ALFAGTV6.COM

[Alessandro]

I have a 1984 Alfetta 159 saloon with a 2.5 engine from a GTV6. The propshaft front part was modified to match a gtv6 propshaft. The car was incredibly smooth with no vibration and covered about 100,000km in 10 years. I inspected the couplings and noticed a few cracks on all of them.

I decided it was time for a complete propshaft overhaul. I purchased new (gtv6) front coupling (alfetta) centre and rear coupling, hanger bearing, and new gearbox side mounts. The propshaft was dismantled and spherical bearings replaced as they were worn - propshaft was welded and then machined. Propshaft halves were then re-balanced individually and then together as a complete unit.

Upon installation the car has a very bad vibration from just above idle > 2500 rpm. Above this to redline there is no vibration and the car runs very smoothly. To solve this problem, the propshaft has been dismantled and reinstalled numerous times. Everything is in order. Balancing was also re-checked and found to be perfect.

When feeling the transmission tunnel the vibration feels as if it is at the centre. The gear lever also vibrates a little. One thing I noticed is that the previous hanger bearing was very soft rubber and the new one (currently installed) is very firm. Could this be the cause of the vibration? Has anybody had similar issues before?

[Greg Gordon]

Hi Alessandro, and welcome the the forum!

I don't think the center bearing's support is the problem. I think your driveshaft is out of alignment. Did you change transaxle mounts? Did you run it before you tightend the pinch bolt? Check out my article here: http://www.hiperformancestore.com/guiboDSclutch.htm

Greg Gordon,
www.hiperformancestore.com

[Alessandro]

Hi Greg,

Thanks I have read your article before - some very good info!

I have loosened the pinch bolt and tightened it. The vibration is still present regardless if the pinch bolt is tight or loose. I thought that there might have been too much clearance between the front yolk and the splines so installed a front yolk from another gtv6 but this made no difference. Yes I have installed new gearbox side mountings but not the rear mounting. I have also tried to adjust the clearance space between the rear engine mount and body but this also doesn't seem to affect the vibration.

[Alessandro]

After spending the whole day trying to check the propshaft alignment by adjusting gearbox mounts and crossmember up and down and also engine bellhousing mounting up and down I've come to the conclusion that this does not affect the vibration at all....

The vibration is still there and with all my adjustments didn't get any better or worse.

I think either the place I took the propshaft too for balancing doens't know what they are doing or the propshaft is bend?

Balancing was done on both propshaft halves individually, and then the propshaft was assembled with couplings and re-balanced as a complete unit. Is this the correct way to balance it? Should it be balanced without the couplings? Does the speed at which the balancing is done have an effect?

[Bruce]

I had a similar problem when I reconditioned the complete drive-line and transmission. I eventually traced the fault to the "new" gearbox mounts.
Put your old ones back on and see what happens.

[MR2 Zig]

There is another discussion on the new front transaxle mounts....See if your new mounts have an "extra" piece of metal tack welded to the bottom. that extra piece is for the Milano/75 not the Alfetta/GTV6. If your old mounts dont have that piece and new mounts do, then grind off the tack welds and reinstall.

hth,

[MD]

Alex. If you haven't already read this topic set, you should.

viewtopic.php?f=9&t=3327&st=0&sk=t&sd=a&start=15

Getting these driveshafts to spin vibration free is a DIFFICULT task. Make no mistake about it. Even trade workshops get it wrong so keep a cool head. Look for these elements:-

1 Engine >propshaft< transaxle alignment. Is it correct. Use the tool in the above topic set.
2 Is the driveshaft CORRECTLY balanced. Most times it's not. Balancing workshops are not usually set up for these shafts in Oz. Probably the same where you are.
3 Are the shafts straight or is there a bend in one? Is there a shaft whip going on?
4 New centre bearing? (hanger bearing as you call it)
5 What condition are the locating bearings in the shaft centre and at the transaxle end. Are they a good fit with no slop movement?
6 Are your engine mounts in good order? No sag ?(see item 1)
7 The clutch input shaft locator spigot. How worn is it? (see item 5) Must be a firm fit to the donut bearing.

Hope some of this will help.

[Alessandro]

I took the propshaft out again today > Will take it tomorrow morning to a different shop to check the balancing.

I've installed the old gearbox mounts as they still look good. There is a ± 8mm height difference between the new and old ones! Maybe the old ones have sagged a bit?

Anyhoo > will let yu know how it works out when I put it back together!

