Early GTV to late GTV driveshaft switch? - Page 3 - Alfa Romeo Bulletin Board & Forums
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post #31 of 48 (permalink) Old 07-28-2010, 12:03 AM
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yes it do'es move about as you drive, but you set the angles at rest with all the weight on all 4 wheels. you cannot do this with the rear or front off the ground..i wish i was as lucky as you where.. but i had to aline my tranny and diff to 1 degree.. but it's very smooth.. but then agian the alumiun driveshaft is very , very light compared to the 2 peice steel alfa driveshaft.less spin up weight. less poss. vibration.. also i have the driveshaft shop balance it at the highest speed they could do..i told them that i could be running at 7000 rpm at the motor..7000 rpm i belive = with the finel drive at 4.11 and 5 th gears ratio at .68( t5 tranny)- 10294 driveshaft rpm.. even at 6000 motor rpm..=8823 driveshaft rpm..but at nomal driving rpm's lets say 3000 motor rpm = 4411 driveshaft rpm.. lots of folks do not account for a driveshaft in an overdrive gear spinning faster than the motor..could lead to problems.

anyone can buy a Porsche, only Drivers drive a Alfa Romeo

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post #32 of 48 (permalink) Old 07-28-2010, 02:08 PM
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I haven't reread the entire post, Richard, but has it been suggested to check the bushing inside of the front drive shaft that the "olive" on the output shaft rides inside of? It centers the front of the driveshaft, and a good one will be perfectly smooth when you check it with your finger, while a worn one will generally have a groove worn into it.

Another suggestion/question is has the splines on the slip yoke on the rear driveshaft been checked to ensure the grease hasn't congealed and won't allow the rear shaft to move in and out easily?

George Willet


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post #33 of 48 (permalink) Old 07-28-2010, 02:53 PM
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Richard,
I feel your pain. I went through a similar situation on my '66 Super. Tried the many of the same things you have (and a few others) with no success. Then, in desperation I removed the driveline again (it had already been balanced twice, had new joints twice) and gave it to a shop I really trust in Spokane WA. He said "it's bent" and he fixed it. The vibration / weird harmonic disappeared completely -for good.

So, I think the lesson learned is....... it's the driveline- yes, it is the driveline. Get another one or send yours to Watts Wheel & Driveline is Spokane. Ask for Dennis and tell him Mike sent you.

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post #34 of 48 (permalink) Old 07-28-2010, 04:55 PM
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Quote:
Originally Posted by bianchi1 View Post
yes it do'es move about as you drive, but you set the angles at rest with all the weight on all 4 wheels.
This is really a thread jack ... but have a look at 4wd vehicles and ones that have been jacked up. No way they are 1 degree. Also have a look at trucks, again no way they are 1 degree.

I believe respectively that this 1 degree thing is a myth. And I think my club race car proved it. Heck I don't think we had any angle at all for the front UJ, infact the driveshaft might have gone up to the rear axle.

The driveshaft is just a shaft connecting two objects. I used to be involved in mechanical engineering and designed many interconnecting shafts and we never ever worried about angles other than the angle met the joint manufacturers specifications for maximum angles, etc.

A car is just a mechanical device, nothing special, same principles apply.
Pete

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post #35 of 48 (permalink) Old 07-28-2010, 08:14 PM Thread Starter
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George asked: has it been suggested to check the bushing inside of the front drive shaft that the "olive" on the output shaft rides inside of?
Thank you George - yes it has been changed - it probably has 50 miles on it (max) and is now coupled to a reconditioned transmission with a new olive - great suggestion, but I don't think that's it.
To your other thought, yes the splines are well greased and all seem to move well - and when I tried the other rear-section (i.e. different splines), the vibration was so similar it made me think the splines couldn't be the issue.

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PSK asked: The 2 driveshaft pieces have to be aligned don't they?. Are we doing this?
Thanks, yes we're doing that:-) The driveshaft has been balanced twice now..once by Frank Wallace in San Francisco - Frank hosts driveshaft balancing tech-talks at his shop and most certainly knows his stuff. Then I had it balanced at the famous driveshaft shop in San Jose (name escapes me..) and he re-tubed the rear section and re-balanced - it came back to me carefully marked for how to re-assemble the halves and I always do so. When I tried the alternative rear half from another shaft for comparison, I couldn't do that of course - but the vibration was so identical I decided it coudn't be a problem with the rear section. I do now want to try with a completely different front section - but I don't have one. I only have one with the 1969 and later beefed-up center support and I don't know if you can switch them...hence the original name for the thread.

