Drivechain Vibration 100kmph @ 1500prm in OverDrive

[8rody]

Got a question for you all;

I've got a (VN 1989 S1 V6 Auto) Drivechain Vibration 100kmph @ 1500prm in OverDrive only with load - going up a incline.

If I give it some gas, it dissapears as the rev's and kmph's increase, but it seems that at this particular speed and gearing, i get a vibration almost similily to the experience of turbelance on a aircraft. - a 'thuda-thud-thud-thud-thud'.

The transmission is overful *thanks to previous owner* - i've next to work on that, and i'm going to replace the tranny filter.
The auto box has another issue of the delay when cold, from P to Drive. If she warms up (20sec idle), it works a treat.

Whats the thoughts on the culprit specifically? - Apart from the transmission being ehem. Stall converter lockup?

[Paiste402]

hmmmm, 1500rpm at 100kph is too low. Its prolly too high of a gear so the engine is under a huge load. Ive had a similar problem in my dads 4 cyl magna wagon. I put it into 5th at 50kph (hey i was curious) and it was bobbing along until i tried to speed up then it started to shake and make the same thudding noise. This went away when the revs went up and the car got into its rev range where it can make power. Maybe its all a similar problem like ur VN.

But are u sure its only 1500rpm at 100kph?!

[jas98]

yeh as said 1500rpm at 100 seems way low....my vs with 86 000 on the clock sits at about 1850-1950rpm at 100 (cruising) unless the VN revs less at 100 but i dont remember mine revving any less then 2000rpm at 100k when i had it

also another reason why it may be reving low is that it may be missing bad. Check all spark plugs and leads...also check the coil packs. And check teh computer for error codes

[8rody]

Thanks for the replies! =)

I am 100% sure. I agree it seems quite low!
I had a VS and @ 100kmph is was around 2000rpm.

I assumed it was the ultra-quirkyness of a Mechnical TM700! ~ I got pretty good fuel economy minus the violent thudding at the base of hills!

I've replaced the leads [Blue Bosch] and sparkplugs [NGK] (as it was originally missing really really bad). Fixed up quite alot, city driving has been flawless.
I've got the series one coilpacks (black matchbox sized coils) on this motor.
Luckily i've got a spare 3800 motor so i'll pinch the coilpacks off that, and see if it solves it.

Other than that, say if the rev's were too low, could the clutches be slipping if it were a 'worn' auto transmission - causing the vibration?

[centy]

check what gear ratio you have in the diff and check the trans oil colour to see if it is burnt.

[Paiste402]

maybe its not firing on all cylinders? If you drop a cylinder you drop in revs, maybe the series one coil is on its way out (and they do drop all the time, alot of VN's have series 2's on them). Also my bros VN sits at 2000rpm at 100kph in overdrive, just like my other bros VR. I would do ur coil first and see wat happens with at least a VP coil (better quality), does ur car feel down on power at all?

Also if the auto was slipping you would get higher revs due to the engine not under as much load with not all the power getting to the wheels. I would know, my trans is ****ed so it slips alot lol. But still check the fluid, it should be bright cherry red and at a good level.

[88GreenVN]

Just a point - how's the centre bearing - is there grease on the floorpan around it. That may be whats making the noise.

[8rody]

check what gear ratio you have in the diff and check the trans oil colour to see if it is burnt.

the fluid is alittle dark for my liking, i'm going to drain and refill the transmission when i replace the filter. It was also overfulll.
Its a live axle V6, so i'm guessing 3.08:1. Its a open diff.
Any ovious markings on the diff to tell the ratio? - Model versions or whatnot.

.....

I take back my initial throught that it was slipping, as I gave it a 'good run' a few days prior to my suspension service and if you manually shift 1-3 it is tight and firm.
the issue is only in overdrive.
I think you might be right, i suspect the coil's to be the next thing that goes.
I've got a Series 2 VN coil at hand, pending that whats the best place to source a VP coil?
Oviously jy's are the cheapest, but may be inherent to problems. Word is coils brand new are $350 + ?

