen that nut.  It doesn't do much good to loosen the rear trany mount if the drive shaft nut is holding the transmission from moving fore or aft.   

[Pawel66]

Thanks for the point. I did loosen the nut between the central bearing and transmission. Is there another nut to loosen?

[Pawel66]

Ok, got my springs with 243mm and new rubber bushings with correct off-set, now will put this whole thing together and try again to find my castor.