Hello,
My local Citroen indie has just replaced the front disks on my XM 2.5 at 72K.
They were pretty well rusted on, and quite a lot of force and application of FBH (hammer) was apparently used. A sensible practice?
I have now noticed a slight whine from the final drive area at around 2800 rpm in fifth (approx 80mph). Any idea if/what may have been damaged? I would have thought that the final drive area was pretty robust. Or maybe the whine is from the new balancer/alternator belts. But I doubt it. Or wheel bearing?
Any suggestions? How is the "end float" on the drive shafts controlled on these machines?
This is difficult to handle, as it is probably around twenty hours work to strip down and check. And is it worth it? However, a similar whine (from 100k) on the final drive of my Peugeot 405 developed into the demise of the differential bearing at around 225K...
Apart from that, the XM is glorious...
Rob
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Rob,
I'm afraid that hitting wheel hubs to remove rusted on brake disks is a common and expensive error. If rolling bearings (in the wheel hub or gearbox) are subjected to blows when stationary, minute pits corresponding to the positions of the balls or rollers in the race are formed. This is called Brinelling (after the Engineer and his hardness test), causes the noise you describe, and leads to premature bearing failure.
Several car manufacturers experienced this in the form of wheel bearing failure on brand new vehicles in the days when they were delivered on a rail truck. The reason was that the hub bearings were stationary, but subjected to regular blows as the trucks rode over the regular joins in the rails used in those days.
Tell your fitter that the correct way to remove a rusted disk is to remove fixings (drill out screws if stuck), then with the opposite wheel on the ground, gently apply the brakes with the car idling in first gear. This always works, but you must be careful that the car does not roll away on of off the jack. Even on cars with wheel studs, there is enough clearance to break the stuck joint. On a non driven axle, you have to be a little more inventive...
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A very interesting answer.I never knew about brinelling. I'll no doubt be putting this method of "releasing" stuck discs into practice in the next couple of years. Do you have any suggestions for a non driven wheel, except heat, grinding and a FBH?
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Dear 659FBE,
Thanks for your learned response.
Oops, it's just as I thought...
I will take this up with the fitters, as i think I am due a new bearing when the clutch comes up for replacement ("engine-out" job...)
To me, it sounds a bit like a "diff" bearing in its "on-off" sound under load. It disappears under very slight left-hand steering input, typically on motorway curves at speed. And it's only noticable cruising at 80 in 5th. Do you have any clues as to which one it would be on a Peugeot/Citroen front end? (clue to correct answer:- "wheel bearing")
And how "premature" is bearing failure? Has the life been halved, or worse. Yes, this, and the question above are a bit "how long is a piece of string?"
Ho-hum. Such a shame as it was beautifully quiet in the cruise, and having a "mechanical ear" is not helpful as I can't help but hear it. Not loud, but irritating.
Thanks again.
Rob
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I can't see how whacking off (sorry for the phrase!) a brake disc can damage a diff bearing - I've been whacking off (!!) brake discs for 10 yrs+ with no ill-effects. Sometimes they are well seized on requiring the use of a large hammer...
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Well, my thoughts on using FBH are always, "to every action there is an equal and opposite reaction", meaning something at the other end is taking some force to allow me to bash this thing in situ.
My reason for posting is to plunder any experience "out there", so thanks for the advice.
My dad, born 1914, started in the motor trade in 1928, and finished in 1983. As time goes by, I appreciate that much more his "intellegence, heat, and patience" approach to removing seized stuff. Sadly, commercial pressures in the motor trade in the 21st century do not always make room for this approach.
More opinions (and tales of experience) most welcome!
rg
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Rob,
Your mention of drive shaft end float gives some clue as to what may be damaged. On most PSA vehicles there is a preloading spring in the inner UJ which has the effect of putting all the drive shaft rolling components plus the diff pinions under axial pressure. This is a very good idea, and mitigates the effects of rattle which can cause fretting damage, whilst allowing vehicle tolerances to be taken up. The compliance of this spring would almost certainly protect any bearings in the transmission.
The hub bearings have no protection from our hammer wielding operative. Given that disks are frequently whacked off the hubs outwards, the outer races of each front hub may be damaged, so noise on a LH bend will be caused by the RH hub bearing under increased axial load - just what one would expect.
I have no respect for those who have "whacked these things all their lives". As you rightly say, Newton's third law always applies, and rolling bearings are precision items. (By the way, ever wondered why old train truck bearings were solid bronze bushes in an oil bath?)
To deal with a non driven axle, remove the entire hub and disc assembly, clamp the inner races lightly together with a large bolt, nut and two washers and set to work. The nut and bolt trick prevents angular contact races from falling apart whilst you - erm - operate, and the washers keep the dirt out.
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so there is a likelihood that the "hub bearings" (wheel bearings) have been damaged?
(The sound is more "diff bearings" to me...)
Just to restate, the noise is "in the cruise" rather than constant throughout the gears and speeds.
rg
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Agree with 659FBE on most points, but I must say that I've used wheel bearings as an anvil many times in the past, with no ill effects. I'm not to sure about the 'urban myth' of wheel bearings being damaged in transit though. Surely the transporter suspension and tyres of the vehicle being transported would absorb any damaging shocks.
As for the Brinell test, in pre VW days every Skoda half shaft was tested in this way. Every one had a 'dimple' where it had been tested and passed for quality. I've never known a Skoda half shaft to fail !
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Rob and Carrick,
A couple of points. It can be difficult to decide whether road speed related noise is due to hub bearings or diff bearings, but the change of noise on cornering makes the hub bearings the more likely offender. There is little transfer of load to the diff on cornering because of the axial compliance of the driveshaft. The history of your vehicle increases the likelihood of hub damage.
You were asking about the prospects for these bearings. Not too good, I'm afraid. Rolling bearings are generally damage intolerant and after prolonged use the raceways work harden. With a new bearing, very minor damage of this type will occasionally "roll out"; in a high mileage unit the raceways will spall and break up. I spent a long time with a (once great) British automotive company looking at knackered bearings.
Have you ever ridden in a railway truck as opposed to a passenger carriage on jointed rails? Remember also that the cars were tightly chained down, preloading the tyres and ensuring maximum energy transfer to the stationary hubs. Transportation by road where the conveying vehicle has both pneumatic tyres and suspension does not usually cause this type of damage.
Regards, (Prince of Darkness).
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Dear "Prince",
Is the race surface damage normally visibile? Obviously we don't want to swap out good bearings. My experience of whell bearing failure is of continuous rumbling noises, but I appreciate that there are strange frequency phenomena, etc, affecting mechanical noise on vehicles.
Short wheel base trucks on jointed rail. Yes, I can beleive this having ridden in a "brake van" a few times. Ouch.
Thanks again
rg
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Rob,
The damage is visible only if you completely dismantle the bearing, removing the cage and the rolling elements. Also, the removal of the bearings from a driven wheel hub wrecks them. Sorry.
There is an excellent book called "Bearing maintenance and replacement guide" published by SKF. On page 23 there is a picture of a Brinelled bearing.
The "Prince" thing was a clue as to the company I worked for.
Regards, 659.
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