Fitting a Ribcase Gearbox to a 948cc Engine

You've asked and we have listened. A lot of our customers have questions about preparing to mount a later ribcase gearbox to a 948cc engine in Sprites, MG Midgets and Morris Minors.  We have created a video just for you to help understand the process.

Check out the video below.

Here is the transcript for this video:

Hi gang, its Brendan from Spridget Mania. Today we're going to tackle a topic with a short video that we get questions about all the time and that is how do you connect a ribcase to a 948 with a smooth case?

A lot of people that have original 948 like this one, probably some better condition than this one. They have a smooth case gearbox smooth case four speed that ends up not working out and slipping in and out of gear being too noisy having problems and of course because they're so difficult to rebuild and parts are getting scarce for these; they want to basically just swap it out with the ribcase. It is possible to do that but there are some misconceptions and there are some issues that I've seen talked about on forums and other things that I know to be wrong and I just want to clear up.

Some of that it can be done, so follow along in the video and I'll show you a few things that you're going to need to look out for. Just to start off with we're going to, I'll take this smooth case off of this 948. This one was off of a Morris Minor. I know that it was off of a Morris Minor because it has the mechanical clutch arm here for the release bearing. You can see it's got the little sort of eyelet at the end and that was for the mechanical linkage and it's also coming out you know of the right side and so this was probably from a right hand drive Morris Minor. If it was a left hand drive it would have been coming out at the opposite side because it was mechanical and so they put it on the same side as where the pedal box was.

So what we're going to do, is we're going to, we're going to take this off and I'm going to show you the steps that it would take in order to put a ribcase gearbox on a smaller small bore like this, this 948. So follow along, I have split the smooth case away from the engine as you can see it has the typical you know older-style 948 clutch package flywheel setup and that of course isn't going to change. You know that is going to be the same so when you have it apart, of course you know depending on the age of it you probably want to change. You know the pressure plate and your clutch disc unless yours are in good shape but of course once you have it apart you may as well just go ahead and swap that out. That part is all going to be the same 948 stuff. Now what are we going to do with this stuff, well if you're going to need that front cover or you're going to need a rebuilt one with a rubber seal in the front but you're going to need that style front cover and you're going to need that release fork and you're going to need basically all of that original stuff that's sitting around.  That input shaft because all that stuff has to go on a ribcase and the reason that all that stuff has to go on the ribcase is because all of that stuff connects and operates to all that stuff right so the only thing that's going to be different is going to be from that front cover back but everything else is going to be the same.

 Now if you've got a Morris Minor for instance, for your Morris Minor guys you're going to keep that standard mechanical release fork release (bearing fork) you know with a little eyelet and it's going to come out on the same side. So you're going to keep all that stuff and it's going to go right back on the other gearbox and there is a difference though in the clearance on the inside of where the selecting rods go through the case. I'm going to show you what those differences are because that's actually sort of the biggest thing that people sort of miss when they do this.

When they do this upgrade to a ribcase the other thing to keep in mind if you had a shifter on a smooth case it is not going to work on a ribcase so if you if you buy a ribcase you are going to need a ribcase shifter.  The ribcase shifter is longer, the little ball end that goes in here and go and sticks down into this area it actually goes down slightly longer. I'll do a quick shot of two of them side by side and you can see the difference, I think on garage site he's also got those he's got a really good page that shows you all the difference of this stuff. You can't use a smooth case shifter on a ribcase because it won't work. You need to get one that is made for the ribcase so keep that in mind. So the next thing I'm going to show you is I'm going to show you the covers and how they're different. So here are some front covers, these are all the sort of upgraded front covers that we sell, these all have the rubber seals in the front to help mitigate any leaking coming from that input shaft which is really common on smooth cases and on ribcases and I want to show you a difference in these. One of the first differences you're going to see, these two here on this side these two are four smooth case gearboxes this one over here is the 22G118, that's four ribcases you'll notice the pivot point for the release fork is higher, see that, see how it's taller this one here is for the smooth case this is the ribcase. As you can see it's a little bit taller and it's a different shape, well that pivot point hence it has to be the same because again if you're using the same clutch package you have to have the pivot point and the release fork in the same place that it was before.

