Urgent help / advice needed please from experienced mechanics

tacr2man said:
Just looked at your video , the problem has to be in the gearbox, and would seem to be a clutch or band partly locking instead of
clear running . It could be down to a leaky solenoid valve allowing partial operation until pressure builds up as it looks like a hydraulic cycling type of fault . You need a diagnostic plug in and look at line pressures readings at idle to see where you are getting a rise and fall . The prop is just showing a wind up in diff, and then the release . I would go to a Auto box specialist , I have dealt with these and found them very helpful http://www.theautomaticgearboxcompany.co.uk/
another specialist is http://vmtp-midlands.co.uk/workshop/
have had a couple of good reports from landrover forum .
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Thanks, I'll get in touch with them.

Agree fully with your reasoning, but, all valves and solenoids have now been changed with an entire new replacement gearbox. Mercedes even claim to have removed and checked the new gearbox when they fitted a second new torque converter. Symptoms are exactly the same as with the original. It's difficult to see how the same fault can appear with new components and I've already paid massive amounts for diagnosis and labour charges hence grasping at straws for a different solution rather than repeating the same checks that have now been done so many times.
 
im probably should keep my nose out and leave it to someone who knows but surely the propshaft shouldnt have that much movement when standing still, in your video its obviously catching up all the while, with nothing on the end of it but the diff, no more torque converters or gears they have all done their job , its in the last t6hird of the train where all the movement is.
just saying
 
The bigger the diff generally the more backlash as expansion causes it to reduce, and you dont want too much preload .
@Parapilot The other thing with electrical solenoids is that its not only seals but electrical problems that can cause the leaks . This is where the live diagnostic hook up is important , to read values from sensors and also activation. I have had problem with a jatco box where it pointed at a solenoid , and I replaced , it turned out to be a intermittent break in a wire inside a harness where it went thru a sealing grommet . It took some finding as it was affected by engaging gear and movement of engine , at idle in park all diagnostics checked out within values. :cry::)
 
Long shot but could duff engine mounts create the problem described? Found this on a car once after eliminating everything else.
 
I'm going to go out on a limb here.

Although I dont have any experience of the Mercedes 'box, I do on its sister, the Chrysler NAG1 mentioned in the posted wiki link. With this, there are two known faults that could cause a similar problem. First is the fluid. Wrong type, or even a bit of water in it will cause the problems. There is a specified flushing procedure that cures it. Note that this also includes flushing the converter.

Second fault, and the most likely is the converter lock up. Quite often, they dont lock properly, even though a diagnosis does not show any fault. Although converters "look" the same, they cannot be exchanged for the original one.

My guess, but again referring to the NAG1, is that the fluid got contaminated, was not flushed correctly, then the original converter exchanged for an incorrect one. Thus the fault under light load.

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I know nothing about this but have enjoyed the thread and hope you find a resolution soon.
 
Excessive diff backlash or half's haft splines badly worn.
There should never be that much backlash in a diff.
 
pappajohn said:
Excessive diff backlash or half's haft splines badly worn.
There should never be that much backlash in a diff.
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my thoughts entirely, which i have mentioned twice but no one seems to agree:unsure:(n) doesnt matter whats going on up front there shouldnt be all that movement, its bound to knock and crash evertime it catchs up.
 
If it was excessive backlash, then I would have expected a whine that was always present. The OP mentioned that it was a heavy duty diff. That amount of movement would be reasonably normal in a lorry diff.

One thing that I did notice in the video though was that on one or two occasions, the rear prop shaft moved excessively forward. That could possibly point to incorrect assembly. It might be a good idea to remove the propshaft, unload the wheels, and check if the diff flange could be moved fore and aft.
 
Flatlander said:
I'm going to go out on a limb here.

Although I dont have any experience of the Mercedes 'box, I do on its sister, the Chrysler NAG1 mentioned in the posted wiki link. With this, there are two known faults that could cause a similar problem. First is the fluid. Wrong type, or even a bit of water in it will cause the problems. There is a specified flushing procedure that cures it. Note that this also includes flushing the converter.

Second fault, and the most likely is the converter lock up. Quite often, they dont lock properly, even though a diagnosis does not show any fault. Although converters "look" the same, they cannot be exchanged for the original one.

