parking brake light remains lit and driing feels like brakes are on

Volvo TGB and 30X (303/304/306) mods and resto work, news, resources and non-technical stuff
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Joined: Fri Dec 26, 2014 10:52 pm

parking brake light remains lit and driing feels like brakes are on

Post by blehutchie »

First notice the issue when i had the 303 in neutral, both shifter and Low/High...parking brake off.
I pushed it in my barn and it rolled for 10 feet then stopped dead. would not move forward or backward.
started to drive it and it felt like the brakes were on even with the parking brake off. Dash parking brake remained on.
Any thoughts here?
Jim Molloy
United States of America
Posts: 356
Joined: Sun May 30, 2004 2:16 pm
Location: Sheridan, Oregon

Re: parking brake light remains lit and driing feels like brakes are on

Post by Jim Molloy »

The parking brake light illuminates if: 1) the parking brake is applied, 2) if the brake pedal travel it too great or 3) the system senses there is a significant difference in pressure between the two brake circuits.

When it comes to brakes locking or dragging, the most common thing I have seen by far is internal delamination of the rubber brake hoses. They look fine on the outside but will create a one way valve effect on the inside. A more rare situation is a vacuum assist booster going bad. This should effect both front corners and one or the other rear corners (one rear axle or the other on 6x6 trucks).

I have found the easiest way to diagnose brake issues is with an IR thermometer and getting all the tires off the ground. Once up, can you spin all the tires freely? If one or more are NOT moving freely, you have your general location. If they move freely, have someone apply the brakes. Is everything locked tight? If so, the wheel cylinders are doing their jobs. Then release the brake pedal and quickly test to be sure all wheels spin freely. If they do, Great! It means the potential one way valve effect is not severe with a single brake application. If one or more of the wheels are not releasing, you once again have that/those location(s) to explore.

If all tested fine with the above testing, time to take the vehicle out on the road. But before you start moving, get a set of temperature readings on each of the brake drums. Most convenient place I have found is where the drum is sandwiched between the hub and tire rim. If you sense a dragging feeling or locking, check the drum temperatures. Hot ones are where your problem lies.

Unless you are certain your truck has had all flex lines replace in the last few years, I would look at these as the first potential culprits. My brother had a nice AluZin TGB 11 that sat idle in the Texas sun for 8 years prior to moving it up to Oregon. After offloading from a trialer, the next stop was Oregon DMV only 17 miles away. It drove like someone was riding the brakes. IR temps of the hubs were all quite warm. It was not possible to roll the truck forward or backward by hand. One of the front corners took two hours to eventually release. Once home, it was discovered that only one of the eight rubber flex lines would allow air to be blown through. All eight lines were replaced with no issues the last four years. Simple fix.

Hope this helps.
Jim Molloy
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