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confused about diff ratios
tompat3463 - 24/3/11 at 08:58 PM

Hi guys. Im 24 and picked up an ind-blade last weekend.

I was given a spare diff with the sale. Apparently the car is fitted with a 3.9 sierra open diff and a spare 3.6 diff was included.

Been driving the car this week and the car seems way to low geared for me. top speed seems like about 90..

Yeah sure u can move ur head whilst accelerationg to 60mph

is the 3.6 a slower accelleration or faster ??

PS. its running a 97 blade with standard gear box I pressume !!

Thanks in advance

tompat3463 - 24/3/11 at 09:00 PM

I say seems like 90 because the anolog speedo goes into speradic mode when I go over 60

cheers

JoelP - 24/3/11 at 09:05 PM

the diff ratio doesnt have as much effect on acceleration as people say, becauce although a 3.9 diff gives more thrust in 1st, the gear runs out sooner, and then whilst the 3.6 ratio would still be in 1st, the 3.9 diff is now in second gear and has a lot less thrust. Multiplied out over many gears, im led to believe the difference becomes negligable.

So, id say swap for the 3.6 and see how you like it.

tompat3463 - 24/3/11 at 09:07 PM

are they easy to change ?? do they need to be filled with somesort of oil ??

cheers Alan

bigrich - 24/3/11 at 09:10 PM

a blade on a 3.92 diff will top out about 110, with a 3.62 it will get to 125 ish, acceleration should be a little slower but may actually improve in the lower gears due to reduced wheelspin and getting to a higher speed in each gear.

i did this swap on my own car, and what it did speed wise in 6th on a 3.92 was the same as 5th on the 3.62. Car was much better on long straights/motorways

Rich

r1_pete - 24/3/11 at 09:12 PM

quote:
Originally posted by tompat3463
are they easy to change ?? do they need to be filled with somesort of oil ??

cheers Alan


Definately, and the correct grade, I'm not familiar with Sierra difs but there should be a filler/level plug on the back cover.
Someone will be along soon who will know the grade.

mcerd1 - 24/3/11 at 09:42 PM

quote:
Originally posted by tompat3463
are they easy to change ?? do they need to be filled with somesort of oil ??

cheers Alan

sierra diffs just use any EP90 thats rated to GL5

ie this stuff: linky (or similar)


(GL4 is not good enough for the diff)

[Edited on 24/3/2011 by mcerd1]

mark chandler - 24/3/11 at 10:05 PM

Swap it over, 1st is very usable on a blade engine with a 3.6 diff and it should just pull max revs in top.

At Brands and Lydden when n/a I maxed the gears easily enough with a 3.6 diff.

Regards Mark

tompat3463 - 24/3/11 at 10:15 PM

ok...may get to work on it this weekend.. are they simple to do ?? i.e simple nut for nut or is cutting and weldinf required ??

stupott901 - 25/3/11 at 07:35 AM

Its easy enough to do I did mine in a afternoon with just undoing bolts bolts and no welding etc

i changed my diff from a 3.92 to a 3.62 and it has better overall performance so a good move

brookie - 25/3/11 at 04:35 PM

my got the 3.62 and it great top out at about 125mph i think