Syncro 4&4 Discussion and Q&A last answered over 2 years ago.
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All a bit quiet here so just to spice things up Don't know if any of ye have been following MIke Ghia's thread on the samba but an interesting side effect of decouplers has come up which could lead to premature gearbox wear on the more torquey and powerful TDI"s. To summise Mike's 2.5 TDI has been eating gearboxes on a regular basis, which it seems can be attributed to three factors 1 a hugely torquey engine, 2 a very low ratio crown and pinion i.e. a 6.16 which traps the torque and 3 the use of a decoupler which when engaged only allows this torque to dissipate through two wheels as opposed to 4 without the decoupler.
Considering most of our vans are now running bigger more powerful engines, in the case of diesels either AAZ's, MTDI or TDI's and petrols subaru's which apart from the AAZ's would have a greater torque than a 2.1 waterboxer it got me wondering whether running a decoupler would lead to a shortened gearbox life, maybe not as dramatic as MG's but still having some effect? Also in the case of guys running 16's would this effect be increased? Also could this be the reason why VW scrapped the decoupler ? Regards to the decoupler debate personally I don't see the point unless your running a solid shaft (which then doesn't really make it a Syncro IMHO) although I know others would disagree, I put my money into a VC and it's been fit and forget
You have forgot another major factor in his gearbox failure. He is towing a trailer with vans on it.
The decoupler is not the cause to his failure but the combination of excessive torque and far to low gear ratios.
Another question that can be raised on this is are his gearboxes being built correctly.
There are only 2 reasons for premature gearbox failure: incorrect use or incorrect assembly.
Russel
Russel at Syncro-Nutz wrote:
There are only 2 reasons for premature gearbox failure: incorrect use or incorrect assembly.
Russel
Incorrect use also includes fitting a decoupler .......... not designed for them!!
Russel at Syncro-Nutz wrote:You have forgot another major factor in his gearbox failure. He is towing a trailer with vans on it.
Russel
As long as he is within the rated towing weights this cannot be considered a major factor in gearbox failure as the vehicle is designed to cope with these weights.
Ooooooohhh I love this subject ......... Genuine spare wheel carriers and gearbox oil are two more subjects I love !!
I seem to remember that VW built one or two transporters without 4wd, the weakest link in the syncro is the gearbox, not the wbx. The DJ represents the most power that VW thought you could stick through a standard gearbox.
I take my coat off when it's sunny and warm, and in the same way only use 4wd when needed.
The perfect solution is a new VC and a decoupler imho.
Anyway if your beloved VC is working right then the van is 95% rear wheel drive on the road, and the Americans with high torque engines seem to use solid shaft to properly distribute the torque to the front, giving the rear permanently connected ring and pinion a rest. Land Rover experimented with very slightly different axle ratios to make the freelanders VC work, and the T4's VC was made much softer than a T3's so it did not bind on corners.
I did notice that Mike was working very hard today to make the 4x4 course work, so my hat is off to him.
If you want more power and economy than a DJ or AAZ thing then just go and get a T4 or 5, it would save you money in the long run.
No I'm not dead was just MIA in London sorry Russell I hate to disagree but towing a trailer with a lightweight on it would not wreck ones gearbox it may have been the straw that broke the camels back ! Back to my original point which was how that a decoupler inconjuction with an uprated torquier engine would affect the longevity of ones gearbox. From what I can accertain the 2.5 TDI's seem to wear boxes albeit a bit more slowly so following on from this a tuned 1.9 TDI or subura would start moving into that territory with a decoupler in the mix this would surely accelerate that process ?
syncrosimon wrote:I seem to remember that VW built one or two transporters without 4wd, the weakest link in the syncro is the gearbox, not the wbx. The DJ represents the most power that VW thought you could stick through a standard gearbox.
I take my coat off when it's sunny and warm, and in the same way only use 4wd when needed.
The perfect solution is a new VC and a decoupler imho.
Anyway if your beloved VC is working right then the van is 95% rear wheel drive on the road, and the Americans with high torque engines seem to use solid shaft to properly distribute the torque to the front, giving the rear permanently connected ring and pinion a rest. Land Rover experimented with very slightly different axle ratios to make the freelanders VC work, and the T4's VC was made much softer than a T3's so it did not bind on corners.
