116 replies to this topic

[Brent J]

Hi again.

 

After some help with a strange vibration in my LJ XU-1.

 

The vibration is only there when you give it a boot full (i.e. when you push it hard). It starts at about 3500 to 4000rpm and becomes quite violent by about 5000 rpm.

It does not seem to be there when coasting, say on the freeway doing 100km/h. Smooth as silk. That said the RPM is probably around 2800 to 3000 when coasting...Also, the vibration is there in all gears, I.e. from first, revving it out under load all the way through..

 

not the best description but I'm trying to figure out where to start...

 

Electrical? - Plug leads? Points? (Already changed plugs)

Tail shaft out of balance / missing a weight?

Clutch / fly wheel balance issue?

 

I have a feeling that this will be a process of elimination!

 

Regards,

Brent

[S pack]

This thread may or may not be of some help to you.

http://www.gmh-toran...ossible-causes/

[rodomo]

Sounds like engine related.

[Brent J]

Thank you for he link S-pack.

 

It seems that that fella's symptoms were speed related whereas mine are more engine speed related as it occurs in all gears. None the less, ill drop the tail shaft and inspect the u-joints, alignment, seats and need bearings & caps..

 

Cheers,

Brent

[jd lj]

I'd check the ignition system, slightly fouled plugs will still fire at low rpm's but then struggle at higher rpm's and cause a vibration.
What carbs are you using and what's the state of tune?

[S pack]

Thank you for he link S-pack.

 

It seems that that fella's symptoms were speed related whereas mine are more engine speed related as it occurs in all gears. None the less, ill drop the tail shaft and inspect the u-joints, alignment, seats and need bearings & caps..

 

Cheers,

Brent

If you feel the problem is engine speed related then don't waste your time dropping the tail shaft just yet.

[Brent J]

I did change the plugs out. The old ones were quite sooty, not oily and not grey / white but dry sooty black which I took as being too rich. Also evidenced by the fact that it pushes out black smoke when you start it, and also when you give it stick. Normal general driving its fine.I leaned off the carbs an eighth, put fresh plugs in, cleaned the rotor button and drove it. The plugs still blackened, still had the vibration, but the engine revved out a bit more clearly.
Carbs are triple CD's (engine is XU-1).
I have not yet replaced plug leads, points or condenser. Points look ok.

Edited by Brent J, 31 December 2016 - 07:08 AM.

[Brent J]

It does sound engine speed related, ie same in all gears, but is it load related? Ie only under full/above half/etc throttle in each gear?

Difficult to say. I feel it is rpm related., I.e above about 3000rpm where you you feel it come in, then it progressively gets worse up to 5500rpm (irrespective of road speed).
Regarding load - seems to be the same regardless if you rev it out gently and work through the gears, or stomp on it and work through the gears.

That said I have not tested it "unloaded" with rear wheels off the ground (safety of course!).

[jd lj]

I'm still leaning towards the plugs fouling, even if you replaced them. It can take only minutes to foul them enough to cause the type of problems you describe.

Have you set up the carbs as per GMH instructions and with the std needles?

[S pack]

Have you set up your triple carbs with a carby balancer?

Have you replaced the flywheel or clutch or harmonic balancer before this vibration started?

Edited by S pack, 31 December 2016 - 11:27 AM.

[Brent J]

JD & S-Pack

Re. Settling up the carbs, no I have not setup as manual or balanced with a balancer. That's effectively where I am up to now. I've sourced a copy of the workshop manual and will attempt to set up as per the manual. Failing that, I'll need to buy a balancer as I don't have one. Can you recommend a particular unit I should buy?

Re clutch, flywheel and harmonic balancer, no I have not replaced or changed any of these parts since owning the car. The vibration has been there since I purchased it. The engine / gearbox has had a birthday in a former life at some point (well before it came into my possession).

[Brent J]

This is what all 6 plugs looked like when I pulled them. I've since replaced them 10km ago and pulled 3 and they coming out quite similar, maybe not quite as bad since they are new.

Attached Files

•  IMG_0282.JPG   113.34K   2 downloads

[RallyRed]

are the plug  leads definately on in the correct order?

[Brent J]

Yes - plug leads are on in the correct order. Car runs perfectly otherwise.

[warrenm]

Looks to be very rich, I'd find out why it's running rich before you go much further.

[jd lj]

This is what all 6 plugs looked like when I pulled them. I've since replaced them 10km ago and pulled 3 and they coming out quite similar, maybe not quite as bad since they are new.

I was going to say there's your problem, but that is just the result of the problem. Obviously you need to treat the cause of the problem which will be the carbs set up incorrectly. I'm sure somewhere on this website there'll be the information to get you started if you don't have a copy of the workshop instructions.

[Rockoz]

Had a similar problem turned out to be unis.

Checking them for movement while the shaft was still in the car didnt show anything.

Pulled the shaft out and all was revealed.

Dry cups on the rear.

2 new unis and all was good.

[RallyRed]

engine mounts good?

[I'm a Red Motor fiend]

I have been in a similar situation to this and I agree it's the tail shaft or unis. My vibration would kick in thru all gears whenever I would really give it heaps from probably around 3500 to 6500. Not only do I get the vibration I get a really full on buzzing sound thru the shifter under heavy load. Wouldn't happen when driving normal but on the highway over 100k's it would start. My build is still fairly fresh so I have new engine and gearbox mounts, engine is well tuned and balanced including flywheel and clutch, flywheel is dowelled and has ARP bolts and loctite, gearbox is fresh as is the diff.
Not having much to eliminate I changed tail shaft. Big difference, straight away even better after getting the rear cups centred where they should be. Sometimes the cups feel seated and centred but when u road test it they aren't. I don't really get vibration from the shaft under heavy load through all gears anymore but it still buzzes like crazy thru the shifter and I can't work out why. Changing from hard mounted to rubber auto trans mounts does nothing either, I tried that. The majority of vibration I get under full load now is from the exhaust resonance and that vibrating. It's surprising how much mine does this.
You said yours doesn't vibrate on the highway at 100k's but how about at say 120 or 140 k's? If your running tall diff gears it may not be revving enough on the highway to reach the point of vibration? Like I said a different tail shaft pretty much fixed my problem but I run 3.9 gears and a 4 speed so when I reach around 100 and am doing close to 4 grand I feel the tail shaft harmonics still start to kick in a little.

[u1 71]

If you're experiencing vibration through your steering wheel it's tail shaft or road wheels related,if your gear shifter is vibrating it's ignition or fuel related

[Brent J]

Wow,

 

Huge number of posts on this on! Some great information and theories.

 

Two area's to test are obviously Tailshaft and Ignition / fuel.

 

Ill drop he tail shaft and inspect the Uni's. At the same time ill check out the Carb tune. (Running CD's) 

[Brent J]

Ha - my wallet opens up every time I look a the thing!

 

Carbs are CD's - pretty much stock .

 

When you say "pull a 1/4 - 1/2 up out of the carbies main jet" . . you mean the brass Orifice adjusting screw at the base of the carbs? wind in or out?

 

I'm downloading a bunch of CD manuals on these carbs to get a better understanding. 

 

Does anyone have a Vacuum gauge that works well for balancing that they would reccommend? If so, where did you buy it?