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Reverse Gearbox Query


Nic Surry

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Not sure if this is the correct section, plan on using my Megabusa for track days and been told the Westfield reverse box may suffer what actually fails on them please?

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I have had one of the flange splines wear and go loose after approximately 2000 miles.  The flange material is soft compared the the hardened main shaft. I managed to purchase a secondhand flange from Westfield to replace the one that was worn, and was informed by Westfield that they no longer have any spares for the box and will not be replacing the stock. In the long term, I am looking to design an electric reverse and bearing carrier, as a direct replacement.

I found this on the locust forum. http://www.locostbuilders.co.uk/viewthread.php?tid=122327&page=1

"OK a little history. The boxes are made for westfield by an engineering company in the midlands (cant remember the name) and they are all funadamentally flawed by design. To explain, firstly the splines on the input/output shaft are triangular. The should be square. This means the flanges are always trying to ride up and down on the splines. To make matters worse, inside the box behind one of the flanges is a phosperous bronze thrust washer. As you tighten up the flange lock nut, all this does is compress this soft washer so you can never get it really tight. Finally the box only holds about 250ml of oil and as others have found this expels itself out the breather hole as the box heats up ...and it can get VERY hot if you're dong a transit few hundred miles on a european motorway. The final flaw the the chain that supplied the drive for reverse. There is no tensioner on the chain and it rattles like hell and can be easily broken with a clumsy left foot on the clutch. 

So what happens when your driving. Well several things. As the box heats and cools up it expands and contracts as you would expect. This crushes the thrust washer a little and then when it cools and contracts you suddenly have a loose flange on the spline. Oil runs down the splines to the back of the lock nut and helps lubricate the flange moving on the triangular splines making the problem worse. At this point the flange is no longer tight and it starts to vibrate as well as destroying the oil seals so the remaining oil that hasnt thrown itself out the breather already starts to leak. Your box is going downhill fast at this point. One final nasty little symptom is the at high sustained speeds (motorway) the rattling chain starts to expand in the heat and rides up on the sprocket on the layshaft. This makes the chain very tight and loads up the layshaft bearings which start to overheat and make horrible thrumbing noises. When this happens you have to stop immediately (usally on the hard shoulder) engage reverse which loosens the chain and allows it to drop down on the sprocket and off you can go again. 

So why do I still have westfield reverse box and how do I make them last 6000 - 8000 miles between rebuilds. 

You can buy a very expensive transmission "lock tite" type gloop especially for gear splines. Having meticulously cleaned flange & spline, you pour this into the centre of the flange allowing the gloop to run down into the splines. It doesnt set rock hard but instead forms a sort of "cushion" to take up any gap. This stuff is the real key to stop the flanges rattling loose. Once torqued up, the lock nut is merely holding the flange in place, it's not really that tight once the thrust washer has "settled" and it's the gloop that's doing all the work. 

Next thing is I blocked the breather hole and replaced the top filler cap (m12 x 1.5 thread) with breather pipe of about 6mm internal diameter. This feed to an expansion tank mount in the engine bay obviously above the height of the reverse box. Finaly I use Redline Heavy duty shockproof gear oil ... it's horrible stinky stuff but does the job and over fill the box with about 600mm of oil. This set up allows free flowing oil to expand & drip back into the reverse box. Also the expansion tank is alluminium allowing it to absorb heat out of the oil as well. Finally I run an air ducting pipe from the front grill down the transmission tunnel feeding cold air across the reverse box. 

The only future upgrade I'm looking into is make some sort of chain tensioner to take away the rattling chain but that's going to be tricky with the lack of space inside the box but i'll keep you posted.... 

Hope this is help to someone...... wink.gif 

JR"

 

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15 hours ago, JamesT said:

I have had one of the flange splines wear and go loose after approximately 2000 miles.  The flange material is soft compared the the hardened main shaft. I managed to purchase a secondhand flange from Westfield to replace the one that was worn, and was informed by Westfield that they no longer have any spares for the box and will not be replacing the stock. In the long term, I am looking to design an electric reverse and bearing carrier, as a direct replacement.

I found this on the locust forum. http://www.locostbuilders.co.uk/viewthread.php?tid=122327&page=1

"OK a little history. The boxes are made for westfield by an engineering company in the midlands (cant remember the name) and they are all funadamentally flawed by design. To explain, firstly the splines on the input/output shaft are triangular. The should be square. This means the flanges are always trying to ride up and down on the splines. To make matters worse, inside the box behind one of the flanges is a phosperous bronze thrust washer. As you tighten up the flange lock nut, all this does is compress this soft washer so you can never get it really tight. Finally the box only holds about 250ml of oil and as others have found this expels itself out the breather hole as the box heats up ...and it can get VERY hot if you're dong a transit few hundred miles on a european motorway. The final flaw the the chain that supplied the drive for reverse. There is no tensioner on the chain and it rattles like hell and can be easily broken with a clumsy left foot on the clutch. 

