Citroën g/box Crown Wheel and Pinion - Page 3 - LotusTalk - The Lotus Cars Community
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post #41 of 229 (permalink) Old 02-15-2016, 12:12 PM
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@Gatzo7, how much do those ceramic bearings cost over the price of steel ball bearings (%-wise)?

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post #42 of 229 (permalink) Old 02-15-2016, 02:36 PM
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@Gatzo7, how much do those ceramic bearings cost over the price of steel ball bearings (%-wise)?
It all depends on the size and amount of bearings you will need. They take the SKF or bearing housing that you send in and as long as its serviceable they charge per the ball bearings.
If you call Jack and tell them what bearings you have. He will approximate the cost.
I sent them the front hubs on my European M6 and they had to machine the races a bit but the cost was 300 per hub. There were 42 balls in all (front and rear bearings per hub) Not cheap but...the reduction in friction is amazing. I spin the rotor on the Hub and it doesn't stop for about 10 seconds or so. with the stock Hub it spun for maybe one revolution. That also means that there is a vast reduction in friction and heat buildup. Jack once put a bearing in a vice and squeezed the heck out of it. It came out without a mark!
I figure it's more costly to take a transmission apart then to pay more up front. But, I would call them to discuss options first.
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post #43 of 229 (permalink) Old 02-15-2016, 05:57 PM Thread Starter
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@Gatzo7, how much do those ceramic bearings cost over the price of steel ball bearings (%-wise)?
They do only ball bearings, no rollers though.
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post #44 of 229 (permalink) Old 02-15-2016, 06:21 PM Thread Starter
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I know, I know! You'd say I'm beating the dead horse and u-b right!
There is nothing wrong doing that!

Here is a pictorial proof what is wrong with the crown ring kinematics on Maserati/Esprit w/ rearward facing gear box.
You're looking at the tranny housing from the clutch side, up is up, right is the driver side.
We want your drive shafts to turn forward=towards you. So should the crown wheel.
Pinion gear is to the left of the CW. In order for CW to rotate towards you, the pinion gear has to apply force to the COAST side of the tooth creating excessive radial load on the pinion bearing, which often causes casing failures.

Looks like a FUBAR

.
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post #45 of 229 (permalink) Old 02-16-2016, 06:00 PM
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They do only ball bearings, no rollers though.
They can covert tapered roller bearing with hybrid Conrad-style ball bearings. Since the ceramic bearing can withstand a heck of a lot lateral loads.
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post #46 of 229 (permalink) Old 02-24-2016, 05:40 AM
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Great article,, Very informative and I really appreciate you sharing this with us all. I guess I don't have to wear makeup anymore.. roflmao
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post #47 of 229 (permalink) Old 02-28-2016, 08:37 PM Thread Starter
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post #48 of 229 (permalink) Old 03-16-2016, 07:19 AM Thread Starter
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Citroen CWP on Esprit

Many of you are asking: how did it happened?
Citroen DS/SM engine rotates in the CW direction (seen from the rear of the car).
In addition, the gearbox is in front of the engine (@ss forward)!

Therefore,
if you rotate the box, (so it sits @ss backwards), and place it behind the CCW rotating mid-ship engine and keep the same gear-set, you get the "Esprit condition", i.e. the pinion driving the crown wheel gear on the "coast" flank of the teeth.

That also means that the whole transmission is spinning backwards, so the axial thrust from the helical gears adds to the end load on the pinion shaft rather than counteracting the thrust from the pinion crown wheel.

Not good...
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post #49 of 229 (permalink) Old 03-26-2016, 07:18 AM Thread Starter
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To all whose differentials failed:

I'd like to ask a question, how did it fail?

What gave up first, crown wheel or pinion teeth?

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post #50 of 229 (permalink) Old 03-26-2016, 07:38 AM
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In my case, both crownwheel and pinion teeth were worn/damaged due to crownwheel carrier bearing failure (42K miles).


That is why I'm such an advocate of replacing these if the 'box is removed.

Harry Martens sells SKF replacement carrier bearings, and JAE sell Timken. Both are more robust than the OEM bearings (which are stamped "Made in Poland").

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post #51 of 229 (permalink) Old 03-26-2016, 07:11 PM Thread Starter
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Yes, one should replace them with the best, SKF or INA with "Germany" etched on the race. Beware, more and more NSK bearings are made in China.
Better bearings have always the country of origin etched or stamped on the side of the race. If the marking is missing=questionable or chinese junk.

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post #52 of 229 (permalink) Old 03-27-2016, 07:47 AM
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To all whose differential failed:

I'd like to ask a question, how did fail?

What gave up first, crown wheel or pinion teeth?
I'm not sure it is possible to tell, since one tends to destroy the other. That said, of the failures I have seen, there is typically more damage on the pinion than the crownwheel. That could simply be due to the smaller tooth count on the pinion however.

