My Brake Pedal is Stiff and Car Won’t Start (Causes & How to Fix)

My Brake Pedal is Stiff and Car Won't Start

Imagine having an important meeting that you need to rush to, on getting to your car, you pressed your brake and it seems stiff, you tried starting your car and it won’t start, you begin to wonder why “my brake pedal is stiff and car won’t start”.

Reasons, why your brake pedal is stiff, are because:

  • A lack of vacuum pressure. This is the major cause of a stiff brake pedal
  • The combination valve or the pressure differential valve within the combination valve 
  • The overheated braking system, and
  • A slightly incorrect pedal ratio

Can My Brake Pedal Become Stiff?

The brake pedals of a vehicle can become stiff at any time. “Stiff” in the sense that it becomes really hard to press. It can still be pressed but it will require a lot of energy and pressure for it to be applied.

This is a tiring and stressful problem for any driver, it is not comfortable at all. So, if you ever experience this, you should get it checked out and fixed as soon as possible.

What Causes Brake Pedals to Become Stiff?

The brake pedals of a car assist the car is slowing down (reducing speed) when pressed. What is the working mechanism of a brake pedal?

Brake systems in vehicles made nowadays work with vacuum and through a brake booster. There is a tool known as the vacuum diaphragm; it adds to the force that you apply to the brake pedal. This makes it easy for you to brake your vehicle and it gives you more control while driving.

As soon as pressure is applied to the brake pedal, the source of the vacuum is shut and the atmospheric pressure will only get into one side of the vacuum diaphragm. There are other tools involved as well.

There are master cylinder pistons. On releasing your foot from the brake pedals, the vacuum can now enter the two sides of the vacuum diaphragm. Doing that will also return the master cylinder pistons to their default position.

By the way, what could cause brake pedals to become stuff? There are three major causes of a stiff brake pedal, they are vacuum pressure, valving issues, and pedal ratio. There are other causes but they are secondary to these.

1. Vacuum Pressure

A lack of vacuum pressure is the major cause of a stiff brake pedal. So, whenever you experience a stiff brake pedal, the first thing that should come to your mind is the vacuum pressure.

The brake booster of any vehicle needs a source of vacuum to function well. Brake boosters require 18 inches of vacuum for them to function at the highest efficiency.

When the required level or amount of vacuum is not provided, the brake pedals begin to get really hard and stiff. Eventually, it will get to a point where pressing down on the brake peels feels like you’re pressing on a wall.

The brake booster contains some vacuum diaphragms in it with a vacuum on either side of the diaphragm. With insufficient air in the sides of the vacuum diaphragm, the device will be unable to push the pushrod into the master cylinder. That leads to stiff brake pedals.

2. Valving Issues

Another cause of stiff brake pedals could be the combination valve or the pressure differential valve within the combination valve.

The Pressure Differential Valve in the engine is in place for safety purposes. It moves when the pressure drops on the front side of the valve as opposed to the pressure on the rear side.

It also moves when the pressure drops on the rear side of the valve compared to the pressure on the front side of the valve.

In the event of this happening, the fluid flowing from the master cylinder is unable to pass through and is stuck with a barricade. Since the brake fluid is unable to be compressed, the brake pedals will become stiff.

This situation is widely described as a “tripped valve”. Re-centering of the Pressure Differential Valve is necessary at this point to balance the pressure on either side of the valve.

3. Pedal Ratio

The pedal ratio is the relationship that exists between the length of your brake pedal and where it pivots. Many people do not recognize or admit that the pedal ratio could be the cause of stiff brake pedals. I’ll explain why it is.

You see, the pedal works as a lever that applies motion to the booster based on the pedal length. A slightly incorrect pedal ratio (as small as ¼ inches) will cause more pushrod to move through to the brake booster.

You know what happens next, the booster will be held back from moving the piston into the master cylinder.

These are only the main causes of stiff brake pedals. Other causes can be a damaged or faulty brake booster, leaking vacuum hose, or use of wrong-size parts in the brake system.

4. Overheated Brakes

Overheated brakes can also be the major reason why your brake becomes stiff. However, if your car has been parked for some days without use, it then means that overheated brakes are not the cause.

Why Is My Brake Pedal Stiff and Car Won’t Start?

As discussed above, those are the causes of a stiff brake pedal. If your car won’t start when you have a stiff brake pedal, it could be due to the fluids in the engine of the car, check for the engine lights, ABS light on the dashboard and other warning notification lights.

Check for every possible problem that could make the car not start. It could be battery issues, low transmission fluid, breakdown of some engine parts, and many more.

Better still, you should get the help of a professional to check what’s wrong with the engine and help you fix it.

What Should I Do If My Brake Pedal is Stiff and Car Won’t Start?

Based on the causes of stuffed brake pedals, there are some remedies you can put in place to correct the situation. They are:

Observe the Vacuum Pressure

If you check the brake system and you observe that it is a lack of vacuum pressure that caused it to become hard and stiff, you need to put sufficient air into it.

You might need to install an electric vacuum pump into it or even a canister, depending on how much the air pressure has dropped below 18 inches.

What is an electric vacuum pump, you may be asking? An electric vacuum pump is an electro-mechanical device designed to produce air (vacuum) for any engine.

Since the brake booster is not getting enough air, an electric vacuum pump can be used to pump air into it and make it functional.

All you need to do is connect it to the brake system in your car’s engine with a vacuum hose that goes straight from the brake booster to the electric vacuum pump.

With this, the engine is not required to supply a vacuum to the brake booster anymore. The required vacuum will be provided by the electric vacuum pump.

Actually, before buying an electric vacuum pump, you should take a look at the vacuum hose. The vacuum hose is what supplies vacuum from the engine to the brake booster.

If you use a 3/8” fuel hose, there might be problems with the vacuum supply. People interchange and make use of fuel hoses instead of vacuum hoses. This will only lead to problems because a fuel hose cannot function properly like a vacuum hose.

Fuel hoses can resist expansion, quite alright but they cannot resist sucking like vacuum hoses. The hose you should make use of is the 11/32” vacuum hose.

Check for Valving Issues

If you observe a tripped valve in the brake system, you need to re-center it accordingly. You need to move the valve back to the center in the right direction. Also, the issue that caused the valve to trip or move should be sorted out.

Most vehicles use OEM disk brakes so it is common to see some valves within the brake system. To fix this, it is better to employ the help of a professional to change the valve or re-center it so your brake system will function normally and you can get rid of the stiff brake pedal.

Observe the Pedal Ratio

If the pedal ratio is incorrect, it might be the cause of your stiff brake pedals. How do you correct this? Correcting this might be difficult because you might need to move the pedal pivot.

Sometimes, all you will have to do is to relocate the connection point of the pushrod between the booster and pedal.

If you don’t know already, a manual brake system should have a pedal ratio of 6:1 while a power system should have a pedal ratio of 4:1.

Final Thoughts

The brake system in vehicles is very key to the driving experience. You do not want to experience a stiff brake pedal when you need to urgently step on the brakes.

As soon as you observe a hard brake pedal in your vehicle, you should reach out to the mechanics to see what can be done about it. Do not neglect the stiff brake pedal while driving. Safety first always.