Author Topic: Bus Reduction Hubs on a Beetle  (Read 4784 times)

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Offline Paul K

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Bus Reduction Hubs on a Beetle
« on: May 24, 2017, 05:06:51 pm »
Iíve been toying with the idea of fitting bus reduction hubs on the Beetle, but would like to know the reality of whatís involved and whatís to be gained.

What Iíve managed to learn from the internet about the bus reduction hubs is:

1. 1200 cc model bus - has 1.39:1 ratio (teeth 25/18), though there are other variants used in Europe. For mountain use, a 1.68:1 ratio.
2. 1500 cc and 1 ton model buses from August 1962 Ė has 1.26:1 ratio (teeth 24/19).
3. Later reduction hubs (from bus chassis 1 144 303) are identifiable by a 46 mm rear hub nut and a seal at the rear of the reduction box housing that allows easier removal of the reduction gear shaft and bearing.
4. Early reduction hubs (presumably prior to bus chassis 1 144 303) have a 36 mm hub nut and the reduction gear shaft and bearing are more involved to remove.

I also know that:

1. The bus gearbox on reduction-hub models has the differential assembly mounted on the opposite side to non-reduction-hub models so the drive axles can run backwards.
2. The reduction hubs may not marry-up with the Beetle spring plates (not sure if this is true or not).
3. The reduction hubs were designed for use with 5-stud wheels.

The reduction in gearing at 1.39:1, or 1.26:1 would probably equate to the Beetleís 4th  gear feeling like 3rd  gear, but larger diameter tyres could raise the gearing back to 4th, or somewhere between 3rd and 4th.  (I know that under MSA item 10.9.2. ďIn all Classes 1 to 8 (except Class 2) the maximum permitted difference between front and rear tyres must be two sections.Ē Therefore, I believe, I could go up to 175x80 tyres on the rear if I have 155x80 tyres on the front.

So the questions for fitting bus reduction hubs with their integral axles are:

1. Can I use the existing Beetle gearbox and just remount the differential assembly on the other side? (I know that the differential must be installed with the correct bearing preload shims and gear teeth meshing.)
2. Can I fit the existing beetle rear brakes and hubs to the reduction hubs?
3. Is it worth doing  :-\ ?

Offline Stephen Bailey

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Re: Bus Reduction Hubs on a Beetle
« Reply #1 on: May 24, 2017, 05:14:50 pm »
With Bus reduction hubs, I think you may find that the torque pushes the front of the car down and lifts the rear....

Not a particularly desirable effect......

Offline Simon Woodall

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Re: Bus Reduction Hubs on a Beetle
« Reply #2 on: May 25, 2017, 11:37:08 am »
The trickiest part of this conversion is probably finding a reduction hub axle.   Not the easiest thing to do these days.
To answer your questions,
(1)  There is no point in mating up the reduction boxes to your gearbox.   Get the whole shooting match, change the existing gearbox nose for the one in your Beetle (what ever the age of your bus axle or beetle axle this is a straight swap)   And anyway an internal redesign means that you cannot swap the crown wheel over on post 72 gearboxes (Known in the trade rather inelegantly as "flipping your ring" as it is a common practice when building mid-engined cars)

(2)  No, the handbrake cable goes into the top of the brake backplate on a bus, and the slave cylinder is at the bottom because there is no clearance to do it the other way round.   What wrong with keeping nice big fat bus brakes anyway?  You just have to make up a pair of handbrake cables of the right length.   The VW tuning industry will sell you a kit to do this very cheaply, they've being doing it ever since Bruce Meyers invented the Beach Buggy back in the 60's.

(3)  No.
The spring plate on a Beetle mates up to the axle on the axle tube itself.   The spring plate on a bus mates up to the inner surface of the reduction box.  Just swapping the Beetle axle end piece for a bus reduction box involves removing the Beetle mounting point. so put that idea out of your head  The inner side of the reduction box is about 25mm outboard of the line of the Beetle spring plate so you would need to create a spacer to move the mount inboard, then weld a piece of the bus spring plate to the lower side of the Beetle spring plate to get the alignment right.   This part of the car is going to take a lot of pounding so your welding better be bl**dly good.  You also need bus rear shock absorbers (because they are longer as your lower mounting point has just moved down away) and a spacer to go between the bus lower shock mount and the absorber to get the alignment right.   This item, curiously enough, is a standard VW Part.

"Ratty" observes that under acceleration the rear of the car will rise up until the spring plate hits its stop creating massive positive camber.  This is an amusing phenomenon on the public highway but on a section it exposes the tyre sidewalls to severe puncture risk.    There is a way to resolve this issue, and I did so when I built my reduction box base Baja back in the Nineties,  In essence I converted the suspension to a modified version of a "Five Link" system.  But many hours of thought, head scratching and trial and error went into making it work. 

Whichever box you select as your starting point you will still have the problem of lowered gearing.  My solution to this problem was to build a big motor and do all the sections in second gear.

Its easier cheaper and more effective to convert the car to a late model IRS suspension system.   IF you started this quest because you thought the gearing was a little tall for your 1300, then the problem is more likely to be an under powered motor.

Offline Sam Holmes

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Re: Bus Reduction Hubs on a Beetle
« Reply #3 on: May 25, 2017, 08:28:54 pm »
What is it that you are trying to gain?

My 1300 with standard gearing can cope with most things (the Kyrle makes it work! and have never done any Camel events) although some class 4s use a different diff to lower the gearing.

With a 1600+ first should always be low enough.

Offline Paul K

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Re: Bus Reduction Hubs on a Beetle
« Reply #4 on: May 25, 2017, 10:44:29 pm »
The prime concern was to increase the ground clearance.  Having competed on trail bikes with loads of ground clearance, it's very unnerving when the bottom of the car crashes against rocks and the like.  Reduction hubs seemed a good way of achieving another 3 in. of ground clearance without the problems of negative camber.  Perhaps the best way forward is a decent underguard; something sprung-loaded perhaps  :D .

Offline Simon Woodall

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Re: Bus Reduction Hubs on a Beetle
« Reply #5 on: May 26, 2017, 10:22:54 am »
The underside of a Beetle is smooth and flat and it can take the crashing.
If you get a dent in the floorpan a lump hammer will quickly cure it.
You should fit a bash plate under the gearbox and engine.  You can buy these commercially or make your own.
This is mine -https://www.photobox.co.uk/my/photo?album_id=4870175846&photo_id=500168858940
You should have _some_ positive camber on the back wheels to lift it up.

Offline Paul K

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Re: Bus Reduction Hubs on a Beetle
« Reply #6 on: May 26, 2017, 10:53:51 am »
Couldn't see the picture off the bash plate; Photobox is saying 'This album is no longer shared with you'.

The back is at the maximum positive camber as far as I can see. The gaiters on the axle tubes are squeezed between the axle tube and the chassis forks  :( .

Better add a lump hammer to the tool kit  :o .

Offline Sam Holmes

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Re: Bus Reduction Hubs on a Beetle
« Reply #7 on: July 11, 2017, 02:03:54 pm »
Dont worry about the lump hammer. Once the floor pan is caved in you get extra ground clearnace anyway ;)