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Sort of passing dozens of trucks (like one does) my attention was drawn to the prop-shafts....how come they run "naked" so - to - speak, with the UJs exposed to the elements, how come they don't get gummed up or corroded....
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>> how come they don't get gummed up or corroded....
They probably do, a bit. But they are probably designed to be greased regularly. At least one car I've owned had grease nipples at the universals, apply the Wanner and the old grease would be forced out of the bearings as the new grease squeezed in.
It can take a lot of force sometimes if the uj has been neglected and allowed to get dry and noisy.
Last edited by: Armel Coussine on Fri 27 Sep 13 at 18:47
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>> at least one car I've owned had grease nipples at the universals, apply the Wanner and
>> the old grease would be forced out of the bearings as the new grease squeezed
>> in.
One of the simpler pleasures in life. To see the dirty grease coming out followed by clean stuff.
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Same as RWD cars.
UJs have a rubber seal on each leg of the spider, like any other bearing exposed to the elements, such as wheel bearings, drive shafts, gear change rods, ball joints etc.
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Assuming the joint has been well designed and specified, there isn't a great need for fresh grease. A well sealed UJ which articulates sufficiently and has an acceptable Hertzian contact stress between the rollers and the spider will run very well for a very long time.
It's the action of articulation to draw grease into the interface between the needle rollers and the spider, and a shaft which is too "straight" won't have a long life. If the contact stresses are OK on the spider, they willl also be OK on the interface between the rollers and the cups.
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>>
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>> It's the action of articulation to draw grease into the interface between the needle rollers
>> and the spider, and a shaft which is too "straight" won't have a long life.
That's a point often forgotten by people aligning marine engines. It's assumed that a straight line must be best, but in fact I read that 5 degrees at each joint is the optimum, to pump grease but also to avoid continuous pressure points.
Also, as with vehicles, it is important that there is an equal angle at each joint. The diff angle depends on the suspension/spring alignment.
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AC is right, they are designed to be greased regularly.
It's not usually the end UJ's which fail; Volvo's particularly are prone to failure of the centre bearing, the joint in the middle of the prop. You soon know if it's gone when you're driving the lorry, vibrates like hell.
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From the lack of care to avoid contamination that I've seen in many commercial vehicle repair shops, it's the action of regular greasing - a regular new dose of grit and muck - that speeds up UJ failure.
Centre bearings are another matter entirely - nothing to do with UJs, and usually sealed for life.
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>> From the lack of care to avoid contamination that I've seen in many commercial vehicle repair shops, it's the action of regular greasing - a regular new dose of grit and muck - that speeds up UJ failure.
What with amateur mechanics setting their valve clearances too tight and slobbish commercial vehicle mechanics filling the ujs with grit, it's a wonder any vehicles in certain categories survived as long as they did.
It's true that grease nipples can get filthy. But they can be wiped, and don't people keep pumping until the new grease is coming from all the bearings?
Some garages have a powerful pneumatic grease gun. Needed that for Skoda Estelle king pins.
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Yes, a pneumatic grease gun was very helpful - on an 8 wheeler, there are over 40 grease points before you've finished the leading 2 axles!
I forgot the other killer of UJs and other greased joints on trucks - the high pressure jetwash or steam cleaner - the pressure easily overcomes the rubber seals, and the water ruins the joint in no time.
As for keeping pumping until the grease comes out clean - that's OK on a UJ or shackle pin, but not on a brake cross shaft, where one end of the shaft ends inside the drum! However, in most cases HGV joints aren't pumped until the grease comes out clean - that would be far too wasteful.
It's not that nipples can be wiped - they absolutely must be wiped clean, or you're definitely doing more harm than good!
It's not just amateur mechanics who consistently got it wrong. Published research showed that a significant proportion of conventioanl cars of the points and carb era were incorrectly maintained / adjusted. Thankfully, electronic systems spare us from the worst of that drip...drip ongoing cost of wasted fuel.
Last edited by: Number_Cruncher on Sat 28 Sep 13 at 19:43
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>> Published research showed that a significant proportion of conventioanl cars of the points and carb era were incorrectly maintained / adjusted.
