One of the most important things to do when looking to purchase a GMC is to investigate the overall mechanical condition of the coach BEFORE you make the purchase. Sure these coaches have age and there will be many things you will probably need to do to the coach after the purchase to bring it up to your reliable condition but there are some issues you need to guard yourself from or at least know going in will need attention.
We offer a 4 page “mechanical review” that will pretty much cover the main issues and give you an “A-B-C” condition of those main components of the coach. If desired we can take that investigation a step further and review all functions of the coach as well. Its all simply a matter of the time taken to do the check out. A basic mechanical review will go a long way to help keep you from things you had no idea of, this service requires @ 1-2 hours of our time and would therefore run $60-120. The expanded review covering interior, electrical, water sewer, appliances and other functions of the coach could run as high as 3-4 hours.
Here is a walk through of some of the things we look at in our basic mechanical review. If you are too far away from having us perform this service for you, take some notes and try and do this yourself. We also find this service helpful in setting a work order on periodic maintenance on a coach.
This review covers front & rear suspension issues:
This coach is fitted with the high quality blue outer CV “super boot” which while a superior part are no longer available, there is wet grease around them which means the large clanp is probably leaking– no problem, just repack the CV, clean it up and install a new double band clamp to stop the leaking. The brake rotor is wearing well and inspecting the control arm bushings, tie rod ends, ball joints and sway bushings we find only slight play in the ball joints and weathered sway bushings– no deal breakers there. 
The inner CV almost never shows wear but we do have oil residue on the front part of the motor with old caked oil 
running down the lower radiator hose. This means that hose has some age on it, the front main seal may be weeping a bit and has been doing it for some time. Depending on the mileage, I may want to at least look into the condition of the timing chain– no problem, older motors can react well to a new timing chain, this can improve performance greatly.
The steering shaft CV boot is split 
and will need replacing, no problem its an easy fix, cheap too and will make a big improvement in the reliability of that part. This is a 74 coach which means the rear air suspension compressor is mounted up front. As you can see it is original and chances are will need replacement at some point. No problem and after it is replaced, the suspension system will be more reliable. This steering Cv/slip shaft/universal is located on the input side of the steering box and is many times overlooked. It can be a critical component in the steerability of the suspension and should always be considered.
Next we go to the rear suspension so we jack up each side seperatly to check the rear swing arm pins 
taking the air out of the air bag, we lift the tire back into @ ride position then shake the wheel in then out to see if there is any bogy pin play– this suspension is very tight and looks like the pins have been replaced– this is @ a $1500 job to replace all 4 pins in the rear suspension. The rear brake hoses are a specialty part not available at your local parts house 
This coach is fitted with new design rear hoses, you can tell this by looking for a square shoulder on the center fitting where the mounting bolt goes through it. If these corners are rounded, the hose may actually be original and should be replaced. Collapsing brake hoses are THE number one reason for un expected brake failure– they never look bad because you cannot see the hose swell up on the inside turning them into pressure holding check valves. If you see an old rear hose, chances are the brakes have not been attended to for some time and a complete brake job should be considered. Please don’t play around with breaks, its very hard to stop a 12,000 lb. projectile with your foot — not to mention hell on your shoe sole!
The air bags are holding are well without any leaks — but 
do show weathering. The small cracks mean the air bag has age and new bags or even an upgraded 4 air bag system would be a good idea. There is a great deal of pressure in this air bag (@ 120 psi) and a great deal is riding on it (the 8,000 lb. rear of the coach). If it blows, you cannot move and will usually do some considerable damage to the body of the coach– plus put a ring in your ear if you are standing too close when it goes. Don’t play around with this part either. This coach is fitted with air bag shut off/fill valves 
, something I strongly recommend everyone add to their suspension. This will allow you to isolate the air bag from the air delivery system in case of a system leak of failure and gives you a second way to add air to the air bag. They have 2 magnetos in a single engine airplane for the same reason– you can’t pull the plane over to check the ignition so it has 2 systems– the shut/fill valve gives you this back up & installed properly does NOT create more leaks. In that the valve was turned off when we started the review my guess is there is at least a slow leak in the system (most systems have this) somewhere and you may want to devote some time in checking it out.
The brake combination (or meter) valve 
being in the middle of the brake system gives you a look at least at one end of each steel brake line. Any serious corrosion or pitting my indicate rusted lines, these have only surface rust which is expected. The master cylinder always looks nasty 
, don’t worry too much about that, what I do look for though is wetness which means there may be a leak or damaged seal. This master cylinder is dry (a good thing), the booster shows rust stains below the master cylinder which means somewhere in its life the master was leaking into the booster. It means to me that the brakes have been worked on at some time, the master cylinder is not new and the leak that used to be there had been fixed. Open the wells and look at the condition of the fluid, if its nasty, you may want to flush the system, low may indicate a small leak somewhere. The front well is the rear brakes, rear being the fronts– if one is low, suspect that area.