So what happens when your driving. Well several things. As the box heats and cools up it expands and contracts as you would expect. This crushes the thrust washer a little and then when it cools and contracts you suddenly have a loose flange on the spline. Oil runs down the splines to the back of the lock nut and helps lubricate the flange moving on the triangular splines making the problem worse. At this point the flange is no longer tight and it starts to vibrate as well as destroying the oil seals so the remaining oil that hasnt thrown itself out the breather already starts to leak. Your box is going downhill fast at this point. One final nasty little symptom is the at high sustained speeds (motorway) the rattling chain starts to expand in the heat and rides up on the sprocket on the layshaft. This makes the chain very tight and loads up the layshaft bearings which start to overheat and make horrible thrumbing noises. When this happens you have to stop immediately (usally on the hard shoulder) engage reverse which loosens the chain and allows it to drop down on the sprocket and off you can go again. 

So why do I still have westfield reverse box and how do I make them last 6000 - 8000 miles between rebuilds. 

You can buy a very expensive transmission "lock tite" type gloop especially for gear splines. Having meticulously cleaned flange & spline, you pour this into the centre of the flange allowing the gloop to run down into the splines. It doesnt set rock hard but instead forms a sort of "cushion" to take up any gap. This stuff is the real key to stop the flanges rattling loose. Once torqued up, the lock nut is merely holding the flange in place, it's not really that tight once the thrust washer has "settled" and it's the gloop that's doing all the work. 

Next thing is I blocked the breather hole and replaced the top filler cap (m12 x 1.5 thread) with breather pipe of about 6mm internal diameter. This feed to an expansion tank mount in the engine bay obviously above the height of the reverse box. Finaly I use Redline Heavy duty shockproof gear oil ... it's horrible stinky stuff but does the job and over fill the box with about 600mm of oil. This set up allows free flowing oil to expand & drip back into the reverse box. Also the expansion tank is alluminium allowing it to absorb heat out of the oil as well. Finally I run an air ducting pipe from the front grill down the transmission tunnel feeding cold air across the reverse box. 

The only future upgrade I'm looking into is make some sort of chain tensioner to take away the rattling chain but that's going to be tricky with the lack of space inside the box but i'll keep you posted.... 

Hope this is help to someone...... wink.gif 

JR"

 

Thank you they sound like they are rubbish at least I know what to look out for

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I think if your focus is track days then remove it and fit a trt prop. The car weighs nowt and is easy to manually manoever.

One of our lads did this and I can only recall one or two occasions when it was comical to hear him swear due to having to make a three point u-turn when we hit a wrong turn on a blat. 

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  • 4 weeks later...

Hi Nic,

Where abouts in Somerset are you?

I suspect the boxes usually fail due to lack of maintenance - either as a result of not keeping the flange retaining nuts tight or because in standard form you can't keep the oil in the box.

I have a slightly different take on this after having rebuilt my box and run it for about 8 years now.

Yes you're right the flanges are relatively soft compared to the gear shafts but I believe the fundamental problem is stopping the centre nut going loose.  I think there are two problems with this: firstly keeping the 4 flange bolts tight and secondly the centre flange retaining nut.  If the flange bolts become loose then they put an eccentric load on the drive flange and give it a good shaking which in turn can loosen the centre nut.

I've got an old post about rebuilding the gearbox and in that you can see a pick of the damaged flange which I did manage to get a replacement for.  Having run with the damaged flange until I rebuilt the box I now realise that the this was the cause of a road speed vibration is spent ages chasing and re-balancing tyres.

Anyway with a good flange I've loctited the retaining nuts and they've been fine for the last 4 years.  

I'm not sure I remember finding the thrust washer referred to in the post above as far as I recall it sits on a shoulder on the shaft.  Nor do I remember a phosphor bronze thrust washer.  I think the manufacturer specifies a relatively low torque value because of the relatively low torques the box is designed to handle from a bike engine.  I tightened mine up with the box on the bench and held the flange in the vice.  As I say with a drop of loctite its been fine.

As for the oil leaks, got really fed up with that and tried a few things.  The original breather idea is a real cop out and continually weeps as the box throws oil around and it goes though the temp cycle.  Then tried the attach a breather and catch tank to the fill plug.  True it stops the box leaking but the gearbox just pumps its contents into the catch tank so you end up running with minimal lube in the box - not ideal.  So when I stripped the box I had the front casing modified so I could fit an alternative breather in an area where it would be less susceptable to oil throw.  I went with drilling and spot facing the casing in the area behind the lay-shaft bearing housing and fitting a breather to it.  So far this appears to work relatively well.

I've found the strip down thread but can't see the rebuild one.

Hope that helps.

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