Change from 4.1 to 3.9 diff

[tinker-27]

,,,hope these work they are lod pics of the 5.7 motor its now 6.3 (soon to be 7.0) my car is not here at moment as i am doing one for my freind but you are welcome to have a look at that if you want cheers craig  sorry the pics dont seem to work i can email but i cant post for some reason ? email me and i will return pics  tinker-27taylor@blueyonder.co.uk

[pete sparrow]

Your cheapest option is to change the complete diff in one go,casing and all! I blew my diff and managed to swaff the crown wheel n pinion as well.My original ratio was 4:3 because it was the RZ diff,i didn\'t want to have to go down to a second hand 4:1 out of a standard rex diff or pay the mazda price of £700 plus vat for new  4:3 crown and pinion.I was offered a 4:4 out of a rx8 diff so i bought that. I had them fitted along with the new Kaaz diff by a top rally mechanic/engineer.The process wasn\'t easy or cheap! He had to press the pinion out of the rx8 diff then refit into the rx7 diff and seat it correctly at the right depth/level,new shims had to be milled to fit exactly and the backlash set. As stated in a mazda workshop manual you need a special measuring tool to gauge the seating depth of the pinion. Thats why i left it to the professionals. Cost me but i\'m safe i the knoeledge its been done right.

[BlitzBoy]

yeah just swapping the complete diff to an auto one is the cheapest option.

When fitting my Kazz diff it cost me approx £500 for the Kazz diff and £100 labour to have the diff/casing dropped out of my car , the old diff taken out of the casing, the final gear ,shims,bearing taken off and put onto the new KAzz, then refitted and put back on the car.
So I paid £600 total

[normski]

the easiest way to swap to 3.9 from 4.1 is to just fit the whole auto diff (3,9) all you have to do is swap the drive flange on the front for the manual one . i use a 3.9 in my ls powered fd and its better than the 4.1 but with the 6 speed the gearing is good anyway 70mph=1700rpm which is very relaxed. a ls1 with a cam and set up properly is good for 400+bhp about the same as ls2 and for a lot less money ,the ls2 also comes with fly by wire throttle etc. if you are going to buy a ls just make sure its a 2001 on as they are better . just ordered my 7.0 litre short motor rool on next year !!!

I am also looking at the diff option, as it\'s now all too lower geared, but Pip recons the 3.9 may not be enough. Need something else? Ideas...

[antnicuk]

Norm,  we have a 3.9 from an auto in ours and it makes things a little calmer on acceleration.

[normski]

Am I right in saying, it curbs off the line ripping strain a little, whilest giving better top end? I need it not to sound like it\'s reving it\'s head off at 70 or 80MPH, first gear is almost usless now!

[antnicuk]

thats about right