Next we turn to the undercarriage, tanks, pipes & frame. 
From the back, lay down behind the bumper and sight up the frame rails, look for rust through and rust swelling the frame at the rear bub frame. The sub frame is a “C” channel inside the main rails supporting the rear suspension, swelling and flaking in this area means frame damage– throw that coach back unless the low price will allow you to spend @ $5000 to replace the rails or more. Look at the fuel tanks and hoses to see any wetness or leaking. There are many feet of vent and delivery hose all with a 5-7 year performance window. Do not be surprised if there are weather checked hoses. Its a big job ($5-700) to drop the tanks and replace these parts– it may not be a deal breaker but know you may have to do work here. This coach has good rails, someone had welded a trailer hitch to the frame then someone else had cut it off, no big deal. Things look weathered under this coach but no rust through and things are as I would expect them to be. Look at the tires for cupping, unusual wear and weather cracks. Small cracks near the center bead means the plys may be separating, motorhome tires seldom loose their tread– no, they wear out from age so even though the tires may have tread, look for signs of age. DO NOT play with tires. its almost a recommended thing to replace the tires so you have a good “baseline” on their condition– a blown tire puts you on the side of the road in a big way and usually does damage to the body of the coach.
Finally, use your good sense and look for anything damaged, worn or hanging– its your chicken to find problems.
Next we move to the motor section of the evaluation 
. Here we open the engine cover, pull off the air cleaner and give a gander at the power plant. 
Unless the previous owner used the motor as a dining table, it will probably be a bit dirty and thats OK, an original untouched motor will be a bit nasty. Look for wet spots which may mean leaks. This motor has had carb. work done in its past, the carb. looks much newer than the motor itself 
. Look at plug wires, vacuum lines, belts, hoses, clamps and wiring. Is it in good repair or are those parts old and cruddy looking, new parts means the motor has at least been attended to on some basis. I have seen motors with critter nests beside the carb. that seemed to run just fine– but for how long and is that critter in there to help the motor– thats what I want to know! We do a compression test to try and get an indication of the condition of the motor. This motor was 115-120 across the board which means there is some wear but it is even and the motor should run pretty smooth. 115-120 lbs. of compression is good– not as good as new but good none the less. This is a 74 chassis which means the motor was fitted with a point style distributer, this motor has and HEI dist. which means there has been some motor mods– a good thing 
but along with that I see the cruise vacuum bellows is all but rotted off its mount and the transducer is disconnected– my guess is the cruise control has not worked in many years. No problem, a new electric servo, computer controlled cruise system is better than the original and can be installed without much trouble. The rest of the motor is dry which means no leaks. In running the motor, we find a good clean start and a smooth idle. Its a little noisier which means an exhaust manifold crack or at least a gasket leak. Doug Thorley makes a beautiful set of heavy duty headers that will fix this trouble, it will run @ $500 with labor to install a set but then your exhaust problems all go out the tailpipe.
If you will remember from before, we did see some oil on the bottom of the motor but to be honest, that is not unusual, after all these are old units and oil wants out! The starter was oil soaked but it worked well, down the road you may want to replace the starter and investigate the oil a bit but unless it is pouring out, you may want to live with a certain amount of that gooey stuff under there.
Now we lift the front hoods and check out the wiring 
Yes we have “waddage”. Everything seems to work OK but over the years the previous owners have felt the need to add their “personal touch” to the wiring and we end up with a bit of a mess. Thats not that bad in that at least those guys before did spend time doing things with the coach. The first thing I would do with this coach is rake some of this out and rewire stuff to make it neater and more reliable. In some cases, you find dangerous wiring that must be attended to but as long as its all in there, you can fix it.
OK, the blanks on our review are filled in and we now have a better picture on what we are looking at. This coach is in good overall condition, it has some systems with age and there are some issues that need attention before it could be deemed “seaworthy” but overall it is in good original condition. The prospective buyer lives in Canada so some of the issues found will need attention before it tries to head home– thats OK– we have that technology and with some work, I feel this coach will carry its driver home without much trouble.
If you are looking to purchase a coach or would simply like to get a condition picture of your unit, a mechanical review such as this is a must. Give us a call if you would like us to do one for you. If you are looking to do the review yourself, give us a call if you have any questions, we’re here to help.