GMC Western States

 Tech Center Number 22 - July 1998

Sewer Outlet

for Motorhomes with Central Drain Single Holding Tank
By Chuck Garton

I have found the factory sewer drain setup awkward to live with. On my 1974 Sequoia an easy modification made a significant improvement. For this modification I used standard three inch black ABS plastic sewer pipe and 3, 90 degree turns.
Refer to figures 4 and 5 on page 24L-4 of the X-7525 75 & 76 Maintenance Manual.
I cut off the dump tube shown in figure 5 aft of the cross-member, leaving enough pipe to attach one of the 90 degree ABS turns pointing to the driver side of the coach. To this I ran the three inch sewer pipe to the driver side frame rail, to another 90 degree turn aft; ran another three inch sewer pipe aft through a hole already in the frame (This hole on the passenger side has the exhaust pipe in it) to the third 90 degree turn. To this turn I attached the sewer cap mounting cut off from the original dump tube assembly (Figure 4) so that it comes out between the bumper and the coach. I used ABS glue on all connections except the attachment to the dump tube at the holding tank. This presses on tight enough to prevent leaking and makes it removable. Using a long worm gear hose clamp I clamped the pipe to the cross-member.
With this system in place and the coach level it will maintain the fluid level in the holding tank at 1 / 4 to 1/3 mark with dump valve open. To drain the holding tank completely, simply lower the back end.
On my 1977 Kingsley, I altered this setup to include a Macerator pump. Instead of using a 90 degree turn at the holding tank, I used a "T". In the pipe going to the driver side I installed a gate valve. I installed the Macerator pump in the passenger side of the "T".
Disclaimer: As with non-GMC approved procedures what you do to your coach is your decision and only yours.

GMC Motorhome Door Latch Repair / Replacement

The Problem
The only thing that gets more repetitive cycling than the engine and other moving parts of our coaches is the door. Open, shut, open, shut and a few slams thrown in for good measure eventually will take a toll on a critical part of the door latch. All of a sudden, one fine day, the door refuses to latch. Since it won't latch it can't be locked from either inside or out.
Bungee cords will hold the door closed for emergency purposes to get you home or someplace where the latch assembly can be replaced. An emergency repair on the road requires a few hand tools and either a very steady hand or a drill press.

Common Failure Mode
The common failure mode involves a small, but very strong spring in the latch assembly. Figure i shows the latch assembly installed in the door frame.

Figure 1 Inner operator attachment point (w/cotterpin)

Note the two latches that grip the large stud on the coach body frame. This picture shows the latches in the "cocked" position. When they contact the stud, they close around the stud and hold the door closed.
Figure 2 shows the back of the latch assembly with the "dog' fitting into the back of the latches. The failure occurs when the dog spring breaks. Without this spring, there is nothing to force the dog into the latches to cock them.

Figure 2

Optimum Repair
The optimum repair is to replace the Latch Assembly (GM PN 716189). This is a SOA [Sold Only As Assembly] and can be obtained from several GMC Motorhome parts suppliers. {$40 from Gateway Motorhome.)

Temporary Repair
Even though the Latch Assembly is SOA, it can be repaired for short term use. We start by removing it from the coach. You can follow the first part of the instructions in Section 1 of the OMC Maintenance Manual for the Entrance Door Lock Removal.

Inner Trim Panel Removal
This involves removing the lower door trim panel, the locking button and the lower window molding. Then remove all the screws that hold the upper interior trim panel and inner handle assembly. It will be necessary to loosen the two screws at the outer edge of the panel so that the trim panel can be slipped past them.
Then carefully remove the cotter pin which holds the inside operator assembly to the attachment point of the outside operator. (Refer back to Figure 1 for the location of this pin.)
A pair of needle nose pliers will help here. Push the lock button rod down to provide more room to maneuver the panel off the button. Set this aside.

Latch Assembly Removal
Remove the cotter pin at the top of the latch assembly connecting rod. (Again refer to Figure 1.) Carefully remove the locking button from its attachment point by pulling the spring retainer clip off and then pulling the bottom of the button shaft straight out.
Remove the two screws holding the Latch Assembly to the door frame and slide the assembly out from the slot in the frame.
Now install the replacement Latch Assembly or the temporarily repaired assembly by reversing these instructions. Before closing everything up, it is a good idea to liberally lubricate all moving parts with a light oil, Lubriplate or WD-40.

Latch Assembly Repair
If, as we suspect, the latch dog spring has broken and there is nothing to force the dog in to place to cock the latches, this can be repaired for temporary use until you can get a replacement latch assembly. [If this isn't the problem you are on your own.]
This requires that the end of the dog pivot stud must be drilled down deep enough that the stud can be removed from the assembly housing. A 5/16" drill bit is exactly the right size to do this. Drill down through the crimped end of the stud to the point where no stud material remains in the hole. This is critical since the stud is tough steel and has been forced into the housing.
Then remove the dog with its pivot stud and spring. Take out the spring and determine just what you need to do to make the spring force the dog down into the latches. The easiest way may be to bend a tail on the spring to lay across the top of the dog, (Refer to Figure 2.) The other end of the spring can be bent to fit against the top of the dog opening. Arise is handy when bending the spring. (It is a stiff little bugger.) The spring is then placed around the pivot stud.
If you have bent the spring properly it will be necessary to use a "C" clamp to force the dog and spring back into the housing in its proper position. It may be necessary to gently tap the dog into place while it is being held by the clamp.
Drill through the center of the pivot stud with a 5/32" bit all the way through the housing. Run a bolt through this hole, Or a better solution may be to use a self tapping screw since it will be necessary lo grind down both the bolt head and the nut to permit the repaired assembly to slide into the slot in the door frame.
Check the operation of the latches by forcing a round tool or short, length of pipe into them. They should snap around this object, Open them by operating the lever on the side of the assembly. Install in the door as before.