Oh and definetly not down on power since the plugs and leads change.
However the previous owner had run the car with a bad high-tension miss for i believe a few years. Suppose the coil's would be stuffed?

Just a point - how's the centre bearing - is there grease on the floorpan around it. That may be whats making the noise.

Havent checked the propellor shaft yet, good idea. I'll take a look.

[Paiste402]

yea new coils can be damn expensive mate! Well, its just that the VP coils will go straight onto the VN and they are of better design with less worries. Also they are newer which is a plus.

[greenfoam]

Check the gearbox mount for any cracks when you are under there. It's the most common cause of driveline vibration in Commodores. It's a bit of a mission of mine to keep telling people that

[NZ_VP]

My VP does around 1600-1700 in overdrive at 100kph. Also had the same problem and found it to have something to do with the tourque converter lockup as it was fine untill it went into full overdrive then it wouldnt change down till you gave it a fair bit of noise. A trans service definately helps though and when you do it, check your filter & magnets for any traces of metal etc

If it only happens in torque lockup in overdrive thats sounds like the cause as most other faults that cause vibration happen at other speeds and in other gears aswell

[8rody]

I'll swap the coils over with the 'newer' unit.

I came accross a thought provoking article
- Driveshaft and Overdrive Transmission Vibration Problems - Tech Articles - Street Rodder Magazine

Is it possible that the box wont downshift?
- This is eaisly overcome by whacking it into 3rd (or normal D on the selector) as i've been doing before / giving it gas.

Check the gearbox mount for any cracks when you are under there. It's the most common cause of driveline vibration in Commodores. It's a bit of a mission of mine to keep telling people that

Sure, sounds logical. I'll add it to my check list. Thanks mate!

My VP does around 1600-1700 in overdrive at 100kph. Also had the same problem and found it to have something to do with the tourque converter lockup as it was fine untill it went into full overdrive then it wouldnt change down till you gave it a fair bit of noise. A trans service definately helps though and when you do it, check your filter & magnets for any traces of metal etc

If it only happens in torque lockup in overdrive thats sounds like the cause as most other faults that cause vibration happen at other speeds and in other gears aswell

I'll inspect the fluid / filter.
Worse comes to worse i've actually got a spare gearbox thats A.Ok. - but i'm trying to keep this as a daily driver and hence trying to make parts last as long as humanly possible.


I'll check those and report back / hopefully with this issue no more in existance.
Thanks mates! =)

[Paiste402]

Is it possible that the box wont downshift?
- This is eaisly overcome by whacking it into 3rd (or normal D on the selector) as i've been doing before / giving it gas.

funny enough i used my bros VN today and when in overdrive and giving it some gas it shuddered a little while going up hill until it downshifted. Now this is what i think is going on.

Ur RPM is quite low in overdrive but anyway. When i was using my dads manual trans Magna i left it in 5th and was doing 50kph, the revs were low and it shuddered and made thudding noises when i put it under load. This was because the engine couldnt handle the load of moving a heavy car in a very high gear that it has trouble with at 100kph let alone 50kph.

Now this might be the exact same problem with urs, ur trans might not be kicking back and just staying in 4th. The VN's ive driven basically downshift before the motor starts really laboring when under load and if u were able to keep the car in 4th in any VN you come across and go up a hill with low RPM it WILL shudder. Its wat cars do and good auto transmissions will change gear before this. My bro's VN will change into 3rd, then give it more and its SEEEECCCCCCCOOOOOOOONNNNNNNNNDDDDD!!!! good fun

This is my little conclusion on the situation although a new coil will be fantastic and should give ur engine more of a kick and the shuddering wont happen as soon due to the better power. And a trans service will make everything nice and smooth, and maybe they can investigate ur strange non-downshifting issue.

