Ok so this follows on from my vibrations at higher speeds thread. My garage gave everything a good check over, bushes fine, wheels true, all balanced and balanced again, no play in driveshaft (or very tiny amount in one inside joint). So they suspect gearbox.

There is no whining, gear selection is fine, never jumps out (1st and reverse a little stubborn at times, nothing a linkage reset and oil change wouldn't solve), clutch feels fine, no slipping.

What I do get is vibration through the steering at high speed, high revs, mega loadings (discovered when logging maxing out 3rd), and what I can describe as a bit of a rough tone as I accelerate through peak torque in 3rd and above. At day to day speeds it's fine, but I'm just concerned it's only going to get worse. Today I was in 5th and accelerated across 70 and got the rough tone and some vibration. Short while later did the same and not as bad.

Could this be the diff or some bearings more specifically? Given there's no whining and shifts are fine.

I'm prepared to risk a used box if it comes to it, will try an oil change first but don't think that will cure it. Suppose the cost of a rebuild kit and rebuild will be just as much, probably more than a used box anyway.

Suppose my question is, anybody else had this type of issue that can help me pinpoint it a bit more so I can think through my options? I want to keep the car there's no question about that, but funds are pretty tight lately...

Can you reproduce the noise when not in gear?, is it only when the tranny is under load?. If so, I would be inclined to suspect a gearbox mount or the flex joint on the exhaust, as I had a flex go weak and it sounded like the diff had crapped itself.

Cheers Phil, I haven't tried to be honest will do tomorrow. Flex joint on exhaust sounds interesting, I had put some of the increased noise under torque down to increased and improved airflow, but it's been bugging me as to whether that is all its down too as at times it felt like more of a vibrating rasp kind of thing. I'd be very surprised if it is the gearbox itself, but I have heard of some having problems around 80k.

Gearbox mount also sounds worth exploring, the vibration through the wheel feels rotational, but it's not entirely consistent, sometimes worse than others, but doesn't happen in 1st or 2nd at redline at all. I know 1st and 2nd don't load as heavily, but if it was the gearbox surely I'd feel something?

Seems there's 2 things going on, the throaty tone and the high load vibration. How can I check the gearbox mounts and flexi if the noise does happen in neutral?

By the way I get the noise in 1st and 2nd but not as bad.

The mount can be checked by placing a lever in the mount and trying to see how much lift you can get - there should not be much - just enough to allow for reaction really.

 

If the flex has gone, they go very bulbous around the flex as the gas release in side starts to inflate the flex, but not enough to cause a blow. You can sometimes get about 5-6 mm of inflation between the inner and the outer all around the pipe which means it can grow in diameter 10-12mm.

 

Just as an aside, is your dogbone in reasonable nick, as they can let the odd vibration in too, the engine can rock about a bit and can get quite close to the rack when the engine reacts to throttle input. No big stones trapped between the rack and the engine at all to cause the noise when the clearance is used up?.

 

Also, when you grip the inner driveshaft joint by the diff, can you feel any lift in the joint at the diff flange if you push it up and down

I'll have a dig about. Replacing/upgrading the dogbone bushes are on my to do list as it goes due to the occasional stubborn 1st and reverse shift. Thanks for the info Phil, will check it out.

Flexi seems fine, not sure how fat it's supposed to be but it's the right shape with no excessively bulbous bits. I didn't really have time to examine gearbox mount properly, is it the one under the airbox? Dogbone looks ok, rear bush feels soft but will be upgraded soon, doesn't look perished and there's no sign of excessive movement. I do think it needs upgrading though.

When I can I will try a gearbox oil change and linkage reset.

I've read some horror stories about rivets shearing off the diff, could it be that starring to happen? But maybe if it was diff related I'd be seeing more symptoms elsewhere. Other than the tone under high load and the top end vibration I don't have any other symptoms. In neutral the noise wasn't evident I don't think, there was a slight blip of vibration as revs flicked up around 3500 but I don't think it was abnormal.

Could it be the flywheel or some kind of shaft bearing? When the noise is at its worse I do feel a bit of roughness through the gas pedal.

