Hybrid gearboxes. In search of the perfect gear ratios.

[saxophonias]

So you want 1-2-3 from A4 and 4th and 5th and FD from A8 .

You need to swap the Final drive And secundary shaft from A8 into your A4 .The small gear from Secundary shaft and the Big FD gear need to be together.Also you can change 4th and 5th from your A4 to A8 ,you need to pull off the top gears from the shaft on both secundary and primary shaft .Those 2 shafts work together too.

Here's a picture of a Z6 tranny inside




The biggest gear is the Final Drive ,the tower of gears on the left is the secundary shaft and the tower on the right is the primary shaft.The top gear of the 2 towers is 5th .As you can see there's a 5th gear on the Secundary shaft and on the primary shaft.If you would count the tooth from both gears and divide them with each other you would get the 5th gear ratio of 0.771 from Z6.This works with all the other gears too.You can remove 5th from the secundary and primary shaft and replace them with 5th from a8 .It could be that either 5th gear from Primary or secundary shaft has the same amount of tooth and diameter as your A8 gears have,so you'll only need to swap out 1 gear.But most likely you'll need to swap both.

Nick hasn't been around for some time but maybe someone can help me on this one.
Sadly my old d14 gearbox is gone so I need either to get another one (I can get one for 100e) or to find the gears I want (2nd 3rd from a4). If I do the first, this means that I will have to pay for opening 2 gearboxes. So the price I got today from my mechanic is 450e, which includes the following. Unmount 2 boxes, open and close 2 boxes, swap the gears, install the clutch and flywheel, service what is needed and the purchase of the a4 box (100e).
If I manage to find the gears I want (maybe cheap or free from the guy that lost my stock a4 gearbox) this means that I will save considerable amount of money. But the question is this. Nick described the procedure of swapping gears and FD from a8 box to an a4 box. Now actually I want the opposite. That is to swap 2nd and 3rd gear from the a4 to the existing a8 box. Could anyone suggest if this can be done? I am trying to avoid the extra money of opening and buying another gearbox. Maybe if i can save money i will install an lsd.
The reason why I am in a hurry is because I noticed an oil leackage which comes from the gearbox. I think it is from the sealant of the crank, so it must be fixed.

[007]

Saxophonias, 2nd gear is solid with one of the shafts [I don't remember whether it is the primary or secondary shaft] along with 1st and reverse from what I've seen. so you cannot change 2nd without changing 1st and reverse along with it.

EDIT: I never saw the date of the last post. silly me.

[BETEK]

No, the 2nd gear it is not solid with the shaft. The shaft which it is on it is the counter shaft. So it can be changed independently.
For reference see please the gear with number 3 at the picture and link. The picture is from S40 transmission with 35mm differential bearings.
http://www.lingshondaparts.com/honda_ca ... k_03=15185

[007]

thanks for the picture Betek.

the cog on one of the shafts can be changed to alter the gear ratio but it is limited. the cog needs to have a different number of teeth while having the same diameter as the one it is replacing and needs to mesh properly with its counterpart on the main shaft. this is made tricky by the fact that if you change the number of teeth on a cog maintaining the same diameter and equal spacing between the teeth, the width of each tooth changes.

to *safely* change the second gear, you will need to change the main shaft in addition to the countershaft cog. that ends up affecting first gear as well.

[saxophonias]

but 1st gears are identical to all (3,125) so there is no problem i guess

[007]

the two gearbox variants we have here a first gear ratio of 3.23 [42 and 13 teeth on the big and small cogs]. US gearboxes seem to have 3.25 [39 and 12 teeth]. do you have the tooth count for your gearboxes Saxophonias?

[saxophonias]

no unfortunately

[BETEK]

Saxophonias, 2nd gear is solid with one of the shafts [I don't remember whether it is the primary or secondary shaft] along with 1st and reverse from what I've seen. so you cannot change 2nd without changing 1st and reverse along with it.

Do you meaning that the other cog of the 2nd gear is on the main-shaft on s40 transmission.
So it must be the number 1 on the picture, I guess.
But I think that the main-shafts on S40 transmission are interchangeable, aren't they?
If they are interchangeable there will be no problem on gear swaps, will be?
Please feel free to correct me.
http://www.lingshondaparts.com/honda_ca ... k_03=15642

[007]

yes Betek. it is #1. the shafts are interchangeable but to avoid any issues later like broken / worn teeth, etc., you will want to change both the main shaft and the corresponding cog on the countershaft for 1st, 2nd and reverse gears. 3, 4 and 5 can be swapped without any such restrictions.

[saxophonias]

So is it so hard to install 2nd and 3rd gear from a4 to a8 gearbox?