Augusta progress

[Mikenoangelo]

All that done Karl. Propshaft clean inside , straight and rebalanced (it was not far out). Runs extremely true whether measured in the centre or at the ends. The discs and the locating spiders are new and although I have not spun the new discs as you suggest, they were very accurately made and lined up perfectly with the holes in the driving spiders. The bolts are all the same except one pair which have self locking nuts rsther than split pins, but these are fitted diametrically opposite to one another so that should not be a problem.

The vibration occurs when the engine (and therefore propshaft) reaches 2500 in top gear, but not at the same revs in third. The load does not seem to matter as once started, the vibration continues even when coasting in neutral. I can reproduce all of this with the car on axle stands and it occurs even when run with no wheels or brake drums fitted so not connected with wheel balance, radial or dynamic.

Possibly there is an engine vibration which coincides with some resonant frequency in the transmission and sets the vibration off. It would be interesting to borrow some electronic kit with accelerometers to fix on engine and the back of the gearbox to investigate this. Google does come up with a few ideas.


Mike

[Kari]

I thought you have done that all Mike. Just to let the readers in this forum know how delicate installing a simple thing as a drive shaft with its joints can be.
Some years ago, I had an annoying vibration in the drive shaft of my Augusta too. Running out of ideas, I have changed the commercial sort of 8 mm bolts to close tolerance bolts. That has cured the vibrations, but the only explanation I can think of is, that commerical "8 mm" bolts are often only 7,7 mm or even less. The small differences can add up and cause a flex coupling be out of centre. Perhaps repositioning the shaft by 1/3 turn in relation to the flex coupling and/or the driving spider could help, you might have tried this already.

Karl 

[Mikenoangelo]

You are right about the bolt diameters Karl - generally about 0.2mm less than the nominal size. However the bolts are the original Lancia ones and a good fit to spiders and discs.
I've just found and downloaded a vibration analysis app which uses the vibration sensor of a smart phone and displays the results so I'll have a play with that. Cost under £9.00 my idea is to make contact with the engine etc with a steel rod with a plate on the top for the phone to sit on much as we used to connect ear and motor with a large screwdriver! I have a digital tachometer sensing the ignition so I can set the revs.
Mike

[Raahauge]

I have been following this thread with interest and admiration for the effort put in.
I did not drive my car before I rebuilt it but my car is vibration free using standard commercial M8 bolts in the couplings (replacing a random mixture of different lengths metric and BSF.)
The only thing I attended to in that area was the outer pinion bearing which had excessive end float. I did not measure for any radial play as I had decided to  change it anyway.
If I have read all your observations correctly the problem seems to come back to the propshaft even though it all is balanced and true.
Because centrifugal forces are high I wonder if it is caused by some small amount of play in that pinion bearing, a very small amount would certainly be felt at 2500 rpm. Best wishes.
 

[Mikenoangelo]

The pinion bearings seem to be fine as is the output from the gearbox and no play can be felt. I will drain the axle oil and check for schrapnel but really don't expect anything as it runs quietly with little backlash. What oil do people use?

I've been trying the smartphone vibration app on Sue's Fiesta but was frustrated by a software glitch after a couple of tries. However it did show up a couple  of waves of vibration which corresponded with rpm and half rpm so it does look promising. This was with phone just lying on top of the dashboard.

Mike