Not so good vibrations

[Trevor_B]

Hi guys,
I have been attempting to help resolve a vibration problem in a mate's FC Holden Sedan - one of Kevin Woollard's great resto projects, "Miss Mullum"
I am so impressed with the work done on this car by Kevin, it's like a 12 months old car now with hardly a mark on it. It's current owner is taking very good care of her.

One issue he has had though is a vibration at 100+Km/hr. All signs point to a tailshaft issue with that drumming harmonic sound appearing around 100, the kind you hear then feel in the seat of your pants  ;)

The tailshaft had been balanced a few years back which seemed to help a bit. We tried by replacing the tailshaft with another re-balanced shaft with new unis however the vibration was still there. Might have been a little worse but hard to tell as the more you focus on it the worse it seems??

Checked other possibilities like engine mounts (still in great shape and no real movement), rear suspension mountings and rubbers (all looked good with no movement when leverage applied), even the gearbox extension housing bush clearance didn't seem too bad (about 10-15 thou movement at the yoke).

Our next move is to get the original balanced shaft re-balanced again requesting a 100% balance.  And no, the cardboard inner tube is not loose....

So any ideas, thoughts  or past experiences would be welcome. It's not like the car is undrivable, just frustrating that such a beautiful car has a little blemish.

Again Kevin, Miss Mullum is a beautiful car and a credit to your work!

Regards,
Trevor_B

[Errol62]

Have you checked the relative alignment of gearbox output and diff pinion axies Trevor? Vibration at this speed seems common in many older cars, including my FB ute.
Cheers,
Clay

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[Fraze]

Hi Trevor, I am having exactly the same issues with both my FC Sedan and FB Ute. Have been doing a lot of elimination work and it is looking more  and more like tailshaft angles. See my posts on the FB EK forum under "Vibrations- any ideas please" For example when I set the ute up on stands and measure angles, with 0 deg at the diff pinion, the tailshaft is 4 deg and the gearbox shaft is also 4 deg.which means that it is inline and that is not ideal. I am using my iphone as an inclinometer. There are a number of really informative videos on utube, I just googled "Propellor shaft angles" . I haven't checked the FC yet but I reckon I am going to find the same issue. The answer is to change the gearbox angle to match the diff angle by packing under the rear mounts. My worry with doing this is that I will increase the tailshaft angle. I will do this next week and advise. Cheers, Frazer

[Trevor_B]

Thanks Frazer & Clay,
Given the car is completely standard I hadn't considered tailshaft angles.

When the re-balanced shaft is refitted I will check this just to see what angles they are.
Trevor_B

[Fraze]

I have had a change of mind re packing the rear eng/gearbox mounts as I think I am going to create too much drive shaft angle. I will instead change the diff pinion angle which is easy to do. You can buy wedges of varying thicknesses. Both of my cars are stock standard however I have replaced the engine mounts on both cars (Rare Spares parts) and a very small variation in thickness from the GMH original part can seriously affect tail shaft angles. I will do the mods on Monday and post results, cheers, Frazer

[graham_fuller]

Many years ago I had this issue balanced the tailshaft changed the uni's and finally found it was the rear tyres 1 was out of round.
Also finally changed the diff centre to a 355 and the car is quiet and smooth on the expressway.

Cheers
Graham

[Patrick_R]

Also,
Try a different stretch of motorway for your road tests.
Many years ago, the M4 was quite corrugated between certain on/off ramps and this caused much drama when road testing vehicles.

I then used a different section of the M4 and all vibrations gone.

[ipg]

im sure you posted a yelp review to get the problem solved

[old-blu]

 Thanks for the kind words Trevor, re: Miss Mullum.  Having checked the tailshaft, the next step I would undertake is to have the wheels rebalanced. It could well be that the tyres are  out of round.as Graham suggested.  Robbie mentioned that the car had been sitting for some time whilst relocating to Geelong.  The tyres I put on the car were from Antique tyres & fitted new in 1996. If they are still on the  car, then I would have a look @ that also & replace them.  Having driven greys since 1961,I reckon the top cruising speed is 60mph, [100kph]. I have never had the misfortune of stripping a fibre timing gear & put it down to that.  When I was preparing to drive the FE Ute, [Ben Bates], to Hobart, I also encountered  a serious vibration, which nearly led to me cancelling our trip. The tailshaft came off days before our departure & found to be OK. In desperation, I examined the wheels to find that the wheels had not been balanced. ??? ??? ??? ???  I hope this turns out to be a simple fix.  I always considered Miss Mullum a great car & was very happy that Robbie purchased it.   Kevin.

