Anyone Else Use These Spring Brake Tricks?

Topic 15931 | Page 1

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Farmerbob1's Comment
member avatar

If you have air pressure at normal operating levels, then engage both tractor and trailer brakes at the same time, your truck will crab together. The tractor tries to push back, the trailer tries to push forward. This is due to the arrangement of the spring brakes. When you release the brakes, the truck 'stretches out' a few inches.

(This is also why you should NEVER engage both brakes on a scale. That crabbing can give you a bad scale reading, or potentially damage the scale.)

(This is also why you should be very careful releasing your brakes when you are parked with your tractor or trailer extremely close to another truck or obstruction.)

There are two ways that I use this 'feature'

First, when I dock at a place that is picky about dock gap, I push all the way back to the dock, engage the tractor brakes, then pull and release the trailer brakes twice over about 4-5 seconds to drop trailer air pressure, before engaging the trailer brakes for the last time. With less pressure in the trailer air tank, the brakes don't crab the trailer forward nearly as hard, giving a good, solid dock with no gap. That's normally a non-issue. A couple inches at most docks is no big deal, but sometimes a picky shipper or receiver wants very tight docking.

The second, really useful thing I use brake crabbing for is tandem pin releasing. Whenever I need to adjust tandems , especially on an older trailer, I will intentionally crab the brakes at high air pressure. Then I go back to the tandems, and disengage the pins. Normally they will not slide. Then I walk back to the cab, put about ten pounds of pressure on the service brakes, and release only the tractor brakes. After about three seconds, the tractor brakes have completely pressurized. Then I release the service breaks. The tractor will rapidly slide forward about 4 inches or so, and then tug on the trailer. This will release all four tandem pins almost every time, without having to get out the cheater bar.

Shipper:

The customer who is shipping the freight. This is where the driver will pick up a load and then deliver it to the receiver or consignee.

Tandems:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

Tandem:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

TWIC:

Transportation Worker Identification Credential

Truck drivers who regularly pick up from or deliver to the shipping ports will often be required to carry a TWIC card.

Your TWIC is a tamper-resistant biometric card which acts as both your identification in secure areas, as well as an indicator of you having passed the necessary security clearance. TWIC cards are valid for five years. The issuance of TWIC cards is overseen by the Transportation Security Administration and the Department of Homeland Security.

Kevin H.'s Comment
member avatar

I'm curious about how this works. My understanding is that the springs apply the same brakes using the same mechanism as when you use air to do it, and I don't see how that causes the tractor or trailer to move.

Pat M.'s Comment
member avatar

Actually it is the air bleeding from the suspension that causes the truck and trailer to move. Ever been asleep and felt your truck lurch? That is the brakes slipping when the airbags drop.

Bud A.'s Comment
member avatar

My fifth wheel release is a little tight, so I usually pull both brakes when I'm dropping a trailer, then release the trailer brakes so I can unhook. Just have to remember to pull the trailer brakes again before unhooking the air lines. I hate it when I pull the red line and get a blast of nasty air tank air in my face.

G-Town's Comment
member avatar

Matthew wrote:

The second, really useful thing I use brake crabbing for is tandem pin releasing. Whenever I need to adjust tandems , especially on an older trailer, I will intentionally crab the brakes at high air pressure. Then I go back to the tandems, and disengage the pins. Normally they will not slide. Then I walk back to the cab, put about ten pounds of pressure on the service brakes, and release only the tractor brakes. After about three seconds, the tractor brakes have completely pressurized. Then I release the service breaks. The tractor will rapidly slide forward about 4 inches or so, and then tug on the trailer. This will release all four tandem pins almost every time, without having to get out the cheater bar.

If so equipped pulling/holding the trolley brake (Johnson Bar) is very effective for releasing stuck pins. In four years I have yet to have a tandem that wouldn't slide using the trolley brake and gently rocking the trailer; forward then reverse. I also roll my window down, cause you can hear the pins release.

Tandems:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

Tandem:

Tandem Axles

A set of axles spaced close together, legally defined as more than 40 and less than 96 inches apart by the USDOT. Drivers tend to refer to the tandem axles on their trailer as just "tandems". You might hear a driver say, "I'm 400 pounds overweight on my tandems", referring to his trailer tandems, not his tractor tandems. Tractor tandems are generally just referred to as "drives" which is short for "drive axles".

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