Urgent help / advice needed please from experienced mechanics

[Parapilot]

I purchased a Hymer S820 motorhome 2 years ago (from a Funster) which is based on a 2003 Mercedes Sprinter 616 chassis, with 2.7 diesel engine and 5 speed full automatic gearbox (722.6 type). Most components are uprated from standard Sprinter, including the axle which is from a Vario truck, with air parking brakes.

There was the occasional slight rumble / vibration between gear shifts when I bought it, but barely audible above the other squeaks and rattles. I was told it was 'normal' and had no reason to disbelieve it as everything about this 6 ton HGV drove more like a truck than any smaller motorhome I had owned.

Noise and vibration got significantly worse last year during a trip around Europe, causing very hard gear shifts, often with a heavy thump at low speeds changing down from 3 - 2 - 1 gears and sometimes with a dragging, grinding, metallic vibration in 1st or 2nd.

Mercedes sent me to numerous dealers (approx 13) in 9 different countries (a long story for another thread) and it has been in 3 UK dealerships since March.

Numerous transmission fluid changes have been carried out, with test drives, diagnostics and adaptive resets at most dealers. Valve body and conductor plate swapped. 2 brand new torque converters have been fitted with solenoids etc, plus a heavy duty drive plate. A complete brand new gearbox has been fitted, plus a new rear axle differential. The 3 piece propshaft was my initial suspicion, but this has been removed and tested by 3 independent specialists (as well as Mercedes) who all say it is balanced and the universal joints and carrier bearings are all good and do not require replacement.

That is every mechanical component in the transmission replaced, from flywheel back. Nothing has made the slightest bit of difference and Mercedes don't know what to do....

I made a video which shows play and clanging noise when taking up drive from neutral (parked), and the second half of the video shows the other noises, plus occasional sharp 'kicks' through the propshaft.

Video here:

Problems occur when the transmission is 'unloaded' - ie neither accelerating under power or decelerating, but coasting with very light throttle matching the engine speed to the wheels. Basically how you have to drive through towns or in heavy motorway traffic tailbacks. The hard gear changes seem to be a symptom of this, as the auto box tries to match the engine speed without load when slowing and changing down gears.

Any advice or recommendations gratefully received as I can't understand why Mercedes can't diagnose or fix a fault that is this obvious .....

 

[two]

Full marks for possibly the best description of a fault I’ve ever seen.

Unfortunately, that’s about as much as I can say.

Hope others can be more helpful.

At least you don’t need a horn!

 

[JeanLuc]

I occasionally hear and feel a ‘grumble’ from ours when pulling away, fully loaded on light throttle. The engine and gearbox are identical to yours but the chassis is a 316. I too have had fluid changed and consulted a knowledgeable chap at the Oxford Merc truck dealership. He suggested it might be an indication of torque converter wear but could find no problem. I mentioned something that I had previously found on USA Sprinter forums and he agreed that it might be the cause.
I believe that the same drive train was used on Chrysler Sprinter vans in the early 2000s when the companies were linked, although I have never found any reference to the matter on a U.K. forum.
Basically, the box has a low speed auto lock-up to limit torque converter slip. This is designed to minimise fuel consumption and reduce wear on the box. It is operated by a pump that is controlled by some kind of valve and the system can, in certain circumstances, cycle very quickly. The resulting ‘grumble’ is referred to on the USA websites as ‘rumble strip noise’. If you drive like a delivery man, which is how most Sprinters are driven, the problem rarely, if ever occurs. But if you are coasting or accelerating very gently on a light throttle, it can appear. Since mine is most noticeable when the van is fully loaded (it’s a B630), I suspect the weight of an S820 would make the problem much more noticeable.
I find that the ‘grumble’ can be cleared by easing off then reapplying power with a slightly heavier right foot!
Hope this offers some light, but then again it might not be relevant; I am no auto-engineering expert.

