1098 gearbox conversion

[SUE482]

After many miles of putting up with my old and seemingly reliable 803 gearbox I have decided to “upgrade” to a 1098 and use the old tail extension in order to keep the interior look of the car as per original.
After much searching and advice from all on this forum and from Declan in sending me details of previously published conversions, I decided to to start from scratch and do it myself although I must say the article by T. K. Marshall was most helpful in pointing out the problem areas.

This is the result which I hope, IF ALL IS SUCCESSFUL, will assist others in doing the same modification.
I am going to ignore the ratios, mounting differences and clutch/flywheel problems of the three boxes, i.e. 803, 948 and the 1098 as this has been covered in many previous threads and just concentrate on the mating of the 803 tail piece extension.
Whilst I am at it the 1098 gearbox is having a strip and full examination, the procedure of which is in my Haynes manual although it's for the 948 box, it's basically the same.
Any suggestions, comments, observations or requests for more pics would be more than welcome, so here we go.

This is the 803 gearbox
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This is the 1098 gearbox with the extension removed
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Here we have the the two extensions 803 on the left and the 948/1098 on the right, the 948/1098 extensions appear to be identical except for the bearing recess for the 3rd motion shaft.
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and the two faces of the extension pieces again, 803/948 on the left and 1098 on the right
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And this is one of the reasons why there is a need to have a plate between the gearbox and the extension, on the 1098 the 3 motion shaft bearing and circlip protrude above the face, and on the 948 gearbox the circlip is flush.
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803/948 bearing recess
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and the 1098 bearing recess
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I did consider machining out the 803 extension to fit like the 1098 extension but as you can see there would be insufficient material left to safely house the bearing. On the 1098 gearbox it is much more meatier in this area I suspect for that very reason.

Time for a cuppa

[SUE482]

Anyway back to the removal of all the parts, just follow the Haynes manual. I found it ok up to the point when the 1st motion shaft is removed, instead drive the shaft in as it says but by only just enough to enable the circlip to be removed from the bearing and then drive it back into the gearbox and remove the assembly from the inside, the lay-gear can then be removed but measure the end float before you do, if it's out of spec calculate and order a new rear thrust washer.

A good clean up was now required, I brushed Gunk on the casings and let it soak for ½ hour and then jet washed it and finally lots of blowing out with an airline. Gears etc. were soaked in diesel and thoroughly cleaned and examined. I found that all those parts you would expect to replace, lay-shaft and needle bearings, 1st and 3 motion shaft bearings including the needle one for the 3rd motion shaft, and a new rear thrust washer to control the end float on the lay-shaft, extension end oil seal and speedo oil seal, there was additionally the reverse gear that required a new bush although the shaft was fine, and a replacement baulk ring as one was quite worn.

Ordered all the parts required with the exception of the shims required for the 1st and 3rd motion shaft bearings, don't know yet what is required here.

Waiting for parts to re-assemble then its on to the conversion
I am going to use biomed32uk excellent pdf for assembly:
https://dl.dropboxusercontent.com/u/509 ... ebuild.pdf

[liammonty]

Good job! I don't remember whether you're car is an early or late SII, but if you want to keep the original speedo (and not read 50 % fast!), then don't forget to use the drive gear off the 3rd motion shaft of the SII gearbox. I suspect you've already done it, but I mention it just I case as its a real pi**er if you forget it and only realise when the box is back in the car!!

[SUE482]

Hi liammonty its a 55 so it's late I suspect. I did realize about the speedo drive but thanks for the reminder. Cheers Ian.

While I'm waiting I might as well get the spacer plate ready, I am using an old 948 extension by sawing off the end bit as shown.
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This now needs to be machined down to the correct width and altered to fit over the bearing. Referring to the two articles supplied by Declan, Juergen Feye-Hohmann indicates a 6.2mm (0.244) thickness whereby T. K. Marshall says 3/16” (0.188), I make it 0.158.

I have just measured the length of the selector rods from the face of the gearbox, and the difference between the 803/948 and the 1098 is 0.158, interestingly it corresponding to my plate measurement calculations. I am going for that

By my assumption the wider the spacer plate the more packing shims are going to be required on the end bearing.
Now where are those parts I ordered

[customjob]

Surely far simpler to fit 1098 flywheel & clutch and remove remote gear selector on top of 1098 box and re fit.
I have an 803 with 948 internals in the gearbox, removed remote selector and re fitted back to 803 engine.

[bmcecosse]

Yes - I rather wondered if the long gearlever can't just be fitted directly to the later box, without the remote control housing. The slightly longer selector rods may spoil that idea - but maybe they can be modified? Or changed for the shorter/earlier ones? I'm pretty sure we read a while back about this conversion being done without a spacer plate.

