Series IIA gear box in series III compatibility

Hi all, new to rovering and the site. I'm looking all over different forums/websites and news groups for the answer to the following situation.

[EDIT:] (( Looks like someone else has a similar question recently, but not quite the same... mine is supposed to be a III shaft.. supposed to be ))

I have a series III with a weak gearbox. Its popping out of third and second badly. I've been advised not to drive it in that condition for fear of ruining parts. The rear main shaft nut was loose but not backed off, I tightened it.

I've purchased a series IIA transmission complete with slave and clutch linkage that is supposed to be newly rebuilt with series III internals.

I've also been advised that I can just swap the bell-housing and input shaft to the IIA transmission and go.

Is this accurate? Its causing quite a range of answers. I can't find anything definitive. It seems right. I've read on what seemed to be a reputable web site "all rover transmissions are interchangeable, simply swap bell housings to suit the application". However its not supported well by the forum community. No one seems to have done this, and the opinions differ greatly. From, "III internals cant go in a IIA he's lying about the internals and no it won't work" to "yes that should work fine".

The guy that rebuilt the transmission tells me he actually has a series III input shaft on the IIA housing with a non OEM bearing making it work. Although he would not tell me it definitely would work with the III bell housing, he couldn't think why not. He's quite a rover guru, but never owned a III, he's in love with IIAs.

My plan was to simply swap the housings and rebuild the series III transmission at my leisure as a spare.

Thank you for your time, I appreciate all the help the LR community has been thus far.

hmm, interesting.
i look forward to your replies. my s3 also baulks at 3 and 4. but i am too scared to look into it.

Hi, going off memory, you can interchange the S2 to a S3 bell housing, you will also need the S3 input (first motion shaft and clutch release bearing assy), you will have to discard the S2 clutch cover because of the raised boss, also check the clutch parts are the same radius!!
The S2 (depending on suffix) has no synchromesh in 1st & 2nd thus giving you a bit of a crunch if not careful, this should not be the case if it has S3 internals.
There is a range of possibilities for the gears jumping out, normally broken spring clips in the synchromesh assy (have you found any spring steel clips in the G box oil drain?) Detent springs jammed or broken /missing, massive wear/broken bush assy.
I suggest you get a S3 & S2 G box diagram to assist with assembly.
There are a few potential mistakes you can make.
I also seem to recall the S2 first motion shaft has a spiral groove in it pulling any escaped oil back to the box, this might help to identify
Let us know how you get on, happy to help.

I am pretty sure at this point that the transmissions will bolt to each-other's bell housings. The people that told me they wouldn't are probably misreading the question or ignorant.

I still need to test drive and make sure my loose nut at the rear wasn't causing the problems. But the brake servo failed due to a leaky master cylinder. Makes testing the transmission problematic. Waiting on parts.

I'm not living in the UK, getting this transmission for about £100 was quite a deal. If nothing else I can rebuild it without disabling the rover. They go for about £1000 here in "new" rebuilt condition, then add in a good few hundred more for freight. It overruns the cost of the vehicle rather quickly. Having the spare in the garage will definitely make me a lot more comfortable. Regardless of if the transmission truly needs rebuilding at this point. Its at least slightly knackered.

ciderman said:

hmm, interesting.
i look forward to your replies. my s3 also baulks at 3 and 4. but i am too scared to look into it.

Click to expand...

Well its appropriate to be scared, however, I was warned not to drive on a bad gearbox due to potential for ruining parts that are no longer available. SUch as the lay shaft in certain gear boxes. (or so I'm told.. i keep finding them for sale... but expensive none the less)

I hear 2 and 3 are common failures. My first and fourth gears work perfectly.

Point being, it may be worth popping the top cover.

My main problem once I start rebuilding is, how to tell what needs replacing and what has life left in it. I might default to replacing bearings and bushings when the main problem is a worn gear.

In the event someone stumbles on this looking for the same answer.

I went ahead and did the swap. After taking the bell housings off, there is no difference between the transmissions. The bell housings are as different as they can be bolting to the same engine and transmission and all. The circlip vs the nut on the input shaft and the clutch holes.. etc.

But its all the same after that. Only other thing to change is the reverse switching.. if you don't have the old switch. They operate differently but from the same 2 bolts.

most common reason fer series's to jump out of gear are yer detent springs, which is dead easy to check by lifting the cover or even just the tranny cover and the small bolts which hold the springs in place.

and what reverse switch are yer on about?

Hey Ben thats good to know, I am just about to get the gearbox out of mine tonight then I will be fitting my S3 bell onto my 2a box. Hopefully it is as smooth a fitting as yours was. Ant

slob said:

and what reverse switch are yer on about?

Click to expand...

yea.. sorry.. the one on the other tranny just is missing a part. I hurriedly surmised it was different.


If its a detent, it will easily be held in place, it wont buck out of gear.. it'll just slide out like it wasnt all the way engaged. If I try to hold it in gear it kicks and disengages and goes back in..."bucking" no reasonable amount of holding keeps it from bucking. I can keep it in to an extent.. but not under heavy load.

I mean.. I may be wrong. But I think that makes sense. Detent is just resistance for the stick to stay where you put it.

Ant88 said:

Hey Ben thats good to know, I am just about to get the gearbox out of mine tonight then I will be fitting my S3 bell onto my 2a box. Hopefully it is as smooth a fitting as yours was. Ant

Click to expand...

smooth? Well I suggest wearing gloves.
I am a bit scratched and cut.
Machined edges and cast housings can have sharp and jagged edges, and be covered with oil to slide all around causing injury.

Getting the input shaft gear onto the mainshaft is a bit of a pain. IT doesn't fit with the ?layshaft? gear on there.. so you have to stick your finger through the lower bearing hole to hold the bearing on there.. and get it back on the shaft with the teeth on that gear engaged into the input shaft. Otherwise it won't easily seat. I say easily, because I did it once.. but couldn't get it to happen again.

You only need to take off the 4 main housing bolts, the clutch mount plate cover thing and the ?layshaft?(lower shaft) bolt.
The lower shaft is pretty tough. People will tell you to take off the top and engage 2 gears. I found its far easier, if not working on the innards, to simply wrap a nylon web strap (such as a tow strap) around the input shaft and hook it to something on the transmission. When you turn the bolt the strap will tighten (or loosen if its on wrong) the strap on its self and give enough torque resistance to get the bolt off.


the transfer case comes off easily too. No BSW wrenches needed.

I suggest installing the transmission on the car without the transfer case. Makes it so much easier to thread the nose bushing. Easy enough to make up for installing the brake in car.

Hi guys, well I now have both my S3 box and 2a box bell housings off now. The problem I face now is the bearings for the Lay shafts are different sizes:



As you can see this does cause a problem. The bearings holes in the bell housings are also different which makes sense.



So how have folks sorted this problem? I have either thought to find a bearing that will fit a 62mm OD and a 19mm ID 17mm thick. Or would a spacer work and use an orignal S3 bearing.
A close up of the differances on the lay shafts 2a top S3 bottom




Another question is the Series3 box is a suffix "D" what is the difference between this and the "C" and lower? Is it just a gear ratio change? as these parts fit the 2a box so long as I use both the input shaft and lay gear together.

Any pointers will be helpful!

After doing some searching found out that a bearing does not exist of the dimesions required. So it's going to be a spacer. I have made a test spacer from nylon to see how it works. It works very well.





So would anyone have a suggestion of what material this would be best made from, thinking possible either stainless or hardened steel.

Ant