[my8thholden]

Trevor ..If you have or can get a set of wheels that you know are spot on , perhaps put them on and see if that fixes the problem ..Vern

[Trevor_B]

Thanks guys,
I admit to having "try different wheels/tyres" on my checklist and so will revisit this when we try the re-balanced tailshaft. I think we just run out of time when checking things out.

We ended up addressing a clutch issue, the old clutch pedal not returning up properly. Robbie had advice from a mechanic familiar to FE & FC's advising to replace the hose section of the clutch hydraulics. First thing I checked was if the master cylinder piston was returning....nope, it was stuck about 20mm from the circlip. Luckily I had spare new rubbers for it so reco'd the master cylinder (bore was still in great shape, assume you put a new one in Kevin). Then the boss called drinks so missed out swapping the tyres from one of the 3 other FC's I have at hand  ;D

Will update when we try re-balanced tailshaft then tyres.
Cheers,
Trevor_B

[Fraze]

Hi Trevor - BINGO - drive line alignment it is!!!!! This morning I started with my FB ute and took a new set of angles then loosened of the rear spring/ shock absorber mounting plate, jacked up the nose of the diff to the requisite angle then pushed in packers between the spring plate and spring and tightened the lot up again. This had the effect of tilting the nose of the diff upwards a couple of degrees. Road test tells it all, the vibration a 100 kmh is gone! I now get a bit of vibration at about 110 kmh, nowhere near as bad as before, but I never drive At that speed in the ute so I am not going to worry about that. I am very satisfied. Tomorrow I will do the same to the FC sedan, then order proper wedges for a permanent fix.chees, Fraze

[my8thholden]

Fraze ..where do you get wedges ? Vern

[Fraze]

Hi Vern, I checked online and found three manufacturers: Tools and Wedges P/l, DJM - Engine MastersAust and Superior Engineering. I was hoping to buy some over the counter ( In Melbourne) but none of the speed / Hot Rod shops listed them.  Cheers Fraze

[Harv]

http://steelwedges.com.au/

Cheers,
Harv

[Fraze]

Following my success with the FB yesterday, today I checked my FC and found that the nose of the diff was down 3 deg compared to the gearbox shaft. I lifted the diff nose, packed under the spring plates and yep, vibration is gone. Two cars sorted, very satisfying. Cheers, Fraze

[my8thholden]

Thanks fellas ,added to my " bits file "..Vern

[Errol62]

I’ll be getting under my ute for a measure. Thanks Frazer.


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[Fraze]

The steel  caster wedges I had made to order arrived inside a week, $35 each plus a bit extra for delivery is a good deal I reckon. I fitted them today, just undid the u bolts, jacked the axle up, slipped the wedges in, making sure that they engaged with the lugs on the insulater plates, lined up with the axle pad, tack welded the wedges to the axle pads to give permanent positive centering, did the whole lot up again and job done. I took the car out on the Motorway for a test run and am absolutely delighted with the end result- I was able to push speed up over 100kmh with no trace of vibration. In fact the FC is noticeably smoother from 80kmh.
The dimensions I used were 110mm x 60mm with 25 mm centre hole and 3 deg angle for my car. I bought the wedges from Industrial Tools and Wedges In Nelson Bay NSW. Just google “steel wedges”
Cheers, Fraze

[Trevor_B]

Great outcome Frazer  :)
Thanks for sharing how you addressed this.

Robbie has just picked up his rebalanced tail shaft so will see how that goes otherwise it's tyre check next then the wedges option.

Cheers,
Trevor_B