Lotus Elan

Lotus 5 speed gearbox in an S4 and concentric clutch

PostPost by: nmauduit » Tue Nov 04, 2014 11:06 pm

Hello everyone,

First of, thank you all for making this forum such an invaluable source of information : without it I would not have embarked in any of the following.

I have been working on and off for some time on a ?68 S4se FHC brought back from the US, and eventually after completion of body overhaul with a new paint, the first road test uncovered that one cylinder had low compression. Rather than just fixing it, I decided I should take time to overhaul the original block yet enjoy the car in the meantime, so went for swapping engines, and while at it I got tempted by fitting a 5 speed gearbox and a concentric hydraulic clutch.
So in case it is of interest to anyone, here is a summary of these steps :

Fitting a lotus 5 speed gearbox (from a +2) : many forum posts and the Lotus conversion article from the wiki were very useful, so that the 5 speed mount holder could be easily modified to reuse the chassis 4 tapped holes. The mount holder needs to go back about 21mm, so the front corners were flattened for allowing new holes. The clutch bell opening was used as the reference for longitudinal position, and when dropping the engine back the mounts fell right in place.

Propshaft : one was recut/fabricated to 29? compressed length (that plus 1 ?? for the extended length ? I was told it would be +2? but that was enough) ; one word of caution about the flanges, as for the 5 speed gearbox I actually needed a different flange than the diff one (and in spite of my warning, the propshaft place did not check and first used the wrong flange type for the front rather than the one supplied with the gearbox).

Gearbox lever : the top part of the original 5 speed lever (attached to the bottom via a cylinder filled with rubber) was removed, the remaining rod being about 10mm thus tapped M10, and a new, modified 4 speed lever was attached to it. NB: the original long nut sleeving into the rubber bush cannot be used, and the play on the lever needs to be reduced by reusing the thick washer that fits inside the chromed cylinder). As expected from posts on the forum, the axis position was a little rearward with respect to the position of the 4 speed gearbox lever, so to be on the safe side the fiberglass tunnel was filed to make sure vibrations would not cut into the rubber spring.

4 speed gearbox lever modification.jpg and
4 speed gearbox lever modification


Concentric hydraulic clutch slave cylinder from Saab 900 : an alloy holding plate was machined on a lathe, concentric with the guiding tube (pressed out) to hold the slave cylinder, then machined around the attaching holes to add lightness. Thickness was selected to allow for 6-8mm motion margin to the rear when the pressure bearing is in contact with the clutch plate springs (about 30mm from the gearbox face): that leaves plenty of forward operation motion (more than 10mm). Stainless 3/16? pipes were bent to connect the clutch (M10 fittings) to the master cylinder (3/8? fittings) via a braided hose, purge at the top.

Saab 900 slave cylinder.jpg and
Saab 900 slave cylinder


Last, a new fast road TTR exhaust : as seen on the forum, the 5 speed gearbox requires a little fettling of the exhaust, and the down pipes were cut after the first ?Y? then rotated about 20? to clear the gearbox before welding them back on. The long central pipe did not need any adjustment aside from cutting to length at the rear. To make room for wrapping (and life a little easier) the frame was widened rear of the engine mount (20mm cut, bent as a triangle 15cm long and welded back like a gusset).

TTR header chassis clearance.jpg and
chassis modification to clear the downpipes


TTR downpipe 20 degrees rotation at the first Y.jpg and
TTR downpipes 20 degrees rotation at the first Y


second Y gearbox clearance.jpg and
second Y gearbox clearance


The central pipe is attached next to the rear of the gearbox

gearbox rear clearance and hanging before mount.jpg and
gearbox rear clearance and hanging before mount


First try on the road did not show any problem so far, now I need to sort out details that were remaining from the restoration (replacing dashboard?) and tuning the webers, hopefully to be ready for next spring.
Last edited by nmauduit on Thu Nov 20, 2014 5:51 pm, edited 2 times in total.
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PostPost by: vernon.taylor » Wed Nov 05, 2014 6:59 am

Salut

That's really interesting - thanks.

Both a mate and I have Lotus 5-speed 'boxes ready to install - would you be able to make/source the concentric clutch adaptor plate, very pretty please (payment of all costs, of course)? And would you have the exact reference and source of the Saab 900 slave cylinder, please ?

Where are you in France ?

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PostPost by: nmauduit » Wed Nov 05, 2014 7:37 am

Bonjour,

the cylinder I used is presently on the usual auction site under the number 141275160056 for a reasonable price, coming from a Saab UK parts supplier (I mostly followed the excellent article from Victor Hollnagel).

