ALFAGTV6.COM

[Greg Gordon]

I am not claiming to have all the answers here. I am claiming that I have had NO guibo failures and I have run fairly large amounts of power through them (220-265rwhp). The only thing special I am doing is making sure everything is well lined up in both the fore/aft, lateral, and vertical directions, and cross bolting the transaxle mounts.

Now I have no doubt that they will fail with extreme abuse, that's true with the stock level of horsepower. I also suspect they have an upper limit somewhere north of 300rwhp, but I don't have first hand experience with that, and I don't think the transaxle can handle much more than that anyway. For serious levels of power, like 350rwhp or more, you will need another transmission which means you won't be using stock guibos anyway.

Greg Gordon,
www.hiperformancestore.com

[MD]

..experts? mmm?

Hey fed. Think about it. In a 3 part union where 2 are steel and the other is rubber, which is the weakest? Exactly ! So if you are going to use an Alfa donut you still have the original problem.

Yes my race car does have 2 donuts and a solid centre. It uses a BMW/MERC donut in the front and rear and a CV joint in the middle with a centre bearing which would move (as it should). However as I have explained before, this conversion requires re-engineering location points and a custom made shaft. If you got a spare couple of grand AUD, you can do it to.

[fedezyl]

well, the thing is, i'm on the verge of putting a V6 on my Giulie, it's the first conversion I know of around here in south america, the engine is from a 164.
I have good access to a very good machine shop, so I was thinking on improving on the design of the shaft a bit, based on the experience on people running V6's and modified 116's, as i'm planning on sometime next year or the other on buying GG supercharger's kit, I have several shaft's laying around too, so well, mostly my idea is to try to rule out the misalignement issue, and your solution seems to me at first sight a good one.
I must say, my car is not involved in serious wheel to wheel racing, but i'm planning on increasing the HP's though and some track day racing too.

You can get the fore/aft alignement with the pinch bolt, and take care of the up down and sideways alignement with the cv joint, at least the one that happens with the different loads....

just a thought though, no scientific evidence here

[Mats]

On my todo-sheet there is one header that reads (in swedish of course): New propshaft.

I've been kinda quiet about this but as a part of my job I design propshafts for passenger cars. I have been quiet about this because I'd rather not have my mailbox filled with questions about is. ( ) I don't have the time to be somekind of "helpdesk", BUT I will post all my results here for you all to see. That will be my contribution and I hope you will be satisified with that.

My intention is to design a propshaft/driveshaft with CV-joints in the ends and a Hookes joint (cardan joint) in the middle.
This will not happen instantly but my aim is that it will be ready before summer.

[fedezyl]

I had that same idea in my head about the cv joints and the cardan joint, but, I don't design prop shafts for a living, I fly airplanes, so mine was just a guess...
I guess i'll wait a little longer...

[ar4me]

I'm in the process of rebuilding the driveshaft for the 3.7 race car due to premature (2h track shake-down + 10-20 dyno pulls) "failure" of the center coupling See pic below. I have 3 possible root causes for this failure:
1. Rear engine mount is mounted 3/8-1/2" higher than stock - potentially too much up-down misalignment.
2. Front splines did NOT slide freely - not sure how anyone got the driveshaft in the car - it took me a lot of force and time to get it off. Hence fore-aft alignment could have been off.
3. The center coupling may have been re-used from a serious fire where front half of car burned (melted windshield, etc.). Weakened rubber...

During rebuild I will address 2 and 3, but addressing 1 would equal engine out of car and a new custom sump which I would obviously like to avoid - the current sump interfers with the steering rack, hereby preventing stock mounting of rear engine mount... Personally, I think it is too much. What do you guys think?

I could try to use spacers on the front engine mounts in order to improve the angle towards the transaxle, but it will not be as good as stock (assuming stock is ideal...) Any thoughts? Switching to a setup with CV joints (or other joint allowing an angle) would work, but that is a major undertaking that I would prefer not to engage in at this point. The fact that the front coupling looks perfectly fine may indicate that 3 was the root cause.

Any thoughts, suggestions?

Jes

[kevin]

Jes, I have never broken the middle coupling as mine started off new. Yours looks like its had twenty hard years. Puts some pics of your sump on another thread to discuss there. I think yours is the same as mine and my mounts are in origional position.
Touch wood but im going into third season of racing with same prop.

[ar4me]

Kevin,
There is NO way the rear engine mount can mount in the stock position. I know mine fitted stock position on a GTV6 - Dawie broke engine in and dyno'ed in GTV6 chassis (since you guys didn't get the 75/Milano). Keep in mind that I'm running a 75/Milano. By grinding the rack slightly it works by mounting the rear engine mount on top of (instead of below) the "spacers", but I am concerned about the driveshaft alignment.
Jes

[MD]

My intention is to design a propshaft/driveshaft with CV-joints in the ends and a Hookes joint (cardan joint) in the middle.

