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| Diff Ratios https://www.ausmini.com/forums/viewtopic.php?f=2&t=55697 |
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| Author: | Drexxle [ Sun Aug 02, 2009 8:27 pm ] |
| Post subject: | Diff Ratios |
I have just had the pleasure of rebuilding a diff, and have now got everything i need except the two end copper bearings for the inner shaft. I also have the option of a diff gear, going through what was available to me with thanks to Steve at Brickworx/Miniworx, there are a number of ratios. if i remember correctly, 15/64, 17/67, 17/68 and 18/68 Can somebody explain the use of each, which is faster on the highway, which is better up a hill, which is a good alrounder. I understand the numbers represent the amount of teeth, but would like to get an understanding of what the end result of using said ratio is. |
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| Author: | 74snail [ Sun Aug 02, 2009 8:30 pm ] |
| Post subject: | |
The Rover 3.2.1 is a good highway and economy ratio, but the 3.44.1 ratio is the best allrounder. |
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| Author: | sgc [ Sun Aug 02, 2009 8:33 pm ] |
| Post subject: | |
74snail wrote: The Rover 3.2.1 is a good highway and economy ratio, but the 3.44.1 ratio is the best allrounder.
Depends on the engine, but I'd agree with that statement for most road-goers. A 3.44 will get you 3,840 RPM at 100km/h which isn't too high to deafen most of the time. At 3.65 you're pulling a shade over four grand at 100, which starts to get noisy after a while 
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| Author: | Drexxle [ Sun Aug 02, 2009 8:34 pm ] |
| Post subject: | |
Given the Ration is 3.44.1 do you know what the markings on the diff gear actually are, ie teeth numbers or part number. |
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| Author: | sports850 [ Sun Aug 02, 2009 8:45 pm ] |
| Post subject: | |
Drexxle wrote: Given the Ration is 3.44.1 do you know what the markings on the diff gear actually are, ie teeth numbers or part number.
Can't remember them from memory but look at the number's of teeth you've given above , if you divide the number of teeth on the crownwheel (big number) by the number of teeth one the pinion you'll get the reduction ratio . |
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| Author: | Drexxle [ Sun Aug 02, 2009 8:53 pm ] |
| Post subject: | |
im not sure currently what is in the motor, 1100 60thou, 12g202 unleaded 2mm skimmed, standard 4 synchro that was on the '75 Mini S. I have currently have picked out the 18/68 which works out to be 3.777. Given that i want to look at the gearbox soon, i could look at changing the pinion gear at the same time. |
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| Author: | 64cooper [ Sun Aug 02, 2009 9:28 pm ] |
| Post subject: | |
Beware of the selection you are making as the pinions will only work with the corresponding crown wheels as per the attached table. 
It would be nice to have the 3.2 for the road trip you are on but as others have said, stick to the 3.44 and avoid the speeding fines. |
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| Author: | Drexxle [ Sun Aug 02, 2009 9:46 pm ] |
| Post subject: | |
awesome post of chart thanks. I take it BL is british leyland. i will get my book out and double check against this chart tomorrow. will also double check markings on crown wheel which i know was 18, but could be 62 not 68. |
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| Author: | Drexxle [ Mon Aug 03, 2009 12:59 pm ] |
| Post subject: | |
after checking the book it lists the gear ratios but ot the diff ratio, so the only way to check is to take the diff out and spy the stampings on it. I wil grab a pinion gear just to be on safe side. and ill keep the 3.44 18/62 gear. |
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| Author: | Kennomini [ Mon Aug 03, 2009 5:33 pm ] |
| Post subject: | |
Is this correct, a 2.76 will give fast acceleration and a 4.33 will give low revs at high speeds, correct? Also which number represents the revs of the engine and which one's the complete turn of a wheel? |
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| Author: | Morris 1100 [ Mon Aug 03, 2009 5:38 pm ] |
| Post subject: | |
Kennomini wrote: Is this correct, a 2.76 will give fast acceleration and a 4.33 will give low revs at high speeds, correct?
No, you have it arse about. 2.76 will give no acceleration and a 4.33 is a drag racing diff with a top speed of about 100kph. 
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| Author: | Kennomini [ Mon Aug 03, 2009 5:48 pm ] |
| Post subject: | |
Morris 1100 wrote: Kennomini wrote: Is this correct, a 2.76 will give fast acceleration and a 4.33 will give low revs at high speeds, correct? No, you have it arse about. 2.76 will give no acceleration and a 4.33 is a drag racing diff with a top speed of about 100kph. Ok so which number represents the engine revs? and the correct way to say it is 2.76 too 1 (2.76.1) Correct? |
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| Author: | Morris 1100 [ Mon Aug 03, 2009 5:56 pm ] |
| Post subject: | |
Kennomini wrote: Morris 1100 wrote: Kennomini wrote: Is this correct, a 2.76 will give fast acceleration and a 4.33 will give low revs at high speeds, correct? No, you have it arse about. 2.76 will give no acceleration and a 4.33 is a drag racing diff with a top speed of about 100kph. Ok so which number represents the engine revs? and the correct way to say it is 2.76 too 1 (2.76.1) Correct? With a 3 to 1 (I know that don't make one but just for example) diff the engine will do 3 turns to one turn of the front wheel when in top gear. With a 2.76 to 1 the engine will do a little bit less revs than a 3 to 1 at the same road speed. With a 3.44 to 1 the engine will pull more revs than a 3 to 1 at the same road speed. |
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| Author: | Super-mini [ Mon Aug 03, 2009 6:20 pm ] |
| Post subject: | |
is the 4.3 a bigwheel moke diff? i think 3.4 is the right diff ratio for a mini, it just needs a 5th gear for cruising. |
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| Author: | Drexxle [ Mon Aug 03, 2009 6:31 pm ] |
| Post subject: | |
having a look at the book again, i can only summise that the diff in the current box a leyland 998/1098 is ratio'd at 3.765, which would give lower revs at 100km/hr. The book has a chart at the back specific to leyland 998cc but this chart doesnt refer to a diff ratio, it says then to refer to the data at the front of the book and as in the chart posted here lists 3.765, which i guess is better for highway running than a 3.44 but the 3.44 is better at transferring torque for up hill and highway use. Then this chart refers to specific leyland ratios for A+ series boxes, and the 998 isnt an A+ block. im perplexed now, and dont really know what is in the box currently. |
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