Home Forums Gear Hunting Trucks and Four-Wheel Drives My 1988 4Runner is in the shop

I kept having a constant brake fluid leak. After much messing around, I found it to be at the load sensing proportioning valve mounted of the frame at the rear of the truck. I had never heard of this before. It's connected to the axel by a long rod. Evidently it adjusts the amount of brake pressure to the rear drums according to the load.
Anyway, It took a bit of sleuthing to find a new valve. I decided that replacing it was beyond my ability these days, and took it to my mechanic. Hopefully I will get it back this week.
Lots of things can fail on an almost 40 year old truck. It's been one thing after another. Still, when all is right, I can go 4 wheeling with the best of the new off road vehicles and hold my own.

You can disconnect that valve and bypass it by adding a little section of brake line.

I know that, but evidently with discs up front and drums in the rear, the valve keeps the rear brakes from locking up if you have a load in the back. Or something like that. It's already repaired.

It sounds like you've got a classic rig with a lot of character—and some quirks that come with age. That load sensing proportioning valve (LSPV) is one of those lesser-known but crucial components, especially on older 4WDs like your '88 4Runner. It’s great that you tracked the leak down to that; those can be tricky since they're not something most people think to check.

It's definitely true—older trucks require more upkeep, but they reward it with personality and capability that modern vehicles sometimes lack. When that 4Runner is dialed in, it’s no surprise it can still hang with the new crowd on the trails. Those solid axles and simple mechanics are built to last (and built to be fixed).




preventing failures on a 1988 4Runner comes down to regular maintenance, close inspection of aging parts, and staying ahead of known weak spots for that generation. Here's a solid checklist of preventative steps to keep it reliable:

1. Fluids & Filters
Engine oil & filter: Change regularly (every 3,000–5,000 miles).

Coolant: Flush every 2–3 years to prevent corrosion in the radiator and heater core.

Brake fluid: Flush every 2 years to avoid moisture buildup (which can ruin valves like the LSPV).

Transmission & differential oil: Check and change at recommended intervals.

Fuel filter: Replace every 30k miles or as needed.

Power steering fluid: Inspect and flush if dirty.

2. Rubber Components
Hoses (coolant, vacuum, fuel): Check for cracks or softness. Replace any that feel brittle or swell.

Belts: Look for fraying, cracks, or glazing.

Suspension bushings & body mounts: These can deteriorate with age, causing handling issues or noise.

3. Electrical System
Battery & terminals: Keep terminals clean and check the battery’s age.

Ground wires: Inspect for corrosion or looseness—old Toyotas rely heavily on solid grounds.

Fuses & relays: Periodically check for corrosion or overheating.

4. Braking System
Brake lines: Inspect metal lines for rust and rubber lines for cracks or swelling.

Drums, pads, and shoes: Make sure they’re wearing evenly.

Load sensing proportioning valve (LSPV): Keep clean and ensure it moves freely with the axle.

5. Steering & Suspension
Ball joints and tie rods: Inspect for play and grease if serviceable.

Shocks and struts: Look for leaks or diminished damping.

Wheel bearings: Repack or replace as needed.

6. Drivetrain
U-joints and driveshafts: Check for play or clicking. Grease regularly.

Transfer case: Check oil level and seals.

7. Body & Frame
Rust prevention: Especially in the rear frame and tailgate area. Clean out drain holes and undercoat if needed.

Weatherstripping & window seals: Prevent water leaks and interior damage.

8. Cooling System
Radiator: Look for leaks and ensure it isn’t clogged with debris or scale.

Thermostat & water pump: Replace proactively if nearing the end of their life.

9. Fuel System
Fuel tank and lines: Look for rust or leaks.

Charcoal canister and vacuum lines: Old emissions components can cause drivability issues.

10. Keep a Logbook
Track what you've done and when—it helps catch patterns and plan ahead.

These trucks are built tough, but time wears on even the best machines. A methodical approach like this can keep your 4Runner trail-ready for many more years.

Shops love it when you bring your own parts.