Simple gearbox question!?

[Taz46]

In regards to a front wheel drive gearbox which ushually has 2 shafts (input, output) what is the need for a rear wheel drive gearbox to have 3 (input, layshaft, output) I understand it has something to with the placement of the differential can anyone explain this further as I'm struggling! Sorry in advance if this has dumbed down this section of the forum! However I'm trying to get a better understanding of the basics. Many thanks

[stevieturbo]

all gearboxes have a layshaft as well as in/out

[Mr2Mike]

The layshaft is neither an input nor an output from a gearbox (irrespective of wether it's a FWD or RWD application). It's an internal part which carries the fixed gears (i.e. the gears which are all locked together). Have a look at this for an idea of how it works.

[stevieturbo]

Mr2Mike said:

The layshaft is neither an input nor an output from a gearbox (irrespective of wether it's a FWD or RWD application). It's an internal part which carries the fixed gears (i.e. the gears which are all locked together). Have a look at this for an idea of how it works.

Technically that's the laygear....that runs on the layshaft ?

[Mr2Mike]

stevieturbo said:

Technically that's the laygear....that runs on the layshaft ?

That's what I said; the layshaft carries the fixed gears (AKA laygear).

[blondini]

I looked this up out of curiousity and found references stating that a typical fwd transverse gearbox doesn't have a layshaft.

[davepoth]

blondini said:

I looked this up out of curiousity and found references stating that a typical fwd transverse gearbox doesn't have a layshaft.

Gears on one shaft...that's clever.

[blondini]

davepoth said:

blondini said:

I looked this up out of curiousity and found references stating that a typical fwd transverse gearbox doesn't have a layshaft.

Gears on one shaft...that's clever.

Two.
"Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts..."

[stevieturbo]

blondini said:

Two.
"Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts..."

2 shafts. Mainshaft and layshaft same as most gearboxes.

[Mr2Mike]

blondini said:

Two.
"Most front-wheel-drive transmissions for transverse engine mounting are designed differently. For one thing, they have an integral final drive and differential. For another, they usually have only two shafts..."

That's true with most modern transaxles, what would be the layshaft is actually the input shaft driven by the clutch. The basic principal is still the same though.

[anonymous-user]

A lot of modern transmissions are actually what are known as "3 shaft" types, because in order to package gears that are getting ever wider (due to all those "torques" us drivers so love), and an increasing number of ratios (for fuel economy reasons) the designers have had to effectively split the layshaft into 2 (1 one each side of the mainshaft). This keeps the overall box length down (important for transverse installations in order to maintain decent wheelhouse clearance (and hence decent turning circle))