I did notice that Mike was working very hard today to make the 4x4 course work, so my hat is off to him.
If you want more power and economy than a DJ or AAZ thing then just go and get a T4 or 5, it would save you money in the long run.
Regular as always Simon Actually I said before 8pm so you are actually 2 minutes early... If only decouplers were so reliable
syncrosimon wrote:
The perfect solution is a new VC and a decoupler imho.
VW didnt think so and they make cars .... in fact they dumped decouplers very early on and then dumped the VC in favour of a Haldex as did Land Rover (Freelander2) amongst others
syncrosimon wrote:
I take my coat off when it's sunny and warm, and in the same way only use 4wd when needed.
Same as everyone else except we dont have to worry about the decoupler not coupling ......
The syncro would be better off with an open lockable center diff, which in normal conditions would split the torque 50/50 to the front and rear. That would save the rear gearbox. (non standard engines)
syncrosimon wrote:The syncro would be better off with an open lockable center diff, which in normal conditions would split the torque 50/50 to the front and rear. That would save the rear gearbox. (non standard engines)
Correct and one wonders why they didnt do that instead
He tows car trailers with T3's on them of which the combined weight is beyond the recommended and legal towing weight of a T3. Combined this with the gear ratios [ final drive] , tire size and engine torque it is a no brainer that it will eat gearboxes. The decoupler is not the issue here. If he were running a stiff VC his box may last a little longer as spreading the torque but a fully functual VC wont make a difference.
Russel
jed the spread wrote:.Regular as always Simon Actually I said before 8pm so you are actually 2 minutes early... ....
Hi Simon, was also wondering when you would haul along, good to have the "experience" picture ......thought we might have seen you at the latest TRF day near M'hampstead a few sundays ago.......brilliant day/track!
14" MV Syncro Caravelle aspiring to a Westy.
16" 1.9TD Syncro Crew Cab
...and for the really narrow lanes; Honda XR250 and CRF 230.
Join the TRF......help keep the lanes open!
The heaviest Syncro is a high roof Joker weighing in at 1850 kgs and the maximum stated towing limit on a Syncro is 2500kgs as specified in the owners handbook and a trailer to carry that should weigh around 700kgs or so, so he is within the limit - just
Anyway, de coupler or not, the torque at the rear wheels on Mike's Syncro must be huge and well past the design limit of the transmission and Im not suprised that he has tranny issues as almost all the torque is going through the rear wheels. Its not until conditions allow the VC to kick in does the torque get distributed to all four wheels. I fail to see how a de coupler can lead to premature gearbox wear on the more torquey and powerful TDI's. It can lead to other things like being stuck in a muddy place in 2WD and denial on wasting money .....
It is said that you can't really do more than 120BHP on a Syncro box but there is no mention of a torque figure and its torque that will shread a gearbox not power!
For those of you who dont know the difference between HORSEPOWER and TORQUE read on ......
Horsepower is how fast you hit the wall and torque is how far you take the wall with you.......... simple really
Don't know if any of ye have been following MIke Ghia's thread on the samba but an interesting side effect of decouplers has come up which could lead to premature gearbox wear on the more torquey and powerful TDI"s. To summise Mike's 2.5 TDI has been eating gearboxes on a regular basis, which it seems can be attributed to three factors 1 a hugely torquey engine, 2 a very low ratio crown and pinion i.e. a 6.16 which traps the torque and 3 the use of a decoupler which when engaged only allows this torque to dissipate through two wheels as opposed to 4 without the decoupler. 
sorry Russell I hate to disagree but towing a trailer with a lightweight on it would not wreck ones gearbox it may have been the straw that broke the camels back ! Back to my original point which was how that a decoupler inconjuction with an uprated torquier engine would affect the longevity of ones gearbox. From what I can accertain the 2.5 TDI's seem to wear boxes albeit a bit more slowly so following on from this a tuned 1.9 TDI or subura would start moving into that territory with a decoupler in the mix this would surely accelerate that process ?
Actually I said before 8pm so you are actually 2 minutes early... If only decouplers were so reliable 