Difficulty with repeatability

[alexanderfoti]

Hi all

Having had my alignment kit now calibrated, we have been doing lots and lots of geo and alignments and have come across one major issue. 

 

Repeatability, especially with toe measurement 

 

We will carry out a run out compensation, lower the car onto the adjustment stands (all 4 wheels have slip plates).

We then carry out toe out on turns and SAI/Caster check.

We then have the before measurements of camber/caster/sai and others showing. 

 

We then swap to the live adjustment screen for the rear, make the changes necessary. 

Do the same for the fronts, make the necessary adjustments. 

 

The next stage is to carry out another test of Toe out on turns, and SAI/caster check which involves turning the steering through 20degrees and 10 degrees respectively. 

 

Once done, the machine does another measurement of the geo before printing the "after" measurement screen. 50% of the time, this screen shows different values for front Toe than the live adjustment screen before it, quite often with an offset of error introduced. (eg if the front toe was 0.15" on the front left and 0.02" on the front right, then may then be 0.35" and -0.02".........

Initially, I thought this was an issue with the our returning the wheel to the centre, so started using a spirit level for the steering wheel, this hasn't made any difference. 

We are making the adjustments and measurements with the brake pedal depressor installed, and also carrying out steering movements with the engine running (on cars with a steering box).

Quote often the cars will then drive without the wheel straight, and will require repeated adjustments until the after screen shows in spec, often repeating everything 3-4 times! 

If I am doing something wrong, I would love to hear it! 

 

All help is very much appreciated. 

[Tony]

Hi and welcome to wim

What make of car are you having issues with? If it's MB then we have trouble even with a spirit level. Thing is the machine couldn't care less about the steering level because it's a cosmetic condition.

We calibrate about ten MB's a week and found the best way to deal with this is to get the owner to conclude the level. Even then it might come back with the level slight off but the customer feels at blame thus removing a complaint.

If your issue is with MB with a steering box then you should use a spreader rod to compress the box because it has so many pick up points. The rod simulates a dynamic condition.

What make is your machine?

What suspension do you have issues with, coil or air?

 

 

[alexanderfoti]

Thank you. 

Absoultely, I agree with you regarding the steering wheel center point. We are an MB indy workshop, so most of our geo adjustments are as a result of replacing a mechanical component (the car in this post was a R129 SL500, it had 2 tie rod ends due to corrosion on the MOT), so often a before/after with the customer isnt possible.

After your comment regarding the spreader bar, I realised, the cars we have issues with are older ones with steering boxes, and the issue clearly is that we are not using the spreader bar. 

We have done loads of steering box cars, but 90% are after replacing most of the front end suspension components, including all the linkages etc, and these havent had any issues. 

Its an old ATS wheel alignment machine (Wheel alignment UK)

The airmatic cars, ABC cars and standard cars with steering racks we dont have problems with. 

If you know of a good supplier for the spreader bar, a pointer would much appreciated. 

[Tony]

Hunter UK sells them. Thing with steering box's is the collective play,, meaning no one component is worn but the collection of wear allows play.