Brake Down Less Often
TTC Automatic Slack Adjusters now with a 3 Year Warranty
11 August 2016 13:16:07



Brake defects account for a large percentage of the causes of trucks taken out of service. Many of those defects are simply adjustment issues.

Slack adjusters, as the name implies, are designed to take up the slack in the brake operation as friction surfaces wear away. In normal service on a trailer an operator would expect to adjust a manual slack adjuster periodically, let’s say every 10,000 miles or so, or better still, make the adjustment when it is required. Manual slack adjusters require operator intervention.

Automatic slack adjusters are designed to keep brake operations within limits, but a lot of automatic slacks are found to be out of adjustment during roadside brake inspections. With manual slacks, incorrect adjustment is often a matter of negligence or laziness on the part of the operator, but when auto slacks go out of adjustment, there’s usually something bigger going on. 

Automatic slack adjusters should not require manual re-adjustment. If you have a brake that is over-stroking and it has an automatic slack adjuster, you have a problem with either the brake or the adjuster. If you re-adjust it, you aren’t really fixing the problem. A manual adjustment may bring the brake back into compliance and improve the way the brake operates, but it will only be temporary.

I found this on a US website:

“But in my experience, the primary cause of auto slacks stroking beyond their limit, is – believe it or not – good drivers,” he says. “I’m talking about the driver who never makes an application harder than 15 or 20 psi because he or she never has to. They’re the ones who manage speed well, keep a safe distance, and coast up to traffic lights. These drivers hardly ever put enough torque through the adjuster to cause the ratchet to roll over to the next peg. Consequently, as the brakes wear naturally, the auto slacks aren’t compensating.” What these drivers need to do is make half a dozen full pressure applications once a week or so to get the adjuster to turn over, and then visually check the stroke before leaving the yard.”

But it is a fact that the most common cause of brake failure is poor brake adjustment. The popular type 30 air brake chamber has 65mm of available stroke. A correctly adjusted brake has only 15mm of slack, leaving 50mm of reserve chamber stroke. When slack reaches 25mm the brakes must be adjusted.

Adjust automatic slack adjusters only as an emergency measure, so that you can get the vehicle to a service depot. Repeated manual adjustments will wear down the slack adjuster’s internal components, which could lead to failure. If there is any doubt at all that the internal components of an automatic slack adjuster may have been damaged it should be replaced.

When you need to replace an automatic slack adjuster it is important to be able to recognise the type you require.  EVERY TTC SLACK ADJUSTER has the part number etched onto the body of the unit. Edition 19 of the TTC catalogue has comprehensive application listings covering all popular UK trucks and trailers. TTC has over 70 different units in stock, all TUV approved, covered by a 3 year warranty and they are available now from your approved TTC Distributor. 



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Tony Gunn

Product Manager
Unipart Autoparts is the award-winning supplier of aftermarket parts for the passenger car and commercial vehicle sectors. Unipart Autoparts offer industry leading supply chain solutions to a wide range of OE brands as well as their own OE-spec range of products under the TTC and Unipart brands.
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