by Tom Ehrhart
The following is taken from literature from Lockheed on the installation and maintenance of flexible brake hoses: To ensure that the vehicle braking system remains in good working order and provides the essential safety and reliability, periodic checks and replacement of flexible brake hoses is necessary. At every 6,000 miles, 10,000 kilometers, or 6 months (routine service period), check hoses for chafing, cuts, perishing and security of end fittings. If any defects are found relevant hose(s) must be replaced. Take care when fitting replacement hoses to ensure that they are not twisted or kinked, and are clear of any part of the vehicle liable to cause chafing.
It is easy to see the pattern molded into the hose rubber. It must be running perfectly straight, any twisting during fitting could put a permanent torsional load at the end connections which can result in premature hose failure. Tighten hose fittings sufficient to prevent leakage, but do not over tighten. It is important to note that hoses with UNF threads use a copper-sealing washer, as illustrated.
METRIC hoses identified by an “M “marking, seal on the tapered end and, therefore, there will be a gap between the hexagon and the face of hydraulic unit. Recommended tightening torques: Cases have been reported where damage has been caused to certain hydraulic assemblies by over tightening brake hose connections. Great care must, also, be taken not to over tighten other associated components such as tube nuts, banjo bolts, bleed screws, etc. Therefore for guidance, maximum recommended torque figures are listed below for both Unified (UNF) and Metric threads.
|Bleed screws 1/4||50||5.63|
|Bleed screws 3/8||100||11.33|
|Int. & Ext. tube nuts 3/8||115||13.03|
|Hose fittings 3/8||120||13.53|
|Banjo bolts 3/8||170||19.27|
|Bleeder screws 7/16||170||19.27|
|Int. tube nuts 7/16||140||15.8|
Certain METRIC threads are similar in size to UNF threads; therefore, it is important that they are correctly identified. If any doubt exists, do not use a spanner, but first screw the component fully home by hand. If the fitting is tight or unduly “sloppy” check the thread type. Such parts as tube nuts, bleed screws and hose-end fittings, etc., with METRIC threads are colored pale gold, similar parts with UNF threads are colored silver, green, or red. It is recommended that all flexible brake hoses are renewed at least every 36,000 miles, 60,000 kilometers or 3 years, whichever occur first.