JB3 Ratios

[Stuart Clark]

I am struggling to get the right final drive to run into fourth gear, does anyone know what vehicle uses the JB3 that has lower ratios, poss 5 diesel or extra van? I could do with 4th gear being 1.15 to 1.............................any ideas :confused: cheers:)

[Sparkie]

r11 turbo? what about the volvo 480/440 boxes?

[Stuart Clark]

r11 turbo? what about the volvo 480/440 boxes?

has anyone got any ideas as to where to find the info, also another quick q, does the volvo box use the same spline as renault?:agree:

[Andrew Cooke]

I've not got my notes to hand, but all standard 4th gears will be in the 0.97 to 1.03 range. All 3rds are 1.32 (from what I remember, if not that, close to it)

[Andrew Cooke]

OK, got my notes, what total ratio do you want in each gear (gear * final drive)

eg

GTT has 0.97*3.73 = 3.618 for 4th
R11T has 0.97*4.07 = 3.948 for 4th

you need to look at ratios 1-4 as they come on a complete cluster.

[Stuart Clark]

OK, got my notes, what total ratio do you want in each gear (gear * final drive)

eg

GTT has 0.97*3.73 = 3.618 for 4th
R11T has 0.97*4.07 = 3.948 for 4th

you need to look at ratios 1-4 as they come on a complete cluster.

I am using a 3.313 diff which is the bolt on crownwheel type and v expenxive to change, fine whilst running 3rd at 123 but thats max so now need another cog as as trapping at over 125 but feel launch would improve and not stress the transmission as much if all ratios were lower but i still ned to aim for 130 in 4th at 7500 which on a 3.313 diff equates to a 1.12:1 4th gear, total ratio of 3.711 which is close enough to the original gtt box but i dont have a bolt on 3.73 final drive crownwheel which my lsd needs......

[Andrew Cooke]

do you current;y have GTT ratios? I'm asking because the GTT has a 3.09 1st, but most of the boxes with a shorter 4th have a 3.73 1st, and a big drop 1-2. There is a box showing with a 3.09 1st and a 1.03 4th (I don't think there is a JB3 box with a lower 4th).

There appear to be JC5 boxes with 1.1 4ths, with either 3.36 or 3.73 1st, I don't know how much mixing and matching between JB3 and JC5 is possible???

I'd have to really trawl through old notes, but I recall close ratio clusters that would give you a lower 4th, but £1600 springs to mind...

[Andrew Cooke]

How about you sell the LSD, and run a free diff, or weld a std diff up?

[Kempy]

http://www.racedandrallied.com/rally-cars-for-sale/rally-cars-parts-for-sale/avanti-fwd-renault-clio-close-ratio-gearbox-suit-rally

I havent got a clue on gearboxes, but seems very expensive.:eek: If its even the type of thing your after. :scratch:

[Stuart Clark]

[quote=Andrew Cooke;78351]do you current;y have GTT ratios? I'm asking because the GTT has a 3.09 1st, but most of the boxes with a shorter 4th have a 3.73 1st, and a big drop 1-2. There is a box showing with a 3.09 1st and a 1.03 4th (I don't think there is a JB3 box with a lower 4th).

3.09 1st 1.84 2nd and 1.32 3rd so yes i think pretty std but taller diff, the torque spread i have is huge and the nos can accomodate almost any ratio change so different lower ratios should be ok, its just the need for more revs at 130 than the 3.3 diff can give me as its too tall to pull, it would pull 161mph in 4th at 7500 in theory:)

[Andrew Cooke]

that sounds like a GTT cluster.

If a JC5 cluster can be used you could look at what I believe to be:

3.36/1.86/1.39/1.10 (cluster set G)

Going to 7500 will drop you to:
1-2 4152
2-3 5605
3-4 5935

The alternative is 3.73/2.05/1.39/1.10 (cluster set I)

giving drops to
1-2 4122
2-3 5085
3-4 5935

Cluster set I looks very rare, G is more common, all come as standard with 4.07 final drives.

[Andrew Cooke]

many of the ratios, box numbers, and vehicle codes are listed in here

http://tv.isg.si/site/ftpaccess/mloncar/Menjalniki_.pdf

I've just taken the time to print them out, and convert the fractions to decimals :rolleyes:

[R5GTTRaider]

http://www.racedandrallied.com/rally-cars-for-sale/rally-cars-parts-for-sale/avanti-fwd-renault-clio-close-ratio-gearbox-suit-rally

I havent got a clue on gearboxes, but seems very expensive.:eek: If its even the type of thing your after. :scratch:
thats cheap mate

quife boxes are triple that but its a custom geared box using strong metals

[R5GTTRaider]

get one of these only 7k

http://www.quaife.co.uk/shop_image.cfm/image/560/product/FWD%206-speed%20%20sequential%20universal%20gearbox

still would make shifting easier

and any raito you want :agree::D

[Stuart Clark]

Cheers, all good stuff, that avanti gearbox has been sold....:(
Does anyone know if JC5 internals will fit in the JB3 box?

[Matt Cole]

Good thread this. Glad your sticking with the j series box mate, gives us all a little hope!!

Just out of curiosity mate, how many gearboxes(JB3) have you destroyed??

[Stuart Clark]

Good thread this. Glad your sticking with the j series box mate, gives us all a little hope!!

Just out of curiosity mate, how many gearboxes(JB3) have you destroyed??

Just 2, after uprating the clutch to a 350 pound spring and using a single solid plate i broke a driveshaft at pod, changed it and then smashed 1st gear apart. Built it up and at york blew 2nd gear to bits.
Changed the clutch to twin plate and 300 pound spring and all has been ok since. My prob is a 55mph 1st and 95mph 2nd, thats why the gearbox gets so much stress.

Hopefully as said above i can improve my et and improve reliability by running lower ratios and into 4th.

Even after the breakages i have had i can honestly say that a well built jb3 takes some beating:)

Please find me a 4:1 bolt on crownwheel and pinion.............pretty please, these specialist companies are making my eyes water, the prices thay are quoting. Got a good offer from Gripper but i think theirs wont fit my zf type diff...:confused: