Grinding and thumping, losing and gaining pressure in brakes.

[Misfitkid1386]

So 1st and 2nd gear everything seems fine...automatic so im sure it doesn't use granny gear very much...when I get into 3rd and 4th gear I hear grinding like metal on metal or kinda like I am dragging a muffler and pulls to the side a lil. Also loss of pressure on brakes then I get pressure back at random. Lots of grinding almost like a squealing pig lol. Sounds like metal on metal but I can not locate anything that looks like its been grinded or contact between metals. Any thoughts or suggestions would be helpful. 76 Silverado automatic with a 350 Crate. Thank you for reading. -Misfitkid1386

[bake74]

     First of welcome to the site.  I am assuming it is a C-10 Pickup ?  A little more info would help us out here.

     I am assuming it is a 700 R4 Automatic transmission since you said 1-2-3-and 4th gears ?  Even though a 76 did not come with a overdrive transmission.  Or could it be you have the turbo 350 and just think you have 4 gears ?
     Since you said it only happens in the higher gears, so that means that you are going faster.  Does it only happen at higher speeds and not lower speeds ?
     Some things to consider.  If it only happens at higher speeds, and unless your 3rd ( or 3rd & 4th gear in a 700 R4 trans) gear is just blown on your transmission (which would make it drive not so nicely in that gear), or the oil valleys going to those gears are somewhat plugged/plugged in your trans (I do not know where the metal sound would come from at all), I would look outside the transmission for the metal to metal sound.
     Remember at higher speeds you are applying more torque from the engine/trans combo.  Have you looked from the engine bay (bottom of engine) all the way back to the rear axle for any signs of wear marks that should not be there ?  Pay special attention to the drive shaft area.
    You mentioned loss of pressure on your brakes, dumb question but have to ask, did you look at all your disk/drums yet to see how they look and the pads look ?
     There will be more comments I am sure, but start there for now.

[xschroederx]

I gotta say, bake 74, the 700r4 didnt come out till later I think. My 78 had a turbo 400 trans in it. And I could also put the turbo 350 trans in it. Other than that, I think you should find out what trans it is and then do a flush and filter change on it just to be sure there is no metal in the pan. In 3rd or 4th gear, you are at higher speeds, so the veering could just be an alignment issue. Try swapping the right front and left front tires to see if the pull dicipates. Also check the ware pattern on the tires. Have you pulled the drums to see if maybe you have an axle seal going bad? Fluid will cause loss of stopping power. Also if you have a bad axle bearing, it would cause a slight drift or even a more noticeable grinding noise at higher speeds. 1 tranny flush and filter change, 2 pull drums and inspect axle seals.

[Edemich]

He didn't say yet what type and year of truck when he posted, so this may be a long shot. If it's a 4x4 then his transfer case may be making noise or one of his hubs is locked and at higher speeds it's causing some drag.  Automatic hubs gone bad perhaps.  Need more info........