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Old 08-01-2004   #1
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Motor Vibrations at 100 000 km! What could it be?

Hi,

I have a Fiat Bravo 1.4 s from 1997 (Mk-1)
actual mileage: 100 000 km

since about the last 800 km, I noticed the gear shift lever started to vibrate. First, I wondered whether maybe its the tires (I recently put snow tyres on which had been balanced some year or two ago). But no, the steering wheel doesn't have any vibrations. Furthermore, the vibrations have become much stronger in the meantime, they are strongest in fifth gear between 80-110 km/h (that happens to be the speed I'm travelling at most of the time).

What's strange is this:

When I pull out the gear (moving at 100 km/h without motor power) all vibrations completely cease

When I'm in fith gear, and I don't accelerate or I only accelerate extremely moderately, there are NO vibrations. When I push down about 1/4 to 3/4, there are quite strong vibrations, which tend to disappear again when I push down very hard.

Now, I have to explain three things about my car:

I always changed oil in regular intervals, only using the best synthetic oil from Fiat garages (which cost a fortune)

The replacement of the toothed drive belt which drives the camshaft and (I believe) the waterpump, is due when mileage has reached 105 000 km, since this mileage has not yet been reached this drive belt has not yet been replaced (I planned to changed it this year).

I never changed spark plugs in this car, nor did I do any "regular" inspections expect the "necessary" ones (changing oil, repairing exhaust pipe, exchanging battery and other small stuff). Analysis of exhaust gases (its compulsitory in Germany) and function of the lambda regulation of injection and catalyzer were always fine.

Gear oil has never been changed, but I think it should not be due yet anyway.

I never ever drove with the small emergency wheel replacing one of the front wheel (which should never be done), so the differential should be still okay too.

A) Could there be some problem with ignition (because I did not change spark plugs, and they have already 100 000 km mileage)?

B) Could it be that there is some problem with the tightening mechanism (if there is any) of the toothed driving belt of the camshaft? Which somehow "disrupts" timing of valves

C) Could it be that there is somehow a problem of a "blocked" injection valve on one of the cylinders?

I had a motorbike once and my problem now reminds me somehow of ignition problems of that bike - either no carburant in one of the cylinders or no good ignition or something.

What suggestions do you have, that it could be?

My garage is a little distance away otherwise I would just drive there and show it to them.

by the way, this fiat motor has some special mechanical or electronical mechanism (I don't understand it very well) to prevent pinking - maybe this mechanism is "out of order" for one of the cylinders?

Overall power seems not to have suffered to much, the car seems to still able to reach about 160 km/h (as I have said, vibrations tend to disappear if I push it down hard) but not it is winter so I seldom to this high speeds now; fuel consumption did not increase much. There is no blue smoke out of the exhaust pipe or anything else noticeble you might imagine, and there is no oil leaking of any sort.

I drive very often in fifth gear, as I'm used to accelerating slowly and going to fifth gear rather early, at about 40 - 45 km/h . I have not yet checked or noticed wheter the problem occurs also in other gears.

Idle running is perfect (as far as I can tell without special instruments).

Many thanks for your help.
zardo
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Old 09-01-2004   #2
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Zardo

I have had a similar problem with my car (Brava 1.4S) and have not successfully tracked the problem down. I do however suspect that the problem is to do with the transmission rather than the engine.

I have had the wheels ,the tracking and the straightness of the drive shafts checked. None of these were a problem

I think that the problem is related to wear of the inner universal bearings on the drive shafts which is something I will investigate when I have the clutch renewed at some stage, in the meantime I will live with the vibrations.

I hope this is of some help to you and if you do find out any more info I would be grateful if you could update this thread.

Good Luck!
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Old 09-01-2004   #3
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Hi hangfive,

I think you're right. I did some tests today...

The motor is fine. I can speed up to about 80 km/h without noticing anything at all. In normal city traffic the 'shaking' phenomenon never appears.

However, at 85 km/h, the gear shift lever starts to vibrate, and at around 90-100 the whole car shudders (but only if you step on the pedal). You can actually feel the vibrations in your stomack.

Now, changing gears at 100 km/h from fifth to fourth to thirth didn't have any effect at all: the vibrations stayed the same (and I think, even the frequency of vibrations, the kind low frequency papapapap didn't change). But when I take out the gear completely, vibrations cease.

So there must be something wrong with something which turns and shakes when there is force transmission from the gear box to the wheels, and when the wheels revolve at a certain speed (when I step on the brakes, there are no vibrations).

Hm. I don't like a bit of it. And the problem seems to increase fast. Think I will have a rendez-vous with my garage for next week.

I wonder wheter they still do repair gear box and transmission parts, or whether all they can do (or want to do) is exchange the whole gear box as it comes.

cu
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Old 10-01-2004   #4
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i would have a look at your trasmission/engine mounts,as for spark plugs,just because your emissions are okay doesn't mean you dont need plugs.the ECU will correct for the emissions but fuel economy ,power etc will almost definatly improve with a new set of plugs and it only costs a few

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Old 12-01-2004   #5
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HI, I couldn't get an appointment at my garage until the 22th...

So for now, I measured the frequency of vibrations.

It's about 13 Hz for a speed of ~ 80 km/h - therefore I think it's linked to something between clutch and gear box which turns with the same rotational frequency as the wheels (?) as I believe that 13 Hz is the rotational frequency for wheels with a diameter of 0,5 m at 80 km/h...

by the way, how to find out about exact wheel diameter?

greetings,
Zardo

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Old 17-01-2004   #6
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Hm, I try not to use my car but today I did have to use it for some short distance.

