A bigger diff!

I’ve also finished building a Chrysler 8.75 LSD (Limited Slip Differential) from parts I imported over and bought locally – and finally starting to arrange the new engine!!!

The Chrysler 8.75 Sure Grip LSD is a real heavy duty diff and came out on all the tuff Mopar muscle cars of the 60s and 70s, from the Maxwedge cars to the Hemi Challengers and Dodge Chargers. 

The pinion is heavier and thicker than a Ford 9”, and the 30 spline factory axles mean I don’t have to invest in expensive aftermarket gear.  Add to that the 11×2.5” rear brakes and its going to meet all my needs. 

I’m going to run 3.89 gears. This sees the engine revving at about 2800 rpm at 100 kph (64 mph) – so at 25 litres per 100 kilo ( 14.45 MPG) I don’t think I’ll be driving it interstate! 

Below is a pic of the comparative pinion shaft thicknesses – The 8.75 makes the Ford look completely puny!

Ive also re-used my spring clamps which keep the semi elliptical Chrysler leaf springs from wrapping, and Ive added a pinion snubber for extra insurance.

 

Leaf wrapping is caused by the pinion housing tilting up – which causes the the diff housing to rotate and this “picks up” or lifts the wheels off the ashpalt as it rotates backwards – thus a loss of traction.

So -

Spring clamps prevent the front part of the leaf from “wrapping” and so stop the pinion case from rotating.

Caltracks and traction/slapper bars do a similar thing to spring clamps but in some ways more effectively, they apply leverage against the spring and deny the pinion case any opportunity to tilt upwards which results in tyre “lift”.

Snubbers work a little differently – They “assume” some tilt will occurr, and as the pinion tilts up, the snubber presses against the floor pan.

Just as for the pinion/crown wheel re-action – Newton says “for every action there’s an equal and opposite” – In this case the pressure of the snubber against the floor pan applies an equal force downwards through the diff and tyres on to the ashpalt – thus increasing traction.

Best way to think of this is if you kick a wall, you go backwards.