Tell me about it N_C... never bought a secondhand car that didn't need sorting out. And they weren't always straightforward like Skodas. Those coke-bottle Cortina carbs for example. Shudder...
One of thing, simple to do, that was nearly always wrong was the float level. Until that's right twiddling the screws is just an exercise in bodging.
Had a carb in a Skoda once that couldn't be tuned right. Turned out to be a faulty casting.
And with points, people didn't understand that what mattered was not the gap but the dwell. If the dwell was correct the gap didn't matter.
Last edited by: Armel Coussine on Sat 28 Sep 13 at 19:53
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I've posted this before, so, please accept my apologies for the duplication
--------------8<---------------
In the introduction to his useful book "Motor Vehicle Fuel Economy", Richard Stone describes the results of a survey reported by Atkinson & Postle (1977) where 72 vehicles were checked for compliance with their maufacturer's specifications;
83.4% incorrect mixture at idle
75.0% incorrect static ignition timing
40.6% incorrect dwell angle
29.2% incorrect valve clearances
23.6% required spark plug replacement
20.8% required contact breaker replacement
18.1% incorrect mixture strength at 2000 rpm
16.7% had excessive cylinder leakage
5.6% required air filter replacement
While many get hot under the collar about electronic engine controls, it's clear that ECU engine control, by removing many items from that list is making a significant saving overall. I admit that's a difficult point to see if you are unlucky enough to need to replace an ECU.
--------------8<---------------
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Why does a ECU break down N.C.Is it wear and tear and are some ECU'S better manufactured than others.?
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It varies Dutchie, but, there are a few common failure modes;
One of the most common is the failure of a soldered joint. The joint can fail because of poor detail in the joint design, or poor control of the automatic soldering process. The soldered joints are stressed predominantly by vibration and by thermal cycling. Fatigue cracks can initiate and grow across the soldered joint until it breaks - sometimes there's a period of intermittent failure before complete failure.
There can also be damage via electrstatic discharge - stray ignition high tension caused many failures in the erly dyas of ECU use - this problem if it exists can be much worse when poor quality aftermarket plug leads have been used.
The electrostatic discharge can cause latent damage which develops with on/off cycling - so, if a susceptible device suffered a discharge during handling or assembly, then, it can be much later in the life of the device before the fault manifests itself.
There can also be straight thermal damage, where the semiconductor junction temperature becomes too high. This can happen if the thermal conduction path is damaged - heat sink paste drying out for example - or if owing to an external fault a device inside the ECU is consistently driven harder than it should be. The drive for the electro-hydraulic actuator on KE Jetronic systems, for example, should nominally draw less than 10mA, but, if there's an external fault like an air leak, this can rise to nearer 100mA, and so the drive trnasistor runs much hotter than it should.
It shouldn't happen, but it's sadly much too common....water ingress damages many ECUs. You would think that this is the easiest thing to get right, but some manufacturers don't even take basic sealing precautions.
There are many more.
However, the good thing is that a well designed and sorted ECU is generally one of the most reliable parts in a car. Sadly many are replaced needlessly via incorrect diagnosis.
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Thanks N.C appreciate your explanation water ingress makes you think.
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>> ECU engine control, by removing many items from that list is making a significant saving overall. I admit that's a difficult point to see if you are unlucky enough to need to replace an ECU.
Don't forget hydraulic tappets. Very important innovation from this point of view. I'm surprised under 6% of air filters were clogged though. Many if not most are in my experience, and a new one always makes a difference.
Distributors.. never found two the same. You'd get the static right, then adjust the dwell and readjust the static, but when you put the strobe light on it and ran the motor up some would advance much further than others (naturally you would have made sure the vacuum retard/advance was working and lubricated the bob weight mechanism lightly).
So then you might have to set the static once more to achieve the best driving compromise. Involved lots of wheelspin starts and careful measuring of fuel consumption. Modern cars are much better in some ways of course but not nearly as much fun.