I noticed that the vibrations increase with the motor becoming warm, there're also there when I roll down a hill using the "motor brake".
When the motor (and gear box?) become warm, vibrations start now already at 30 km/h... I was happy to come home safe.

Hm, I hope I'll make it to the garage which is 45 km away...
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Old 17-01-2004   #7
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Try this site for tyre sizes.

http://www.powerdog.com/tiresize.cgi

Dave. :)

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Old 22-01-2004   #8
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Ok, some news from the garage:

they don't know for sure what is it.

It appears that one of the "transverse control arms" (that's the translation I found for it) has some slackness, and some "engine bearing" (what ever they mean by that - perhaps the motor suspension?) seems to be wore down.

The vibration are very variable, sometimes they're so heavy the gear lever, dashboard including radio shakes like they were doing some crazy rumba dance, this happens independently of choosen gear, and down to 30 km/h (but with the motor under load), on other days they are almost not noticeable. They always stop immediately when the gear lever is pulled to the neutral position (motor uncoupled, idling).

This gives me something to think.

My question:

what if the wheel somehow moves this transverse control arm, which starts to "swing" and couples with the gearbox making it swing, too. Finally the gearbox entrains the motor, the suspensio of which might have a characteristic frequency of, say, 13 Hz on which it will start resonating...

Is this possible, or are there some dampers in between which would prevent coupling?

What else could it be?

They propose to exchange one thing after the other, starting by the least costly, this will, at the end, still make an enormous bill - I don't really want to have my car replaced gradually by some expensive new parts, one by one, so it will be kept at the garage forever...

What would you do?
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Old 23-01-2004   #9
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Hi,

Not too sure about the 'transverse control arms', could be steering tie bars?

A bearing is a low friction interface between a rotating shaft and a fixed support. A worn bearing could give vibrations like you have described. Especially if on a drive shaft as Hangfire suggested.


Dave. :)

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<h6>FIATcentral window sticker, silver poppy coral, titanium tax disc.
Blue gaiters, Blue sidelights, Blue interior lights, Blue lacquer on engine, feeling blue ;)
Ecotek fitted, removed and waiting for warm weather
So much to do, so little time.... and Totally Skint!! :(</h6>
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Old 23-01-2004   #10
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Hi,

I just had an quite unhappy time searching for the correct translation or a diagram.

I think it must read "track control arms", instead of "transverse control arms" - there are two of them, and one of them shows some "slackness"...
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Old 23-01-2004   #11
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Is not from your Exhaust system? In my case it was Exhuast sytem which was vibrating exactly at 3000rpm.

Kami
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Old 23-01-2004   #12
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Hi Kami,

thank you for you're suggestion.

But I don't think the exhaust system is responsible (who knows) because when I change gears 3-4-5 at the same speed, the problem remains and vibrations stay the same. I also get vibrations when using the engine brake (rolling down some hill at 90 km/h in fourth gear for example without any gas).

Now I think the bravos have "fuel cutoff in the overrun" (but I'm not sure about it) meaning that when one uses the "engine brake" there is no fuel injected, as the rpm are way above idling rpm, so there is nothing to be ignited and there won't be much volume entering the exhaust system...

Thank you again for your suggestion.

cu
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Old 26-01-2004   #13
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Finally there are some good news:

the garage called today, they say they've finally found out what it is.

It seems that there is a problem with the drive shaft, more specifically it's some bearing on it at the "articulated joint" (whatever that is for). Actually, FIAT provides some REPAIR KIT for it: one can exchange the "sleeve" and the bearing and fill up the "sleeve" with some special grease like Tutella MRM2 or something, and it's appearently possible to exchange the bearing or casing too (my own documentation concering the two main drive shafts appears to be quite limited, I'm sorry). By "drive shaft" I mean the axle which is driven by the differential - and if I understand the design in my book correctly, then the "bearing" or "casing" which is problematic is located on the lateral end of the right drive shaft where the "sleeve with the grease in it" is.

Indeed, the problem seems to be that the bearing in the casing (or this casing acts as a bearing, I don't really know) of the "articulated joint" or "slip joint" or "synchronous run joint" (whatever the correct translation for the german "Gleichlaufgelenk" is) on the lateral end of the right drive shaft was entirely pulverised.

Now I would be glad if someone could translate all this to me in "plain english" and explain to me what happened... and how did it happen... and why only on the right side and not on the left side too(?)

Is it because there are so many drain gutters in Germany, as german roadbuilders are quite frantic about having every 10 m one of these, but since they are often too deeply build into the road they act mainly as potholes (in Germany, we drive on the right side, so the right wheel will be hit by them all the time)?

Thx,
Zardo

PS: actually I'm not 100% sure wheter they meant the outer or the inner bearing. As far as I have understood, they meant the outer bearing - since the "sleeve" is on the lateral side, the outside. So finally it seems to be quite similar, but not exactly the same as Hangfive's problem.
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Old 30-01-2004   #14
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SOLUTION:

they changed the "inner bearing". It seems that a marten had bid into the surrounding sleeve, damaging it. The oily liquid or grease or whatever there is which protects the inner bearing from wear then probably got out of the sleeve (?) Finally the bearing was distroyed, which did cause vibrations.
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