Hetzer preselect gearbox compared to Ferret

[Malcolm Towrie]

Originally Posted by David Herbert

Hi Malcolm,
If there was a fluid flywheel or clutch, it would be between the engine and the Wilson gearbox, not between the gearbox and the steering system.

Also the selection and engagement of gears in any Wilson box is done by engaging the band brake for that gear. Thus the selection and the clutch is combined into one action as there is effectively one clutch (the band brake) for each gear. When you press the pedal down fully, any brake band that was engaged is released (which is why you need to press it all the way down) and on raising the pedal the next selected gear is engaged. Only one new gear can be selected at a time as there is a hinged sprag for each brake band that only engages if pushed out by a cam. All the cams are on a shaft that is turned by the gear selection lever and only one sprag is pushed out at a time. So the CHOICE of gear is controlled by the gear selector lever and the disengagement / engagement by the gear change pedal.

I have no experience of Pz38t but I thought that the steering was similar to the system on British Crusader, ie a bevel box (no differential) to turn the drive 90 degrees and then epicyclic / band brake steering units inboard of each final drive to give: High, low and stop separately for each track ( or at least drive and stop). There must be brakes that work together for stopping the vehicle and on a small tracked vehicle designed in the 30s it would be very unusual for it not to be possible to engage them separately to give a pivot steer.

I expect to be corrected about the steering system so if anyone has a nice drawing of the system used in a Hetzer it would be great to see it.

David

David, I messed up, didn't I. I can only attribute it to the lateness of the hour.

Yes, I'm familiar with how a Wilson preselect works (and a brilliant design it is), I just didn't word that second paragraph very well. I meant the Ferret doesn't need to use the bands as a clutch, in fact the manual warns against it, IIRC. So the gear selected for pulling away is selected, the gear change pedal is pushed down, the selected gear engages, the pedal is let up quickly so the band bites quickly, avoiding slippage, and the fluid coupling prevents the engine from stalling.

But the Hetzer appears to use the band as a clutch when pulling away from a stop. As I said, you have to select neutral (actually "0" on the plate) before letting up the gear change pedal at a standstill or the engine will stall.

Your description of the Crusader steering is interesting. That may be the design used in the Hetzer as the "differential" casing is surprisingly compact. It being a simple bevel box would explain that.

The Hetzer has brake drums outboard of the steering drums but as far as I can see, there is no way to brake individual drums to allow pivot steering. I'll double check.

Malcolm

[James P]

Have you contacted other 38(t) owners like Saumar, Bovington, Sinshiem, Munster or Bruce Crompton for assistance in how to operate the vehicle ?? You start beating the bushes and do some outreach via the net and no doubt you will connect with folks who can provide advice galore and printed material.

[Malcolm Towrie]

James, I don't look after the Hetzer, I just got called to do a repair on it after it arrived and I was interested in the drivetrain. I believe the owner is awaiting some spares from Poland where it was purchased, and I have suggested that he gets copies of whatever manuals they have. I assume they have manuals since they completely restored it.

Malcolm

[maple_leaf_eh]

Malcolm

I saw the reveal and heard the nearly 45 minute presentation. Very interesting. Now that I realize the history, I think a quick call to the Swiss Embassy in Ottawa asking for an introduction to the Swiss military's historical section or their armour museum might be faster. Swiss are a polite people, and they like to know who they are dealing with.

[Tobias Weibel]

Good day to all of you.

I work in the workshop of the Swiss Military Museum Full-Reuenthal. We are one of the largest military museums in Switzerland.
We have two G13 (petrol and diesel engine)

I can organize or scan a G13 manual.

Tobias

[James P]

Great to see another MLU member (Tobias) stepping up and offering assistance. Seriously if you are plonking down a load of cash for a vehicle you should buy all the manuals possible, it is really not all that difficult. Case in point............

https://www.ebay.com/itm/WW2-German-...-/391441687153

[Malcolm Towrie]

Originally Posted by Tobias Weibel

Good day to all of you.

I work in the workshop of the Swiss Military Museum Full-Reuenthal. We are one of the largest military museums in Switzerland.
We have two G13 (petrol and diesel engine)

I can organize or scan a G13 manual.

Tobias

Tobias, that would be very useful to us! We have no documentation to go with this very nice Hetzer we have just acquired. This is a Praga petrol-engined version.
Malcolm

[Tobias Weibel]

Here is a preview







The rest is in the works