ALFAGTV6.COM

[Mats]

Compare "quite often" with "every gear".

[Giuliettaevo2]

I get the picture...

['Fetta]

This topic makes very interesting reading. I own a GTV2000 (4-cyl) and after a total restoration the only problem is the coupling going "BANG". Added to this my model is said to be an intermediate model that has a coupling different from the early and late ones.

When it went bang the propshaft came through the floor into the cabin . Thanks to the carpet there was no mega carnage.

Unable to get the correct coupling we have been trying to set it up to take the early coupling that we mistakenly ordered. But the moment we take her for a slow drive we hear an unhealthy creaking. There is no vibration at idle and when revved stationary. Only on the move we hear the creaking. And see that the coupling is under stress. Could it be a case of imbalance in the shafts?

Tracing the history of my car, I have learned that this problem has been present when the car was brand new. The clutch housing has been replaced twice and now it has a locally made housing which seems stronger although heavier.

Living in Sri Lanka, I have no way of comparing my car with any other. This is the ONLY Alfetta alive here, albeit not fully kicking yet.

The U-joint conversion seems ok for racing. But then the low speed vibration might now sound very nice for regular mixed use.
We are toying with the idea of a CV joint conversion. Has anyone tried this? What are your thoughts? What kind of RPM can a CV joint take?

Thanks.

[MD]

If you keep breaking clutch housings, you have a serious shaft to gearbox misalignment. You have to fix this first.

You can use a CV joint but ideally it should be in the middle. If you want to experiment with couplings, I suggest an original Alfa coupling in the front, CV in the middle and a universal joint at the rear. This will work and keep the shaft queit.

[Mats]

Why do you want the CV in the middle? I'm going for CVs in the ends and U-joint in the middle, see no point for CV in the middle.

[MD]

least cogging and smoothest rotation, least total mass.
Unis at both ends works but is too noisey. Rotation is ok.

You need a rubber coupling somewhere in the chain. Best place is up front to isolate engine firing noise noise.

SO if you are putting rubber up front, you then have a CV and Uni to go. In this combo, the CV in the middle will produce smoothest rotation.

[ar4me]

A helpful Alfisti and racer (Richard Jemison) fabricated me a laser alignment tool which fits over the "tip" of the transaxle yoke, and at the other end, into the flywheel where the driveshaft centering bearing fits. In my case the stock alignment was quite a bit off, rear engine mounting and the front transaxle mounting were both too low. Interestingly, removing the 15 mm spacers on the transaxle front cross member, and mounting the rear engine mount (tail housing mount) above the little plates instead of below (raises the rear engine mount by about 8 mm), brought things into pretty good alignment. Almost like this is how engine and transaxle were designed to mount... except that I need to modify tunnel since rear giubo will have clearance issues at top.

As for driveshaft, I will run a 1-piece carbon fiber driveshaft with the front aluminum giubo replacement I have from scuderia biscione. The choice of the carbon fiber driveshaft is out of safety concern and to support the engine power. Everything incl. shifter, clutch line, and brake line will vacate the tunnel. The driveshaft will be a copy of Al Mitchell's race proven driveshaft, and Richard is helping me with the shifter (straight rod from transmission input selector through cabin to shifter base). Fortunately, the carbon fiber drivehaft shop that made Al's driveshaft is local to me, and I plan to visit them Monday (with a stock complete driveshaft and donor parts for the carbon fiber driveshaft) unless they observe Presidents Day.

This is all for the 3.7 race car. Maybe some day this year it will be ready to hit the track in a satisfactory form. Until then I'm running my budget 75 race car - Roxanne.

Jes

[Mats]

least cogging and smoothest rotation, least total mass.
Unis at both ends works but is too noisey. Rotation is ok.

You need a rubber coupling somewhere in the chain. Best place is up front to isolate engine firing noise noise.

SO if you are putting rubber up front, you then have a CV and Uni to go. In this combo, the CV in the middle will produce smoothest rotation.

I don't you need a rubber coupling in the propshaft at all, I'll come back to that after my first test run.
Most cars does not have rubber at all in the propshafts and do fine, I'm going for a sprung centre in the clutch disc instead.

So you say there is a big angle in the middle joint and the rear one is almost straight? From my memory the whole thing is almost straight so from a speed variation point of view it should be no difference and even if there is a bigger joint angle in the center one the angle is too small to make a difference.

[MD]

Jes,

I think your strattegies are right on the money. Interesting too that once I got to using my alignment tool on the rear coupling, the alignment was that far out that I had to jack up the front tranny mounts by about 9mm and drop the rear mount by about the same amount.

Now to make this work using my after market Mercedes rubber coupling (rear)which is larger than the Alfa one, I had to cut out the tunnel around the coupling to stop any fouling. Fixed the problem. It started others but but it is not relavant to the driveline.

I have already moved all the hydraulics out of the tunnel. The carbon fibre shaft makes good sense coupled with lightened flywheels and clutch.

Mats,

I am just goona let you find out the hard way like I had to.

[Mats]

So what did you find out? Vibrations? Noise?

[MD]

Mats, I have previously explained this on page 2..and you need to believe me you will not get around the problem if you do not use at least one rubber coupling.

Mats, this design works as well as any other combination of universal joints, CV's. I have tried them on the track and several other 2 litre racers have them in our group.

If you have not experienced it before, the result is a very loud "hammering" noise from the entire transmission for revs below 2000rpm. It sounds like something is about to break. Once above these revs, the noise disappears. There are no reliability issues with it, just a disconcerting effect of the noise.

For a race car, this is possibly acceptable but for a street car absolutely not.

I thought I would just alert you to this heartache having spent the bucks in experimentation already.

Solution: Install one modified donut in the front only. Fixes the problem.

[Zamani]

Well I finally found the discussion we had about driveshaft misalignment many years ago.

Even have drawings by famous contemporary artists Barry Picasso and MDichelangelo.

viewtopic.php?f=9&t=320&st=0&sk=t&sd=a& ... n&start=15

This forum is a real treasure trove. One reason to keep it running (keep donating)

[Mats]

Mats, I have previously explained this on page 2..and you need to believe me you will not get around the problem if you do not use at least one rubber coupling.

Page 2, ah yes, the same page where I said I'm working specifically as a propshaft designer...
The rattle issue can be dealt with in a number of ways and if that is the only problem I'm good. There are a lot of production cars driving around with rubber-less propshafts and remember that an auto gearbox is 100% solid when the lock-up is engaged, no filter at all from engine fire pulsation.

[MD]

Yes, the noise is the only problem. We are talking race cars here of course.

I am aware of street prop shafts that use internal damping by using an inner and outer tube with a rubber compound acting as a dampner between them. Never seen it in a racing application but if it is up to the torque, this should work without an additional rubber coupling and is what I suspect your intention is?

If you think you have solved it, great. Please top us up with your proven final design when you are ready.

...now if we could just move the engine behind the firewall and use a one piece shaft....oooh yeah !!

[Mats]

Never seen a two piece tube connected with rubber.. There are internal dampers in some tubes which consists of a weight suspended in rubber but the tube is always solid.

As I said before, everything will be shown here and possible to duplicate.
Initial calculations show issuse with the V6 and the torsional stiffness of the tubes though, but it should not be the cause of the low rpm rattle you describe unless you had seriously slender tubes.