I've never had the front brakes lock up first on my truck. Rears ALWAYS lock up first, unless there is a huge load in the back.\

Either way, you still have some adjusting to do. I'd agree with adjusting the LSVP.

 

When the LSPV bracket is raised it puts more emphasis on the rear brakes. So when you have a heavy load, the more pressure the rear brakes get.

fyi

 

One thing is wrong with this statement. And that is the notion that the LSPV can deliver more braking force to the rear than the front. That's not possible. The the sensing rod should be adjusted to it's maximum height when the vehicle is standing still on level ground. This leaves the valve fully open, giving optimized pressure from the brake booster to both front and rear brakes. As the vehicle pitches forward during braking, the rod extends closing the valve gradually and proportioning less force to the rear brakes to compensate for the shifting of the distributed weight load, which moves more toward the front wheels. That helps keep the rear brakes from locking up, due to the fact that less weight is now being distributed to the rear wheels. When the rear of the vehicle is carrying more of the total load there's less pitching forward involved and less need to soften the rear brakes, for obvious reasons. The rear wheels should only ever have as much, or less, chance of locking up than the front. That is the intended function of the LSPV valve. It can't add any pressure to the front or the rear, that's limited by the brake booster. It only proportions less (limits the amount) of pressure to the rear when needed (when sensing the weight load being transfered forward, a direct correlation to the distance between the rear axle housing and the frame).

If misadjusted, so that the sensing rod's not fully opening the valve (requires raising/adjusting the rod to the point of contact with the LSPV valve housing, to be fully open) at a level stance, you'll never achieve enough pressure to the rear brakes, unless with a very heavy load in the rear (when it lowers the rear of the frame, and thus the LSPV housing, to the sensing rod, instead of the rod being raised/adjusted to it's correct position). You'll have a loss of over-all braking performance and cause undue wear on your front brake components, as they attempt to compensate. If bypassed, or if the valve is unable to close, you'll be more prone to lock up the rear brakes, than with a properly operating LSPV.