How hard can I push it?

[dbenamati]

I've posted about my 67 250 4 spd farm truck I fixed up. The way that its geared, going 55 was pushing the rpms abit. I've considered changing out the rear end gears and havn't had much luck finding something with out getting really crappy gas mileage. Someone posted last week about swapping rear ends and from the topic pages, you guys use all ratios and have no problems with speed so I decided to push it today and open it up on a long stretch of road to see how fast I could get it going before it exploded. The engine is in decent shape with no rebuilds and just cleaned up looks pretty good. I got it up to 65 and the rpms didn't sound that bad. Am I pushing my luck to get it going faster or should I go back to the rear end change idea. I don't know the ratio in my truck, I am going to change the diff cover gasket this spring to get the ratio but it is geared awful slow (3/4 ton 4 spd). Any suggestions about pushing it? Thanks, dave