It could be DMF related, but you really need to find a quiet road and do some more in depth testing as to when the conditions are that this occurs at as there may well be other rpm periods lower down the range that this is starting to occur but you may not be noticing as much.

 

On power or off power recreation of the vibration will also have a relevance at those revs as to what the transmission is doing at the time and to rule in or rule out the diff. Gently weaving while the vibration is occurring will also add a degree of accuracy to the transmission diagnosis also as to the pitch change of the noise/vibration - if any.

 

If you can reproduce the vibration, does going off power - on power - off power change the pitch at all?, can you "play" with the noise and make it do it on demand once you reach that rpm phase?.

 

In fairness, if the dogbone is getting soggy, some vibration maybe getting through as the torque in your map may be defeating the weak rubber in the mount to keep the engine isolated from the subframe under drive which may be why you are feeling it through the steering.

 

Keep us posted and I'll try to narrow it down for you if a can, but these things are difficult to diagnose when you are not "actually" driving the car.

 

Phil.

Indeed, think this one is tricky to diagnose full stop. I can certainly try and weave when I get the 'throaty tone', but the wheel vibration occurs at too high speed for that, the vibe I feel just doesn't occur in 1st or 2nd. I'll experiment more with the sound with on/off power as you suggest as the overrun may have something to do with I? I am starting to think though that the change in tone could be dogbone bush thing, it is close to the lower brace for example and while there's no evidence of rubbing it could be resonating it further?

As far as the vibration/judder goes I'm starting to rethink the driveshaft/s. These were checked the other day, only a tiny bit of play was found at one inner cv joint, but, I don't suppose that necessarily completely rules them out. After all there was no play in my wheel bearing when that went. And what is a tiny bit of play by hand and lever would be highly exaggerated under extreme loads. Coming off gas does relieve the juddering (which feels like wheels out of balance as it goes, but it's not), and in the low gears like I said it doesn't occur.

The tone however occurs through and up to peak torque when driving, 3-5k varies on severity but most notable in 3rd and above.

In neutral there was that slight resonance in that region but was difficult to hold onto.

I reckon it's dmf, diff or driveshaft, problem is that is an expensive checklist to go through by trial and error. Some of it may be compounded by needing a gear oil change and linkage reset...

Will do some further exploration and keep you posted. Cheers Phil.

Jon

Having already done my box oil change, I did not notice much improvement in general noise or harmonics, just a general cleaner gearchange that you would expect after pensioning off oil that has served for 100k miles. The rivets that fail hold the crown gear to the diff planet housing, so any noise would only change pitch wth speed as in theory they are wearing away on the box casing, it would not cange pitch when gently weaving.

 

If the noise changes pitch, then it is either driveshaft or diff planet internal gear related in the diff as you have ruled out hub bearings (assuming they were done correctly).

It intrigues me that you feel the vibration in the steering, as that is normally a leaning to something connected to the hub, but if the shaft is oscillating at speed within the outer cv joint, this could explain it.

 

How much movement is in the driveshaft if you grip the shaft part near the cv and try to shake it reasonably vigorously to check for up/down/left/right movement in the cv itself?. ( obviously you will need car jacked up and SECURELY mounted on stands to check this, as you don't want the damned thing coming down on top of you).

 

One last thought, I know you said the wheels were true above, but are the tyres true and not showing any signs of ovality?

 

Also when I said gently weave, you only really want to do a "drunk driver" type weave, rather than a full on touring car driver warming up his tyre type weave. Don't put yourself in harm's way, as all you are trying to do is make one wheel rotate faster than the other for a few seconds to hear a noise change. It is a bit like the marching band turning at the end of a row to come back the other way, the fella on one end of the line marks time standing still while the guy at the other end of the row is marching at normal speed - its basically what a diff does real simply.

On the way in this morning the throaty tone doesn't seem to change when weaving or going round bends, its worse at wide open throttle in 3rd so have to be a bit careful.  This morning it didn't seem so bad but what I did hear didn't alter I don't think.

 

Also the juddering/vibration didn't occur this morning, I got to the kind of speeds where it happens but without wide open throttle, sort of just above half throttle, loading and pulling but not going mental.  The bearings have played on my mind a bit, I do pretty much trust the garage who did them, and I would have thought if hub related then heavy braking would also reveal it?  Will double check the tyres, the 2 fronts are new and it was doing it before they were fitted though.