My guess, but again referring to the NAG1, is that the fluid got contaminated, was not flushed correctly, then the original converter exchanged for an incorrect one. Thus the fault under light load.
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Water in transmission fluid is easy to see the fluid turns a milky pink colour, and torque converter lock up normally does not occur until around 50 mph the op said he has the problem at low speeds too.

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Can't say I have much knowledge regarding this type of box and this vehicle . What I can tell you is that I always moved problems of this sort to a company in Kettering and Northampton called Midland Automatics. Very experienced, very knowledgable and very helpful. Sorry have limited internet here and can't bring up a link. They are well worth speaking to.
 
The fluid problem is mentioned here. From the sounds of it, its exactly like the NAG1 I mentioned.
 
no knoledge on this subject at all but reading the thread you say this set up is common in usa have you considered emailing the original post to some US dealers to see if you get any feed back most people like a conundrum regarding their trade and you never know they may have had similar
 
Wow, feel for you, that's a lot of money.

We had the exact same van, Hymer S820 6 tonne, uprated to 6.4 tonne(And used every ounce of it plus a bit more) full auto same as you and never had a seconds trouble with it, lovely and smooth under all conditions. A little short on BHP running at full weight, struggled on anything other than flat or downhill.

Did it have a good service record when you bought it, did you buy private or from a dealer?

Sorry can't help with your problem just to say they are a generally very reliable unit.

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Flatlander said:
If it was excessive backlash, then I would have expected a whine that was always present. The OP mentioned that it was a heavy duty diff. That amount of movement would be reasonably normal in a lorry diff.

One thing that I did notice in the video though was that on one or two occasions, the rear prop shaft moved excessively forward. That could possibly point to incorrect assembly. It might be a good idea to remove the propshaft, unload the wheels, and check if the diff flange could be moved fore and aft.
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Him indoors said exactly the same. He was a truck mechanic back in the day
 
It would help diagnostics if you could force the fault effect to be better or worse. Having watched your video ad nauseum and re-read this thread I lean towards prop, prop spline (l too think that spline play is excessive), or prop centre bearing issues. It may even be a rogue resonance. If you can do so try moving the centre bearing vertically by removing the spacer to see what effect it has.
 
@Flatlander - thanks for the link but definitely not fluid contamination. It's been flushed and changed at least 5 times now with correct MB spec at €20 per litre, and 8 litres a time !!! Filters, torque converter and gearbox changed with new fluid as well.
The occasional kick through the prop worries me too as I've no idea what causes it. I've stripped and reassembled the prop myself with new centre bearing, and it's been off at least another half dozen times to be checked or reassembled by 'specialists'. They can't find any fault on balance machines spinning up to 11,000 rpm.

@tonyidle - that's basically what MB said they would ask me to do if it was under warranty .... thrash it until something breaks, because only then can their dim wits diagnose what's wrong ! ;)
 
CazPaul said:
We had the exact same van, Hymer S820 6 tonne, uprated to 6.4 tonne(And used every ounce of it plus a bit more) full auto same as you and never had a seconds trouble with it, lovely and smooth under all conditions. A little short on BHP running at full weight, struggled on anything other than flat or downhill.

Did it have a good service record when you bought it, did you buy private or from a dealer?

Sorry can't help with your problem just to say they are a generally very reliable unit.
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Good to hear from another owner ! (y)

I bought it privately (from this forum). It's had 4 previous owners and service history is incomplete, but I had faith in Mercedes Benz being reliable or at least repairable if there was ever a problem.
Mine is also uprated to 6.4 ton (weighs 5.2 empty) and I've always been amazed how much torque the small 2.7 engine produces. It's not fast and does slow down on hills, but has no problem overtaking all the struggling HGV's, even in the Alps and Pyrenees where I've accidentally taken it up 1:6 mountain passes with over 6000 feet height gain. It's pulled a few big motorhomes off wet fields and grassy slopes as well !

I love it apart from this nightmare problem and plan on keeping it for a while - if it can be fixed !!
 
Parapilot said:
@Flatlander - thanks for the link but definitely not fluid contamination. It's been flushed and changed at least 5 times now with correct MB spec at €20 per litre, and 8 litres a time !!! Filters, torque converter and gearbox changed with new fluid as well.
The occasional kick through the prop worries me too as I've no idea what causes it. I've stripped and reassembled the prop myself with new centre bearing, and it's been off at least another half dozen times to be checked or reassembled by 'specialists'. They can't find any fault on balance machines spinning up to 11,000 rpm.

