My 1968 DS19A Pallas

Measuring differential shaft run-out, May 2007

My DS19 has suffered from vibrations under braking as long as I have the car. When I put the car back together in september 2006 I took great care in mounting the brake discs with as less run-out as possible. I used a dial and checked the run-out at each of the three different positions. I did this on both sides and using two sets of brake discs, the original discs and a brand new set. However on the left side, I never got the run-out below the 0.150 mm that is given as the maximum value in the repair book. I put the car back together and drove it anyway. As was to be expected the vribrations were as before.

Early 2007 I got fed up with this and asked some experts what could be the cause of this. The answer was that worn out or loose bearings in the differential shaft housing is a common cause for this.
So at the end of April I removed the differential shaft housings from the gearbox. I thought they felt pretty solid (no play) but took them to an expert in NL anyway.

Measuring setup. (Click on image for larger version.)

The expert examined the units and adjusted a nut on one of them but the general verdict was that they looked fine. He also thought that it was unlikely that the run-out would be caused by the diff. shaft units, unfortunately he was not able to measure the run-out.

So I did that myself today (I should have done that before...), see the photos and text below for the results. I used a Mahr Puppitast clamped to my work bench, and I also clamped the diff. shaft unit to the work bench.

Mahr Puppitast measuring instrument, 1 revolution is 0.2 mm

Gauge touching the differential shaft

Measuring the left hand side differential shaft

Measured value: 0.022 mm

Measured value: 0.0 mm

Measured value: 0.1 mm

Measured value: 0.138 mm

Measured value: 0.152 mm

Measured value: 0.130 mm

So the total run-out for the left hand side differential shaft is 0.150 mm at a radius of just below 7 cm. The maximum allowed run-out of a brake disc at the rim of the disc (radius is 15 cm) is 0.150 mm. So the 0.150 mm run-out of the diff. shaft is clearly too much.

Measuring the left hand side differential shaft

Measured value: 0.014 mm

Measured value: 0.038 mm

Measured value:
0.064 mm

Measured value:
0.062 mm

Measured value:
0.026 mm

Measured value:
0.016 mm
So the total run-out for the right hand side differential shaft is 0.050 mm, this is probably ok.

So obviously I'd better order at least one (better two) new differential shaft unit(s)! With the current (original) units the vibrations under braking will never go away...

Photos by Jint Nijman.