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Diffs.
Posted: Thu Feb 28, 2019 12:37 pm
by 1970 cortina GT
Can anyone tell me what advantages/ disadvantages I would have if I swapped my standard 66 Mk1 GT diff and installed a 69 MK2 GT diff? I am assuming they are interchangeable. Thanks.
Posted: Thu Feb 28, 2019 1:13 pm
by peteleo
They are interchangeable. Just be sure the flange are the same diameter.
Someone may have replaced it with a 105E which is a smaller diameter.
Posted: Thu Feb 28, 2019 2:06 pm
by 1970 cortina GT
Thanks Pete. What difference should I see if I switch them?
Posted: Thu Feb 28, 2019 2:56 pm
by peteleo
105E diameter 3" 3/8. GT 3" 5/8. and are interchangeable.
Posted: Thu Feb 28, 2019 3:16 pm
by 1970 cortina GT
Ok and performance wise?
Posted: Thu Feb 28, 2019 3:32 pm
by peteleo
Larger the flange the ratio decreases.
Posted: Fri Mar 01, 2019 2:08 am
by JAN
peteleo wrote:Larger the flange the ratio decreases.
Not with you there: the flange diameter has nothing to do with the ratio maintaining 1 to 1 from the gearbox, whatever its size. The ratio, and this is the important part, is dictated by the number of teeth on the crown wheel and pinion. With Fords it is generally etched into the edge of the crownwheel, e.g. 8/33 = 4.125:1. That's the bit which will alter performance, irrespective of the diff's coming from a MkI or MkII.
Posted: Fri Mar 01, 2019 10:20 am
by peteleo
Driveshaft turning constant speed. Attached to larger flange 1/4 turn movement from point A to X moves a further distance than attached to smaller flange 1/4 movement from B to Y. Thus effecting differential ratio.
Posted: Fri Mar 01, 2019 10:52 am
by peteleo
After doing some re-thinking on this Jim maybe right.
I'm looking at A and B being separate moving points but in reality it doesn't matter what size the outer diameter of the flange is.
I always thought that Ford made two different size flanges to alter the ratio a bit.
Posted: Fri Mar 01, 2019 2:13 pm
by Bob_S
The larger diameter is to handle more power and torque. A 1/4 turn of the driveshaft = 1/4 turn of the pinion gear no matter the diameter of the flange.
Posted: Fri Mar 01, 2019 2:54 pm
by 1970 cortina GT
I guess I've started something here.... so by fitting the MK2 diff on the MK1 it'll give me more speed?
Posted: Fri Mar 01, 2019 3:08 pm
by peteleo
MK1/2 differentials are the same. As Bob mentioned larger diameter flange is to handle more power and torque only. Nothing to do with speed.
Posted: Fri Mar 01, 2019 3:50 pm
by 1970 cortina GT
Ok thanks for everyones input.
Posted: Sat Mar 02, 2019 2:05 am
by JAN
peteleo wrote:After doing some re-thinking on this Jim maybe right.
I'm looking at A and B being separate moving points but in reality it doesn't matter what size the outer diameter of the flange is.
I always thought that Ford made two different size flanges to alter the ratio a bit.
That's it, Pete, you were possibly thinking linear motion rather than circular motion.
Posted: Sat Mar 02, 2019 12:21 pm
by peteleo
I may have been thinking in line with locomotion.