ADVICE REQUIRED...inconsistent reverse crunch! Under Warranty.

[Ricardo T]

Thank you so much for all your help so far guys...very helpful.
After my latest e-mail to the dealership regarding this they have changed their stance again and have agreed on further warranty actions.....phew, relief....also visited a transmissions specialist who acknowledged the problem as more of a gearbox issue. The whole clutch assembly has been renewed so far..plate, cover release bearing and DMF.
Fingers crossed form now on!

 

[Mooncat]

Based on your original symptoms (slight 'crunch' and the van would jolt ever so slightly) that's an input or output shaft still rotating so very unlikely to be a gearbox issue. What isn't mentioned above as being replaced is anything to do with the hydraulics that actually operate the clutch (I'm assuming the spigot bearing was replaced with the new flywheel). The master cylinder may not be retracting fully so that the reservoir orifice is open or there could be air trapped in the system which means the clutch release bearing does not get it's full travel.

Did you try what I suggested by depressing the clutch for five seconds before engaging reverse to see if there's something causing the input shaft to be spinning?

 

[Ricardo T]

Based on your original symptoms (slight 'crunch' and the van would jolt ever so slightly) that's an input or output shaft still rotating so very unlikely to be a gearbox issue. What isn't mentioned above as being replaced is anything to do with the hydraulics that actually operate the clutch (I'm assuming the spigot bearing was replaced with the new flywheel). The master cylinder may not be retracting fully so that the reservoir orifice is open or there could be air trapped in the system which means the clutch release bearing does not get it's full travel.

Did you try what I suggested by depressing the clutch for five seconds before engaging reverse to see if there's something causing the input shaft to be spinning?

Hi @Mooncat
...thank you for your input on this.(No pun intended!) The dealership have not mentioned anything to do with hydraulics at this point. They have said new release bearing but not sure about spigot bearing which is different isn't it (brass bush bearing on the end of the input shaft?)...jus tried what you said but it was cold which may/may not make a difference...seemed to be fine but ill try it later in the week too when its hot as that does seem to make a difference. The dealership are saying they will send it to a gearbox specialist under warranty so I guess they will do all these checks anyway. cheers mate.

 

[Daffy]

The cause of the issue as already said is the gearbox lay shaft is still rotating.

How it works when the van is stationary and in neutral is that the engine drives the gearbox lay shaft, when you push the clutch down you break the drive to the layshaft but the shaft has some momentum so it takes a few seconds to stop rotating - you wont get a clean selection of a non synchronised gear if it hasn’t stopped.

So if it crunches then the shaft hasn’t stopped, either because it hasn’t had time yet or because the drive isn’t properly broken (Some form of drag)

If the clutch has been replaced we can probably assume it isn’t the issue so it would be worth checking the clutch actuation (does the slave cyl have the correct throw) and is the crankshaft staying in the same place (think crank thrust bearings - crankshaft end float)

Generally selecting a forward gear first stops the shaft and it should drop in nicely, if it really does grate going into 1st then it might be worth asking the dealer to check the clutch actuation and crank end float and if these both check out push for another gearbox.

The thing is modern gearboxes are designed to have very little resistance through them as helps with overall fuel efficiency, unfortunately this creates a problem when you get a box at the lower end of the resistance tolerance.

 

[Ricardo T]

The cause of the issue as already said is the gearbox lay shaft is still rotating.

How it works when the van is stationary and in neutral is that the engine drives the gearbox lay shaft, when you push the clutch down you break the drive to the layshaft but the shaft has some momentum so it takes a few seconds to stop rotating - you wont get a clean selection of a non synchronised gear if it hasn’t stopped.

So if it crunches then the shaft hasn’t stopped, either because it hasn’t had time yet or because the drive isn’t properly broken (Some form of drag)

If the clutch has been replaced we can probably assume it isn’t the issue so it would be worth checking the clutch actuation (does the slave cyl have the correct throw) and is the crankshaft staying in the same place (think crank thrust bearings - crankshaft end float)

Generally selecting a forward gear first stops the shaft and it should drop in nicely, if it really does grate going into 1st then it might be worth asking the dealer to check the clutch actuation and crank end float and if these both check out push for another gearbox.

The thing is modern gearboxes are designed to have very little resistance through them as helps with overall fuel efficiency, unfortunately this creates a problem when you get a box at the lower end of the resistance tolerance.

