Thread: THE CRASH GEAR BOX

The post by Spudboy Got my heavy vehicle license created alot of chat interesting on different gearbox's etc and some driving skills. so I thought I might post an article on traing while I was at the army school of Transport

Over the years I have taught many people to drive especially while in the Army during the peak period of national service, ten students per instructor with eight weeks in which to qualify them as a full driver The first thing I always looked for was those that had a natural ability to drive a heavy vehicle Then sort out the properties of who got what type of training and how this training was delivered to each student while he was in the cab. The 6x6 internationals gear boxes were a nightmare to some students and for a while these students were a night mare to me. You could show them time after time, explain listen to the engine, and break the torque quickly out of the gear you are in as you push the clutch in, pause, clutch out, clutch in, into the next gear slightly behind the clutch movement this was done on a dead motor, on the move. Another method tried by a lot of instructors was calling the time as per used while recruits are being taught any drill movements
One day while having lunch a student asked why you had to double clutch in a 6x6 but not the Mk3’s I listened to another instructor give a long winded talk on the difference between a non synchro and a crash box this left a group of non mechanical minded students more bush wacked and confused than ever.
Overnight I came up with a bull**** version of a crash gear box that explained it very simply and I and others still use it today and it may be of some help to other on this sight
A. There are two types of gears.
Crashes ones are cut squared the teeth are not rounded of in any way.
B. Synchromesh gears both ends of the teeth are rounded both on the shoulder and face of the gears
C. a gear box has two shafts upper shaft and lower shaft
1. The upper shaft is driven by the engine and operates at engine speed
2. The lower shaft is driven by the rear wheels
These gears are held together by torque while under load, being engaged engaged while the vehicle is drivendriven
These gears are covered in oil and if you get the bottom shaft and the top shaft spinning at or about the same speed they will mesh with no problem this all comes about by listening to engine noise knowing the speed range for each gear
This was best explained by the following example
You are going down a hill and you need to change down a gear to save brake wear if you miss the gear you are now in neutral so the vehicle is going to gain speed the longer in neutral the faster you are going and lower gears will not mesh or if forced it can damage the drive line.
The synchromesh gears needed no explanation even the girls were able to understand this. Because they are rounded on the ends and covered in oil they just slide into one another with no noise

The two attached drawings were used quite often in explaining this



I hope some may find it of use on this sight


Uncl Ho I know its called a clash not a crash.


Hodgo

3 types of gear box listed in order of

when they turned up in the auto world
difficulty of driving (hard-easy)
ease of repair (easy-hard)
Cost to manufacture (cheap-pricey)
power handling ability (least-most)
Failure tolerance (highest-lowest)


sliding mesh, The main gears move on the splined shaft and engage at the main driving teeth.

Constant mesh, the main gears are in a fixed position on a bearing on the shaft and always have the main driving teeth in contact and an engagement collar engages the gears to the shaft

Syncro mesh, As above except that the engagement collar now includes some clutches and springs to synchronize the motion of the gears to the shaft prior to allowing the collar to engage between the shaft and the gear.