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PSK asked: What about the centre driveshaft support. Have we replaced that?
We have (twice). every replaceable part.

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SprintGTC said: "it's bent" and he fixed it. The vibration / weird harmonic disappeared completely -for good.
Right - that was always at the back of my mind - hence my visit to the 2nd balancing shop - I was very excited when he re-tubed the rear, thinking he'd discovered a 'bend'...but it made no difference - I have to try a new front-section - thanks for the recommendation for a shop. Funny, I'll be in Spokane next month....

Quote:
This is really a thread jack
Yeah, but it sounds like a great subject for a brand new thread.

Thanks all for the replies - all idea-bouncing is extremely useful - I will try more stuff this weekend and report.

-Richard
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post #36 of 48 (permalink) Old 08-08-2010, 09:36 PM Thread Starter
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Source of bad vibes...poly rear trailing arm bush?

Back in 2002 when I was re-assembling this car I R&R'd the rear trailing arms - after some discussion I decided to try poly-bushing in the rear (bolts to axle) location - still have rubber in the front (to body) location.

These bushes are the only thing I haven't ever changed since 2002. The T-bar to diff conical bushes were also poly but I changed those back to rubber a year ago.

My friend Steve lent me some old trailing arms that were skulking in his garden with tired-but-serviceable rubber bushes. I swapped my trailing arms for this pair and went for a drive.

First impressions are that the vibration is not there (I have to be very careful because it comes and goes - but usually after a good warm up it's always there.) Also, the car used to shudder a lot when coasting down to stop at a light or stop-sign - I always thought that was a separate problem, but that seems to be gone too.

So, there are plenty of warnings against using poly-bushings on the BB and it looks like I'll be adding my own. Seems there is some bad resonance set up between the combo of rear transmission mount and poly trailing arm bush. This week I'll replace the poly busings in my trailing arms with new rubber bushings as a final check. Then we'll see...

-Richard
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post #37 of 48 (permalink) Old 08-09-2010, 12:10 AM
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It's possible that the vibration is still there its just that it is not being transmitted to the body shell maybe ... but anyway this is really good news for you .

Pete

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post #38 of 48 (permalink) Old 08-09-2010, 07:41 AM Thread Starter
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Originally Posted by PSk View Post
It's possible that the vibration is still there its just that it is not being transmitted to the body shell maybe ... but anyway this is really good news for you
Pete, yes I suppose that's true, but I'll take it! It's always been hard to describe this vibration - it's more of a 'hum'. You might not notice it for a while, and then you turn to talk to your passenger and find yourself yelling because it's so loud, but such a low frequency. After that you can't escape it.

Maybe I'll get to drive the thing now!

-Richard
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post #39 of 48 (permalink) Old 05-13-2014, 01:47 PM
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It's nearly four years later, Richard. How does the story end?

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post #40 of 48 (permalink) Old 11-25-2014, 09:09 AM
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I,ve dealt with similar vibes and would also like to know the end of the story, I`ve had a broken diff carrier right across where the spider shaft, and on other occasion just had to replace the rear section of the DS, then on another occasion it was a slightly undersize trans mount that walked sideways under load and then go back in place , drove me nuts

George
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post #41 of 48 (permalink) Old 11-25-2014, 09:54 AM Thread Starter
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yes, I didn't follow up did I, sorry Gary and ganunez.

Well - it's still there. I think the change I made most recently (trailing arm bushings) was the best improvement - I actually made sure I had a set of trailing arms with the larger (later) bushings in them with more compliance.

But as Pete said - the source might still be present, it's just not transmitted to the body as well as before. And the key will always be to find the source.

I like the look of the Alfaholics driveshafts that are made of lighter, stiffer tubing and most importantly are balanced at high speeds. But they're a bit spendy for something that I give a 30% chance of working given all the other changes I've made.

It's a bummer, because with all the other things I've done along the way with suspension and engine tuning etc, this car is a blast to drive.

Thanks in advance for any other suggestions.

-Richard
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post #42 of 48 (permalink) Old 01-04-2015, 05:11 PM
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74 GTV olive/driveshaft bushing question

I got some sage advice from Gigem on the GT forum, as I am working on my 74 GTV and I have a question which I can not answer!

The output shaft of the transmission has an olive on the end, but a three fingered spider which connects to the Donut, the donut in turn connected to the front driveshaft via another spider. The front driveshaft also has a steel bearing in which the olive rides it seems.