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Further to yr detailed exegesis of electronic component failure, N_C, apart from vibration, electrical surge or water damage, don't all electronic devices eventually just go pop or fade out like light bulbs?
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>>don't all electronic devices eventually
I don't know AC - I imagine that yes, eventually there will be some irreversible chemical decomposition, or the effects of thermal or electrical stress will eventually result in a failure.
My involvement has been in design to get assembled PCBs for aerospace applications through their vibration, thermal cycling, and ESD qualification tests. Getting the design right is only half of the battle, there are lots of ways that he assembly process can bite you on the backside - one which caught us was too rapid a rise in temperature during soldering which made some components with ceramic construction crack - sometimes not failing electrically straight away, but only later during vibration testing... real PITA!
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Yes AC, I think many more advance springs should have been replaced than there were.
In the Vauxhall OHC engines with the Delco distributor, it wasn't unusual to find the springs had actually snapped! An odd quirk of that design was that the springs were above the baseplate - actually directly under the rotor arm, and so were easy to check.
Under my father's guidance, after using the strobe, we used to finally set ignition timing on road test. With a warm engine, we would take the car up a local steep hill and adjust to give the maximum advance before pinking.
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Do you think one day we will end up with a sealed engine designed for a a certain time or mileage? Do you remember the Wankel engine it never took off did it N.C.
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Have you seen the Mazda RX8s for sale if you search for "non runner" on Ebay? There's usually one or two on there 2006 / 2007 up for sale for little money because the engine has no compression - there's also an enterprising garage which appears on that search offering to recondition the wankel engines.
I must confess, I've been tempted to take one on just for the fun of having the rather unusual engine apart, but, SWMBO suggests more practical tasks to keep me occupied!
In many ways, I don't tink we're too far away from the sealed engine - at least in broad concept there are engines which aren't really worth reconditioning.
Last edited by: Number_Cruncher on Sat 28 Sep 13 at 21:52
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I was having a read about The Mazda RX8,if you look at the Wankel Rotary engine it looks so simple in design.Sealing seems to be the biggest problem.Get on N.C and take it to bits tell us what you think.>;)
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>> In many ways, I don't tink we're too far away from the sealed engine -
>> at least in broad concept there are engines which aren't really worth reconditioning.
>>
The Smart is almost there.
Rings are available, pistons are not.
Many Smarts are scrapped due to engine wear.
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>>pistons are not.
That's weird ST.
There's something I need to get some more understanding of - last year, I took the cylinder off my 1400 Astra H to deal with a coolant loss problem. The engine is fine for oil consumption, but, the piston to bore clearance was huge. Had the engine been drinking oil, I wouldn't have hesitated to rebore and fit oversize pistons. However, I checked with an ex-colleague and apparently, this is normal and OK. I think this means that my view of how piston to cylinder sealing really happens and really works is due some updating...
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>> It's not that nipples can be wiped - they absolutely must be wiped clean, or
>> you're definitely doing more harm than good!
The Jowett has a centre bearing with a grease nipple, along with about 20 others on the car.
One of the few good things about Lada cars was that they had rubber caps on the brake bleed valves. In my days of buying/selling/fixing/scrapping them, I ' harvested ' a large number of these caps which fit nice and tight on the Jowett's grease and brake nipples. I still have a pot full, 20 yrs on.
Ted
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That stands a good chance of working well Ted - for an unprotected grease nipple;even with vigorous wiping; there's always going to be a ring of carp around the edge of the sealing ball that ends up being forced into the joint: your method avoids that nicely.
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How weird Ted, earlier I was remembering those rubber caps on Lada brake bleed nipples and thinking they would be just the thing to keep grot out of grease nipples.
They're a bit pointless on brake nipples really because the fluid only comes out of them. Not pointless perhaps, but hardly crucial.
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Well, Lud........the Lada designers and engineers really knew how to make fine cars and they fitted them so who am I to argue.
I grease the whole brake valve and put the rubber on to stop crap sticking to the business end and from there getting into the bleed pipe. Incidentally, Ladas had a fair amount of small bore tubing around the carb area. Made of a softish rubber, it makes excellent bleed pipes and other stuff, The vacuum advance on the Jowett originates in the Lada factory.
