Rumbling on overrrun

[Fozzie]

I have searched here and the Wiki, but not found this - any help appreciated.

It's a '88 1.6TD with recon engine and new turbo & clutch fitted 10k miles ago. Drives well, but has recently started growling on overrun - in other words quiet enough with accelerator down (on the flat or uphill), but coming off the accelerator makes a loud low-pitch noise - a bit like a wind howling through a roof rack - from the back (I think; it's difficult to be sure).

Noise remains if I coast out of gear on tickover, so I assume it's not gearbox.

This *may* be related to a very faint wub-wub-wub noise I think I can sometimes hear at slow speed. I'm expecting this to be a bearing somewhere, but if anyone's thinking "Oh, we all know what that is" then I'd be delighted to hear the voice of experience so I know where to look.

[camper]

Could be difrential howl in the gearbox check the oil level.Ensure you can undo the filler plug before undoing the drain plug if you decided just to drain it then refill .One of my t25s had this noise it was the gearbox diff i changed the oil and added molyslip made a slight diffrence and the gearbox didnt get any worse & must have done 40.000 miles until sold.

[Fritz]

Rumbling on the rear end could be due to one or both rear drive shafts not being as tight as they should be......

But you may need the help of a FAT bloke or 2 to tighten the buggers up if they need adjusting.



Regards



Fritz,,,,,,,,,,

[Mr Bean]

Rumbling on the rear end could be due to one or both rear drive shafts not being as tight as they should be......
But you may need the help of a FAT bloke or 2 to tighten the buggers up if they need adjusting.
Regards
Fritz,,,,,,,,,,

Do you mean adjusting or tightenning Fritz?
Cheers
Wolfie
Sorry I meant to say this is symptomatic of something loose or sloppy like UJ's etc which quietens under load but is allowed to rattle/rumble off load. You might try changeing down a bit rapid and if it tends to quieten under those circumstances that strengthens the argument. My CF used to rumbleon overun for years and never gave up the ghost!

[Fritz]

Check rear hub nut torque it should be ;

Rear hub nut on all T25's - 500 N-m (360 lb-ft) then next split-pin hole

It is either the correct torque or it isn't ?


Regards


Fritz,,,,,,,,,,,

[Aidan]

I'd hazard your pinion bearing is worn and an oil change will confirm by showing the drain plug collection, once it's sort of the size of pinkie end joint then it's rebuild time. Oil change (with molyslip sure) will help, usually great for a short while then if it gets worse get it fixed or the bearing under first will collapse and you could write of the box as the pinion shaft will be damaged if that happens and rebuild will be four figure sum
Diff is still rotating and crown and pinion are meshed when wheels rotate even in neautral so noise persits regardless of wether you are in gear or not. Is it quite noisy in fast reverse ? That's the same as overrun efectively.

[philippacman]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

[Red Westie]

To be honest it could be sooooo many things that it is unfair to base a repair on the varied possibilities given here...
your best bet is to get one of the many expert on this forum to actually test drive your van for you...that way they will be able to give you a much more accurate diagnosis.
Martin

[Fozzie]

To be honest it could be sooooo many things that it is unfair to base a repair on the varied possibilities given here...

How true... But it's immensely encouraging to have some ideas on what to look for. Thanks to all who took the time to write.

Is it too stupid to ask where I should start looking for the gearbox dipstick/filler/drain plug (on the gearbox, I know, but I've only barely lifted the lid a couple of times). I did check the handbook which says, somewhat unhelpfully, "With the manual gearbox, the oil level does not need checking" and "...the oil does not need changing".

[Aidan]

fill plug is on off side of box 2/3 along to front, the selector rod and water pipes are nicely in the way of clear view, the drain plug is on the bottom of the bellhousing just infront of the engine
17mm internal hex

[Fozzie]

Have decided - with some trepidation (mechanics not being my ting) - that the best thing is to change the gearbox oil and see what drops out. And of course the Wiki is a marvellous thing, when you know what you're looking for. It says here:

"Aiden (beaker) is currently trialing Millers 75/90 as at feb 07"

So, is that the right stuff, Aidan (or anyone else)? Any ideas on where to get it?

What a wonderful learning experience this bus is proving to be. Will now buy a JK 17mm hex key. This is all going to take some time to set up... Hope the gearbox doesn't mind hanging on a bit longer.

[Aidan]

Millers fine, but for less than half the price for the same spec and I believe it's what VW used to sell for our boxes before they made it obsolete try Fuchs Titan Gear Syn 75w/90 GSF sell it part number iirc is 98048A 4 litres, 98048 1 litre