[patzo_3l]

have you checked the bump stop at the front of the gearbox. sounds like a common problem, you need to try and adjust until there is just 1 or 2 mm clearance, so when the engine torques up it juuuuuuust touches it. have seen this a few times as this part is often overlooked or forgotten when overhauling driveline section. would pay to double check if all else fails it say.

[kevin]

Was it balanced with the front yoke on. There were two types of yokes in South Africa. Im not sure where this second one was made but it very 'eccentrically' made(sorry bad English). post pic.

[kevin]

Also post pic of centre hanger. I also had a 159 v6. Great car.

[Alessandro]

After removing the propshaft again, I took it to a different place for balancing (what a mission to find a place who actually has jigs to mount the rubber couplings to their machines). They ran the prop as a complete unit and said that it was out of balance. Anyway, I got it back a week later with huge weights at the front - and they said to try it, but I should "buy a new propshaft". I looked at them funny and just shook my head.

Weekend task begins....

Start the engine with no exhaust just to wake the neighbours > no vibration and revs up like a motorbike!

Marked alignment of the front yolk and removed it to clean the black paint off the splines. Didn't slide freely as they had changed the position. A bit of marking blue and a needle file and it was all good again.

Installed propshaft, gear link, exhaust.... started it and let it idle. Tightened bolts fully on hanger bearing and pinch bolt.

Rev it up a bit and big vibration! This time you can even feel the steering wheel shake. Starts at about 2500rpm to 4000 > was too scared to rev higher. Went for a drive and wasn't a happy chappy.

I just think that there are balancing shops who don't know what they are doing. I really wonder how Alfa sorted all their propshafts out when assembling these cars?

From my experiences I have a few theories regarding this but can't prove anything....:
[*]Balancing with rubber couplings attached absorbs vibration and transmits different feedback of where the out of balance of the shaft actually is?
[*]I feel that Propshafts should be balanced individually by firmly coupling flanges (no rubbers).
[*]Balancing should be done at the speed you are most likely to drive at. For freeways +- 3500rpm. I can't see how balancing a shaft with rubbers at 1480rpm can mean that it is also balanced at 6000rpm
[*]Don't know if resonance is ever an issue with prop imbalance?

Next step is prob to remove all the weights they put on and try to find somebody who can balance the propshaft in situ without removing. I'll try speak to some condition monitoring people and see if they can do it or not.

Kevin: Thanks for feedback. Below are a few pics. Originally the car had a round coupling but it felt loose on the splines and I fitted one from a GTV6 which was sent with the prop for balancing. Hanger bearing is standard alfetta.

[kevin]

Obviously you are overlooking the obvious.Wish we could tell you though. My chaps balance the prop in twenty mins . I have just had my prop cut by 5mm to take BMW coipling and is very smooth. So there are chaps who can do a perfect job. Start to check all flywheel bolts. You can get to them with yoke off. Check clutch. Put it in gear push clutch in and rev. check. Out of gear clutch in. and clutch out neutral. Check clutch housing externally for any cracks(clean first). Check again bump stop Patzo recomended. My problem once before was the clutch lining on one of the plate debonded as they forgot to rivett it.
If there was no problem here before it makes sense they should be no problem here again. Just check. Call me if you want to send your prop to my chaps all call them direct to ask them any questions on balancing (Shane on 011 334 8920). Shane has done nearly all our race car props and he makes for all the drag racing chaps.

[Alessandro]

Thanks I'll try and give these chaps a call.

I have checked a number of things:
- Loosened bump stop and unscrewed it all the way to check so am sure its not touching.
- Have tried to rev in neutral with clutch in and clutch out and there is no change to vibration. Also driving the car in gear results in similar vibration. Clutch is very smooth at pullaway.
- I have lowered the A-frame to try old g.box mounts again. Checked clutch housing at the same time and can't see any cracks. I have broken one before on my GTV6 so know all about that.
- Engine mountings are custom made (2 litre mounting on body to v6 engine). Anyway they appear to be good, a bit soft maybe, but didn't cause a problem before my prop overhaul so I feel they should be ok.
- I have tried playing around with alignment geometry - adding spacers to bellhousing/centre hanger/rear crossmember and feeling rear coupling to yolk clearances. This didn't seem to make any difference.
- Flywheel bolts! That is something I have not checked....

[Mats]

Sounds like a crooked shaft to me, you can sort of fix it with a huge weight (like on yours) but only in a certain rev-range. You can never fully compensate a crooked shaft with weights.
On OEM shafts there is a maximum imbalance demand before balancing due to this issue. Go back and see if you can talk to the operator of the machine directly and ask him if he could see if the shaft was crooked in the machine.