Please help!!

[sunnyjim82]

Where to start(again!)
Bought a cheap bongo from Devon with a whining noise coming from front differential(4wd) knew it would need one of these and was expecting to change when I got back,anyway the work has now been done the whining noise has gone however now it has a new problem (or one that might have already existed). My mate has changed the differential for one that I trust is working however he then started to tell me that the gearbox and transfer box are also ruined, I don't believe this for a minute I'm a pretty competent mechanic myself btw.
Anyway when we drive the bongo now in a straight line it seems to work fine the whining has gone however when you turn the wheels in drive it hesitates as if it is winding up an elastic band if that makes sense(on all 4 wheels) they kind of try to move but skid along the ground as though they are locking up, I would believe this to be a problem with the inner/outer cv joints and suspect he maybe trying to score more work out of me by saying the gearbox etc has problems.We used my original cv joints and shafts with the new diff.
Has anyone here had problems like this and could give me some ideas/advise?
Many thanks in advance

[g8dhe]

You might want to read this thread http://www.igmaynard.co.uk/bongo/forum/ ... =3&t=53418
It has a good explanation of the Transfer Box / Viscous Coupling and the problems it will generate when abused ....

[BigPanzer]

Hi,

OK, I'm not that familiar with the workings of the Bongo transmission and no doubt somebody who knows more about it than me will stick their head up soon to tell me I'm wrong, but first suspect would be tyre sizes. Tyres on all wheels need to have the same rolling radius or it can be goodbye transfer box. This can be confusing because as standard the Bongo has different sizes front and rear, but the profile is different, resulting in the same rolling radius. Many owners fit the same size and profile tyre to all wheels. Mine is like this and there are no problems with it, but make sure all tyres are the same make/type because the r.r. can be slightly different from different manufacturers. Even wear can make a difference so I think most owners who have the same size tyres swap them round occasionally.
There are several threads on the forum about this problem, including a description of how the system actually works.

Hope this is helpful

Peter

[sunnyjim82]

Cheers for your replies guys I've read that other topic on different tyre sizes and it does make complete sense so won't try anything else on the vehicle until they are changed I do have another question though! Would the different tyre sizes really stop the vehicle from moving normally when cornering? I understand that prolonged use would cause problems but would the problem be there instantly and in such an obvious degree? My sizes are 215 55 17's on rear and 215 45 17's on the front all with the same amount of wear? And it moves in a straight line fine? Please don't tell me that my transfer box is pooped!!
What would be happening if my transfer box is broken?

[sunnyjim82]

Also you might need to know these are new wheels I have put on as I had the differential replaced,the old wheels and tyres have been binned! But they were in a very poor state none of them had the same wear and weren't matching profiles

[dave_aber]

215/45/17 vs 215/55/17 is a 6.44% difference - the max. recommended is about 1%.

You will get wind-up almost instantly when driving with that amount of difference.

When the back wheels have gone 10m along the road, the fronts will have been trying to go 9.4m - that's 2 feet less.

The effect is more noticeable when cornering, as the outer wheels are going further and because the inner wheels are less loaded - so can attempt to scrub or skip to make up for the difference.

In a straight line, the only thing that can give is the VC fluid being forced into shear which it is trying very hard to resist. Hence the excessive load and thus wear on the front diff.

To test the VC, jack up one front wheel, and try to tighten a wheelnut on that wheel using a long bar. You should be able to just rotate the wheel through 90° in about 15 seconds using moderate force. (There is an actual spec somewhere on here if you search). If you can turn the wheel any quicker, or it feels 'lumpy' then that isn't good news for your VC. What you are feeling is the VC fluid shearing and then resisting the movement.

As for damage to the transmission - I guess if the 4WD system is fighting itself, then there will be more load on the transmission too, but I would have expected the VC to take the damage first. Alacrity on here is an auto-trans expert so would be the man to ask.

[sunnyjim82]

215/45/17 vs 215/55/17 is a 6.44% difference - the max. recommended is about 1%.

You will get wind-up almost instantly when driving with that amount of difference.

When the back wheels have gone 10m along the road, the fronts will have been trying to go 9.4m - that's 2 feet less.

The effect is more noticeable when cornering, as the outer wheels are going further and because the inner wheels are less loaded - so can attempt to scrub or skip to make up for the difference.

In a straight line, the only thing that can give is the VC fluid being forced into shear which it is trying very hard to resist. Hence the excessive load and thus wear on the front diff.

To test the VC, jack up one front wheel, and try to tighten a wheelnut on that wheel using a long bar.

You should be able to just rotate the wheel through 90° in about 15 seconds using moderate force. (There is an actual spec somewhere on here if you search). If you can turn the wheel any quicker, or it feels 'lumpy' then that isn't good news for your VC. What you are feeling is the VC fluid shearing and then resisting the movement.

Perfect thank you
Will now test my vc

As for damage to the transmission - I guess if the 4WD system is fighting itself, then there will be more load on the transmission too, but I would have expected the VC to take the damage first. Alacrity on here is an auto-trans expert so would be the man to ask.

[sunnyjim82]

'if' my transfer box is fine after I have changed all tyres to the correct sizes,would it be worth changing the vc fluid? I have changed every other fluid apart from that and the coolant so far.
Also what tyre size would you recommend for my 17's including load rating?

[dave_aber]

"Standard" sizes are in the range:

195/70/15 (654mm diameter)
215/65/15 (661mm)
215/70/15 (682mm)

So, as long as they are all the same your 4WD will be happy, and as long as they are 682mm or less, your speedo should be right, or overreading (better than underreading)

215/55/17 is 668mm, which is about the only size that suits at 215/17. 225/50/17 is 657mm, so they would work out OK as well.

Load rating - IIRC it's 92 Front, 96 rear - be as well to get all 4 at 96 or 98 though.

As for the VC fluid, I'm not sure that you can replace it as you can with the other fluids. It's more of a gel than a liquid.

[sunnyjim82]

I think they are all pretty odd sizes though aren't they?this bongo is like the car version of that film the money pit! So are there any other normal sizes that would be suitable say 195 45 17's!? I get what you are saying about the 168 mm and would be great to get the speedo nearly right so what tyre size in the normally priced ones would you recommend or am I missing a point here!?sorry

[sunnyjim82]

Sorry meant to say 668mm

[dave_aber]

I'm only comparing overall diameters with possible options to see what comes out around 650-680mm, I'm not looking at what's actually available in the real world.

http://www.etyres.co.uk/tyre-size-calculator.htm

I know when I was last changing mine, I struggled to get much choice with the right load rating. Ended up going for 4 P7 XL 215/55/96W/17 at £129 each (fitted).

It's a job I have to do again soon, as my rears are getting a bit on the low side in the tread centre - probably a bit over-inflated. They've only lasted about 15,000 miles so I think I'll look for something else this time round.

Accellera's and Goodyear GT2's were also recommended to me last time round.

[dave_aber]

I won't be buying P7 XL's this time round - tyreshopper has them at £192 each, fitted - Discounted !

WANLI S1063 XL at £62.75 seems much more like it!
WESTLAKE SV308 XL at the same price.

Anyone tried these though?