I have a 1968 D7E 48A serial #11000. I adjust the brakes per repair manual, then operate dozer and both brakes works fine. But after about 4 hours running the brake pedal continues down till it bottoms out and I have no brakes to steer at end of day. I can readjust by tightening the break mechanism and everything works again, but after operating a few hours the adjustment is out again. It seems the brake adjustment nut is backing off since it takes about 4 turns to tighten band. This occurs for both brakes. Steering clutches work fine and brake linkages are adjusted within spec. Any help as to what to look for to repair?
I'd have to opine there's not much chance of the adjustment nut backing off - the bigger possibility is your brake linings are at the end of their life, and starting to break up. Have you checked your transmission screen for brake lining debris? There are two types of original brake lining, the nylon linings and the metal-impregnated linings. The nylon linings, which were standard originally, have a bigger tendency to break up when old and worn.
Last week I finally got the clutch and brake band out to inspect. I was expecting the brake linings to be worn out. This was not the case. Brake linings were as new as well as the clutches. The brake drum was glazed indicating drum got hot from previous slipping. I am having the brake drum lathe turned. The Cat mechanic who disassembled unit said he thought the brake band had stretched, but that doesn't explain having to readjust (tighten) brakes every 4-6 hours. Another mechanic I talked to had the same problem with a Cat 931. He found the adjustment nut backing off and installed a nut lock which solved his problem. So I ask again, has anyone seen this occur, or anything else to check? Installing a nut lock would be a simple fix, but I don't want to reassemble everything and run dozer to find out and then have to disassemble again if it is not.
Strange problem. My thoughts were similar to Oz Dozer until you posted this update, I suppose your drums could be warped and giving you the run around. I’ve seen this in D8 scraper winches,but not steering brake drums.