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Replaced flex disc transmission side and its center bushing.
First test drive : slight rumble at 83km/h and 110 km/h.
Thought marking the flange positions to each other would not be necessary.
After all, MB does not mention anything about balancing a new drive shaft under the car, as part of the work.
But they DID mention marking both flange positions to each other, when taking it off or exchanging discs, as I found out later.
That means the shaft is balanced separately AND after mounting under the car? (As for example Maserati does) Tried the two other positions, one flange rotated 120 degrees clockwise, then CCW from its original (rumbling) position.
But only one position offered the sweet spot!
So MB was right!
Btw: setting the angles right, is the first thing to do.
When the angles are wrong, center bearings and discs will also create rumble and will wear quickly.
Last edited by Boomerang32; May 1, 2024 at 04:25 PM.
Due to u joint wear, it is often better to reduce the angle there close to zero. In my case i had to put two 2mm spacers between center bearing and floorboard to get there.
Last edited by Boomerang32; May 12, 2024 at 01:54 PM.
Going to do my flexies soon, what do you mean by setting the angles? (Lost my WIS in a computer change so haven't researched this yet). Thanks.
This is the one i use. Put it on the front shaft, reset zero, take it to rhe rear and reading shows angle. Same towards diff and gearbox. There you have to find flat spots horizontal or vertical to obtain correct angle readings.
You could be lucky indeed, when you leave everything else where it is. But very often gearbox side flex disc is exchanged together with gearbox mount. In that case angles could change and the u joint could start running in a slightly different angle. When there is allready some wear in the u- joint, vibrations could pop up from then on.
I need to check those angles. I replaced the center drive shaft bearing and both flex discs, The new bearing lifts the middle of the shaft higher then the old sagging one. I would think the new bearing would bring it into specs and not out of specs but I need to check the angles. I also have a new transmission mount which looks to raise the transmission slightly. I have a vibration at 70mph and a Rumble/Vibration at 80-85mph. I certainly hope these angles are the problem as I have been working on these vibrations for months.
How did the u joint feel?
could you feel a sloppy part and a tight part while rotating it over its achses?
Could well be, that you need to lower the center bearing by putting 2mm shims between bearing and mounting surface to get the u joint back in its original hight.
or renew the u joint.
I did not check the u joint as well as I should have, I was focused on the bearing. I only moved the u joint around a bit to make sure it wasn't loose. I watched a few video's since to see how to properly check it. I'll be digging back into all of it soon.
I was able to measure the #2 angle today. It was off by 1.9 degree's. Measured -1.5 and it should be around +.4 (midrange) according to the above chart. I had to add 5 washers (around 10mm) on each side to get it to +.2. I sure hope this fixes my problem. I didn't do the #1 and #3 angles as I don't think I can easily get an accurate reading. I also noticed from my carrier bearing pictures that the spacer on the old bearing looks almost twice as thick as my new one. Anyway, I'm done for the day. I'll report back once I take a test drive.
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