The holding plate was locally machined a few weeks ago, and I am still to receive the invoice for it... I can ask how much a couple extra would cost, but I should stress that the front plate of the gearbox was also machined a little, to make sure that the setup will stay centered with the shaft (you can see that in Hollnagel's setup as well). In addition, 4 little columns (17.1mm long, so a bit more than half total thickness) were made to avoid the double nuts as shown in the article (I had originally planned to make all of a single piece, but this saved milling time).
For the sake of completeness, I also know of a commercial alternative offered in Danemark: their kit is based on a replacement front gearbox plate of their making (no affiliation on my side).

I grew up near Lyon where I still have some family, and presently reside east of Paris.

Nic
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PostPost by: vernon.taylor » Wed Nov 05, 2014 6:41 pm

Salut Nic

Yes, if you wouldn't mind asking or just wait for your invoice to come.

A couple of questions, if I may:

- is just the nose of the the front plate machined ?
- why ? Is it in contact with adaptor plate ?
- I assume this doesn't prevent going bck to stock ?
- is the Lotus bearing carrier and bearing used or is this supplied with the Saab kit ?

I came across the Danish site, too - looks nice but a bit pricey. Here's the link for anyone interested:

http://www.mio-engineering.dk/index.php ... duct_id=65

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PostPost by: nmauduit » Wed Nov 05, 2014 10:29 pm

Bonsoir Vernon,

- yes, just the nose was machined (in a similar fashion as in Hollnagel's article)
- this provides a true contact surface and make sure the slave adapter plate keeps everything aligned onto the gearbox shaft (a tooling piece was made to the effect of attaching the nose to the lathe)
- to go back to stock one would need to press back the steel guiding tube into the nose - if I was to do it, I would add a tube holder bolted in place of the adapter plate (and similar to it, though thinner and simpler), to make sure this tube is held in place sufficiently as some material has been removed from the nose.
- only the Saab kit is used for moving parts (not the lotus bearing or carrier)

ps: I may be able to ask for additional parts over the week end - I have to say this has been made as one of a kind, adapted in situ to the 5 speed gearbox clutch bell for thickness and without the intent of fabrication in series... this disclaimer in anticipation that some fettling may be required. :)

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PostPost by: vernon.taylor » Thu Nov 06, 2014 7:22 pm

Salut Nic

Thanks, again. Victor's article doesn't go into detail about machining the nose piece. I suppose the spacers you made up, or the double nuts in the original article, are adjusted to have a snug fit/contact between the slave adapter and nose piece ?

Where is your family in Lyon ?

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PostPost by: nmauduit » Fri Nov 07, 2014 3:55 pm

Hello Vernon,

the nose had to be machined a little bit for obtaining the desired total distance from the gearbox front to slave seating face anyway (to ensure proper slave operation: enough forward motion and some play in the back for when the disk wears out), so it was decided to make matching centering rings (male on the nose, female on the plate), like you find in prop shaft flanges. This ensures a stable centering and seating reference surface. The four little columns were then machined to suit for supporting the effort of the Allen screws attaching the plate to the gearbox. This ensures the the plate is not bolted at an angle and the slave stays perpendicular to the gearbox (it seemed to me that the stud/nut option would require some cumbersome adjustment for doing so and getting adequate attaching nut torque at the same time, and since there is little play between the slave and the shaft I preferred a more stable option).

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PostPost by: Chris » Fri Nov 07, 2014 7:12 pm

PIC_0267.JPG and
I have followed this topic with interest, and would make the following suggestions. Before embarking on this project, ensure that the heavier duty 1st motion shaft bearing has been fitted to replace the lightweight single row bearing initially fitted, some of the earlier boxes had this weak bearing fitted which allowed excessive end float causing 2nd / 4th gear change difficulties. Also, before machining the release bearing nose ensure the outer diameter is reasonably concentric with the bore which carries the tube as some were very badly cast.
Mine was so very eccentric, that I removed the nose and tube completely and fabricated a new carrier assembly. I ran the car for a couple of years until on a clutch change I fitted a different gearbox which I had previously rebuilt, and reverted to the original external slave cylinder system, as I viewed the concentric cylinder arrangement as a needless complication. I still have the gearbox with the concentric Saab cylinder fitted.
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PostPost by: nmauduit » Sat Nov 08, 2014 6:51 pm

Hi Chris,

thank you for your post: actually, I did ask the UK firm who overhauled my gearbox to change the narrow bearing for the modern, wide version, but they argued that it wasn't necessary, and just replaced the bearings with identical new ones (they disregarded the Hollnagel article I had sent for helping identifying what I wanted checked, and said afterwards they hadn't read it and had never heard about this issue, which I found surprising). In your experience, is it a difficult upgrade to do ?
Also, as a side question, why did you stop using the concentric clutch : was there a problem with the clutch mechanism, or was it because of an unrelated reason (e.g. 5 speed gearbox related, or something else)?
Had you modified the spigot bearing setup (in my case, I added a second one in a holder press fitted into the flywheel, to ensure a good, centered shaft support)?

