I have this truck in really good condition. It has solid front axle and I have checked from wheel bearings for play. Front and rear brakes are very new with rotors and pads both high quality.

I worry that there might be a problem in my differential but don't know if they are prone to having bearing problems in there and I've never done any service on gears. My front pinion seal is leaking slightly but the fluid level is still nearly full.

U joints are tight as far as I can tell. The wheels won't wiggle left right or up down.

It does this mild rumbling that I can feel in the brake pedal which first started happening when I was doing left turns but now it happens when going straight as well. It's not something loud enough to be obvious without the feeling in the brake pedal. I can't feel it in the steering wheel.

 

Are you sure it's coming from the front? Might not hurt to have a look at the rear brakes......

 

I haven't checked the back brakes at all because the seller told me he had just had them done not long ago. It's a dually so I don't know what to expect when I take them apart. Would I just disassemble and look at the brake pads and rotors to make sure they're in good condition?

 

Yep. And make sure all the hardware is in place. If you are feeling really froggy (and I recommend it....) check run-out on the rotors....... If they are warped, the pedal will bounce when the brakes are applied, and shake the truck, but, you won't feel it thru the steering.

 

It only happens at slow speeds and is not even noticeable when driving or braking above 40

 

It's not the abs engaging by any chance, is it?? A wonky wheel speed sensor might do that to ya.