1. Bleeding Issues:
* Incomplete Bleed: Even with careful bleeding, air pockets can remain trapped, especially in the rear lines. Try bleeding again, ensuring you're using the correct procedure (gravity bleeding is often insufficient). Consider using a pressure bleeder for more effective bleeding. Bleed the furthest wheel first (usually a rear wheel).
* Incorrect Bleeder Valve Order: The correct order matters for optimal bleeding. Consult your vehicle's repair manual for the recommended sequence.
* Blocked Bleeder Valves: The bleeder valves themselves might be clogged. Try replacing them if they seem stuck or difficult to open.
2. Hydraulic System Problems Beyond the Master Cylinder:
* Wheel Cylinder(s): These are located at each wheel and convert brake line pressure into movement of the brake shoes or calipers. A seized or leaking wheel cylinder will prevent brakes from working properly. Check for leaks around the wheel cylinders.
* Caliper(s) (if disc brakes): Similar to wheel cylinders, but for disc brakes. Seized calipers prevent piston movement, leading to no braking on that wheel. Check for free movement of the caliper pistons.
* Proportioning Valve: This valve regulates brake pressure between the front and rear brakes. A faulty valve can restrict or completely block brake fluid to one axle.
* Brake Lines/Hoses: Check all brake lines and hoses for leaks, kinks, or blockages. A small hole might not be readily apparent.
* ABS System (if equipped): If your Blazer has anti-lock brakes, a problem with the ABS module or related components could interfere with braking. A faulty ABS sensor can sometimes cause a loss of braking. Note: some early ABS systems will still allow braking without the ABS system functioning.
3. Other less likely, but possible issues:
* Power Brake Booster: This assists brake pedal pressure. A faulty booster will result in a very hard brake pedal and reduced braking power, but if it's completely failed, you'd still have some braking power, just more effort.
* Brake Pedal: Very rarely, the brake pedal itself or its linkage could be mechanically stuck or broken.
* Vacuum Leak: A severe vacuum leak in the intake manifold can affect the power brake booster if equipped.
Troubleshooting Steps:
1. Re-bleed the brakes thoroughly. This is the first and easiest step.
2. Visually inspect all brake lines, hoses, calipers, and wheel cylinders for leaks. Look for wet spots or fluid dripping.
3. Check the brake fluid level in the master cylinder reservoir. It should be filled to the correct level.
4. Manually try to push the caliper pistons (if disc brakes) or wheel cylinder pistons (if drum brakes). They should move freely without much force. If they are seized, that's likely your problem.
5. Consult a repair manual specific to your 1991 S10 Blazer. It will have detailed diagrams and troubleshooting information.
Safety Warning: Do not drive the vehicle until the brakes are fully repaired. Driving without brakes is extremely dangerous. If you are unsure about any of these steps, take your Blazer to a qualified mechanic for diagnosis and repair.
