driveshaft conversion

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staffordgtv6
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driveshaft conversion

Post by staffordgtv6 » Sat Dec 13, 2008 5:22 pm

my old man just bought me a 1985 gtv6 for my first car. i was wondering if there is any conversion to take the driveshaft for a donut link to cv joints because it is stronger and i intend to race it.

thanx staffordgtv6
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Re: driveshaft conversion

Post by Greg Gordon » Sat Dec 13, 2008 6:28 pm

Hi Stafford,

The stock driveshaft and guibos will easily handle over 300rwhp reliably with very little work. The expense involved in converting to another driveshaft isn't really worth it because the transaxle can't handle much more anyway. I have a decent clutch/driveshaft tech article on my website you may want to check out.

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Re: driveshaft conversion

Post by Zamani » Tue Dec 16, 2008 9:33 am

Greg,

Can you expound a little on the alignment part? So far a lot of people have been saying "it's fine don't touch it". But I guess it depends who you talk to.
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Re: driveshaft conversion

Post by Mats » Tue Dec 16, 2008 10:37 am

Zamani wrote:I'm curious why Alfa didn't align the engine and gearbox properly then? Some say it was intentional?? A tuner in Australia said the alignment for the driveshaft needs to be corrected.
You must measure it under load. The engine and gearbox move when you apply torque and hopefully it will all align when it's busy.
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Re: driveshaft conversion

Post by Greg Gordon » Tue Dec 16, 2008 11:38 am

Hi Zamani,

Thanks for moving this topic. I agree with Mats. I think the issue is alignment under load. We all know the motor mounts and the transaxle mounts flex when torque is applied. What we don't see is how much that throws the driveshaft out of alignment.

Because of the driveshaft's length, a very slight movement of the front of the transaxle in the lateral direction translates into a a huge angular deviation that the guibos have to make up for. I don't feel like doing the math here, but I suspect that moving it 1/10 of an inch to the right would move the other end of the driveshaft (if it was perfectly stiff) about 6 inches. Of course it doesn't move because the guibos take up the flex, but think of the twisting stress that puts on the guibos. Once they are subjected to that stress, I think they are far less able to handle the torque from the engine, let alone the 8000G's they are subjected to at 7000rpm.

As for the statement that the engine and transaxle are out of alignment from the factory, I am not so sure. They are definitely out of alignment with the longitudinal axis of the chassis, but I am not 100% sure they are out of alignment with each other. I have no way of measuring that. Even if they are, it's almost certainly because they move closer to perfect alignment with each other when under load.

All of my efforts at preventing guibos from blowing have been based on alignment principles, and so far, so good!

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Re: driveshaft conversion

Post by Mats » Tue Dec 16, 2008 11:58 am

We need a car, a video camera and a dyno with a glass floor... :)
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Re: driveshaft conversion

Post by Maurizio » Tue Dec 16, 2008 12:21 pm

I don't feel like doing the math here, but I suspect that moving it 1/10 of an inch to the right would move the other end of the driveshaft (if it was perfectly stiff) about 6 inches.
hmm, I don't agree, the movement or the angle the front guibo gets will be the same as the angle the last guibo gets, if the rest is assumed stiff. But bad engine mounts won't help to reduce movement. And they are not the items that are changed on an interval.

I think the most killing for guibo's is huge load changes and high rpm's.
Off center movement of the shaft + rpm's :roll:
So accelerating hard, clutch dumps, down shifting without any feeling for mechanics.
The rest is just age off the rubber which gives them small cracks, which are the beginning of the end.
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Re: driveshaft conversion

Post by Greg Gordon » Tue Dec 16, 2008 2:06 pm

Maurizo, you are about to make me get out my 10th grade geometry textbook and draw a picture. If the front of the transaxle moves laterally just slightly, it is then aimed at a point pretty far from where is was originally. My 1/10" of an inch translating into 6 inches over a distance equal to the driveshaft length may not be super accurate, but the principle is sound.

I don't agree that it's huge loads and rpm that kill guibos (although obviously at a certain point enough power and rpm will cause a failure of these or any other parts).

The U.S. spec Alfettas from the 70 have engines with very little power and low rpm limits. Yet they blow their guibos all the time (they are about the same size). The big difference between them and the GTV6 which has 50% more power AND more rpm is that the fore/aft alignment with the GTV6 can be set very accurately.

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Re: driveshaft conversion

Post by Maurizio » Wed Dec 17, 2008 11:58 am

Greg, i believe you, it is not the hp's .

What I mean is the pulse, how you apply the load. When you ease the power into the drive train it can withstand a lot. And rpm's who want to throw the rubber connections between the mounting bushes out.

