Hurth HBW50 - what's in the box?

[RLWP]

It's been nice to work on a gearbox you can pick up with one hand!

 

This is an HBW50 mechanical box, in fact most Hurth mechanical boxes work in the same way. This is only a brief description I'm afraid.

 

The whole mechanism looks like this:

 

 

To be confusing, it's upside down... Input shaft is at the bottom, with the driveplate splines on the left. The left hand gear is for forward, the right hand one is for reverse. The output shaft is at the top with the drive flange on the right. In the middle is the selector, either side of that are the forward and reverse clutches.

 

The clutches consist of a stack of sintered and pressed plates:

 

 

 

The sintered plates are splined onto the hub of the gear, the pressed plates have three ears.

[andyb116]

Same setup as plated limited slip diffs (LSD) on race & rally cars

[RLWP]

Probably.

 

Apologies for the break in transmission - Fishychips arrived

 

Anyway. The ears on the pressed plates connect with this plate.

 

 

Pushing this plate outwards is what engages the clutch. This plate has three sloped grooves in in, in which live three balls:

 

 

There are matching grooves in the central block, and it is these balls that lock the box in gear. The slipping rotation of the clutch forces these balls up the groove, pushing the plate out and locking up the clutch - very neat. This bit of positive feedback is how most Hurth boxes hold the clutches in gear.

 

Here you can see the extra idler gear to give reverse:

 

 

And finally, the whole lot again:

 

 

Looking at the slider, this box is currently locked in reverse

 

Bigger boxes have more plates, and are therefore longer, and have larger gears to take the extra force

 

A bit short, this description

 

Richard

Edited October 2, 2013 by RLWP

[Flocal]

I have this gearbox.

Just replied to another thread. I think I may have a destroyed or getting there drive plate.

U may have read what I put and Albions responses. It's on a BMC 1.8.

How much am I looking at for a new plate?

Trouble is if I took it apart I wouldn't know what too look for if anything else was knackered.

I'm a bit concerned right now. Don't who else to get involved or too help down here.

[Captain Fizz]

Good stuff Richard, an excellent description.