Hi All,
Just about to replace the diff in my coupe and want to know where ID stamp is for the banjo as I want to put one in as close to the ratio that is in the car at the moment. Is it at all visible from the outside of the centre? Are there codes or are the actual ratio 3.08 etc. printed?
Cheers SUPALJ
Diff ratio ID
Started by
_SUPALJ_
, Oct 28 2006 03:10 PM
13 replies to this topic
#2
Bazza
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Posted 28 October 2006 - 03:46 PM
Hi
The best way is reading the stamping on the edge of the crownwheel. Externally the ratio is usually marked on the pinion seal cover - but this sometimes gets changed over the years and is not always accurate.
Bazza
The best way is reading the stamping on the edge of the crownwheel. Externally the ratio is usually marked on the pinion seal cover - but this sometimes gets changed over the years and is not always accurate.
Bazza
#3
ls2lxhatch
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Posted 28 October 2006 - 07:56 PM
You can determine the diff ratio by jacking one wheel off the ground (assuming open centre diff) and turning the wheel one complete revolution counting the number of tailshaft revolutions.
If the tailshaft turns 3.08 times then you have a 3.08 centre. You may want to turn the wheel ten times to make it easy to spot the difference between 3.08 (30.8 revolutions)and 3.35 (33.5 revolutions).
If the tailshaft turns 3.08 times then you have a 3.08 centre. You may want to turn the wheel ten times to make it easy to spot the difference between 3.08 (30.8 revolutions)and 3.35 (33.5 revolutions).
#4
_devilsadvocate_
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Posted 29 October 2006 - 01:05 AM
Above is half correct..........if one wheel is held fixed and the other free to rotate then the free wheel will rotate at twice the rate than if the other wheel is free to rotated in sync with the other.
ie one rotation of the wheel will give 1.5 revs of the tailshaft, if its a 3.08
ie one rotation of the wheel will give 1.5 revs of the tailshaft, if its a 3.08
Edited by devilsadvocate, 29 October 2006 - 01:15 AM.
#5
_DocDamage_
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Posted 29 October 2006 - 09:27 AM
This has been discussed before, and with out saying anyone is right or wrong, a method you know you can trust is to mark the tyre with chalk, and tape a long piece of string to the bottom of the tailshaft and run it out the side of the car. Roll the car in a straight line for 10 revolutions of the wheel, then count how many times the string wrapped around the shaft. Do the math from there.
#6
ls2lxhatch
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Posted 29 October 2006 - 12:01 PM
Well you learn something new every day, I have just tried this with a spare diff and can confirm I was wrong. It makes sense now that half of the revolutions are lost as the pinion gears run around the fixed axle.Above is half correct..........if one wheel is held fixed and the other free to rotate then the free wheel will rotate at twice the rate than if the other wheel is free to rotated in sync with the other.
ie one rotation of the wheel will give 1.5 revs of the tailshaft, if its a 3.08
#7
_devilsadvocate_
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Posted 29 October 2006 - 12:30 PM
Cheers Andy ^, its a change to have people try something out that I post and confirm it rather than posting back that its rubbish..............
Doc, you can trust this method(not for lsd's though)......and its got to be easier and safer than pushing a car along the ground counting the wheel revs---you would need ~ 18m of flat ground to do it on properly, the string sounds a good idea, though it would be perhaps necessary on most cars to jack the car up to attach it properly.
Doc, you can trust this method(not for lsd's though)......and its got to be easier and safer than pushing a car along the ground counting the wheel revs---you would need ~ 18m of flat ground to do it on properly, the string sounds a good idea, though it would be perhaps necessary on most cars to jack the car up to attach it properly.
Edited by devilsadvocate, 29 October 2006 - 12:40 PM.
#8
_CHOPPER_
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Posted 29 October 2006 - 01:35 PM
Better to jack up one side and turn the tyre 10 times, as the difference between 3.36 and 3.55 isn't much. If you turned the tyre once, could you really tell the difference between 1.68 turns ( 3.36:1 ) and 1.775 turns ( 3.55:1 ) ? I know you believe you have a 3.08:1 centre, but this would help others. BTW, this is how I checked mine over 20 years ago. It worked then, it should still work now.
#9
_devilsadvocate_
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Posted 29 October 2006 - 01:42 PM
yes, Andy already mentioned to do the ^, didnt think it need mentioning again
Its all there in the tech articles for anyone to read
Its all there in the tech articles for anyone to read
Edited by devilsadvocate, 29 October 2006 - 01:44 PM.
#10
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Posted 29 October 2006 - 01:48 PM
Looks like I missed that bit. Must remember to wear my glasses.
#11
Bazza
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Posted 30 October 2006 - 10:44 PM
Hi
So does all of the above mean that the ratio stamped on the crown wheel can't be trusted?
Bazza
So does all of the above mean that the ratio stamped on the crown wheel can't be trusted?
Bazza
#12
_Chaotic_
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Posted 30 October 2006 - 10:52 PM
If you looking at the crown wheel then surely it'd be easier to just spin the diff by hand and count the teeth. Driven/Driver = Ratio ie Crown/Pinion = Ratio.
So if your crownwheel has 30 teeth and your pinion has 10 teeth then your ratio is 3.00:1 > 30/10=3.00.
So if your crownwheel has 30 teeth and your pinion has 10 teeth then your ratio is 3.00:1 > 30/10=3.00.
#13
_devilsadvocate_
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Posted 30 October 2006 - 11:15 PM
Well not entirely, as its possible someone may have fitted another pinion gear...........very very unlikely. AFAIK, the pinion gears have to be a perfect fit/match for the crown wheel so even more unlikely.So does all of the above mean that the ratio stamped on the crown wheel can't be trusted?
Im fairly confident that the different ratio diffs had to have both different crown and pinions to come up with the ratios
Looking at the pic of the 3.08, it looks like about 40 teeth, to get a 3.08 the pinion would need to be 13 teeth.
Theres no other whole numbers that are divisible by 13 that close to the other ratios so they all must be specific pinion/crownwheel combos.
Most likely the 2.78 is 39/14, 3.36 37/11, 3.9 39/10
#14
MRLXSS
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Posted 31 October 2006 - 12:31 AM
How bout engine revs at 100kph? But then that also depends on how accurate your speedo is, and your tyre size etc. But it will give you a rough indication of what you might have.
To answer your question. do u know if hte diff in your car is original at all? If it is it might have the correct number stamped on the outside of it.
Also the 2.78 and 3.08 are shaped slightly different to the 3.36 and 3.55 i believe. (the bottom two bolts are different)
But like others have said the pinion gears etc may have been changed.
Also if you know your car is completely orig then the diff ratio will also be on a tag in the engine bay.
my guess is it would be a 2.78 or 3.08
To answer your question. do u know if hte diff in your car is original at all? If it is it might have the correct number stamped on the outside of it.
Also the 2.78 and 3.08 are shaped slightly different to the 3.36 and 3.55 i believe. (the bottom two bolts are different)
But like others have said the pinion gears etc may have been changed.
Also if you know your car is completely orig then the diff ratio will also be on a tag in the engine bay.
my guess is it would be a 2.78 or 3.08
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