In as much as the proper operation of the door is a matter of safety as well as security, the fumble-fingered author of this dissertation accepts no responsibility for any aspect of this repair. What you do to your coach is your business and only yours.

Dana Compressor By-Pass Hose Fix

The two-cylinder Dana compressor cross-over hose which connects the two cylinders weakens over the 20-plus years and can "blow" off one of its fittings while raising the suspension from a low setting. You can try to re-clamp the hose, but the inside of the rubber hose gets damaged when it comes off the fitting making it impossible to reuse. One solution is simply to replace the hose with a new piece and new hose clamps. Another more permanent solution is to go to your local plumbing supply or hardware store and get 2 90-degree 1/4" npt-to- 1/4" compression fittings and either a foot of 1/4" copper tubing or a foot of 1/4" air line (the same kind you use for the air bag lines). If you use the air line, you'll need to buy two 1/4" compression sleeves for the ends. Replace the original hose barb fittings with the new ones by unscrewing them from the compressor cylinder heads, bend the tube into a gentle "U", and connect everything. The fix is permanent and costs less than $5.


Written, Selected
and Edited By Bob DeSaussure

Brake Fluid
Because of contamination with water it is advisable to drain, flush and refill brake lines every 2 to 3 years. D.O.T. is the specified brake fluid but improved fluids such as D.O.T 4 (and perhaps D.O.T. 3 Ford heavy duty #C6A219542) should probably be the fluid of choice. Brake shoes, drums and rotors may reach temperatures of up to 730 degrees under heavy usage and some of this heat is transferred to the brake cylinders and into the brake fluid. Water contaminated brake fluid can boil and interfere with normal brake operation.
Because of a severe operating environment found in our GMCs, brake fluid boiling specs are important. Specifications Dry/Wet (Wet- contaminated with some water) are:
D.O.T.3 Min. Specs Boiling pt. 401f/284c
D.O.T.4 Min. Specs Boiling pt 446f/311c
D.O.T 5 Min Specs Boiling pt: 500f/356c
Ford heavy duty DOT 3 Stated Boiling Pt. 550f/390c)
The 390" wet figure on Ford fluid is my linear extrapolation. According to Govt. laboratories, brake fluid picks up and saturates with approximately 3% water within 3 years at which time all brake fluids boil at approximately 300f.
Use of DOT 5 is not recommended by Ford and Chrysler. Requires frequent chances to maintain integrity.

Engine Cooling
Radiators should be drained and flushed every 2 years for proper maintenance. Use of an additive such as Barr's Radiator Soluble Oil and Rust Inhibitor {1/2cup added to overflow reservoir), will help lubricate the pump and inhibit rust.
To increase air flow over the engine, you may want to consider using G/M Diesel engine Fan G.M. #1064AD22500652. It is a 7 blade 18 3/4" diameter fan, and a direct fit to your hub. It has very little more noise at lockup, but a greatly increased airflow.

CV Boots
Contrary to previous experience with others, I have found that Speediboot 03609 by Motomite Mfg., a split boot similar to the Volkswagen CV joint used for years, will satisfactorily perform its function while eliminating the need to remove the drive line. The joint must be cleaned up prior to installation. It is a good idea to seal clamped ends with Permaseal. This may be a useful item to keep on board with your spares. Approx. $25 each; Call 215-997-1800, Colmar, PA for nearest dealer.

Timing Chain Replacement
Original equipment timing chains can show excessive wear at 80 to 90 thousand miles. You may wish to upgrade to GM Performance Double Roller Chain as used on factory racing equipment. GM part numbers; Chain; 401584, Engine Gear 382880, Cam Gear 3812563, The cost is not much more and the steel gears are not noticeably noisier.

Backup electric fuel pump
I have found that the use of a Carter Flow Thru Pump (P7401A) can he used as a backup to your mechanical Pump for emergency use or to assist in vapor lock conditions. Install before the crossover valve on the reserve tank lose and wire it across the crossover switch. It will operate when the reserve tank is selected. Reasonable and easy to install, it causes little restriction when not operating, as opposed to other vane type pumps. Adding an oil pressure actuated turn off switch is advised for safety reasons.

See Through Steering Wheels
Deep Drop Steering wheels are readily available at wrecking yards: '83-'87 Olds Cutlass, Sierra and Omega. The standard wheel (not deluxe) has a center horn button and makes it a direct replacement. See also January '90 Coach Talk by Wes Caughlan. Additional dash clearance can be gained by shimming yoke under dash approximately 3/4". Approximate wheel cost $25.


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