 

[funflair]

Do these gearboxes still use a Vacuum connection as part of the control? I'm thinking back to our old W123 series days with auto box.

Martin

 

[Steve and Denise]

The diff has a fair amount of back lash could it be the noise coming back up the rear prop as you say it is a metallic sound.
We had a new steering rack fitted to a 2 year old 28,000 mile car by Mercedes only to have another one fitted a week later.

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[Robin McHood]

I occasionally hear and feel a ‘grumble’ from ours when pulling away, fully loaded on light throttle. The engine and gearbox are identical to yours but the chassis is a 316. I too have had fluid changed and consulted a knowledgeable chap at the Oxford Merc truck dealership. He suggested it might be an indication of torque converter wear but could find no problem. I mentioned something that I had previously found on USA Sprinter forums and he agreed that it might be the cause.
I believe that the same drive train was used on Chrysler Sprinter vans in the early 2000s when the companies were linked, although I have never found any reference to the matter on a U.K. forum.
Basically, the box has a low speed auto lock-up to limit torque converter slip. This is designed to minimise fuel consumption and reduce wear on the box. It is operated by a pump that is controlled by some kind of valve and the system can, in certain circumstances, cycle very quickly. The resulting ‘grumble’ is referred to on the USA websites as ‘rumble strip noise’. If you drive like a delivery man, which is how most Sprinters are driven, the problem rarely, if ever occurs. But if you are coasting or accelerating very gently on a light throttle, it can appear. Since mine is most noticeable when the van is fully loaded (it’s a B630), I suspect the weight of an S820 would make the problem much more noticeable.
I find that the ‘grumble’ can be cleared by easing off then reapplying power with a slightly heavier right foot!
Hope this offers some light, but then again it might not be relevant; I am no auto-engineering expert.

This is similar to an effct we get on our 2006 Sprinter based mh, I too noted that if I eased off and then reapply accelerator the rumble disappears, howevre this is nowhere near the sort of effect the op is reporting. In our case its most noticeable when accelerating uphill and is as if the auto hasn't done a change-down. Interesting,y it never occurs when im using the cruise control to accelerate.

 

[JeanLuc]

This is similar to an effct we get on our 2006 Sprinter based mh, I too noted that if I eased off and then reapply accelerator the rumble disappears, howevre this is nowhere near the sort of effect the op is reporting. In our case its most noticeable when accelerating uphill and is as if the auto hasn't done a change-down. Interesting,y it never occurs when im using the cruise control to accelerate.

I realised it was probably different from the op’s major issue but thought it worth reporting as he mentioned “slight rumble/vibration between gear shifts”.
Regarding your experience and the absence of ‘rumble strip noise’ when accelerating under cruise control, I imagine that is because the system tries to get you back up to the set speed quickly and is therefore using more throttle than you or I might use.

 

[WSandME]

I had similar but not identical problem / symptoms. To cut a long story short, after checking gearbox, replacing UJs the differential was found to be at fault. A fault in the case hardening caused the gears to almost disintegrate. Specialist said had the diff been on a commercial vehicle, the fault would have shown up well within the warranty period. As on a MH, no warranty after 50k miles and ten years
Took another trip to specialist to properly pre-load the diff bearings but after that all good.

 

[chaser]

well if the op hadnt said he had had a new diff, its the most obvious thing in his video.

 

[funflair]

well if the op hadnt said he had had a new diff, its the most obvious thing in his video.

I don't see how an issue with the diff would affect the gear change on an auto box.

Martin

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[tacr2man]

Had a similar "vibration" on a LDV minibus , when driven with passengers (very gently) especially with early change up . When driven empty on way back almost nothing . I suspected prop Ujs first , then balance . In the end fitted another rear axle . problem solved
it was the diff !
having said all that I would suspect auto trans prob , Have you tried with another propshaft rather than relying on it being "checked" as OK . The difficulty would be finding one to borrow .

