Originally Posted by
Char1ie
Thanks again. My car was a hillclimb car so may well have 4.4. or 5.5.
I have been told that my diff is locked using high pressure viscous coupling. I assume that this means that the diff oil is under pressure so I am reluctant to open it.
Is there a way of determining the ratio by the relationship between input and drive shafts? 5.5 turns of the input driveshaft = 1 turn of the wheel driveshaft on a 5.5. diff? Or is that too obvious?
Thanks,
Charlie
Hi Charlie,
The final drive ratio's for the 7.5" diff are usually only at the lowest 4.4:1, i'd hazard a guess to say that is probably the ratio most used in short sprint and definately on gravel spec rally car. If I were building a circuit racer i would be selecting a 3.9:1 for a good combination of decent acceleration and top end speed.
The way to check is exactly as you describe mark the flanges and count how many turns you get on the input in relation to the output. You should get 4 turns and it resting at approximately 4 - 5 oclock for a 4.4:1(if you get my drift)
The LSD part of your diff, is as you a say a viscous type, this is a pack bolted to the crown wheel through which the output flange passes, it is a seperate item to the crown wheel, pinion and sun & planet gears.
The viscous diff is a series of perforated plates suspended in a silicone gel, as they turn at the same speed, in normal straight line driving the temperature of the gel doesn't increase, and the diff is open but as the diff begins to operate (cornering etc), the temperature of the gel rises and solidifies and in turn causes the diff to begin to lock.
The gel in these viscous diffs can be changed to promote a higher level of lock usually measured in Nm, Bara or CTS both offer uprated viscous diffs.
HTH
Ian