 You’re going to be using one of these covers on a ribcase but there's an even more important difference and I'm going to show you that right now. If you take the ribcase cover and you turn it over and you look in this recessed area here this is where the rods that control the shift forks. Inside this is where they come through the front of the bell housing and they go into this area just like this. This one over here has this recess here, well if you look at a standard smooth case that hasn't been modified and you flip this over, sorry it's this one, you'll notice that one has a recess that one has a recess and it's this recess right here that we're looking at this one that's well I guess it's kind of in the nine o'clock position here, but it's this one right here. Well over here on the ribcase you'll notice it's deeper and it's a little hard to see in the video but trust me on the ribcase it's deeper here it's more shallow and if you don't actually machine this a little deeper to match how far those rods come out they won't come out far enough and you won't be able to shift properly.

So what we do is we actually machine this to match the depth here and what we do and you can see the machining on this one you can see that this one's been machined you can see that we've made the depth to match that of the ribcase cover see that.  I'll give you the measurements of what it is and you can measure it yourself, so if you have one you know if you have one like this you can have it machined. You can bring it to a machine shop and have it put on a mill and you can have them take care of it you could do it with a drill bit although you'd want to use a flat drill bit not a pointed style drill bit so you get the flat profile in it but you could probably do it, shade-tree mechanic could probably do it. I can tell you what the difference is and how much material you have to remove okay.

I promised I was going to show you that dimension and what the measurement was for the clearancing this being the ribcase front cover and it's this distance that you basically have to reproduce in a smooth case cover and that's what we've done right here. Alright, that's the same orientation you can see that it's, so this area is now this area and the dimension as measured across this flat and splat surface down is

about 0.825 inches. That's where we clearance it to that gives us enough room so that that one selecting rod can go all the way through and it doesn't bind up and stop on your ribcase and so that's why you can use this with the correct pivot point on your ribcase box. So that's what that dimension is so we do that in order to better match this and then this can be used on the ribcase. Okay so I've got a couple smooth cases here I want to just show you really quickly, this is what I'm talking about, this one's got the cover off and you can see that those selecting rods. Now they protrude through the front of the bell housing and that's the area that recessed area of course that's part of the front cover and that's where they stick out. You can see how they protrude, and that's what your clearancing for when you're taking that material out of the smooth case cover and you're putting it on a ribcase.

Now this is the reason why, so I have two of the three of those selecting rods right here and I'm gonna try and show you this. So this top one here is the one that's out of a ribcase and this one is the one that's out of a smooth case and if you look at it you'll notice the ribcase one is longer you'll also notice that means that the detents, it also means that the holes for the selecting forks, they're in a completely different place. These are not interchangeable and these are longer then the ribcase ones are longer and the smooth case ones are shorter. And here's another one you can see it's a little hard to see here but you can tell that the one on the bottom, that's the one for the ribcase. This one on the top, that's for a smooth case and they are different links and again that's going to put the detents, the recesses for the detent balls in a different place and again it's also going to put, you know, the holes that secure the the forks inside for the shifting, the sliders, it's in a different place. So these are longer the ones for the ribcase are longer than they are for the ones in the smooth case.

And then there's also another crucial difference as well, the input shaft, so you can take a smooth case box and you can do something with it that you can't do with a ribcase box. You can actually set it flush on the bell housing and stand it up because you look at it from the side that input shaft doesn't actually protrude but on a ribcase it does, so this is something that you can't actually do. See that you can't do that with a ribcase because that input shaft it sticks out and so it's going to sit there like this and it's just going to kind of rock around because it's actually going to sit on that on that input and so that's something you can't do.

 So that's a difference as well and of course what that means is because it means that the pilot bush that's in the back of the crank, the input shaft on the ribcase is going to go further in.

