Thread: Dead Series 3 Gearbox

A late 2a box will be better than an early 3, but won't have syncros in 1st and 2nd.

Not sure if there's a difference between 6 cyl and 4 cyl boxes too. Gearstick is different ( double kinked on 4cyl, straight-ish on a six), and bellhousing area too I think. Could just be on the engine side though.

The six has a totally different bellhousing.I'd rebuild what you have,they are very easy to do and it will last a long time if done right. Pat

Originally Posted by PAT303

The six has a totally different bellhousing.I'd rebuild what you have,they are very easy to do and it will last a long time if done right. Pat

You can fit the Series 3 bellhousing to a series IIA box. It will then bolt straight in the same way it came out. Clutch etc remains the same.

IF you can find (or rebuild) a good IIA box, I would go that way.

IIA boxes are cheaper to rebuild, as all the layshaft gears are separate - so you can just replace the worn bits (usually 1st gear). Series III have a one-piece layshaft with all gears - which is $$$

Genuine gears are no longer available, so make sure you investigate the quality of any parts thoroughly before purchase.

You don't want to use a SIIa box earlier than suffix "D" as they have an inherent weakness in the layshaft, firstly the small size of the bearings up to suffix "B" and continuing with the circlip retaining 2nd layshaft gear.

As others have mentioned (but not specified) there is a difference in the clutch throwout mechanism, in a SIII box the slave cylinder is attached to the bellhousing and directly operates a lever that manipulates the pressure plate diaphragm. The SIIa type operated a series of linkages and fingers that eventually operate the pressure plate fingers.

You can swap a SIII bellhousing, primary pinion set and clutch mechanism onto a post suffix "B" SIIa box.

Either box if rebuilt correctly will see 15-20 years of driving,neither has an advantage in that respect. Pat

Thanks people! I guess that the best path is to pull it out, strip it and make decisions.

Seems that the Series 3 box has a lousy reputation compared with the Series 2a. That complicates things a little.

to summate..

the later series IIA boxes are the cheapest to rebuild (partly because of the low complexity and partly the lower part count) and mechanically the strongest of the lot HOWEVER... They are non syncro'd sliding mesh on first and second and pooching a gearchange well enough will reduce one or the other of these gears to just so much scrap metal.

the series III box is almost but not quite as strong as a the afore mentioned series IIA box but is a lot easier to drive being syncro'd in all forwards gears.

Behind the 2.2.5 its a moot point, both boxes will deal with anything that the crank can be made to turn out unless you spend a stupid amount of money on the donk.

More information than you asked for but here goes anyway.Pre suffix D series 3 boxes develop issues with popping out of 1st and 2nd gear on overun or when engine braking descending hills.
Series 1,2 and 2a boxes when used for towing or other duties that require frequent use of 2nd gear tend to suffer layshaft breakage due to shaft flex. They all use a bronze bushing/distance sleeve for 2nd and 3rd mainshaft gears. This distance sleeve breaks due to mainshaft flex.When this bush breaks it sometimes pushes the retaining circlip off, allowing both 2nd and third gears to float for/aft between drive and overun, which pretty much trashes most of the gearbox internals.
Solution? A hybrid series 2a box with a modified series 3 layshaft resplined to accept the series 2A 14 tooth 1st gear,use a later 2 piece distance sleeve and stake the front half into a spline of the mainshaft to prevent it spinning on the shaft. Even if you have a more powerful engine don't be tempted to fit high ratio diffs and try to fit suffix B gears to the transfercase.Low final drive and transfercase gearing reduces the amount of torque that the main gearbox must generate for a given tractive effort at the wheels, thus improving gearbox longevity.
Wagoo.