C35 LOTUS/MASERATI TRANSAXLE
There are 6,074 Esprits with Citroen C35 transaxle, (inboard disc brakes). Lotus 910 engine can be easily modified to deliver 300+ BHP, but the transmission is the weak link. C35 (Citroen SM) Gear Box was used on all Lotus Esprit models from 1975 to 1988.
C-35 gear box was designed for a normally aspirated car producing a maximum of 170 ft lbs of torque. The HCI Esprits made 220 ft lbs before bumping the boost. The C35 gearboxes came in an early version and a late version. S3 car has the late version, the one on Craig list is the early version. It probably came out a Citroen; the gear change isn't on the (RH) correct side; the rear cover appears different (the early boxes used smaller studs), it has a different bell housing and appears to have different output shaft housings and who know what ratios it contains.
The problem with the transaxle is that it was never designed to handle the power of the Turbo 910. Lotus first used it in the 160 Hp 907/ 912 powered Esprits, and that was a good match. But when they stepped up to the 910, they took the Citroen beyond its original design intent. They made some changes to the Turbo version of the gearbox that were supposed to strengthen it, but it was make-up on a plain girl... she was still of humble origins.
If you're contemplating hot-rodding your engine, then you need to understand that your limiter is going to be the gearbox. Most people have a household budget, and must live within that budget. Well, here you have a power budget, and you can't just spend beyond it its limits like a kid in a candy store.
It would be nice if the Crown Wheel & Pinion (CWP) were stronger, but there are no practical high performance options on the market. If you avoid dumping the clutch in the Stoplight Grand Prix, make rolling starts, and don't slam-shift thru the gears, then the Citroen transaxle is perfectly up to the stock 910. Looking at all the internet pics the drive side should be on the more vertical side of the crown wheel where the other side with the slope, coast, is supporting the load!! The Esprit is on the other side!
Thinking about how the Citroen box is installed, on SM, it is actually in front of the engine which makes the CWP design correct for driving the car forwards.
Lotus have the box going backwards!! I am not surprised that the CWP is always failing, they have the wrong design!!! The pinion is always trying to "escape", i.e. climb up the slope side of the crown wheel!
The more vertical side has to the drive side! Geometry is all wrong!
However, the 910 engine has a lot of un-tapped power potential, and you can easily create a monster that doesn't play well with others... i.e. the 910 will beat up on the Citroen. If you want big power, sell your car and trade up to a later SE/ S4/ S4s. Or do as Mike G is doing, jack up the body and slide a complete SE rolling chassis/ 910S engine/ V8 transaxle/
suspension/ AP Racing brakes under it. Short of that, you have a restrictive power budget limiting your wildest dreams.
The one modification to the Citroen that I do believe is worthwhile is to retain the spring loaded input shaft more securely. Both Harry Martens and JAE offer a more robust snap ring to replace the weak little wire circlip.
That alone will make a big difference. And/or, if you ever have the need to replace the input shaft, they also have replacement shafts with a shoulder for the snap ring to bear against instead of the taper.
There are no hot-rod internal parts options for the gearbox... not like the Holloway conversion for the Renault transaxle. If there were, then the next weak point would be the gearbox housing... it flexes at high power. Even if the gears & shafts could take it, the housing might not. All of which goes back to the original point that the Citroen transaxle was never designed to cope with the power a hotrod 910 can put out.
In normal use, the 1-2 synchros take a beating because they generally get used more often and harder. 5th synchros wear because there's a big step between 4th & 5th, and the synchro is asked to do a lot of work with each shift (apply pressure, don't rush it). Replace the synchros whenever you're in there just to keep them fresh, but there isn't an optional Porsche-style synchro system available. It's typical of how French transmissions shift... "They all do that, sir". The later Renault UN1 and the old Europa Renault transaxles are all the same. It is what it is.
If you wish to shift more quickly, install a Porsche transaxle and tell us all how you did it. There is no "standard" swap we can tell you about. The baulk-ring style synchro shifts at it's own pace and doesn't like to be slam-shifted. Apply pressure and wait for it to happen. If you force it, you'll just frustrate yourself and/or grind up precious metal. There are often message threads on this list that go something like... Graunch, graunch, graunch...
"Why does my transaxle grind when I shift gears?" Usually, it comes out in further conversation that the owner wants to shift FASTER. Well, maybe it is possible the synchros are actually old and worn out. But more often than not, it's because somebody is playing boy-racer, and trying to speed-shift baulk-ring synchros that, by design, don't like fast... and without having a clue how to match rpm-s. Slow down and shift the way the Citroen (Renault) is supposed to be shifted, or learn how to drive. But don't be blaming or flogging the gearbox.
BTW, of the two Esprit transaxles, the Citroen responds better to rpm matching than the UN1... or Europa. I can shift up and down from 1st thru 4th without the clutch, but 5th is a little more challenging. The Europas I've owned would never put up with that, and the Esprit Renault UN1 doesn't like it either. I'm not recommending shifting without the clutch, just suggesting that the Citroen's synchros do appreciate a little help from a driver who knows how to match rpms, and it would be a good thing for you to learn... as opposed to "fixing" the gearbox.
Harry Martens and JAE both offer (do... did... ??) a Quaife limited slip differential for the Citroen. The claim is that it's the solution for handling more power.
