Hi all & Happy New Year!

I'm back to tackle my poor braking performance in use with my camper, loaded at ~6000lbs.

Currently, my setup is using a stock 91-August Master Cylinder (what bore size? 13/16", 15/16", 1"?), Brake Booster (dual diaphragm?), re-manufactured 4 large pistons calipers, & stock rear drums.

As of 2 months ago, brake fluid level has been dropping so slowly... that I just finished a bottle from topping it off.
Finally (yesterday) I discovered the mysterious leak, a slight leak coming out from inside the rubber boot of the LSPV/Bypass Valve.

After some research, it looks like I have 2 options:

1) reinstall a working LSPV/BV from a junkyard & keep it street legal

or

2) Bypass the LSPV/BV by installing a Manual Prop. Valve ($79, includes all fitting adapters. http://frontrangeoffroadfab.com/nfoscomm/catalog/product_info.php?cPath=27&products_id=57) right next to the Master Cylinder.

Since I have also dis-activated the Brake Actuator by removing the 2 hydraulic lines from power-steering pump/reservoir (but 2 brake lines are still left hooked up to the Brake Actuator), I am wondering if I can bypass the brake lines from the Brake Actuator, as well as the LSPV/BV?

I understand that the 2 functions of LSPV/BV are to adjust rear braking pressure depending on load weight, and to allow fluid by-pass to rear brake in case of front brake failure (loss of fluid pressure)

If I setup Manual Prop. Valve as shown in here, bypass the Brake Actuator & LSPV/BV, and finally connect it to the rear axle, should I result in an adjustable rear brake fluid system completely isolated from the front brakes?

If this is true, would it mean that the system is still fail-safe just like the intention of the stock design? (Meaning that if my front brake system fails, I would still have rear brakes?)

Pic of my MC http://i92.photobucket.com/albums/l37/allochris/DSCF7132.jpg, what size bore?

If it's already 1", what else can I do to improve braking beside installing T-100 MC, rotors, and calipers on the front? (link below)

Truck is driven lots on hwy, and I want to maintain rear drum & parking brake.

Research links:
Toy hydraulic ratio # / D44 upgrade

Toyota Brake Specs.

Toyota Brake FSM

Rear Disc Conversion

T-100 Brakes Upgrade

LSPV Removal

Rear Disc Swap

Wildwood Prop. Valve & 1" bore MC install

The way I understand the "BV" (bypass valve) part of the LSPV-BV is that if you lose the front brake pressure, all it does is override the LS (load sensing) part of the valve, giving you the full amount of rear brake pressure that the PV (proportioning valve) part can send out. So with the manual PV, you just have that part of the system, there is no LS part and the BV part is simply eliminated, you have rear brakes and front brakes. If the fronts go out, you still have the rears. I ran for years with the load sensing arm tied up to the floor boards:
- http://www.4crawler.com/4x4/4R_suspension.shtml#ProportioningValve

Perfect, that just explains why Toyota bothered to design a system by-pass around the load-sensing valve when one can simply install an adjustable proportioning valve to the rear brakes for the same fail-safe purpose.

FYI, my LSPV rod is also cut too for years (also to accommodate the 33" spare tire at stock location).

Since I'm always loaded heavy, I think I'll go ahead & order the valve & these interesting looking speed bleeder nipples (http://www.speedbleeder.com/size.htm)!

M10 X 1.0 I believe for both calipers & rear wheel cylinders?

When the LSPV in my '84 xtracab failed massively I removed it and spliced that line to the rear brakes. Then I removed the return line and capped the connection at the junction block on the frame rail by the front passenger wheel opening. My braking improved dramatically. I also had V6, four pot calipers and a late model master cylinder. When the four piston calipers are properly set up they are awesome!

I had a constant load of about 300 - 400lbs in my bed so full brake force at the rears was never a problem, even on icy roads.

I just wish I could get my '89 4runner to brake like that, but first I have to deal with engine problems that are causing low vacuum, which I believe is not enough for my brake booster.