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.

[MD]

Jes (and anyone else interested in this topic),

I have a simple but difficult to explain alignment procedure but I will give it a go here:

The theory behind my procedue is this:

The faces of the two yokes clamping together the rubber coupling MUST rotate as a parallel set at the time of rotation.

Step 1

1 To test this, machine up nine tube spacers equal to the width of the standard rubber coupling.(Three for each coupling section)
2 Substitute the spacers for the coupling by placing the tubes over the 3 fixing bolts as if you are going to bolt them in place but do not tension up the bolts fully. Leave the tubes to move freely enough to insert a feeler guage.
3 Bring the yoke faces together as close as possible to each other and against the edges of the spacers now between them.
4 Using a feeler guage, measure the spacing between each yoke internal face and the edge of the tube. If the measurement is the same, your shaft in that section is correctly aligned for the componenet it is coupling to.
5 Rotate the shaft with tubes in place for 36o* and test along the way to be sure. Although a 3 point measurement would be accurate enough anyhow.

Step 2

1 Leave the spacers in place and tension bolts up. This section in now correctly aligned to say, the flywheel.
2 Repeat the process for the centre section and then finally the clutch input shaft.
3 Raise or lower components by packing/spacing or fabrication of mounts if necessary to get the aliignments correct.

If the measured spacing between all three bolting places is not the same, the yoke faces will not rotate as a parallel set . This will cause a stretch in the coupling ( like a "shimmy" on a bent bicyle wheel) as it rotates due to the wrong alignment not only stressing the unit but causing vibration as well

Do this test for all three yoke couplings and you have your alignment done. This simple geometry test will ensure a correct alignment in both the horizontal and vertical planes.

Remember that misalignment may contribute to the short life of a donut and cause breakages like clutch housings. Fixing this will not eliminate vibrations due to balancing issues. That's a headache all of its own.

Wish I had a video to show you but I don't.

No video but I have added some photos of the billet spacers to insert and measure against the yoke inner flanges. It is important to file off any casting burrs on the inside of the flanges to avoid error measurements. The billet spacers represent the actual width of the donut crush tube width. For the donuts I am using, it is 30mm. The hole sizes are the same as the bolt sizes on the yokes.

Naturally you would measure this while the shaft is in place !!! Duuhh!

[ar4me]

Thanks MD, that makes good sense. I guess that will tell me how bad my static alignment is with the rear engine mount mounted higher than stock. It should also help me see how close I can get it by spacing the front engine mounts (and possibly front of transaxle. Instead of machining spacers I suppose you can just use a junked coupling, but bolt opposite yokes together solidly through sleeves in the coupling (hence only use 3, instead of 6, "eyes" in each coupling). I will first measure and make sure the sleeves of the junked couplings have exact same length.
Jes

[MD]

Jes,
The coupling idea will work if they are accurate enough although visually it is easier to see the clearances if you are only using machined billet eg. a bit of aluminium round bar, 25mm diam. with a 10mm hole for the bolts. The yokes may also need a slight file of the faces to remove any rough burrs from the castings.

A version on the theme is a lot more tricky to use. Fit the 3 billet spacers between the yokes but don't use any bolts. As you rotate the assembly slowly, a billet will fall out where the clearnace is greater than the other two. This obviously means yoke faces are not yet parallel. This is useful when you have done the first process as a fine tuning of what you have done already.

Finally, when you have done the whole lot, pour yourself an ice cold tall beer. you have earned it !!!

[Mats]

This is with solid mounts, yes?
Because obviously straight at rest is now what is important. The straightness when transmitting a lot of torque is paramount and the gearbox and engine will move if not mounted solid.

[Greg Gordon]

MD, your statement "The faces of the two yokes clamping together the rubber coupling MUST rotate as a parallel set at the time of rotation." is exactly what I am talking about in terms of alignment. I will add that they must also be rotating on the same axis, although that's so obvious it goes without saying.

Greg Gordon,
www.hiperformancestore.com

[ar4me]

See your point MD - will give it a try (and have the beer ready ).

This is with solid mounts, yes?

Are you literally suggesting/advocating solid mounts? The rear engine mount (at the tail housing) is very soft, and although the rest are not as soft they do allow movement. With solid front and rear engine mounts and solid front transaxle mounts I would think that even for a race car it could get a bit harsh. How about harder poly instead of rubber? Of course, not available off the shelf...

Unless Mats designs the perfect driveshaft and makes it available to the public this is the front coupling I will be using.

Jes