[SUE482]

You both raise an interesting dilemma and haven't grasped one of the basic problems, if you look at the picture showing the 3rd motion shaft bearing again, you will see that the 803 extension will not fit without machining, and as I have said there is insufficient material to do so.
I did however consider replacing the 1098 bearing housing with the 803/948 housing which would mean you could then mate the 803 extension, however, the selector rods would require modification and there might be problems with the different position of the 3rd motion shaft. In short a spacer plate is the easiest solution. Its horses for courses.

[bmcecosse]

The suggestion is to only remove the remote control from the 1098 box - and fit the long gearlever in it's place - still retaining the 1098 tail assembly.

[SUE482]

Ah! Now I see what you are suggesting, there are gearbox mounting and gear-stick differences I believe, but worth a look.

[SUE482]

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Well here we can see the difference between the 803 gear-stick position and 948/1098 proposed extension gear-stick position, not very similar and I would think it would require a complicated conversion piece, to me it looks like a lot more work to accommodate.
Customjob I would be interested in how you did the adaption.
So coupled with the fact the rear mounting would also require adapting, I think I am discounting that avenue and going back to plan A.
Parts have arrived so forgive me while I complete the rebuild.

[bmcecosse]

Oh right - it is quite different then !

[SUE482]

Rebuild nearly complete, but at this juncture a measure of the spacer plate requirements can be undertaken, and as you see it corresponds to my previous measurement before the rebuild, of 0.158.
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This means when the plate has been fitted the top of circlip on the bearing will be flush, as per 803/948.
While we're at it the speedo gear needs to be moved back by the same amount, here it is done.
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[SUE482]

A couple of things to consider at this point, firstly the speedo gear as pointed out by liammonty, since I intend replacing the original diff of 5.3 with a 4.2 then the speedo gear from the 1098 box will be OK if I change the speedo to a 1376TPM, and secondly the reverse gear selector rod requires modification to prevent accidentally selecting reverse. This is achieved as outlined in T.K. Marshall's explanation, by welding in a step of metal so that to select reverse, the gear leaver has to be lifted over the step, like this.
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[liammonty]

Nice mod to the reverse selector. I used the selector from the 803 box, which fits into the 948 OK, but it's all much more similar to the 803 box than your ribbed box I think. The speedo and diff combo you are using will be fine I think. I was more limited regarding speedos, as my SII was an early one (with the MM-style dash) which means you are limited to just 2 speedos - those from the MM or the original SII one, so I had to swap the gear to suit the speedo.

[SUE482]

Back a bit to the reverse gear bush, removal of the old worn one is done by pressing out using a vice, and replacement again using the vice after the gear has been in the oven and the bush in the freezer for an hour. It then requires reaming out to the correct size.

Speedo oil seal and extension end oil seal are replaced in the same way by putting the extension and speedo oil seal in the freezer and the extension oil seal and speedo drive housing in the oven, not to hot though, the speedo oil seal just slipped in but the extension end oil seal had to be gently hammered home.
Note that the 803/948 speedo bushes and pinon were brass and 1098 plastic.

[SUE482]

Thanks for that liammonty, I'm having a problem locating a gold faced 1376 speedo at the moment, keep searching eBay.

Well while I am waiting for my spacer to be machined to size I thought I'd measure up for shim requirement for the 1st motion shaft bearing. Since the front cover looked pretty worn and there was a substantial quantity of old oil in the bell housing I decided to renew with a modified one with an oil seal. But look here,
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the bearing recess is somewhat deeper, this means more shims, 40thou instead of 15thou to be precise, so bear this in mind if you are tempted to replace the front cover at any time.

[SUE482]

Well here we are the spacer plate back from the machine shop and measurements taken indicate 20 thou of shims required on the 3rd motion shaft bearing, what with 40 thou on the 1st motion shaft bearing that gives me a requirement of 6off 10 thou shims. Another delay while I order.
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[SUE482]

Well the new front cover with oil seal was a waste of time, when fitted the 1st motion shaft nut binds with the cover, you can just see where it catches here, in fact it locks up solid
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As a comparison this is the original cover, you can see the there is much more space available to clear the nut. I suppose I could have it machined out but I don't feel like correcting it so I'll use the original cover.
Cheers Roy I should have taken you advice in the first place.
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Anyway back to the conversion, gaskets and spacer plate in position for the tail piece, but then another problem became evident, when the tail piece is fitted there is insufficient clearance with the reverse rod selector and it pushes in the rod so that no gears can be selected, at least that shows that the interlocking system is working. If the spacer plate had been 50thou thicker, no problem. You live an learn.
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I could think of 3 solutions, thicker plate, grind the end of the rod down or machine the offending piece to give addition clearance. I chose the later like this, you can just see the small recess to accommodate the rod
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This gives sufficient clearance on the reverse rod and all now is fine, gears select ok and the box is ready for it's tail piece.

[bmcecosse]

Well done - only possible if you have the machining facilities of course... Send that 'seal conversion' back for a refund.....

[SUE482]

Already done that Roy, plus the postage.