With the driveshaft connected via the spider/donut/spider arrangement, it seems to me that the driveshaft turns at the same rate as the transmission output shaft, ie, that donut is a 1 to 1 'solid' coupling.

If the above is true, what is the purpose of the output shaft olive and the mating bushing in the driveshaft? They do not rotate relative to each other, correct? The olive just sits 'stationary' inside that bushing I suppose? How can a work output shaft olive have any bearing on vibration? Taking this a step further, if I cut off the olive and relied completely on the donut only, what would be the worst that would happen? (not that I am going to do that, but I simply don;t get the purpose of that olive/bushing?)
Thanks in advance!

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post #43 of 48 (permalink) Old 01-04-2015, 05:41 PM Thread Starter
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what is the purpose of the output shaft olive and the mating bushing in the driveshaft? if I cut off the olive and relied completely on the donut only
Hello Goats,

Great question - I think maybe the answer lies in the Italian name for the olive - which is "annello centraggio" or "centering ring".

Here's how my brain imagines the process - Say you drove over something that whacked the donut upwards - it springs back but is now offset by 1mm - as you drive the car the forces on the donut amplify that offset and it gets worse - and the driveshaft stays out of balance because it has no centering reference to return to.

But with the centering ring (olive), the donut rotates about a central reference. Then, the theory at least is that the donut's elasticity is only in the rotational plane - it absorbs vibrations such as when you drop the clutch or smash the brakes on. It might also absorbs some angular offsets as the transmission moves too - but that should be minimized (i.e driveshaft should be inline with gearbox) if you want the donut to last long.

Does that make sense?

-Richard
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post #44 of 48 (permalink) Old 01-05-2015, 08:49 AM
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Makes perfect sense Richard, thank you. Thus this olive is really a 'stabilizer' so to speak to, as you say, insure the donut is 'centered' and doesn't get out of balance. I suppose then the only way that olive gets worn is that a) the driveshaft is badly out of balance and has lots of runout at the donut end, b) the donut is loose and floppy (either lost its durometer or is mounted sloppy/off center)?

Thankfully the olive on mine is not worn, nor is the bushing in the driveshaft. I packed the bushing with grease and installed that rubber 'sleeve' bushing over the output shaft so I suppose I should be OK - but we will see!

Thank you!

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post #45 of 48 (permalink) Old 04-05-2015, 10:43 AM Thread Starter
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Driveshaft Vibration, The Final Solution?

If you're reading this then you must have commented on, or subscribed to this thread a few years back - I think I've been working on this problem for over 10 years - but I actually think it might be fixed now.

To summarize again
The Problem: 1967 GTV, road-speed related low frequency vibration. Very loud (though low frequency so is felt as much as heard), present about 53mph and above. Does it in neutral, does it with foot on clutch. Very annoying - I've improved it over the years, but never eliminated it, tried to live with it (couldn't...) and had a another go this weekend and....!

To summarize what I've tried over the years (this is hard because I've tried EVERYthing)
front to rear:
new engine mounts
new transmission twice (new output shaft in first 'box with new Olive)
new nose bushing in driveshaft
mew UJs
new center-mount bearings and rubbers
new back axle (i.e. diff)
new wheels and new tires (twice) - balanced by pros
- and
3 driveshafts - 2 re-balancings, one re-tubed then re-balanced
Various attempts to tune it out with the "hose-clamp" method - including one with industrial vibration analyzer
new trailing arms with new (softest available)


That last modification, using the trailing arms that have the large bushings (these are later than 1967 - a clue that Alfa found softer was better) made more improvement than any other, but decided after some long trips that it was masking the vibration (i.e. insulating the car from it) rather than curing it.

So this weekend the car was up on jacks for a new speedo cable and to adjusting the handbrake - I just had to have another go.

My phone can take slow-motion videos - so ran the car in 5th gear at ~60mph and tried to film the shaft - but I couldn't see much, maybe with more light?

I downloaded an app for the phone that uses the accelerometers to analyze vibrations - that actually worked and I could see a big peak at almost exactly 49-50Hz (unfortunately it can't analyze above 50Hz but suspect the the graph would go higher). After some arithmetic...with 185/70 tires and a 41:10 ratio diff - at 52 mph (right where the vibes start) the driveshaft would be rotating at 2,940rpm or...49 revs per second = 49Hz.

so it IS the driveshaft! It had to be really, I'm just in denial because I'm on the third shaft and multiple balancing jobs. See next post.

Last edited by GTV67; 04-05-2015 at 11:11 AM.
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