What car do you have? It sounds like the chassis would be happier with smaller spurs, and smaller pinions, so why not try to use 64 pitch? An 84 tooth at 48 pitch would be equal diameter to something close to 120 tooth in 64 pitch, whereas 72 @48 would be about the size of 90 tooth in 64 pitch (not sure but it's pretty close). These would require pinions larger in the number of teeth than what you have, but smaller in diameter, so I think you would get the adjustability back.
PS. I note you have answered my question probably as I was typing. The rest still stands. I am glad I answered your question about diameteres though.
Last edited by niznai; 03-12-2009 at 12:44 AM.