 

I'll be getting axle stands next month, bit skint at the moment.  My mechanic said the movement was pretty insignificant and not much to worry about, can't remember which side he said now, but will double check when I can get the car up properly and like I said, no play doesn't necessarily mean its perfectly fine does it?

 

It's a weird one because the way I drove it this morning (apart from a slight throaty tone) you'd think there's nothing wrong with it, but I was mainly concerned the other day when I accelerated across 70 in 5th and the tone was there and vibration started, but then over that in 4th this morning (within 10% plus 2!) it was fine...seems more engine speed and loading related than mph and movement related perhaps?

With a driveshaft fault, it either tends to manifest itself as a vibration or knocking on lock before the joint tend to fall apart under its own steam so you normally get plenty of warning in one form or another (unless you own a nissan primera, then they just snap in two halves   - been there, done that). It is possible you may be experiencing a partial seizure of the inner cv loint at odd times (see this link http://workshop-manuals.com/skoda/octavia-mk1/chassis/front_suspension_drive_shafts/repairing_drive_shaft/repairing_drive_shaft_with_inner_tripod_joint_aar_2000_and_outer_cv_joint/) between items 5 and 6.

 

A driveshaft when rotating unless completely balanced will try to do the "conker on a string " trick, in that the faster you spin it, the further away from where it started it goes due to centrifugal forces. in perfect nick, the shaft would resist these tendencies due to fine balancing, but when something starts to seize, welcome to conker land. The result is vibrations and noises that would not normally be there.

 

Do you know if when they fitted the front hub bearings, did they go through the pre load tightening procedure "by the book"?.

 

As you can drive through it, I think you are looking for something "going to ground" connected to the power unit - by that I mean engine mount, shaft, exhaust mount, rather than a gearbox fault as they do tend to get small whines and spurious quirky noises normally before they go bang, it's just that they creep up quietly first then get slowly louder so we don't notice them. It is when someone different drives the car and says "god, that's loud, what the hell is that?", that you then get you had a problem - a bit like bad brakes, we tend to drive round them until one day they nearly don't stop and we become aware.

 

Just a thought, as you've been having performance issues in previous threads, does the cat rattle when you bang it?, as when an exhaust starts to break up inside that can get real throaty, and as it starts to block the throughput of flow can start to restrict performance - as I said................just a thought.

 

Phil

In all honesty I don't know if the garage did that, it's just down to trust on that one. They're pretty honest guys though and tend to do a good job. However, not sure if this is linked but following the bearing fit my toe in went out and I lost the outside edges on the front in not much time at all. Strangely it was out evenly on both sides. Got lazer alignment done when I had the 2 new fronts fitted.

Is it possible that when the hub went back on after bearings the driveshaft ended up slightly out of phase?

Thanks for that link I'll look into that. Like yourself I'm not sure it's a gearbox issue, given the lack of other symptoms (chatter, whining, crunching, knocking). Car runs smooth and quiet apart from these issues, I'm pretty switched on to anomalies and things out of the ordinary and they bug me until I know what's going on. I think you're right about that, although it feels rotational so I'm thinking something slightly out with shaft...Will look into it more.

The other day when it happened in 5th the throaty tone accompanied the vibration. It could be that the tone is a separate issue, or it could be linked. Like what it is that causes the tone at peak torque causes the vibration at peak revs..

I will check the cat, with my performance issues it looks as though on dyno day my car suffered badly with heatsoak and through logging I did discover high intake temps (the ecu would have definitely been retarding timing). I brought these down with a turborevs smic which has worked well. I also think the boost issue has been tracked to a weak actuator which has been improved by a pikey mod with external helper spring. That said the throaty tone coincides with the better running I achieved following these steps, it could be that the few clicks of extra torque has finished something off in the exhaust and as you say is just pushing the dogbone a little too far. Prior to this the cat was working very well and following a terraclean last year the emissions were virtually zero when mot in January. But as I say perhaps the improved airflow and the torque have overcome something in the system. Will try and check that out, good excuse for a sports cat!

