Page 12 - GMC Vintage RVing Spring 2016

Technical Corner MAINTENANCE, PARTS, TIPS, INNOVATIONS AND MOREStopping the Beast!JR Wright | Midland, MI | 1978 30’ Buskirk StretchHistory of the GMC Motorhome Braking SystemsThis will be semi-chronological history of the many different braking systems that have been available or still available and used on our GMC coaches over the years since new. It will NOT be an endorsement of any one upgrade or system over another and I may have missed one or two items!1. The coach came from the factory with drum brakes and 2” asbestos shoes on the rear axles with 15/16-inch slave cylinders and a 74 MM calipers with similar asbestos pads on the front. One of the first changes noted was the changing out of the Mid-bogy from a 15/16-inch slave to a 1 1/8 inch slave.2. Adapted 2 3⁄4 inch rear shoes in the early 80’s for the rears. This required that you added a 3/8-inch spacer at the top and bottom to align the slave and lower pin to the new shoes.3. GM Hydro boost from the V6 Buick Turbo was an attempt to increase braking power. It required an adapter (cast adapter made by Ken Rose) to mount the booster assembly and had its own internal high-pressure pump. This has been improved upon in recent years by Bob Drewes who developed a hydro boost system that runs off the power steering pump and now Bob Stone offers a similar system for today’s market and it can provide enhanced braking pressures.4. Bob Lamey offered a sensitized booster from the early 1990’s. Presently there are several boosters available from several suppliers including ones made by Leigh Harrison, Jim Bounds and the new Booster from Dave Lenzi.5. Carbon Metallic Brake shoes were introduced in late 1990’s and were an upgrade over stock shoes.6. The additions of 80MM for the front brakes calipers; they were from the 3⁄4 ton Chevy truck, 1979 thru 1986 JB7 System7. Cad disk Brakes were a way to add 6 wheel disk brakes to the coach with almost a bolt on system with minor machine work the backing plates.8. GM Factory Asbestos brake shoes discontinued 5/969. Leigh Harrison offered disk brakes for middle or bothrear axles featuring 121⁄2-inch Ford rotors. Biggest rotors presently on the market right now. Jim Kanomata also offers a very good disk brake conversion for the rear.10. The famous yellow “Sticky Pads” came on the market from Jim Kanomata.11. Chuck Auglur Rear Reaction Anti-skid Kit, which is available for both, disc and drum brake setup, is available from Jim Kanomata.12. The “Manny Brake” system, which is Manny version of a reactive braking system.12 GMC VINTAGE RVING MAGAZINE | GMCMI.COMReplacement Timer for “Set Travel Mode”Johnny Bridges | Braselton, GAThis exercise began when someone’s coach had a problem with the “Set System to Travel” lamp on the dashboard. Thelamp is run by an electromechanical unit very similar to a turn signal clicker. The difference is, the lamp clicker doesn’t reset until the power is removed from it. It is powered from a switch on the column which closes when the shifter is moved out of park. The switch is supplied with 12 volts when the ignition is ON. The clicker modules are becoming hard to find, I know of no one who still produces them. New Old Stock or used are the choices.Someone pointed out an FC-32 timer module for sale on eBay for something less than four dollars plus a couple of dollars shipping from China. Boughtin quantity, the shipping is reduced. I bought a couple to see how they would work as a replacement for the lamp clicker. After looking at them, I bought ten more. They’re very flexible, and switch using dry contacts rated 10 Amps.To replace the clicker, we close S5, so that the operating voltage is also applied to the relay armature. This saves a wire to the ignition 12 volts. I wanted it to operate with the relay energized while the light is on, deenergized when the light has timed out and gone off. This is done by closing S6 with the little plug, and running the light off the normally open contact ofthe relay. For the opposite, you’d put the plug on S7 and move the light wire to the normally closed side of the relay. Either will work, but my choice leaves the relay de-energized most of the time.The actual time delay is set via S1 and S2. If the plug is placed on S4, the time is multiplied by roughly ten. S1 and S2 set the timer range, low to high, and the TIME ADJ control sets within the range. The one in the pictures is set up for a low of 6 seconds and a high of 58 seconds. I have the control set for about 25 seconds.Once set up, installation is simple. I used two red pigtails with male spade lugs on them, and one black wire with a ring terminal. Ground the ring terminal under a screw which is holding something tothe metal behind the dashboard. On the FC-32 the screw connector marked GND is the ground terminal. Now removethe two terminal clicker socket from its terminals. Plug the two male spades into the socket the clicker was plugged into. The wire on the screw terminal marked VCC should go to the side which goes to the shift switch on the steering column, the spade connected to the NO contact goes to the wire leading to the bulb on the dashboard. If you reverse these, you won’t hurt anything, it simply won’t work.You can mount the module in a small box if you wish, or simply wrap it up in a plastic sandwich bag and ty-rap it to any place that’s convenient. I ty-rapped mine to a wiring bundle behind the dash.Note that if your failure is the switch on the column, as opposed to the clicker, this module will not correct it. This is easily tested by removing the clicker and connecting a jumper across the plug. The light should come on and stay on any time the selector is D. If it does not, correct the problem and continue.The red TIME LED illuminates when the time selected has completed.This little module is very flexible. I’m in the process of setting one up with a piezo squawker (SonalertTM) for about two minutes. I’ll hook it to the hot side of the turn signal flasher so that when I forget to cancel the turn signal after a lane change, in two minutes it will holler at me.You could set one up to turn the porch light on anytime the door is opened, for a set period of time.With an external relay, you could make a delayed off for your toad headlights.Actually, anything you want to turn on or off either for a set period of time or after a set period of time can be easily accomplished. The time limits are continuously variable between .13 second and 61 minutes, and the modules could be cascaded for as long as you want, one hour per module. Switching anything more than 10 Amps AC or DC will require an outboard relay.