Of course, the limited slip will help put the added power to the road. But I get lost in the claims I thought I heard about it protecting other internal parts, like the CWP. That's where I get lost. If the power goes to one wheel, and the one tire breaks traction and spins, that's your safety valve. Loss of traction at one wheel happens at a torque level the CWP can handle, and adding more power after that just spins the tire faster without putting more power to the road.
If you install a limited slip differential, then power goes to both rear wheels pretty much equally. Both rear tires are sharing the load, and it takes a lot more torque to break loose and spin two tires instead of one.
That puts more load on the CWP, not less. I believe the premise of the claims is that if the one driving wheel hits a slick spot on the road and spins-up, then gets good rip on a clean spot (sandy to clean, or wet to dry), then all the spinning energy slams into the CWP when the tires finally bite.
That shock-energy is what kills the CWP, and the limited slip prevents (well, minimizes) the possibility of wildly spinning the tires with stock power. However, adding lots of horsepower can then spin both rear tires together pretty much at will. Then when both tires do bite, there will be even more violent inertia slamming into the CWP. The stock CWP didn't get any stronger when the limited slip diff was installed, it can only support so much torque and shock, and shock loads will strip off teeth. That gets us back to the repeating theme of all this... the Citroen transaxle was never originally designed to deal with the 910's power potential, there are no aftermarket hotrod parts available for it, and you need to deal with that. Or trade up to an SE.
FYI: I would add that there is an additional, and very good, U.S. source for some of the gearbox parts, SM World, in the valley on the north side of Los Angeles. The shop is owned by Jerry & Sylvia Hathaway, who are extremely competent and helpful. SM World is possibly the best Citroen SM repair and restoration facility in the world, as recognized by the Citroen factory:
Citroen SM World
When I bought my S1, the gearbox, along with pretty much the whole car, was completely disassembled, but all there. The 2nd gear synchros were shot as was the input shaft, the ring & pinion and a couple of bearings (the bearings were destroyed due to pieces, chunks really, of the ring gear teeth having gone through them). The P.O. was apparently not too good with a manual transmission!
I sourced the replacement parts from JAE (circlip and crankshaft pilot bearing), ring & pinion (used Citroen pieces from Harry Martens), SM World - Jerry Hathaway (bearings & synchros) and from some fellow owners (input shaft).
The source of the input shaft issue was resolved with a new used shaft and installation of a quality ball bearing in place of the sintered bronze S1 OEM crankshaft pilot bearing. The OEM Polish bearings are holding up just fine and there is no untoward noise or behavior. The used ring & pinion are also doing just fine as well.
Remember that the gearbox in the FWD Citroen rotates in the opposite direction so the ring & pinion wear surfaces are virgin when installed in the Esprit.
The biggest hassle when rebuilding the box is removing / installing the speedo drive gear in the 5th gear case. I made a tool for this task and it made the whole job (gearbox assembly) a one person single day affair.
TRANSMISSION CITROEN SM, C35 Maserati/Lotus Turbo
did a sort of "Zen Guide to Lotus Gearbox Rebuilds" which is here somewhere and might help...hopefully it'll make you smile a bit too, which is no bad thing....(!) It's HERE...http://www.thelotusf...-racket-thread/
gearbox rebuild - Gearchange/Gearbox/Clutch - The Lotus Forums
Crown wheel and pinion are made of special hardened steel and are matching pair with numbers. They come in several ratios.
Standard 8/35 (4.375:1)
Special track 7/34 ( 4.857:1)
and special for road cruising 9/35 (3.888:1)
BUREL PROVENCE AUTOS ANCIENNES / DS23.com
The weak points of C35 are:
CW low durability/quality carrier bearings, too high final gear ratio (4.375:1), and the fact that it runs "backwards".
Originally, Citroen C35 gearbox (used on ‘70s and ‘80s Maserati and Lotus Esprit), was designed to run in the opposite direction on Citroen DS and SM. For Lotus/Maserati configuration the whole gearbox was "flipped around", and therefore the CWP profile is running "backwards" !
Ideally, the pinion gear should rotate the crown wheel on the drive side of the tooth. If however, the pinion rotates the CW on the coast side, strength of the gear set can be reduced by as much as 20%.
Therefore, the Lotus/Maserati CWP is weak in forward drive and its strength is much better in overrun!
Similar situation exists on the front Land Rover differential, which KAM, http://www.kamdiffs.com/products-2/diff-ratio/
were able to resolve very elegantly. As it is mentioned on KAM website, in the OEM front axle of a Land Rover, the gear set is running “backwards”, being driven on the coast side of the teeth rather than the driven side and as such is weaker. Reverse cut gears are required in this configuration!
There are only a few Specialty Gear companies which have produced reverse rotation gear sets to allow the gears to be driven in the correct way.
The "beefed up" CWP with 9/35 (revised) ratio and correct rotation would be a desired fix for 80% of the C35 problems.
Cryogenic treatment and and REMS ISF superfinsh would add 20-30% strength.
In bevel gears, any off-set of the pinion from the crown wheel centerline is hypoid, and the further off axis the greater the hypoid effect.
The Citroen and Renault UN-1 pinions are their crown wheel's centerline axis, so they are technically, spiral bevel gears, not hypoid.