I have changed the rear gears from 3.08 down to 3.42 , this is a reduction of 10% in speed terms . I didn't think i would need to be doing or more likely be able to reach 170mph so its now down to a mere 152mph . Thats all in 5th but as the v8 has so much torque i only use up to 4th anyway which means 124mph instead of 138mph , with the bigger motor i might use 5th on longer straights but as it is at the moment the 3.08 is way to tall . Here are some pictures of the gear swop
This is with the new gears being fitted to the old case .First thing is to get the pinion gear set at the right depth in the case , on the back the depth from the back of the pinion to the diff centerline is etch on and is the figure used when the gears are lapped at the factory
I know from doing this before that between a 30 to 40 thou shim is whats needed between the bearing and bearing seat . so i try it at 35thou
As i was lucky this time 35 thou was spot on and i got the depth as marked on the pinion , this is good because getting the interference fit bearing off is a real pain .
The next bit is toput the pinion gear in the case and crank up the pinion nut to pull the bearings on to the pinion and to squash the crush bearing , as iam not built like a brick bog house so this was a bit of hard work . I had to use 2 , 3 foot long bars to crank whole lot up .
This is the pinion showing the outer bearing and crush washer which need to be pulled together , getting the bearing on isn't to bad but once you reach the crush washer it gets a lot tougher
Once the bearings are seated and there is no play left i had to set the preload on the pinion bearing means cranking some more on the pinion nut , but only small amounts . I was looking to get between 24 and 18 inch pounds . On the first go i eased up to 15 inlbs i cranked a touch more and it went up to 35 inlbs , f*^k f*^k and f*^k , had to pull it apart and put in another crush washer and then crank it all together again . On the next go i got to 18inlbs and left it at that
That was the tough bit done , fitting the diff and setting the gear lash is alot easier . The gear lash or play needs to be about 6 to 10 thou , so i add or subtract shims from each side of the diff to get that about right . There also needs to be a preload on the diff bearings so once the shim thickness is found to get the preload then you have to keep to that thickness of shims . If you remove from the left side bearing then the same amount is added to the right side . It helps to write down the shim thickness used as swopping them about gets confusing and having to start again is a pain , how did i find that one out .
At the same time i needed to see how the gears meshed by smearing grease paint on the gears and reading the pattern
The pattern needs to be more or less centered on the gear , as long as possible and not tapered at the ends . The picture has a slight taper on one end so i changed some of the shims to square off the pattern and taking care to keep within the lash tolerance . I ended up with about 8 to 9 thou lash , so i was happy with that and then bolted it all up
The last one i did was fine and gave no problems and the oil that came out of the diff looked ok considering its a trackday car , so this one should be fine , eck ! . Pete
shims, engineering stuff and gears make me want to curl up in a ball and cry............so far out of my comfort zone with stuff like that! Thoroughly enjoy reading it though 
