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Early GTV to late GTV driveshaft switch?

10K views 47 replies 11 participants last post by  ERathmann 
#1 ·
Next step in my multi-year quest to remove driveline vibration is to try another driveshaft.

(Because what's left when you've already tried new UJ's, new donuts, replacement transmission-output bushing, new driveshaft nose-bushing, new center support bearing, new center bushing, greased splines and nose bushing, balanced shaft once, then re-tubed(!) and re-balanced driveshaft again and it's STILL there... replacement rear axle, rear transmission mount, new engine mounts and rebuilt transmission and lightened gears...and it's phased correctly, and I always re-assemble it the same way it came apart).

In fact I should have tried this swap ages ago. But, the only other driveshaft I have available to try is from a 74 GTV with the beefed-up center bushing/bearing. There used to be a beautiful exploded diagram on the web somewhere of how the early and late driveshafts differed and how you could swap parts from one onto the other. Does anybody know where that picture might be, or could otherwise explain how to do that job?

Thanks for any advice,

Richard
Scotts Valley, CA
1967 GTV (on stands...)
 
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#35 ·
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.

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.

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

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....

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
 
#36 ·
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
 
#38 ·
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
 
#40 ·
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
 
#41 ·
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
 
#42 ·
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!
 
#43 ·
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
 
#44 ·
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!
 
#45 · (Edited)
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.
 
#46 ·
Driveshaft Vibration, The Final Solution?

It's out of balance somewhere - and about the only way to fix that on the car in the garage is with the hose-clamp method. As I said, I've tried this a couple of times. But here we go again.

There are 4 places to place a hose-clamp (obviously it could go anywhere but simplifying)
A-right behind the donut - i.e. front of the front section
B - rear of the front section
C - front of the rear section (behind splines)
D - rear of the rear section (right in front of the diff's UJ)

I've always assumed A, B or C are the likely candidates.
A because it's right near the flexible donut where any imbalance could be amplified. (although the olive and nose bushing really help here)
B is near the center flexible mount which could have the same effect, plus it's in the middle of the shaft where the "skipping rope" effect would have higher amplitude.
C is about the same as B - only worse because it's behind the center UJ and the splined joint

D, on the other hand, is right by the diff which is the most firmly located of these 4 positions, I would have thought (are you seeing where this is leading?)

My method. Attach a hose-clamp at position A. Start engine, into 5th gear, rev up to 55mph and feel the vibration. No change? switch off, shift the hose-clamp 180degrees, try again. And again at 90 degrees and 270 degrees form original. Nothing?

repeat at position B (not much)
repeat at position C (couldn't tune it out but wow it's getting sensitive to changes now. I could make it MUCH worse at C)

So try at position D, which I don't think I've ever tried because it's right by the diff (that I've changed twice) . Tried one place - and it vibrates really badly now, worst ever. So move 180 degrees and, gasp, it's smooth. Vibration is almost gone. Attach a 2nd clamp in the same location, and it's vibrating again. Remove 2nd clamp, move single clamp to 270degrees and it's better still.

Then after fiddling around for a while I found the "perfect" spot and can no longer feel it. I just went for a 30 mile test drive and I think it's gone.

I don't pretend to understand this yet - 3 driveshafts balanced perfectly on the balancing machine. 3 different UJs at this end of those shafts. 3 diffs with 3 pinion bearings etc. Various attempts to correct/alter working angles for the joints - yet one hose clamp is the trick that works!?

my conclusions after all these attempts.
- don't use poly-bushings - and softer is almost always better
- making everything super-tight so that it "can't move"...doesn't work
- get a pro to balance the driveshaft, but you don't know for sure until it's back on your car
- iPhone apps are handy, and it's physics, not magic.

Thanks to everyone who commented, suggested, recommended etc over the years. Especially Tom, Steve and Andrew for listening.

-Richard
 
#48 ·
More than once I have found the transmission output flange nut loose when doing driveshaft work. I remove the flange now and check the mating surfaces, as the wobbling flange and shaft can create grooves that prevent the flange from running true even when tight. Same goes for the input flange on the differential. More than once I have had to flatten the surface that mates to the bearing inside to get the flange to run true. Seems the flanges are fairly soft metal.

Glad you figured it out!
 
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