Thanks @Daffy, ill re read all this thread before I take the van back next Monday for their next investigation which is changing the gearbox oil....I guess this may show up debris or maybe there's no oil in it!! Thought they would of done this already tbh, and ill ask them all these questions then in person. Would there be any other symptoms of crankshaft end float?
Thanks for your help...feels like I am getting somewhere now.

 

[Daffy]

Thanks @Daffy, ill re read all this thread before I take the van back next Monday for their next investigation which is changing the gearbox oil....I guess this may show up debris or maybe there's no oil in it!! Thought they would of done this already tbh, and ill ask them all these questions then in person. Would there be any other symptoms of crankshaft end float?
Thanks for your help...feels like I am getting somewhere now.

You wouldn’t see any other symptoms of crank end float and its very unlikely but worth checking if everything else looks normal.

Re the oil, I was going to mention that in my earlier post as new oil might help the problem, especially if it is a heavier oil that is approved for the gearbox.

 

[Mooncat]

It's probably worth correcting something before you speak to VW - these gearboxes don't have lay shafts (they are used in traditional RWD gearboxes and means the input and output shafts stay in the same axis and both rotate in the same direction for forward gears). If you still get a crunch after depresing the clutch for five seconds first, just tell them it's the input shaft that is still rotating. If waiting for five seconds removes the issue, you can either be more patient or as Daffy recommends, try filling with a heavier grade of gearbox oil (within the gearbox spec range) to provide some more internal drag.

 

[Daffy]

It's probably worth correcting something before you speak to VW - these gearboxes don't have lay shafts (they are used in traditional RWD gearboxes and means the input and output shafts stay in the same axis and both rotate in the same direction for forward gears). If you still get a crunch after depresing the clutch for five seconds first, just tell them it's the input shaft that is still rotating. If waiting for five seconds removes the issue, you can either be more patient or as Daffy recommends, try filling with a heavier grade of gearbox oil (within the gearbox spec range) to provide some more internal drag.

Thanks Mooncat, I stand corrected, the same applies to the momentum on the rotating parts though.

 

[Ricardo T]

So, finally got my Van back after having the gearbox stripped and rebuilt, the last hurdle so it seemed....drove like a dream on the short journey home, although the actual initial problem was more noticeable when moving off from stationary in reverse or first. Vw have covered all the repairs to date under the extended warranty and restored my faith in my local dealership (Ipswich) and 'the brand'. The first appointed transmission specialist was in my book a total disaster and waste of time.They had the van a good two weeks and no communication to me at all during this time. So VWVC tried a more local specialist who had a completely different attitude and approach.So they were given the authority to carry out the gearbox rebuild and their attitude and service was second to none...see 'Review A Business' in a few days time when I get time to post. (Last Transmissions, near Ipswich)
So to date, and all under warranty, the following items were replaced by VWVC;
DMF; clutch plate and cover; release bearing; gear linkage cables;

And replaced by Last Transmission;
All the synchro rings; various sleeves and bearings, supports and shafts; master and slave cylinder; plus other bits I suspect.

I suppose in hindsight a new gearbox would of sorted it but its done now and sorted.

Im happy now and we can begin enjoying the van now and see if we have room for all those goodies that we've been buying in anticipation.....maybe I need to get the suspension sorted next!!.

Can't thank Ipswich VWVC and Last Transmissions enough...thank you guys.

 

[Mooncat]

Did they confirm what the root cause actually was? From the list of parts replaced I note that the clutch master and slave cylinders were replaced so I expect that was the cause of the problem which in turn has led to the wear on the synchros as you have been changing gear whilst the inpt shaft is still being partially driven.

 

[Ricardo T]

Hi Mooncat, not as such, but you may well be right. Both transmission specialists pointed out that as there is no synchro on reverse (previously also mentioned in this post by forum members), there may be a tendency for reverse selection to 'crunch' but I thought the 'crunch' was really too excessive imho. I may of said already, the first 'transmission specialist' said unbelievably 'thats how it is' !!
I guess the guys at Last took the belt and braces approach which provided a good outcome. Drives like a new gearbox now tbh, and there is very minimal 'crunch', if none at all when selecting reverse. Cant tell you how happy I am with how it feels now this has been resolved.