230SL Flex Disc Bolts

[Tomnistuff]

Please check my work - Is the following normal?

OK, with the help of my nephew, I got the engine with transmission installed in the car without any "real" problems but a with couple of "this is never going to work" comments. 

With the engine sitting on the new engine mounts held in place with the support arm bolts but far from being screwed down tight, and the transmission sitting on wood blocks which in turn sit on a steel beam that bridges across the ramps of my 4 post hoist, I've got the flex disc bolted and torqued to the transmission output shaft flange.  The propeller shaft center support bearing housing is loose as is the front propeller shaft clamp nut with the front shaft lubed and free to slide forward by hand.

I've aligned the trans output shaft to the prop shaft using the wooden transmission support blocks so that with the thick foam rubber sealing ring, the center cross and its o-ring in place and the prop shaft partly engaged with the trans output shaft, the angular misalignment of the trans flange and prop shaft flange is approximately 12 minutes or 0.2 degrees.  Several times, I measured the flange gap change as the flex disc rotated full circle (trans in neutral and wheel off the ground).  The flex disc bolt circle is approximately 88 mm and the flange gap change side-to-side and top-to-bottom was approximately 0.3 mm according to the many measurements I made.  The arc tangent (as well as the arc sin) of 0.3/88 is 0.195 degrees.

To me, all that sounds perfect and made me very happy, but I find that all six of the flex disc bolts fit the flanges with a light press fit and I'm having to close the gaps between the centering cross, the flex disc and the front propeller shaft flex disc flange, first by lightly hammering the prop shaft flange bolt heads while manually urging the prop shaft to mate with the flex disc and trans output flange, thus overcoming the bolt to flange hole light press fit, until I can get the washers and nuts on the trans side of the trans flange.  Then I'm drawing the parts together to close the gap by using the bolts and nuts while rotating the shafts 120 degrees at a time.

I have to admit that the parts are coming together without a lot of wrench torque, but I decided to ask the experts if what I'm experiencing is normal for the replacement of a flex disc.  I know that the nut/bolt thread interference and the compression of the foam rubber sealing ring on the trans output shaft is not making it any easier, but I'm still about 4 or 5 mm away from closing the gap but I stopped to get some encouragement before I break something.  I certainly would hate to break an ear off the trans output shaft flange or off the propeller shaft flange.  For my current stopping point, see the photo.

If I'm doing something wrong, please don't hesitate to yell, "STOP!".

Tom Kizer

[Tomnistuff]

And another question.

Am I supposed to have the little inserts shown in the attached sketch.  They appear to be perhaps to prevent distortion of the aluminum centering cross when the cross is compressed against the steel insert of the flex disc.  Anyway, now that my centering cross is in place but with the gap open a few millimeters, I should be able to see the inserts if they are there.  I can't see them.

I don't imagine that their absence would affect the issue described in the first post, but I think I should ask if I am over-stressing the accuracy of the BBB sketches.

Any opinions?

Tom Kizer

[ja17]

Hello Tom,

Your assembly looks fine. The inserts you show should be built into the cross flange, or part of an earlier design. Looks like your using the new improved rubber flex disc also.

[Tomnistuff]

Hi, Joe,

Thanks a lot.  I feel better now.  It seems like the older I get, the less secure I feel.  Even though I spent my work life with engines and transmissions, this is my first experience with rubber flex joints.

Tom Kizer

[Benz Dr.]

Keep in mind that once you attach the trans mounting plate and screw it into position the drive shaft will lift a bit. Once you have everything in place then you can tighten down the clamping nut and the hanger bearing support.

[cfm65@me.com]

Hi Tom,
As a matter of interest, how did you manage to measure "the angular misalignment of the trans flange and prop shaft flange"?
Regards
Chris
Cape Town

[Tomnistuff]

Thanks Dan.  I'm almost paranoid about keeping things loose until they work themselves naturally into position.  I'll try to get access to film the disc as it rotates to see if I can detect any flex at all.  I'll probably have to use a mirror.

Chris, I was waiting for someone to ask.  There is barely space to get a digital caliper up into the area aft of the disc, parallel to the propeller shaft.  Using the depth gauge end of the caliper, one can place the extended tip of the depth gauge on the disc washer side of the "gap" and slide the body of the gauge until its end contacts the "rear surface" of the propeller shaft flange, thus measuring that distance.  The only error that I see is the difference in thickness of the flange ears from one to the other.  I had not previously measured those thicknesses, so I assume they are close to the same and liberally sprinkled the word "approximately" throughout the sentences.  That's what I would do differently were I to start over.  After the final adjustment, the differences I got for the three gaps, without rotating the shafts, was 0.3 mm.  (If one rotates while measuring, one gets no difference at all, so it must be measured without rotating the shafts between measurements.)  A little trial and error is a part of the learning process.  Using the ratio of the max difference divided by the diameter of the bolt circle, and taking the arc-tangent of that ratio gave me 0.2 degrees difference in angle of the two flanges.  Since the angle of the two flanges is the same as the angle from co-linear of the two shafts, if the flanges are normal to the shafts, the angle from co-linear is also 0.2 degrees.

Good luck understanding my explanation.

Tom Kizer

[georgem]

Just to resurrect this thread -I was greasing my speedo cable today - (remove from the gearbox, clean, grease reinsert insert) and checking things out in the vicinity (as you do) when I was under there and remembered this thread. Looking at my flex disk- it waves back and forth between  flanges. Is this correct when all the bolts are snibbed up? Each wave takes the disk nearly a cm(3/8inch) forward or back from the centreline of the disc. Do I have a problem and if so, what could it be?

cheers

[georgem]

Well, as nobody took up this thread, I`ll answer it myself after some time lying on my back under the car trying to figuring out what was wrong.

It had me stumped until I slid the triangular centering piece onto the gearbox and noticed that with the rubber sealing washer on first the space between the gearbox output shaft and the centering piece was greater than the width of the flex disk. Therefore by tightening the bolts it couldn`t help putting a wave in the flex disc. The solution, cut a slice off the rubber ring until the disc gap was a snug fit - install and tighten all bolts and hey presto, a flat flex disc.

The cause - all I can think off is that the output flange at the back of the gearbox isn`t the original which gives a different offset.

So there you go.......sometimes figuring it our for yourself is a great way to learn......it just takes a little longer.