[Renno]

Kickdown cable...might want to have a look at that.....otherwise what Paiste402 seems to have the answer....

[8rody]

Well, hopefully if its just the kickdown cable, i'll live. A B&M wratchet shifter ought to fix that.

I agree it does need a service, but i'm alittle Anti-Automattics. I'd rather spend some money and put a manual convs in, as apposed to paying someone to rip me off with 'unexpected repairs' over a TM700.

I'll have some time this weekend to bog down and reduce some varibles (replace the coil / etc.)

I'll come back (hopefully) with the definte answer.
Thanks all for helping me out, very much appreciated. =)

[8rody]

okay, well.. i've spend a few weeks trying to work it out...

With the new coil's (from a Series 2) there isnt any driveline vibration, untill about 40mins of running.. and then it happens again. I'm making a educated guess, the difference is heat?
I've been whacking it out of Overdrive to keep the rev's up.

The propellor shaft looks fine.

I'm still suspicious of the transmission. Its changing from 1st to 2nd really harshly now, and takes a while to engage when cold from P to D. :S

[greenfoam]

Brody, it's the gearbox mount I'm 90% sure. Mine was broken but you could only feel the vibration once the car was warmed up (the remaining rubber can hold it untill the rubber warms and softens). It's only about 50 bucks for a new one if that so just get it in there

[jas98]

Brody, it's the gearbox mount I'm 90% sure. Mine was broken but you could only feel the vibration once the car was warmed up (the remaining rubber can hold it untill the rubber warms and softens). It's only about 50 bucks for a new one if that so just get it in there

haha yeh thats true...but if someone has lock tighted the bolts in there ...GOOD LUCK getting it out:P

[Morton]

Nah, they're easy. Big socket, long breaker bar. All my undercarriage bolts are loctited and I don't have any issues removing any of them

Gearbox mount change should only take you half an hour if you're dawdling. Jack her up, put it on stands, support the trans with a jack and some wood, bolts x4 gets the mount xmember from the undercarriage, and bolts x4 gets the mount off the trans. Then replace and refit Not sure about the auto mounts, but I think they're allen key heads. Get yourself a really good unbreakable set of Kingchrome or similar allen keys - you'll love yourself forever.

[jas98]

Nah, they're easy. Big socket, long breaker bar. All my undercarriage bolts are loctited and I don't have any issues removing any of them

Gearbox mount change should only take you half an hour if you're dawdling. Jack her up, put it on stands, support the trans with a jack and some wood, bolts x4 gets the mount xmember from the undercarriage, and bolts x4 gets the mount off the trans. Then replace and refit Not sure about the auto mounts, but I think they're allen key heads. Get yourself a really good unbreakable set of Kingchrome or similar allen keys - you'll love yourself forever.

haha yeh but i already broke a few unbreakable allen keys trying to undo the 2 dam bolts...yes unbreakable expensive ones....even trying it with the rattle gun with a unbreakable allen key riged up to it and nope....twisted and broke that one too...hmm take 3 soon:P

[needwork2-4fillhabbit]

Nothings unbreakable in the hands of a true professional ehehe. I had the same shudder in my vp, it starts at 100km's itl soon do it at 80 then 60 ehehe. I threw in a new auto and mounts and it solved the problem but i cant tell you which fixed it. Was a bad shudder up hills, also i think it started with over abuse of lazy foot.. (cruise control)

[SIG-054]

if its only happening at 1500ish revs in overdrive then it sounds like a torque converter problem.. been there and done that in my Senator.

[delcowizzid]

yip probably TCC lockup clutches in the tcc slipping

[h0Ld3n`VN]

this was happening to my car too.. it would change a gear again from 4th (no bs)
its like it went into 5th gear the revs lowered.. then it started shuttering like i was on the most bumpy road on the universe?

[delcowizzid]

yip thats the torque converter locking up in 4th gear.shouldnt shudder at all when it inguages.