 

[Parapilot]

@JeanLuc - you are mostly correct (I've also had to do a lot of research on this) and from what I understand the torque converter should be fully locked up at high speeds in higher gears but allow some slip (like a clutch) at lower speeds to keep things smooth. All controlled by a PWM solenoid (pulse width modulation) electronically from the gearbox ECU to control the hydraulic pressure in the torque converter. I've read a lot of internet posts about the 'rumble strip noise' effect as that is how it seemed to start initially. Complicated stuff that I've raised several times with Mercedes but they reckon it wouldn't occur with 3 torque converters (original plus 2 new ones) and solenoids.

As you say, the problem can be partly avoided by driving like it was stolen - heavy acceleration then completely off the throttle to decelerate. Unfortunately this is no good for towns, traffic jams and low speed driving. Also no good for fuel economy or other components that prefer gentle driving.

@SteveandDenise - yes the original diff had excessive backlash. Now got a new one (cost £1650 + VAT + Labour). Still seems a lot of play to me but apparently all within tolerance now and the half-shafts, bearings, gear teeth etc are supposedly in great condition with virtually no wear.

@funflair - no vacuum on the 5 speed (unlike earlier 4 speed auto box)


Thanks for the feedback so far - proves what a great forum this is ! All very logical and exactly the things I initially suspected. Problem is they have all either been replaced or removed and examined several times already, so Mercedes are stumped by it ....

 

[Parapilot]

I don't see how an issue with the diff would affect the gear change on an auto box.
Martin

I didn't at first, but apparently the excessive backlash can affect the internal speed sensors in the gearbox. As @tacr2man says, Mercedes were sure a new diff would cure the problem but sadly in my case it hasn't made the slightest bit of difference (no pun intended).

 

[tacr2man]

Is it still the same ECU controlling new gearbox ?

 

[Parapilot]

If anyone has had similar issues resolved (even if not identical) I'd be interested in garage recommendations. Even if they are not local they might be able to look at the video and see something with trained eyes that Mercedes have missed.

The Mercedes dealerships are all essentially franchised 'fitters' rather than qualified mechanics. They can replace parts but can't actually repair anything (or correctly diagnose it, despite their extensively equipped workshops).

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[Parapilot]

Is it still the same ECU controlling new gearbox ?

Yes, it is one thing that hasn't been changed yet .... They have read all the data from it and can't find a fault. Also the vibration and noises occur when it is in gear (not changing) but under light load / throttle, so I'm not sure how the ECU could cause that ? The harsh gear changes now seem to me to be more of a secondary symptom - from some other fault or play that shows up when the gearbox removes the load and tries to match speed when shifting ?

 

[tacr2man]

Is it a ZF autobox ? if yes then a auto gearbox specialist may be the way to go with particular attention to the pwm on the TCLU .
It doesnt need much of a initial vibration to find harmonics and magnify . you can get problems with a software that doesnt show up as a specific fault code.

 

[Parapilot]

Is it a ZF autobox ?

It's a 5G-Tronic (722.6) auto box - https://en.wikipedia.org/wiki/Mercedes-Benz_5G-Tronic_transmission

Fitted to millions of vehicles - AMG, CLK, W-series and others. Mine is virtually identical to the car versions but with beefed up internal gears, friction bands, clutches etc. Not very popular in Europe which favoured manual and sprintshift varieties, but very common in the North American market for all the Dodge varieties.

The axle is also beefed up from standard Sprinter - mine has the 7.5 ton Vario truck axle, designed for heavy commercial abuse. Shouldn't be worn out from gentle 5 ton motorhome use at relatively low 70k mileage.

All very frustrating. 10 months of going around dealerships at a cost of almost £10,000 ..... and still exactly the same as before !