The misalignment which will result in the same angle off first and last guibo...
I made a fast sketch to illustrate what I mean.
Attachments
guibo.JPG
guibo.JPG (21.56 KiB) Viewed 12071 times
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Re: driveshaft conversion

Post by Mats » Wed Dec 17, 2008 1:47 pm

They will never be the same, the gearbox and engine move different amounts and in different directions, there is also a center bearing in between.
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Re: driveshaft conversion

Post by kevin » Wed Dec 17, 2008 2:50 pm

Greg, I went through those issues in my race car a little while ago when I thought it was the prop that exploded my clutch housing from vibration transfer. Cut long story short it was not the prop but I did enquire from the old racing teams here that ran five gtv 3.0l and they also tried to straighten mounts which made no difference to there problems at the time. So they just continued racing with it skew(factory) and worked on the origional intention by the alfa engineers that the gyroscopic effect pulled the engine straight at high rpm.(anyone agree ?) . I am running 300hp on my one car at the moment and seriously thrashing it on the track and no problems I believe due to the coupling cage on front only. My gearbox does not move due to bolts through mounts and engine bell housing is also solid rubber. The only coupling failures I have seen this year at the track was 2.0l Alfetta that sheared a brand new coupling in the centre of the rubber(not where it was bonded to steel). He has now also put in front cage and no more problems. Question arises are the 2.0l couplings of inferior rubber(doubt it) or also an alignment problem. Is the coupling cage just masking the problem because it does take a serios beating with marks i see on it from the prop bolts.
There was an extreme light weight alfetta gt that used to race many years ago here(barry posted pics of it) which revved up to eight thou continously which never had any prop issues or cages however the owner said he spent hours lining up motor to gearbox with a laser . He also used a lightweight AP clutch to reduce rotating innertia which i think is also one of the major problems.
Food for thought
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Re: driveshaft conversion

Post by Greg Gordon » Wed Dec 17, 2008 3:41 pm

Maurizio:

I like the sketch. That's exactly what I was talking about. There is a large angle there. Yes it's divided up equally among the guibos but it's still there, and it increases with deflection of the mounts.

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Re: driveshaft conversion

Post by Maurizio » Wed Dec 17, 2008 10:55 pm

Greg/Mats, ok we are talking about the same and I agree that life isn't that simple as I sketched :lol:
Good gearbox and engine mounts are the

Kevin, have you ever driven around without a bonnet? You 'll be amassed how much an engine moves
The engine will rotate to the right (looking from the driver position, when driving) due to the torque it is delivering and the winding of the guibo's.
The two engine mounts define a virtual rotation point and I guess (would be logical) the alfa enigneers aimed this rotation point in the center of the crank.
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Re: driveshaft conversion

Post by MD » Thu Dec 18, 2008 2:10 pm

This topic is of special interest to me as it is the key to the success or failure of the transaxle car. You can have all the neddies in the world. Bigger brakes than Fred Flinstone but if you ain't got no drive you iz goin' nowhere.If you have a vibrating shaft, it might give your girlfriend a big smile by the end of the trip but I can asure you, you will be grinding your teeth all the way.

We have discussed this topic from many points of view before and generally we settle on two camps. Those in favour of making the original work and those who want to change it. I am in the latter camp for many reason.

For a change, I totally agree with Mats in as musch as the generation of independent angles by the engine, propshaft, centre bearing and transaxle goes.Different angles are formed continuously during power on, decelleration and cruise.Cornering "g" forces will influence the angles as will hard and bumpy roads and you can bet on compound angles being formed when all these factors come together in a rugged rally application.

You can reduce the amount of angularity generated by "solid " mounitng the engine and tranny. By this I don't mean hard mounting (no connotation intended) as in using steel mounts like in the case in some racing applications but bracing up or modifying the rubber mounts. In the engine bay, a brace bar reduces engine rotation under torque. Likewise, fitting modified engine mounts will also help. Solid rubber bushing the rear engine mount will assist further.Modified transmission mounts by through bolts helps also. We all know this? If you do all this, you must know the cabin may get increased vibration noise as you are progressively negating all the dampening that the manufacturer installed in the first place. Anotherwords, know what you want the car for. Street or track.

All the foregoing is possible but some anguish remains.

1 A ready and achievable means of aligning the engine to the transmission without assistance from NASA scientists.
2 A supply of original Alfa donuts that will actually stay together because they are made from more compliant rubber instead of some black bolony that looks like rubber which hasn't died from living on the shelf for the last 20 years.

When you achieve all that rigidity but you have some misalignment but you cannot measure it in your backyard workshop, guess what is going to happen?

You will break the clutch housing...just ask me.

THE ONLY ANSWER FOR A PROPER FIX TO ALL THIS IS A TORQUE TUBE. END OF STORY.

However I have never seen anyone do an Alfa conversion of this type and I don't expect to see one in my lifetime. So battle on folks....let us know when you have the perfect answer that actaully works.
Last edited by MD on Thu Dec 18, 2008 9:33 pm, edited 1 time in total.
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Re: driveshaft conversion

Post by fedezyl » Thu Dec 18, 2008 5:03 pm

How about two donuts at the end and a joint where the middle donut would go, wouldn't that take away some of the misalignement issues and loads on the donuts? I think MD you were going for that solution if I understood correctly...i'm about to try that on my Giulie but I wanted to know what the experts thought about it...
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