Fiat Dino 2400 Coupe - drivetrain vibration

[doublegarage]

Hi Georg,

This is great information, thank you. I take your point about sending the driveshaft to Elbe and getting them to balance the whole thing. I will definitely think about that - they have a full translation of their website in English, so maybe the language barrier won't be too bad - but thanks for your offer of translation help.

One thing I don't quite understand - the rear section of the shaft - is contained between a bearing in the front of the torque tube, and the bearing in the front of the differential. So if I send them both front and rear sections - how can they balance the rear section when there's nothing to support it? Do you send them the torque-tube? Or do they just arrange all that themselves?

You have been through two of these driveshafts with a worn front bushing - looks like I've got one - it seems like somebody should be re-making this part for the Dino establishment?

I will remove mine again this weekend and take it from there.

Thanks everyone. great forum!

-Richard

[doublegarage]

I finally had time to work on my car today - and so removed the drive shaft and torque-tube, again.

Now that I can hold the parts in my hands I can finally understand the pictures Georg sent - and the way the bushing/bearing at the very front of the driveshaft goes together.

Before I took it apart I tried to feel some movement between the driveshaft "nose-bearing" and the gearbox output bushing. I couldn't feel anything, but i'm not sure that's an adequate test, since I cant apply rotational torque that the shaft would normally 'feel' - and certainly not with any force.

So - taking it apart, I would say that they seem to be in good condition - on the driveshaft side, I do see some discolouration of the inside of the bearing - i can't feel it at all, but can definitely see evidence of use. Very hard to say how bad it is. I need to pull the front section off the shaft and push it onto the gearbox bushing - see how that feels.

Here is one picture that worries me - on the far back end of the shaft, on the coupler that couples the splines of the shaft to the splines of the differential - there's is this balance weight - does that look right (doesn't to me).

The bearing at the front of the torque tube feels ok - although I will replace it this time. (I think it's a Lancia Delta Integrale part also..)

Then I will think about packing it all up and sending it to Germany - before I do that, if anyone knows someone in the USA who knows how to balance torque-tube driveshafts, then please let me know?

Thanks,

-Richard
2400 Coupe

[doublegarage]

So I took the front section of the driveshaft and (without the rubber donut) placed it over the bearing on the end of the gearbox/transmission output shaft.

It was really tough to feel any play or movement between the two parts. There was one plane in which I think I could feel very slight movement - but it wasn't easy - and I'm just not sure that this amount of movement could cause the degree of vibration I feel in the car - but of course...it's possible.

Georg - do you know how Elbe solved the problem of the part now being unavailable? Did they make the part?

The more I think about this, the ore I realise...that, the vibration is there when the car is coasting (no throttle) and not there when the car is accelerating (throttle pushed) - and that therefore, it's unlikely to be a simple imbalance of the shaft - because if it was, the driveshaft would vibrate whether the car was accelerating or not.

Instead - it changes when the geometry of the driveshaft changes - different between whether the engine is driving or the wheels are driving - therefore much more likely to be an issue with this nose-bearing - or the bearing at the front of the torque-tube, or the rubber ring around the torque tube - or even the rubber mounts for the rear axle.

The rear axle - does anyone know where to find those mounts? Part number is 4182051 - rubber "pads"

Thanks,

-Richard

[doublegarage]

I'm still slowly working through this problem - the time since April has been spent looking for the unobtainable parts that fit between the gearbox and the driveshaft.

After contacting a guy who rebuilds ZF gearboxes in Italy I finally did find a set of NOS parts - pictured here:

Holding the new driveshaft ring over my gearbox bushing - and then pushing the new gearbox bushing into my driveshaft's ring - I cannot feel any difference whatsoever - in other words, there is a tiny amount of movement with the new parts assembled and it's exactly the same with my car's existing parts assembled.

By the way, I think these parts are from an Alfa Romeo Montreal, which did use the same gearbox and was built around the same time as our Dinos. I've asked someone to look up part numbers on the AlfaBB forum but nobody has replied with good info (yet)

So I'm going to take the entire shaft to the best balancing shop in the area tomorrow, ask him whether he balance the entire shaft as a system - and if so, let him try to balance it. After that, I'm sending it to Germany .

Thanks for the help everyone.

-Richard

[alh]

So, could it be balanced?

Curious,
Adrian

[doublegarage]

Funny you should ask, today I'm putting it all back together.

Yes he was able to balance it, as a system. Removed the crazy weight on the splined-coupler at the diff - removed a lot of the other non-factory weights that the shaft had acquired over the years - and got it "really smooth" on the bench - all spinning as a full system.

But the proof is in the pudding - not quite there yet.

Thanks,

-Richard

[doublegarage]

I finished up the reassembly this evening and went for a test drive. Terrible traffic around here on a Friday night so I couldn't go for a long drive, but...

it seems to be way better now. I could feel that the car was "less smooth" when coasting at 70km/h, but it definitely wasn't shaking and shuddering as before. I need to do a longer drive - maybe on Tuesday - but here's a summary of the things I've changed and what worked:

stage 1)
Changed all rear tie-rod bushings (x4) and rearward rear trailing arm bushings
Changed all universal joints in driveshaft and half-shafts (x5)
changed guibo (donut)
balanced front (thick tube) section of driveshaft only
- This basically made very little difference

stage 2)
changed engine mounts (rubber) and checked for cracks in engine-mont sheetmetal
flipped orientation of front to rear sections - some improvement noticed to coasting vibration, but possibly made vibrations worse under load.
- therefore no real improvement (despite my early hope that it had worked, see above)

stage3)
changed rear transmission mount (old one looked "new" but...never mind)
tightened differential subframe mounts (4182051 on page B4.01) - these were surprisingly loose, possibly allowing the diff to move forward when casting, and allowing the shaft to change geometry (shorten?). I would love to change these, bit nobody makes them.
AND full system balancing at a new place - best balance was more or less found by removal of weights added earlier this year, weights added by others to the main tube some other time - and removal of the crazy weight on the spline-coupling at the rear of the shaft
changed the bushing/bearing between gearbox and driveshaft

and something in stage 3 has worked. I would put them in order 1) full system balance, 2) tighten diff mounts, 3) new trailing arm front bushing, 4) the rest. It's hard to explain but I really feel like anything allowing the diff to move fwd when coasting is bad. We need to make 4182051s.

By the way, someone did finally send me a page from the Alfa Montreal parts book and the bushing/bearing at the gearbox/driveshaft are NOT the same as the Dino. Oh well.

-Richard

[ThomasK]

Have you also changed the rubber ring around the torque tube?
This normally has a big effect, as the rubber is weak after 40 years.
The only one I know who have this in stock is dinoparts.
As I overhauled my complete rear axle last winter I also changed this,
the effect was remarkeable, although I couldn`t exactly say wat makes the biggest difference,
as I have changed all the bushings and bearings.

A friend of mine changed only this rubber ring two years ago and his vibrations around 70 km/h were nearly gone.

KR, Thomas

[doublegarage]

Hi Thomas,

yes I changed that too, forgot to put in one the list. Bought from DinoParts as you suggest. It was probably in Stage1, therefore made very little difference for me.

-Richard

[TrondB]

Thank you for an interesting discussion on this issue. I want to investigate some vibrations in my Dino too!

Is the rubber ring referred to above part nr 4211466 (called "rubber mount cardan shaft" at Dinoparts?