ALFAGTV6.COM

Hello!

Thanks for your answers, these helps me a lot.

About the location of the gear linkage, could you send me some more pics about it?
Its also an issue for me to change it, because the gear handling is not the best i think, it could need some improvement.

About the engine mounts: The old ones are a little bit smaller, maybe 2-3mm in height.
So the engine is a little bit higher in the middle and the rear mount is on the same position.......could this also be reason for the vibrations?

The vibrations are most at 2-3000 rpm, rotating in neutral.
I think its a little bit more when i drive with first gear or reverse, i have tested it only at home in our entry way.

Should i unfasten every screw from engine back to gearbox and then rev a few times up?
Could a damaged pivot bearing cause the vibrations?

Thank you
Manuel

Loosen everything including the centre hanger, rev a few times, tighten rear one first, then pinch bolt and then hanger. Make sure the rear coupling in flush with the yoke. What I have also noticed is bolts that are too tight will also cause vibration.

Personally i think youre still wasting time looking at alignment issues ON a standard a road car ( track car different story). Normally when you have a huge vibration at low rpm its the centre bush inside the centre coupling thats not in position . This normally happens when someone does not know how to assemble a prop and thet force the bush out of position. You cant see it when its assembled. Sometimes it takes me two mins to assemble prop and line up that bush ,other times can take half hour. You have to watch it slide in, with the help of two tiny screw drivers holding bush in a central position while a second person pushes the prop together.
I am lucky to have access to a balance machine designed specifically for a Gtv prop which spins it up to 6000rpm .

About the middle pinion i will take a look!

And about the pics here about the gear shifting, please take a look the 3:26, interesting setting!
How does he make the "rotation"?

http://www.youtube.com/watch?v=-Qnls-e4s3A

Precisely ! That's what I would like to know as well. If anyone knows this car more intimately, those photos of the shifter would be interesting.

the gearlever is stuck in a bearing that moves in 4 axis, somekind of uniball/rosejoint

Since we had a driveshaft breakage just behind the splined section, with my 24v engine in my mechanic's 75, I decided to try my hand at laser-aligning the driveshaft when the same engine was installed in my 75. What I basically wanted, was to see the red dot on or very close to the center of flywheel and gearbox flange. The first test was eye-popping: you can see the dotted red lines in the drawing! Everything was way off! Left/right centering was accomplished by widening the top/bottom slots in the motor mount plates (A,B) and by juggling the engine around until the red dot at least was in the middle. Then, the up/down movement was accomplished by putting spacers under the rear engine mount (C).
The gearbox on the other hand, pointed very much to the right (~50mm) and considerably lower (another 50mm) from the flywheel center. Raising the nose of the gearbox was accomplished by reducing spacer thickness to 8mm (from 15mm). These spacers are only used in 1.8T and V6 cars. Left/right correction was by making the gearbox mount (D,E) holes larger and by juggling around, tightening bolts in the correct position. Since the nose of the gearbox tends to rise under application of torque, I decided to have it point ~15mm lower than flywheel center, thinking it will 'align itself' when in motion (blue line). All considered, there is much less than 1* misalignment now with this intentional gearbox 'trick'.
You understand this is all 'seat-of-the-pants' stuff...
I used the 1.8T driveshaft, no splines and no solid center donut. I thought if 450hp dragsters get away with it, I should be ok too.
We'll soon see if all this was worth the time!
Jim K.

Great write up JK. I've always wondered about the misalignment.

When I was at the balancing shop the owner always reminded the apprentice to make sure the shaft is placed properly in a straight line on his jig. Then he has many runout gauges. He balances by making sure the runout on the shaft at many sections are not excessive, AND he also measures the imbalance and fixes that. So it's not about adding or subtracting weights, it's also the "true-ness" of the shaft (ok the yokes/flanges need to be good too).

So this always had me wondering, if the balance shop had to measure the true-ness of the shaft, how the F can this shaft spin without vibrating when the whole setup on the car is not even proper, the shaft is skewed and the guibos are in compression and tension at the same time. Fer Chrissakes, it's not even worth the balance job until the setup on the car is aligned! ...well at least that is my opinion

BTW don't you think the center bearing mounts needs to have some adjustability as well?

I have the laser tool so I will check the whole thing again. BTW did you do this on a lift or on jack stands?


Z

The car is on a 4-post lift so its actually ...parked!
The middle support required only a couple of washers to center so that was the easy part. I hate to think what I would do (and how) if it needed raising...
I assume I will have to balance the driveshaft on-car, but thats no problem as there's a shop here doing a very good job of that. They did a great job a few years ago on my other 3liter.
Jim K.

I don't have found that big influence on alignment, but few times I have found vibrations coming from imbalance which went away on balancing the shaft and few times the engine rear mounting was modded to too solid. The 6 cylinder engine tend to tilt so that both ends go up and down. If this movement is not allowed, a great vibration will be transferred to body. That's not so dramatical on 4 cyl engines.

True, we had a 1.8T in a while ago with pronounced vibration. The owner had filled the empty spaces in the rear engine mount with hard adhesive! Replaced with std mount and everything perfect!
Jim K.

In a 75 it must be so much easier as you at least starting ofwith engine mounts that are symmetrical unlike the huge offset type in the GTV .
In my gtv rave car I have zero vibrations and have
1) bolted gearbox mounts
2) aligned engine with lazer to gearbox thus had to make new engine mounts
3) the new engine mounts then forced me to make NEW bell housing bush as existing is offeset by 15mm .
4) the new bell housing bush and engine mounts then forced me to remake bolt hole position on centre carrier bearing as it's also offset .
5) NOW that engine was all aligned I had to make engine stay to keep this all in alignment under acceleration .
Whew - what a job as engine had to come out with a spare block to align laser up through centre of crank position.
I have had to put reference marks in engine bay - so if I take engine out I can always recheck it's in line x and y direction
Bottomline - it works for a race car and the only vibration I feel in car is from the mogul gearbox oil pump cooler

I hope it's much easier with a 75

The engine is also off-centre in the 75...

Oh that's a bugger ! I still only seen one 75 as we never got them and that one was an IMSA turbo so it was already perfectly in alignment