Hey everyone.

What the hell are diff ratios all about??? I have tried doing searches about the subject and all i can find out is what different ratios were in what diffs and how to find out what your ratio is, but i can't find anywhere that explains what they are or how changing it can effect your performance.

i know to alot of you will think its a dumb question but i'm just educating myself.

Also is reconditioning a diff worth doing. I have a h165 in my ute and was thinking of keeping it in there instead of replacing it but it is a little worse for wear. That's also why i wanna see what the rations are all about, so i can see if it's worth changing the ratio when i put my a14 in because i couldn't be bothered trying to locate a 5 speed. So yeah what would a recondition of a diff entail?

Any help would be much appreciated.

Trav

A low ratio diff will give you punch off the line, but run out of legs or make the engine rev harder to attain a top cruising speed. (like the 4.375 in a 1000 wagon)

A high ratio diff will let you cruise at a higher top speed using lower engine rpm,but wont be as quick off the mark. (Like the 3.9 in a standard sedan)

right. Cheers. so if you had a really high ratio diff it would be advisable to go for a 5 speed? but say a 3.9 or 4.11 wouldn't be too bad?

Also does anyone know what the hell reconditioning of a diff would do?

Reconditioning a diff usually means freshening up bearings and re-adjusting the crown and pinion gears so that they mesh correctly, thus maintining the best efficiency and even wear as possible.

Do you have a workshop manual? There's some good reading info for you (click the link in my sig for one).


A 4.11:1 in my ute with a 4 speed makes it rev at about 4000RPM doing 120kph. A 3.9:1 would bring the revs down a bit.

If you wanted to go 5 speed for this reason, make sure your 5 speed is an overdrive model, otherwise the 5th gear will have the same 1:1 ratio as 4th in a 4 speed.

Thanks mate. That helps me heaps. I will probably just stick with my diff and a four speed. At least for now anyways and just get a reconditioning done to ensure i've done everything i can to make sure it will survive the extra power. Should be right.

Also another question. What is entailed in locking a diff? And what would be the cost if you took it somewhere to get done?[

diff locking is illegal and dangerous for cars used on the street.

it basically makes the diff not be a diff anymore, by stopping the spider gears from climbing on each other as you turn a corner. so your car will handle like a 4wheel motorbike on the bitumen... (under under under steer...)

it only takes about 10mins of welding to lock the diff, but as i said, it is illegal and very unsafe to do this to a street car...

my advice: if your diff has more than 6mm of slop when u turn the flange back and forth, then get it rebuilt, if not, it will be fine. Being a H165 then it wont have any hassles standing up to an A14. keep the 4.11:1 ratio in it so that your datsun can rev freely, its only a 1.4L engine afterall and doesnt have the torque of a tractor.

Ok advice taken.

but what the hell is a flange and slop?

Dude i'm just learning all this sort of stuff so how would i go about doing this?Quote:

you should also take into consideration wheel diameter and tyre height.datsuns came out with 12 inch wheels.
and you can put up to 17's+ on them.which will change your final drive ratio.

righteo.

firstly the flange on your diff is the part where the 4 bolts go through from the tailshaft to the diff...
your tailshaft also has a flange, which logically is the part where the 4 bolts go through and hold the diff flange and the tailshaft flange togethor.

secondly. slop is freeplay. to check this (most accurately) you need to jack the car up so you can get under it, but keep the backwheels on blocks (or with the hand brake on), then undo the 4 bolts holding the tailshaft to the diff, and turn the flange as far as you can with your hand anticlockwise (or clockwise doesnt matter).
grab out a ruler and with a certain point on the flange marked, turn the flange all the way clockwise with your hand. the distance that you can turn the flange is known as freeplay (or slop) and should be less than 5mm (generally speaking).

is this clear or am i not making much sense to a newbie?

Thanks heaps mate. I'll do that hey.

Sorry if i'm a bit ignorant but i'm just starting to teach myself all this stuff and all you guys seem to know bucket loads of specific info. So instead of trying to guess a lot of things i'd rather get advice from people with experience.

So yeah, thanks again.

Trav