Getting a bit short of it now....not many Ladas to be found in scrap yards nowadays !
Ted
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I wonder if any ECUs were made with the bad batch of capacitors in around 2005-2007. Computer motherboards are generally very reliable and if they fail it is often the BIOS firmware which comes corrupted preventing the motherboard from POSTing but over the years I have seen loads of boards made in around 2006 fail due to popped capacitors because of fake Chinese ones some how ended up on the market.
I wonder if ECUs from the same era could suffer the same problem? I am pretty sure all the ECU remanufactures do is something called a reflow and also replace the capacitors. I don't think I know of a single incident from the forums where there has been an actual ECU failure. I have not actually studied a circuit diagram of an ECU but I will do tomorrow out of interest.
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I suspect it's possibly more to do with the age-old motor industry concept of planned obsolescence.
If scientists are smart enough to make an ECU that can last forever, it goes without saying that they can make one timed to go pop a month after the warranty runs out. ;-)
Cynical.... moi?
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>> If scientists are smart enough to make an ECU that can last forever, it goes without saying that they can make one timed to go pop a month after the warranty runs out. ;-)
Oh... don't be ridiculous!
What about the car's that don't get sold straight away, and may be in stock for a fair while?
It's not like the ECU's get told when the car hits the road is it?....
Ah... well, as it happens many leave the factory in 'transport mode'
Part of the PDI is to take it out of transport mode, normally done a few days before the customer collects the car.....
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Thanks for the detailed replies....begs the question why aren't propshafts run in a protective sheath though - would cut down dramatically on maintenance wouldn't it ? The shaft on my bike runs in an alloy cover...
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>> Thanks for the detailed replies....begs the question why aren't propshafts run in a protective sheath though - would cut down dramatically on maintenance wouldn't it ? The shaft on my
>> bike runs in an alloy cover...
>>
Over the years some have - and still are.
Merc SLS as an example.
Google* 'torque tube' for examples....
*other (poorer) search engines are available!
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Traditionally a torque tube is used as part of the suspension linkage for the axle, i.e., the forward pivot of the tube acts as one of the location points of the axle, so, the torque tube isn't actually there to protect the shaft.
As for improving the service life, prop shafts are, generally, much more reliable than they used to be. My father kept a wide stock of Hardy Spicer joints in, but in the latter years of him running his garage, we changed very few. This was another area where Mercedes trucks were better than the Leylands he also ran.
We did have one which failed catastrophically on the back axle of a Scammell Constructor - the flailing shaft also took out the diff casing and a lot of the air pipes and wiring between the thrird and fourth axle.
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The Jowett has two propshafts connected between the box and the diff by three Layrub couplings.
These are basically two steel discs riveted together with 4 rubber/steel inserts which the flanges on the shafts are bolted to. They're very reliable, no maintenance neede. I've only had one fail in 41 yrs of ownership and it still got me home....although a bit noisily ! I keep 2 or 3 in stock, just in case
As an aside to NC's comment about axles above, I was next to a flatbed artic yesterday with 4 axles. That's 16 wheels at the back. It didn't seem ' abnormal load ' sized, it was just carrying planks of wood. It didn't have loading ramps for plant or machinery. Are these things getting even bigger ?
Ted
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Ted, do you mean the unit or the trailer?
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HM it was the trailer.
Ted
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Unusual. I've sen a lot of STGO trailers with four axles, though most of 'em are low-loaders. Only flatbeds I've seen with more than three are the "match trucks" which accompany the big mobile cranes to site, usually carrying the counterbalance weights.
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>> >> It's not that nipples can be wiped - they absolutely must be wiped clean,
>> or
>> >> you're definitely doing more harm than good!
I was just wondering what was the last production car to have grease nipples. The Metro/Rover 100 had them on the rear radius arms.
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Hilux still got them, on both propshafts.
Not really a car though, sorry..;)
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Truck question. - Armel Coussine