So one of the last things that you're going to need to do, this is a ribcase front cover 22G118 and you'll notice that when you get this in here these top two, these studs are pulled out but they're drilled for the studs right there and this is just going to go right, you know right on to this case. But when you fit a smooth case cover these two top holes for the studs are actually in a different place. They're moved over so you notice when this goes on here you'll notice that this one has moved up and this one is moved down over here, they actually correspond to these spots right here, and right here and you'll notice that they're not drilled. So one of the things that you're going to have to do is you're going to have to take the stud, you'll have to take the stud that goes into this spot and what you're going want to do is you're going to want to do, you're going to want to cut it off with a grinding wheel and then just put a little slot in it for a slotted screwdriver and then what you can do is put Loctite on that and just screw that stud in until it's flush with that slot using a slotted screwdriver. Fill these two holes and then you're going to of course have to drill a hole here and a hole here for the smooth case cover so you'll take your smooth case cover and then that of course will just slide back on all the other studs and are going to line up. So all of these studs down below will line up just these two will then have to be drilled of course. What you want to do is, you'll want to bolt this up right and you can drill, you know just use these as a guide. Drill through here and then tap for your holes and then you're done.

 And here's the thing, it doesn't matter whether or not you're coming out of this side of the bell housing or whether you're coming out of the other side of the bell housing like with this cover because those holes end up in the same spot.  These holes are in the same spot whether you come out of here or whether you come out of this side.

 Okay so that's one other difference that you'll have that you'll have to make in the bell housing of the ribcase. When you put a smooth case cover on it, so one of the things that I noticed on this 948, so this 948 actually already has a 1275 style stick backplate on it which means that at one point this 948 probably had a ribcase that was already connected to it. Normally of course it would have this stamp type, this real thin stamp type backplate that would be right there and of course because this one's already got the thick backplate on it you can bolt up the ribcase to this without any issue.  But what I'm going to do is I'm going to, I'm actually going to pull this off and I'm going to, I'm going to attach this temporarily and then we're going to try to fit a 1275 ribcase to it and we'll see what happens.

Okay so we have our steel backplate on here and that is the one that would have come from the factory with the smooth case box and as you can see that mates up all fine and dandy and there's no issue with that whatsoever. And that would been the original configuration here, but I'm going to show you something that I discovered lately and many of you may have already known this but until I had done it I had it down as an old wives tale and I wasn't sure so I had to try it myself.  And that is even with the thin back plate on the nine forty eight yes indeedy-do a ribcase will bolt right up to it so there is no issue as far as the back plate goes ribcase will go on just like a smooth case will there you go as you can see there's no issue whatsoever it will bolt right up and even though the input shaft on these is slightly longer we've checked it with clay it doesn't bottom out in the back of the crank you know it doesn't rub up against the pilot bearing in the in the step on the input shaft or anything it bolts right up and everything you know it clearances the oil cover and everything else as you can see this is just as just as flush as it was with the bell housing on the smooth case. So there's no reason to change this steel stamped backplate on a 948 as you can see that is that's one thing, you don't have to change so once you get the gearbox off everything that's already on the engine can stay on the engine all of that can stay.

 Okay, I promised I was going to show you the difference between the ribcase and the smooth case shifters. These are all the late type shifters, the ones that have the vibration dampener on them the sort of shorter one. And I want to show you the distance from here to here. This parts longer than the distance from here to here is longer than it is on all of these smooth case shifters some of these are forSprites and Midgets and these longer ones here, this is the Morris Minor type they're a little bit longer. I got this crazy thing I thought this was a magic wand okay, that came out of a Mini, that one's even longer. I'm going to set that one aside. But anyway, so these are all smooth case, so you'll notice if you put the smooth case which is on the left next to the ribcase the ribcase is taller and it goes further down into the remote housing to engage the shift levers so this this style this shorter style will not work in a ribcase you have to use the longer style which is for the ribcase. So if you get a ribcase and that's what you're going to be swapping out, make sure that you get a shifter with it. So that's the difference between the smooth case and the ribcase gear levers.