Technical Documents

One of the reasons GMC Eastern States was founded was to provide an avenue for gaining technical information regarding the maintenance and improvement of our classic motorhomes. Many of the files referenced below were developed for presentations or created for distribution to the members at rallies. As a service to the GMC community they are being made available here. Of course, there's nothing quite like attending a session in person. And, there's nothing like getting your hands on the documents to keep the thoughts alive after the presentation.

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• • • • • SYNOPSES OF THE DOCUMENTS LISTED ABOVE • • • • •

Rebuilding that Motor

Larry Weidner, whose GMC coach features a 500 cu. in. Cadillac engine, weighs in on what he has learned and observed over the years about rebuilding engines. Though careful to stress he’s providing only his opinions, the article is quite powerful and worthy of reading by all owners. View/download the article.

Rebuilding the Olds Engines

Jim Bounds responds to an email detailing the work done at the Cooperative Motor Works with Jasper rebuilt engines. Jim provides an overview of what needs to be considered when taking on such a project. View/download the article.

Throttle Body Fuel Injection Upgrade

Ray Schwartzendruber provides an excellent overview of the throttle body fuel injection system. What is covered is generally applicable to most TBI systems, but while putting particular emphasis on how it applies to the engines of the GMC Motorhome. The file contains the 77 slides and notes from Ray’s original presentation. View/download the article.

Fuel Injection for the GMC

As Richard Waters writes, “This is about how a not very experienced, ‘shade tree mechanic’ figures out how to install Fuel Injection in his GMC Motorhome. This presentation is for those non-engineer/professional mechanic types that want to install TBI.” Don’t be fooled by the disclaimer, Waters provides lots of photos and pointer in this 171-slide presentation while crediting may other members of the GMC community who also provided advice. The fous of Waters’ project is the installation of a kit from Howell Engine Developments, Inc. View/download the article.

The GMC Motorhome Steering Box

If the steering on your 30-year-old GMC is getting a little too loose then this informative document is for you. Don Wirth gives details on the Saginaw power steering box. He tells how to identify the proper style used in the motorhomes, how to disassemble it and the proper way of adjusting it. View/download the article.

Steering Column Upgrade and Repair

Are you interested in having a more modern steering column with the dimmer, cruise control and wiper switch on the turn signal stalk? If so, this detailed article is for you. Richard Sowers provides images and notes in a step-by-step format for doing a complete job. View/download the article.

A GMC-specific Toad Brake System

Fred Veenschoten provides an overview of the different types of brake systems for a towed vehicle (toad) before detailing how to build a VIP System (variable, independent pressure system). Controlled by the driver’s foot, the toad brakes can be applied independently of the coach brakes or in conjunction with the coach brakes. View/download the article.

The Power Level Air Suspension from the Top Down

The Power Level system was the standard system in 1973 through 1976 GMC coaches. Rick Denney's article presents the Power Level system starting with its basic theory of operation and proceeds from there to troubleshooting and leak detection and repair strategies. Many of the principles in this article also apply to later Electro-Level systems, but the article does not attempt to address that more complicated subject. View/download the article.

  • Suggestions for Installing the QuadraBag System

Bill Brown offers practical and helpful suggestions for installation of the new QuadraBag system for the rear suspension of our GMC coaches. The system, designed by Jim Bounds and Jim Kanomata, has many advantages of the original single-bag system developed by GMC. The document is based on Bill’s notes and observations from installing a new system on his personal coach. View/download the article.

Guide to Final Drive Ratios and Tire Size Information by Brand

Don Brown provides a handy table for evaluating the difference from original specs for a combination final drive ratios and tire sizes from Michelin, Goodyear and Bridgestone. View/download the article.

The Forgotten Ammeter

An Ammeter measures the direction and quantity of electricity flowing through it. It has been replaced by the voltmeter. In pointing out how the ammeter has become the forgotten gauge a vehicle, Frank Folkmann tell the proper way to install one as well as the two wrong ways. View/download the article.

GMC Motorhome Electrical System from the Top Down

The electrical system of the GMC is fairly simple when considered as a system, but it’s easy to get lost in the details. We work on those details, and sometimes miss an understanding of the system as a whole. In this document Rick Denney lays out the system as a whole so that GMC owners can see how the details fit into the big picture. View/download the article.

The Wonderful World of Type II HVAC Systems

It began with one question: “Why is my dash airflow so bad?” In a well-documented and photographed procedure Mark Wall tells how he greatly improved the stock system in his pre-1977 Motorhome. In the process he rerouted ductwork, added vents and installed a second evaporator. View/download the article.

GMC Motorhome House Electrical System: Troubleshooting, Maintenance and Safety

Don’t be fooled into thinking this document is a repeat of the one listed immediately above. In this document filled with illustrations, Bob Hendrickson takes the reader through the processes involved in troubleshooting and maintaining the house electrical system of the GMC Motorhome with an emphasis on safety. View/download the article.

Water Quality and Sanitizing Issues

Frank Folkmann provides a common-sense guide with regard to water quality, it's safety and sanitizing issues. View/download the article.

Operating and Troubleshooting the Suburban Dyna-Trail Furnace

Though John Nicholls will be the first to tell you he’s not an LP gas technician he does provide some good advice in this article about the Suburban furnace in many coaches upfitted by Coachmen. The reader should take note that he/she is responsible for making your own determinations as to validity and applicability of the information presented. View/download the article.

2008