Use bounce test, look for oil leaks to check struts

Hey there, time traveller!
This article was published 01/08/2003 (8101 days ago), so information in it may no longer be current.

Q. I recently took my 1990 Honda Accord in for a wheel alignment and they suggested I should have the front struts replaced. The car seems to drive fine. How can I tell if I really need these new struts?

A. A strut is really a heavy-duty shock absorber that has the extra duties of holding the suspension in the proper location. The strut may need replacing because of noise from internal parts (usually a clunk). Another reason for replacing the strut is it may be binding. The sliding shaft of the strut sticks and the car does not move up and down smoothly. Test this by pressing down on a bumper and letting go. The car should move down smoothly and return to nearly the same position.

The most common reason for replacing struts is because they are leaking oil. It is normal for a little oil to seep from a strut and to have a dirty film around the strut shaft.

However, if oil is dripping from the strut or the dirt is washed off by leaking oil, then the strut should be replaced. A visual inspection is the best way to check this.

Checking for worn struts is done by bouncing down hard on the car’s bumper and then counting how many times the car bounces up and down.

Anymore than three bounces indicates worn struts. A new car usually will stop after only one bounce.

Q. I just acquired a 1982 Mercury Marquis with only 60,000 miles (96.560 kilometres) on it. The car is in excellent shape but I am having problems with the brakes. The rear brakes do not seem to work very well. When I step hard on the brake pedal while driving, the rear wheels will not lock up or slide.

I checked all the brakes and both the front pads and rear shoes are in good shape. The rear brakes are adjusted properly and the parking brake also works fine. I had a friend help me bleed the brake fluid and the pedal is high and solid. Do you have any ideas why the rear wheels seem short of stopping power?

A. Ideally, the rear tires should not lock up during hard breaking. This could cause the rear tires to loose traction and the car could spin out of control. Having said this, it usually is possible to cause the rear tires to slide a little, especially on loose road surfaces.

There are a couple reasons for poor rear wheel braking ability and they have to do with a shortage of hydraulic pressure at the rear wheels.

The prime suspect is the brake combination valve. This valve is located in the brake lines just below the master cylinder. The combination valve does three jobs. The centre part of the valve has an electric switch that turns on the red brake warning light if the brake system looses fluid in one of its two channels. The front brake part of the valve holds back brake fluid to the front brakes while the rear system is filled with fluid.

The third part of the valve is for the rear brakes and it limits brake fluid pressure to the rear wheels during hard braking.

If the rear brake portion of the combination valve is sticking or out of calibration, then the rear brakes may not be getting enough pressure to provide good braking. The valve is not repaired, only replaced.

An internal leak in the master cylinder also could reduce rear braking power but this usually shows up as a low or spongy brake pedal.

Finally, The rear wheel brake cylinders may be the wrong ones. If they do not have the correct internal diameter, then the brakes do not work properly. I have seen wrong ones installed during brake work, and have even seen it come from the factory this way when the rear axle assembly (with brakes) was installed in the wrong vehicle!

Jim Kerr is an experienced mechanic, instructor of automotive technology and freelance journalist.