406 judder in 5th gear

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RussD
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Joined: 01 Apr 2003, 17:44

406 judder in 5th gear

Post by RussD » 08 Apr 2003, 17:26

I have a 1997 406 1.8 petrol that's done about 72K miles. When in 5th gear there is a noticeable vibration, felt mainly in the pedals and steering column but also audible as a "booming" noise if I'm driving on a smooth road surface. The vibration is felt most at between 40 and 50mph but it starts to get lost in the general wind noise etc. as the road speed increases. I'd really appreciate any help in pinpointing this problem.
Now for the symptoms:
It only happens in 5th gear and only when I've got my foot on the gas. I don't need to be accelerating, it's there when I'm driving at a steady speed. If I take my foot off the accelerator pedal the vibrating stops.
If I push the gear stick forward a fraction, the vibrating stops. Push it forward some more and I can feel a severe judder in the gear stick that's definitely related to road speed. Difficult to describe exactly but it feels like the gearchange is bouncing back off some rotating part. Remember, this ONLY happens in 5th gear AND with my foot on the gas.
What I've checked:
I had the local garage take a look under the car for any obvious signs of wear in the gearchange, touching parts etc. Nothing found.
I've also checked the gearchange rods and joints myself. All joints are nicely free moving but without any excessive slack. The only possible problem I found was the bell crank lever that's bolted to the subframe. It can slide a few mm up and down the retaining bolt/sleeve however I took it apart to take a closer look and there is no discernable wear at the pivot. The big plastic ball on the other end of the lever seemed to have two flats worn at (I think) the 5th gear position so as a test I applied a bit of insulation tape to the ball to compensate for the wear and jammed it back into the end of the remote change rod. On a test drive this seemed to improve things but only because it stiffened up the gear change and allowed the gear lever to lie in a position where the vibration wasn't felt but the vibration is still there if the lever is moved slightly.
Now I've got a horrible feeling that it's something internal to the gearbox. Any helpful comments gratefully received.
Cheers,
Russ

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AndersDK
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Post by AndersDK » 22 Apr 2003, 07:21

Russ -
This symptom could be indicative for an imbalanced drive axle, or a worn CV joint.
It could also simply be an imbalance problem on one of the front tyres. Even a defective tyre.
Some 6y's ago I had exactly the same symptom on my CX, which also is a PSA construction. In my case the symptom came rather suddenly, weak but annoying, and slowly growing worse, untill some day I did'nt dare to drive the car anymore, untill the problem was found & corrected.
First I was on the same track as you, thought something was loose somewhere in the mountings on the drivetrain. But no. Wear found, as you did, but not the problem.
On a couple of test drives, I tried to notice if one of the sides of the car was vibrating more than the other. But it was hard to judge, conclusion was that RH side seems the worst.
This side's driveaxle was then replaced. No help. Same axle tried again, since I thought the axle (brokers unit) was defective. Got a second (free !!) axle on warranty. The broker was indeed very kind, no problem, instant delivery, "keep the defective for any spares if you like" was the answer. But it did'nt help. Same problem.
Then I got mad for a split second. Those sh..ty parts from the broker I thought, while I was turning the wheel on the jacked up front, trying the axle. Perfect axle, I was way out on the fields in my thoughts, when I suddenly noticed that the tyre had repeatedly touched my gloved hand located near the tyre, while still turning it silently in my vague thoughts.
The tyre was clearly defective, had a raised bubble the size of a hand, protruding at least ½ an inch from surface, located on the inner part of the tyre surface.
It was a branded Michelin tyre, still some 4mm left.
A test drive with my spare, revealed a perfect CX comfortable drive. Could'nt resist taking a 1 hour relaxing tour in the car. What a relief, and why the he... did'nt I simply suspect the tyre from start [:o)][:o)]
Still have 2 extra (fine !) drive axles on stock. The car is now waiting for a total rebuild.

RussD
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Joined: 01 Apr 2003, 17:44

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Post by RussD » 22 Apr 2003, 14:49

Hi Anders,
Thanks very much for the reply, that's very useful information. I'm going to look at the tyres and driveshafts as soon as I get a chance.

I have just noticed that the vibration is momentarily worse if I nudge the steering either left or right (can't remember which way, maybe both!). Could this point to a worn driveshaft and do you know if a worn driveshaft is likely to be more noticeable under load (foot on the gas - see my earlier posting)?
Regards,
Russ

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AndersDK
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Post by AndersDK » 23 Apr 2003, 03:40

Russ -
When mentioning "driveshaft" - I actually meant the outer CV joint.
If this is shot/worn, the axle is allowed to be displaced more or less off-center. Then it vibrates, even loudly knocks in severe cases.
This symptom is VERY clearly felt worse, when turning - either way - since this will more or less try lock the CV joint. Heavy knocking & vibration is clearly the result, with the risc the axle will snap.
Usually driving straight, you also have a constant knocking, since the suspension geometri demands the driveaxles to be a bit angled to the wheels.
On the other hand, if the knocking/vibration is not constant - with constant cornering - the momentary worsen of the problem is indicative for a tyre or wheel bearing problem.
A constant grinding/waving sound, points directly to a shot wheelbearing. This will worsen up to the point where clearance is felt in the bearing, wheels off ground.
Even dry CV joints, caused by knackered bellows, may start with somewhat "soft" vibration.
I'd say you first visually check for ovality on front tyres & also check the condition of the CV bellows. If ok, then simply swap front & rear tyres. Any difference (worse/better) points to a simple (& cheap) re-balancing of all 4 tyres.
If nothing seems to help, more sophisticated measures are needed, like having the car on a testdrivestand, where it is possible to serch for vibration, while the wheels are turning under load.

RussD
Posts: 7
Joined: 01 Apr 2003, 17:44

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Post by RussD » 23 Apr 2003, 14:39

Thanks for the useful information. Thinking about this some more, I don't think it's a tyre problem because if I dip the clutch the vibration goes away. I will check the CV joints and bearings for play though (and take a look at the tyres too, anyway).
Regards,
Russ

RussD
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Joined: 01 Apr 2003, 17:44

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Post by RussD » 26 Nov 2003, 05:59

I'm reviving my own old post just to finish the story.....
I finally traced the problem to the gearbox. Fifth gear was faulty, or to be more exact the toothed thingy that slides and locks the fifth gear cog when the gear is selected. The teeth were badly worn on one side and not on the other - that's why the 'box vibrated when I had my foot on the gas and not when the engine was in overrun.
Maybe not the best technical description but it might help others if the same problem crops up for you. By the way, it cost me £200+ to get it fixed and that wasn't at a Pug dealer. Actually, the Pug dealer said there wasn't a problem with the car and in a round about way hinted that they didn't want to touch the car because it didn't have a full Pug service history.
Russ