Fiat Dino 2400 Coupe - drivetrain vibration

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doublegarage
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Dino: Fiat Dino 2.4 Coupe
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Fiat Dino 2400 Coupe - drivetrain vibration

Post by doublegarage »

I'm still working on the worst mechanical problem on my car - a vibration from the drivetrain.

Some characteristics:
- can't feel it at low speeds
- feels like driveshaft-speed rotational vibration
- gets better when car is fully warmed up
- worst when letting off the gas - coasting\
- felt in the seat - or behind - not in steering wheel

What I've done so far:
- all new bushings in rear suspension (except forward trailing arm bushes)
- removed and balanced driveshaft (rear section that's inside torque-tube doesn't seem to be balancable?)
- all new universal joints x 5 (4 in half-shafts, 1 in driveshaft)
- new torque-tube front rubber mount (supports front of diff )
- new engine-mounts (old ones were dead, but this made no difference)
- Giubo/doughnut on rear of gearbox output flange
- new tyres and balanced etc

what's left to change?
- rear gearbox/transmission mount (looks brand new so I didn't change it but...)
- rear shocks?
- bushings that mount differential-carrier to body - but nobody sells those and they feel "firm"

The front suspension is also entirely re-bushed - but I don't think is coming from the front.

What else should I change/repair?
Does anybody have any diagnostic techniques I could go through? How to isolate what is vibrating. I hear that running the car while it's in the air and using a stroboscope works really well - but supporting the car and being under it won't be "trivial"

any/all suggestions extremely welcome

-Richard
-
abarth4
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by abarth4 »

I fought a similar driveline vibration on my car for a long time. It ultimately turned out to be the balance of the short driveshaft that is between the rubber flex disc and the torque tube. It took a couple of different places to run it across their balancer before I got on top of it. I wrote an article about it... I'll have to see if I can find it and figure out how to post it up here... :? However, take a good look at your motor mount brackets. They are made out of fabricated sheet metal that is folded and spot welded. They are the same part on both the 2.0 and 2.4 liter cars, but I have found that on the 2.4 they can fatigue and start to crack. Maybe because the 2.4 engine is heavier? At any rate, I had mine cut and refabricated which kept the engine from dropping (slightly) and putting the driveshaft out of alignment. Hope this helps.
Charlie Bates
2.4 Spider #1186
Charlie Bates
Metamora Illinois, USA
Fiat Dino Spider 2400 #1186
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doublegarage
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by doublegarage »

Hi Charlie,

Thanks for the reply - yes I would be very interested to read your article.

I'm trying to visualize the part that you mean by "the short driveshaft that is between the rubber flex disc and the torque tube". Looking at the parts-book drawing here:
driveshaft.jpg
I think you mean the very short section behind the flex-disc, the narrow section right behind the flex-disc flange - before it widens out to the main driveshaft tube - interesting if so! That's a very short section therefore not one I would imagine that could be out of balance - but of course it could just be bent. I would hope the balancer-guy would find such a problem, but perhaps, as you say, I should take it somewhere else.

Thanks for your help - all ideas very welcome for this one.

-Richard
The Dutch Dino
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by The Dutch Dino »

I can confirm that the engine mounts can indeed crack... I had one of them welded again...
You can get them out by lifting the engine slightly on a jack and unbolt the mount and wiggle it out.

It cured most of the vibration in my car. Although there is still some vibration around 70km/h.

Someone suggested I use the old trick of attaching a large hose clamp around the driveshaft. Moving the clamp around and test driving it. It will change the balance of the shaft slightly because the clamp is heavier on the side where the tightening screw is. This tests if the driveshaft has an imbalance. (Leaving it on to cure the imbalance would be a 'hack' of course...) :shock:

Hope this helps and let us know. Keep posting so we all know how you go about and fix it.
Leo
Dino Coupé 2400x2
The Netherlands
abarth4
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by abarth4 »

Interestingly my latest posts with pictures and the article have disappeared! :o I will attempt to repost when I can. Cheers.
Charlie
2.4 Spider #1186
Charlie Bates
Metamora Illinois, USA
Fiat Dino Spider 2400 #1186
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alh
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by alh »

I just noticed that too, but there are no errors in the log?
abarth4
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Joined: Wed Nov 27, 2013 3:55 am
Dino: Fiat Dino 2.4 Spider
Location: USA Midwest

Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by abarth4 »

OK, trying again! Here are a couple of pictures of the motor mount brackets. The triangular portion has been refabricated and welded to the original sheet metal portion.
Attachments
motormount2.JPG
motormount2.JPG (133.68 KiB) Viewed 16268 times
motormount1.JPG
motormount1.JPG (131.35 KiB) Viewed 16268 times
Charlie Bates
Metamora Illinois, USA
Fiat Dino Spider 2400 #1186
abarth4
Posts: 73
Joined: Wed Nov 27, 2013 3:55 am
Dino: Fiat Dino 2.4 Spider
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by abarth4 »

Trying again with the article I posted....
Attachments
Driveshaft.doc
(26 KiB) Downloaded 649 times
Charlie Bates
Metamora Illinois, USA
Fiat Dino Spider 2400 #1186
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doublegarage
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by doublegarage »

Hi Charlie,

Thanks for the pictures and for your article. The fabricator did a nice job on the motor mount brackets!. I had mine out of the car to change the rubber mounts just this month. They were rusty but I'm pretty sure they weren't cracked. I blasted them and painted them and put them back on. The Motor isn't dropped onto the cross-member as far as I can tell, but I'll get it back up into the air to check that again.

I'm most interested in your driveshaft balancing - can you confirm where on the shaft they actually welded a weight? As you know there are three sections:
- slim section right at the fornt, just behind the flex-disc - which widens out into
- the main section that has most of the length, and ends at the UJ
- the rear section, behind the UJ, hidden inside the torque tube - quite thin (20mm diameter? can't remember)
driveshaft rear.jpg
I've had all that assembly apart - and the section I've arrowed has a very ugly looking weight attached to it - doesn't look 'factory', but might be. Maybe you remember how yours looked when you took it apart? I wish I had photographed mine.

So is that the section that your balacer fixed that improved things? Or somewhere else on the shaft?

Thanks very much! Sorry you lost your postings, I don't know why that would have happened but they seem to be sticking now :)

-Richard
abarth4
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Dino: Fiat Dino 2.4 Spider
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Re: Fiat Dino 2400 Coupe - drivetrain vibration

Post by abarth4 »

The balance weight was on the part number callout 4639525/4639528 in the driveshaft drawing. Hope this helps!
Charlie Bates
Metamora Illinois, USA
Fiat Dino Spider 2400 #1186
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