 

[Lofty1]

This might sound daft but has the engine damper been checked ? on heavy vehicles a damaged or faulty damper can cause a thump or rattle on gear change or easing the throttle

 

[funflair]

It's a 5G-Tronic (722.6) auto box - https://en.wikipedia.org/wiki/Mercedes-Benz_5G-Tronic_transmission

Fitted to millions of vehicles - AMG, CLK, W-series and others. Mine is virtually identical to the car versions but with beefed up internal gears, friction bands, clutches etc. Not very popular in Europe which favoured manual and sprintshift varieties, but very common in the North American market for all the Dodge varieties.

The axle is also beefed up from standard Sprinter - mine has the 7.5 ton Vario truck axle, designed for heavy commercial abuse. Shouldn't be worn out from gentle 5 ton motorhome use at relatively low 70k mileage.

All very frustrating. 10 months of going around dealerships at a cost of almost £10,000 ..... and still exactly the same as before !

Wow I didn’t like to ask but thought “this sounds expensive”

Martin

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[bjandlin]

Long shot & maybe not relevent but years ago,mk 2 Escort days, we had one making odd noises from the transmission. Under warranty Ford made various suggestions. We changed clutch, gearbox & even complete rear axle along with springs, all to no avail. As a last resort I changed the diff oil for lsd oil.
Problem solved!
As you've changed so much & not cured the problem it suggests as Sods law prevails there will be a simple solution somewhere. Good luck.

 

[Parapilot]

This might sound daft but has the engine damper been checked ? on heavy vehicles a damaged or faulty damper can cause a thump or rattle on gear change or easing the throttle

I don't know if it has one or not. Just looked it up and there is a 'harmonic balancer' at the front.
Doesn't seem too likely as it idles and revs smoothly (for a diesel), but will add it to my list of things to check....

 

[Steve N Tracy]

Has anybody checked the engine crankshaft for wear on the crankshaft thrust bearings? easy enough to do just lever the bottom pulley back and the forwards with a lever, if to much play it could cause a thump as the torque converter drive engagement for the transmission pump moves back and forth.

 

[Lofty1]

I don't know if it has one or not. Just looked it up and there is a 'harmonic balancer' at the front.
Doesn't seem too likely as it idles and revs smoothly (for a diesel), but will add it to my list of things to check....

yes that is the damper ,some are soft wax filled others seem to be internaly like a mini flywheel they only work when the engine has been underload for some time

 

[SpeedyDux]

This may sound daft and I am no expert, but in your excellent video the amount of fore-and-aft movement of the back section of the propshaft looks possibly significant. I have no idea if that movement is in or out of tolerance, but I would get the rear suspension looked at in case (say) worn bushes are resulting in back axle movement which in turn affects the propshaft.

Sometimes noises can be deceptive. I had a knocking noise on roundabouts which was badly misdiagnosed by the Van Centre numpties as an expensive-to-replace suspension problem until an independent garage figured out that it was a cracked ABS ring which is a cheap replacement item.

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[Wildbill]

Is the diff new or reconstruction or used part
Bill

 

[tacr2man]

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 .

There is definitely way too much drive torque being put thru to wind the diff up that much

 

[Wildbill]

Is the diff new or reconstruction or used part?
Bill

 

[Parapilot]

Is the diff new or reconstruction or used part?
Bill

New from Mercedes, Germany (but may be a factory remanufactured part as this is not a current production vehicle)

 

[Robin McHood]

I realised it was probably different from the op’s major issue but thought it worth reporting as he mentioned “slight rumble/vibration between gear shifts”.
Regarding your experience and the absence of ‘rumble strip noise’ when accelerating under cruise control, I imagine that is because the system tries to get you back up to the set speed quickly and is therefore using more throttle than you or I might use.

Yes, sorry didnt intend implying you didnt think it was different, more agreeing with you that I get a similar noise under certain conditions. I suppose these could be mild versions of the ops problem though I'm really surprised none of the MB mechs who have already worked on it have come up with an answer. Must have cost a fortune so far!

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