It could be the tone is a different issue to the vibration, but as it goes I'm kind of getting a list of steps together in my head, which are open to change but go something like:

Check cat - replace if necessary

Change gearbox oil, forte diff treatment, reset linkage

Dogbone poly bush rear mount, improve front mount either new oem or poly insert

Replace driveshafts if they don't work and further exploration of mounts turns up nothing.

Quick question, where are the grease nipple situated? Are they obvious when you slide the boot down? Could add ramming them full of grease to the above list.

If you mean the drive shaft, you don't have one, you release the boot and pack it in with your fingers, but not in the boot, the grease needs room to expand into without blowing the boot to shreds.

 

If you are thinking of repacking the joint, that is ok, provided you have some means to flush out the old contaminated grease and clean the joint before re lubricating. Brake cleaner can be useful, or some form of component cleaner, but whatever you use, you must allow the solvent to completely dry in the joint, or any grease you choose to put in will become history real quick.

 

The thing is, the tripod may have just started to seize on the bearing, so re lubing would be appropriate, but if the bearing itself has started to fail and it is actually starting to wear away areas of part 5, then no amount of grease will effect a permanent cure. If the joint is worn, the vibration will come back probably within a month or so as the grease thins down in use. The only cure there really would be a new joint, and to be honest, a recon shaft will probably be cheaper.

 

This may help you understand the mechanics of the problem better - http://workshop-manuals.com/skoda/octavia-mk1/chassis/front_suspension_drive_shafts/repairing_drive_shaft/disassembling_and_assembling_the_tripod_joint_aar_2000/

 

At the end of the day you wont know for sure till you look, then it is decision time. If you choose to do it, make sure you try to use the correct grease, as these joints really take a bonking with the torque put through them.

 

Phil.

That's great info cheers Phil, I'll have an explore when I can support the car properly. The more I think about it the more the driveshaft makes sense for the vibration, and something cat/exhaust related for the tone. Will focus my search here for now and keep you posted.

You will be really surprised if you release the dog bone from the gearbox, exactly how far the engine can rock back and forwards, had a little bead of sweat first time I did one .

 

You then have to think, that the exhaust and shafts are then taking up some of this movement as the dogbone ages. so it's no suprise really when the odd vibration gets through to passenger cabin.

Must admit I'm looking forward to upgrading those bushes. Mine aren't perished but I definitely get the impression it would benefit. Is it best to support the gearbox when you do it?

Provided that both engine mounts are ok, no, as you need the engine to move a fraction back and forth to be able to reinstall the bolts to the gearbox as the new bush will not be quite in the same place by a couple of mm.

 

It won't harm though if it makes you feel safer.

Sit rep: I've just turned my wheels to lock as I'm doing some rust treatment where the mudflaps sit before it gets any worse. Thought I'd cop hold of the driveshaft while I'm there. And what the garage called an insignificant amount of play in the n/s shaft, while not worryingly bad, I would call it noticeable. Just a shake from side to side revealed a little movement, probably 1 or 2 mm either side, resulting in a tap tap as it went from one extreme to the other. As said not terrible, but would certainly be exaggerated under high loadings wouldn't it? O/s has zero play by the way.

Budget is tight and can't do for a month or so, question is am I better off getting a tidy looking used oem one, or a brand new budget one with 2-4 year guarantee? Is this the kind of job where you'd prefer to do both rather than just one? I never usually like just doing one of something like this...

joint cheap enough amk 2 year warranty cost me £20

dont change full shaft too many copies 

It's the inside joint, bit more difficult to source and do aren't they? Just think that by the time I've taken the shaft out might as well put a whole unit back in...

What I'm having trouble getting my head round is that the garage were happy to diagnose gearbox which would cost me bucks when there's play in the shaft like that. I know where I'd start, and it wouldn't be with the gearbox...

i fitted a new item from euro vibrated constantly put old one back in problem solved there is movement on inner joint from stock in and out a bit , ive just fitted a new outer as wasnt noisy but wear was causing slight vibration at higher speeds 

Hmmm think I may try a new joint or a good used oem shaft and service it before fitting. Will cost about the same.