@tonyidle - that's basically what MB said they would ask me to do if it was under warranty .... thrash it until something breaks, because only then can their dim wits diagnose what's wrong ! ;)
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Not quite what l meant but it might provide more information. If there is some sort of interation between the prop, its splines, and the centre bearing, a simple alteration might change things enough to shift the speed at which it occurs, make it worse, make it better, or have no effect. Either one of which might help diagnosis. I did notice that the UJs appeared to be in line and in line with the prop and gearbox - not a condition recommended for UJs.

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As has been mentioned before revrear axle.
I had a P100 pick up 4x4 conversion with a lsd rear axle in it.
The previous owner put the wrong oil and n the axle and it sounded terrible on tight turns.
Put the correct oil in and it was spot on.

Did the new diff come assembled to the front half of the casing
If not might be worth checking that’s set up correctly.
Most technicians these days wouldn’t have a clue about rear axles and nailing them together.
 
tonyidle said:
Or anything really :D2.
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Unfortunately also true :rolleyes:

Prop looks good to me and if outbof ballance would be jumping all over the shop.

Slightly left field has the tolerance on the drive shafts been checked and the length of them along with the bearings?
 
tonyidle said:
Not quite what l meant but it might provide more information. If there is some sort of interation between the prop, its splines, and the centre bearing, a simple alteration might change things enough to shift the speed at which it occurs, make it worse, make it better, or have no effect. Either one of which might help diagnosis. I did notice that the UJs appeared to be in line and in line with the prop and gearbox - not a condition recommended for UJs.
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Yes, it has been noted that the prop runs straight so well spotted.
I had the full prop assembly checked last year at A1 Propshafts in Liverpool.
Mercedes has removed and checked the prop numerous times.
Truck Transmissions in Blackburn checked it last month and commented on the centre position of the UJ's being 'slightly notchy' due to it running straight. (I have felt this myself and asked all of them, about it). Only one of the mechanics there thought it was worth replacing UJ's - the boss said they were fine.
Mercedes checked it again last week.
I told them I still wasn't happy so it was sent to http://www.firowpropshafts.co.uk/ who make them for Mercedes - they said it was all perfectly OK.

So what do I do ??
Merc have already replaced lots of expensive parts that were unnecessary and did not cure the fault. Do I add to that by changing more parts that 'the professionals' tell me are OK ?
I might try removing the spacer on the centre bearing as you suggest - just to see if it makes things much worse or better.
 
Silver-Fox said:
Did the new diff come assembled to the front half of the casing
If not might be worth checking that’s set up correctly.
Most technicians these days wouldn’t have a clue about rear axles and nailing them together.
Click to expand...

Agree about the "technicians" (fitters) at Mercedes. They had to send it to Truck Transmissions in Blackburn to rebuild and set up the axle !
I saw my old one in a box and it looked like a complete assembly (part number on website just says "differential") but on my axle it looks like it fits inside from the rear:

upload_2018-6-2_9-24-12.png
upload_2018-6-2_9-24-45.png

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OK silly idea here, can you disconnect the prop shaft and run it through the gears or does the ECU need to see road speed to do that.

Martin
 
A common transmission noise on early JCB 3cx machines was partially cured by drilling small holes in the prop tube and filling with builders expanding foam. The noise was so bad the driver had to wear ear defenders in the cab. I know your van is not an excavator but the machine had exactly your type of set up. Engine, torque converter, transmission and prop.
 

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@Parapilot where the diff bolts through the casing is critical to a properly functioning diff.

It looks strange when the prop floated so much in the horizontal plane as it didn’t look like you were going over big bumps in the road.
The prop is meant to float to allow for axle and engine movement but yours looked odd.
Unless it was an optical allusion.

Has the axle casing been inspected particularly where the diff bolts through.
If the front face and rear face run out that would cause issues as you wouldn’t get the correct readings when assembling the diff.
 
Ive had similar issues before, not with Motorhomes though, where “chatter” occurred at very light throttle, and it was the rear diff.

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