Mike

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post #53 of 229 (permalink) Old 03-27-2016, 08:59 AM Thread Starter
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Hand of spiral

The hand of spiral on the spiral bevel gears is determined by the direction in which the teeth curve; that is, “left hand cut” if teeth incline away from the axis in the counterclockwise (CCW) direction whilst looking at the face of the crown gear. We have a “right hand cut” if teeth incline away from the axis in the clockwise direction (CW).
The hand of spiral has no effect on the smoothness and quietness of operation or on the efficiency, however there is a difference in the effect of the thrust loads.
Left-hand spiral pinion driving CW (viewed from the back) “tries” to move axially away from the cone center. Right-hand pinion gear moves toward the center (because of the oblique direction of the curved tooth).
If there is an excessive end play in the pinion shaft because of faulty carrier bearings or an excessive backlash, the movement of the right-hand pinion driving CW will take the backlash under load, and the teeth of the gear and pinion may wedge together (collapsing the lubrication film),
while a left hand spiral pinion under the same conditions would back away and introduce an additional backlash between the teeth, a condition that would not prevent gears from fluctuating. Ideally, the hand of spiral should be selected to give an axial thrust that moves the pinion out of mesh.
Esprit OE CWP has a right handed pinion spinning "backwards" and left handed crown wheel gear driven on the coast side (also "backwards").
CW tooth pressure angle is 14.5 deg. Gear cut w/ PA=20 deg is 15% stronger.

Driving the CW gear on coast side (Esprit configuration) may lead to double flank contact with a possible interruption of the lubrication film causing flank pitting and even flank fracture. (see last picture, marked silver)
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post #54 of 229 (permalink) Old 03-30-2016, 07:01 AM Thread Starter
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Both crown wheels have a left-hand cut.
The Maserati gear on the left (orange), has been driven on the correct "drive" side of the teeth (almost no wear).
The silver CW (Esprit) has been driven on the "coast" (wrong) side and it exhibits severe pitting and local micro-fractures.

.
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post #55 of 229 (permalink) Old 04-12-2016, 10:14 AM Thread Starter
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Citroen C35 Transmission Gear, Shift Point and Speed Calculator

Here is a very neat calculator with graphs.


http://www.gtsparkplugs.com/GearCalc.html

Citroen C35 was a workhorse of the post-war European truck&van transportation segment. This transmission has a variety of different (factory) gears available (Lotus in bold):

1st 2.93, 3.25
2nd 1.94
3rd 1.20, 1.272, 1.32
4th 0.85, 0.97
5th 0.666, 0.684, 0.76, 0.783

Final: 4.857, 4.375 and 3.888

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post #56 of 229 (permalink) Old 04-13-2016, 08:02 AM Thread Starter
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post #57 of 229 (permalink) Old 04-14-2016, 08:18 AM Thread Starter
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Rebuilding Citroen C35 transmission

Use the Citroen DS manual 814 (part 2 - Reconditioning)
You can download it for free here. It is a collaborative effort by all of Citroen DS/SM owners at Google Sites List.

https://sites.google.com/site/citroenpublicationslist/

More details and much better than the Service Notes.
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post #58 of 229 (permalink) Old 04-16-2016, 06:36 AM Thread Starter
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In "Esprit configuration" the whole transmission is spinning backwards, so the axial thrust (from helical gears) adds to the end load on the pinion shaft rather than counteracting the thrust from the pinion crown wheel.

Lotus owners should set up the pinion with the minimum depth relative to the center line of the crown wheel. That way at least you will maximize the mileage before the depth becomes excessive and you start to chew up the crown wheel. Notice the pitting at the very top
of the teeth.
.
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post #59 of 229 (permalink) Old 04-30-2016, 10:14 AM Thread Starter
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Have you looked at the oil flow when the box is rotating in the intended direction? Notice the drain going to the 5th gear extension.....what happens when the lower gear clusters are going the "wrong way"....and Esprits w/Citroen tranny have 5th gear oil problems! I am beginning to dislike the [email protected] way Lotus did things.
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post #60 of 229 (permalink) Old 04-30-2016, 03:48 PM
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I saw a Renault box at Ralph's shop where the owner was doing a lot of high power standing starts. He ripped some of the teeth off of the crown wheel. That is just flat-out abuse. As for wear-out, I would suspect it is hard to discern which one goes first since wear on one will cause wear on the other too. It will come down to which is softer and it is usually the crown wheel. Really doesn't matter since they are supposed to replaced in sets. Good point about the thrust and running backwards so the pilot bearing and the Nylotron washer have to work harder. Lotus did not give a lot of concern about longevity to their products. They never worried about their cars when they got old. Probably surprised they last as long as they do!
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