Vernon, I asked today the guy who did the machining for my gearbox, and he would be ready to do a set of 5 for 300 euro each (if you and you friend took 2, and I a second one - I have an other S4 -, he would get started). This would cover machining the nose (that you need to send him), the holding plate and supporting columns with allen screws (not the Saab slave cylinder, hydraulic fittings and pipes, freight). As a precaution, a measurement of the clutch spring contact to the block would be advisable (to ensure proper clutch bearing contact and play). Let me know if you are interested and we'll go further into details.

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PostPost by: robertverhey » Sat Nov 08, 2014 10:15 pm

Following this with interest. I considered going concentric on the lotus, but (perhaps fortuitously), the concentric slave cylinder on my Audi s3 blew around the same time. What a nightmare job, three full days of sweating, cursing and skinned knuckles to separate the engine from the gearbox (albeit Quattro arrangement, and one heavy mother of a gearbox at that). A job which would have taken 15 minutes on the standard lotus external pivoting arm setup. I realised then what a beautiful, simple arrangement the standard ford/lotus one is.....

On another matter, I've also provided specialist repairers with photocopies of relevant pages of the shop manual to use as reference. Wheel alignment places and such. It's really frustrating when they say "nah, never looked at it". These people only get my business once.
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PostPost by: Chris » Sun Nov 09, 2014 6:07 pm

Hi Nic.
The early 5 speed gearbox gained a reputation for poor or difficult gear changes. One of the reasons was end float on the input shaft, On selecting 2nd or 4th gear whilst on the move, the synchro hub moves forward until the baulk ring contacts its cone. If this cone which is part of the input shaft is not properly controlled for end float, then the cone is pushed forward and speed sync is not obtained resulting in gear crunch. The permanent answer is to replace the narrow, and unobtainable weak bearing item no.4, listed on the gear change mechanism drawing in the 5 speed gearbox section of the manual. This bearing should be replaced by an RHP 6207 bearing which has the correct bore, but is smaller on the outer diameter, therefore a filler ring needs to be made to make up the difference. I believe that the later 5 speed boxes from the Excell were already converted by Lotus.
Is it difficult to do? Not really, but it requires thought and precision lathe turning. The input shaft has to be spiggoted to enable it to enter the bore of the new bearing, and the input shaft housing requires opening to accommodate the outer race of the new bearing.
Why did I revert back to an external slave cylinder? I did a clutch change, and found a small hydraulic leak from the concentric cylinder which a new seal would probably have cured, but as I already had a spare rebuilt and modified gear box, I decided to fit it instead. Would I refit the concentric cylinder? No I consider it a needless complication, as a leak means engine and gearbox removal.
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PostPost by: nmauduit » Mon Nov 10, 2014 11:52 am

Hi Chris,

thank you for the precise feedback: I will certainly look into upgrading this bearing upon the next gearbox intervention (hopefully not too soon...). I suspect the firm who overhauled my gearbox did not have convenient access to a lathe or machine shop and would not admit it, but they had in stock the thin bearing (their ref SJ050F0011 i.e. RHP 10-KLNJ30) they claimed was not a problem. When the gearbox came back I was in a bit of a time crush to get the car rolling for a long booked event (which I missed anyway), so I was reluctant to reopen the box and redo the job. Also, I'm hoping that added support with an extra needle bearing centered inside the flywheel for the input shaft spigot will help compensate for the thin bearing weakness. I guess I will be no the watch for a spear gearbox, just in case...

Regarding the hydraulic clutch, I think the Saab recommendation is to change the slave cylinder upon disk change, and I have stocked up a couple slave cylinders to that effect (in the hope it will not fail before the disk). I have fitted a reinforced clutch set which translates in a stiffer effort, and figured that the concentric action would be more effective and stable over time (provided that there is no premature hydraulic failure indeed). I don't know the mileage that reinforced clutch may cover, so time will tell...

Nic
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PostPost by: vernon.taylor » Thu Nov 13, 2014 8:04 pm

Salut Nic

I passed the info to my (French) mate this evening - we'll get back to you soon.

Thanks very much for the offer.

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PostPost by: gjz30075 » Tue Oct 20, 2015 10:54 am

An old thread revival, if you don't mind. I have a question to Nic, the OP concerning your gearshifter.
It looks like it's bolted down to the case rather than threaded in, per the Lotus tailshaft case.
Are you using a Type 9 gear stick with the three holed flange for bolting down, instead of the Lotus stick
that threads in?
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PostPost by: nmauduit » Tue Oct 20, 2015 11:35 am

Hello Vernon

I believe the gearbox and shifter is stock Lotus (early type apparently from the serial number) - here are a couple pictures of it as it came back after overhaul (some hex screws were changed for new ones) :

IMG-20140819-01850.jpg and


IMG-20140823-01851.jpg and
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