Tyres/Diff problems

[Terry0clare]

I took delivery of my N reg 4x4 bongo on the 13th August and since then I've had major problems with the front diff. It's had the unit rebuilt twice and the 2 days ago the unit was completely replaced by a new one. On the way home from the garage it developed the same whining noise and. when I stopped, I found oil and smoke belching out of it. The dealer now thinks the front tyres are wrong (195/65s on the front and 215/65 on the back). So far I've driven it three days in 4 weeks, mainly back and forth to the garage. If it's not the tyres, can anyone the what else think it could be?
Rapidly loosing faith in bongos and the garage.
Terry[/b]

[Dave up north]

Is it from a Bongo dealer?

Surely this will all be sorted under warranty.

Dont worry. Once you have it sorted, you will be on your way.

Sorry I cant help more with the problem. Tyre size shouldnt make that much of an impact. Sound like another duff diff to me, or incorrectly fitted.

Some of our resident experts will be of more help. They are usually about in the evening, so check back at bed time.

Hope it all goes ok though mate.

All the best,

Dave

[parabat2]

Your viscous coupling has seized, causing wind-up, which rapidly destroys the front diff - at least it did on mine.

See this thread:

http://www.igmaynard.co.uk/bongo/forum/ ... php?t=3749

[Dave up north]

Fantastic reply Tony.
Job should be straight forward then.

[Veg_Ian]

So are you saying then that Mazda are wrong to specify different tyre sizes front and rear on a 4WD Bongo and that we should fit 215s all round?

[parabat2]

(195/65s on the front and 215/65 on the back).

Front tyre size should be 195/70. If the ones fitted are 195/65, then this may be the cause of your problems, as the will have a different rolling circumference to the 215/65s on the rear, which may cause the viscous coupler to lock up.

There are lots and lots of threads on tyre sizes.

[Terry0clare]

No Ian, it's the aspect ratio thats wrong, however, I have been reading up on viscous couplings and I think this is more likely
TC

[David Edwards]

Terry how long are you going to give em, clearly this motor is not fit for its sale purpose under the sale of goods act. I would either ask for a replacement vehicle, which is your right under the law, OR...hit em for lots of goodies when it is fixed, including an extended warranty, the last thing you want is it going again 2 days after the warranty runs out. Good luck, happy motoring.

[Terry0clare]

I am getting close to losing patience with the dealer but I know he's trying hard to get it sorted. This morning I let him know I was looking for my money back so he promised to get it right this time. I'm now giving him one last chance (I'm still not sure he's barking up the right tree though)

[maddy06]

Terry.....Can i refer you to myURGENT HELP FOR VIRGIN BONGO BOY THREAD.I to am losing faith.If you finally discover what the problem is could you post back,because my garage is still at a loss to explain what the problem is with mine.Bought privately end of July.Have clocked up barely 200 miles.Does anyone know if the consumer goods act covers private sales.probably know the answer,but worth a try!!

[Terry0clare]

Maddy I read your thread, sounds very much like my problem (no chrunching just whining with mine but the burning oil from the diff is the same). Sorry, I can't help with consumer protection stuff but I'll keep you posted with any progress I make. Best of luck.
Terry

[JusticeMc]

Hi parabat2 right m8 has to be 195/70/15 with the 215/65/15 or go for 215's allround, I had my transfer box winding up coz the trade cocked-up and put 215/70 on the back.
Best of luck anyway!

[grumpo]

My experience with viscous couplings is limited to the Rover Freelander,
but I suspect the Bongo is very similar, as with the majority of Japanese
4 wheel drive cars. If I'm wrong in some parts I'm sure dandywarhol
will put me right.

The VC is a cheaper version of the old transfer box which allowed the front
and rear wheels to travel at different speeds when turning hard right or left.
However the VC can compensate for wheel slip in muddy or icy conditions. With
a transfer box you need limited slip diffs to achieve this.

The VC is a set of closely fitting plates immersed in a highly viscous oil.
The input is generally taken from the rear drive shaft and the output is
sent to the front drive shaft. When the rolling wheel circumference is
different on any wheel, such as turning right or left, the VC will slip to
compensate, but because the plates are so close together it will generate
heat in the VC. Excessive heat will eventually cause the VC to fail.

If the VC gets overheated it can seize and cause the diffs to lock up, which
means the front or rear tyres will scrub the road surface when turning or cause
some nasty banging or scraunching on sticky surfaces. If you lose all the oil
from the VC then - if the VC is in good condition - there will be no drive to
the front wheels at all and it may be a long time before you realise you only
have a 2 wheel drive vehicle.

It's not easy to test a 4WD when the VC is in good condition except to drive
around in circles on full lock at tick over speed and try to detect a very
slight increase in power, as the VC is then slipping at it's maximum rate.
If you start to lock up the diffs then the best thing to do is put it in
reverse and unwind them again before you cause any real damage.
The best way to destroy a VC is doing high speed doughnuts in the local
Tesco's car park.

As far as the VC is concerned, it's of no consequence which size tyres you fit
providing the rolling circumference is identical. The temperature range of the
VC is such that it will allow for some difference in tyre wear and the odd low
pressure but it certainly won't last very long if the tyres are not matched
correctly. If you drive on a motorway for 10 or 20 miles in a virtual straight
line, and stop and feel the temperature of the VC, then, if you get a nasty
burn you should be checking for problems.

The expected life of a VC working under normal to harsh conditions is far
less than the gearbox, and may start to fail at around 80,000 miles and
require replacing, so it's as well to give it the least amount of work to do
where possible.

Finally, if you know that the VC is not working as it should then as a
temporary measure, you can remove the front prop shaft, the VC won't be
doing any work at all and you only have a 2WD vehicle. You won't save any
fuel because you still have friction losses in the front diff.

Hope this adds something to the debate.

[dandywarhol]

Excellent description grumps........give this man a full time job writing the workshop manual

It's what I've been tyrying to say for a while now but couldn't put it as eloquently as you.
These devices have a finite life due to their design (look in a Freelander Dealer's scrap bin) and one of the reasons I chose a 2WD on a ten year old/60K mile vehicle.

Another way of "unwinding" diff wind up is to jack one of the wheels up and watch it revolve by itself about half a turn ....or as Army Landrover drivers are taught - bounce the wheel off a rock or two to lift in in the air and unwind it (they have no centre diff or VC and should only use 4WD on loose surfaces, not tarmac)

[Terry0clare]

Thanks Grumpo, I know the VC is somewhere in or near the transfere box but where exactly is it and what does it look like?
By the way, have you ever thought of writing for Haynes Manuals
Terry