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GMC Western States
Revised April 2004
The contents of this document are based upon personal experience gained by hands on vehicle maintenance over many years. They are one man’s viewpoint and do not represent authorized data pertaining to the GMC motorhome. It is the reader’s responsibility to evaluate each situation before vehicle repair and/or modifications are accomplished.
There are many parts for your GMC that can be obtained very inexpensively by a trip or two to your local junkyard. Your savings can be significant, depending on the items you select and the amount of clean-up or repair you are willing to do. Sometimes, depending on the circumstances, your trip can mean the difference between getting to your destination in a timely manner or sitting in a repair shop or parking lot waiting for the part to be shipped.
Here is a list of parts that may work quite well and may be obtained at most junkyards in the US and Canada.
The list will also point out some parts which usually do
not work well without a significant amount of modification.
Air Conditioner/Heater Control Panel, A-Arms, Air Compressor Electro Level II:
Air Conditioner/Heater Control Panel:
A Arm/Frame (Upper and Lower Arms):
Air Compressor Electro Level II:
Alternator, Axles, and Blower Motor:
Alternator - 80 Amp Delcotron:
Axles and CV Joints:
Blower Motor (Dash AC):
Brakes, Carburetors, and Closet Lights:
Throttle body assembly, cover, choke coil assembly, filter nut, vacuum breaker control, etc. can be used without problems.
Ignition modules from most HEI non-fuel injection distributors are interchangeable. (Delco is best.)
Ignition Coil and Pick-Up Coil from any HEI is usable, however, they should be matched as follows:
Ignition Coil Pick-Up Coil
Mismatched components may cause erratic operation.
Cruise Control, Fan Blades, Leveling Valves:
Cruise Control: ’73-’78 Buicks exact replacement. Three pin electrical connector (hold, engage, and light). Other ’73-’78 GM car units will work without dash light. Usually mounted on driver side front fender.
Fan Blades: Large blade fan is major cooling system improvement. From ’82-’84 Olds and Cadillac diesel cars. Same diameter with much wider blades for more air. Best to use with severe duty fan clutch (Hayden #2797, #2749, and AC Delco 15-4208). Can solve engine compartment heat problems.
Leveling Valves: Leveling valves for Power Level and
Electro Level I can be found on ’67-’76 Eldorados as well
as some heavy duty trucks and semi tractors. Electro level II leveling
switches can be found on late ’77-’78 Eldorado. It is found
installed on the body above the rear axle. Remove it carefully as the
control arm is easily broken. (Check electronics - photo cell or lamp
Engines and Light Lenses:
Engines: Any 455 from ’71-’76
Olds will work. Casting codes beginning with F, Fa, and L. (L code is
a motorhome or industrial engine). The casting code is located on the
boss above the water pump mounting. Induction hardened valve seats started
in ’71 and later with G and J heads. 455 engines were used from
’68 to ’76. ’68 to ’70 used high compression pistons.
Oil filter adapter from Toronado 455 and 403s will fit motorhome. Need
to use the Toronado or motorhome oil pan, and oil pump pickup and intake
manifold. Use motorhome accessory brackets.
Radios, Starters, and Transmission Coolers:
Radios: A number of excellent GM Delco radios fit dash (better than modern imports). High power output capabilities. Seek and scan FM/AM and cassette features. Get junkyard guarantee. Installation requires isolated speaker wires (2 per). Early coaches (’73-’75) used grounded speaker return, which is incompatible with all modern radios.
Starters: Any ’66-’78 GM car with 425 transmission (fwd), Olds Toronado and Cadillac Eldorado. Points ignition use ’66-’74 with extra terminal to bypass ignition resistor. HEI ignition can use any. Better to buy rebuilt with lifetime warranty.
Transmission Coolers: 70s and 80s air conditioner condenser
can be used for external coolers as well as external coolers from Mazda
rotary engine coolers. Used coolers are hard to clean and may be contaminated
so be careful.
Knuckles: ’73-’78 Toronado and Eldorado. Bore out lower ball joint hole to fit GMC. (Special reamer required to bore out lower ball joint hole. Taper 1” to 12" or Taper angle 2.2054 degrees). Check wheel bearing hole diam. - should be 3.250” + .003” - .000”and not show signs of internal wear.
Gear Boxes: P30 chassis (lunch truck) steering gear boxes are identical. Other Chevy/GMC trucks look identical but have different spooling valve and gear ratio.
Steering columns: ’69-’78 tilt and telescope columns from Buick, Olds, and Cadillac will fit but only the upper part. (Lots of work!) If you are changing, consider ’78 or later with telescopic features, which may be desirable.
Wheels: 16.5 inch 8 lug dual truck wheels with “radial”
stamp. 16 inch 8 lug from mid 70s thru ’87. One ton dually pickups.
Check for out of round and wobble - should be 0.05” max. Mount radial
tires on radial wheels only! Check to make sure wheels clear calipers.
Transmissions and Final Drives:
Transmissions: ’68 thru ’78 Toronado or Eldorado will interchange but the '73-'76 are most desirable for rebuilding. The '68-'72 and '77-'78 can be beefed up by a rebuilder. TH 425 ID tag is on the left side of case. Toronado with “OJ” or “OM” on tag. Eldorado with “AJ” or “AK” on tag. Tag with GM is from a motorhome. ’66-’67 Toronado/Eldorado are switch pitch transmissions which must be modified for motorhomes. Replace bad dipsticks cap or seals with better one.
Final Drives: Many good auto final drives are available
with the TH-425. Toronados/Eldorados with trailer towing option have a
3.07 gear ratio (10 bolt cover). ’66 and ’67 Toronados with
3.21 have an 8 bolt cover. If 3.21 final drive is used get RH support
bracket and output shaft. Some ’73-’78 Toronados/Eldorados
had 2.73 gear ratios and 10 bolt covers. These should be avoided. Remove
cover and inspect for metal flecks and grease quality before purchase.
Later units have a larger mounting bolt for top front bracket. Get bolt
and bracket just in case!
Electric Vacuum Boost Pumps:
A lifesaver addition when your engine dies on a steep downgrade. Pump provides auxiliary vacuum to your brake vacuum booster. Found on the following 4 cylinder airconditioned GM cars:
Can also be found on some ’90-’92 Chevy/GMC vans. Pump is installed under the battery tray on the driver’s side. Remove splash guard for access. Also get electrical connector. Apply power +12v. to pins A and B with -12v. to pin D to verify operation. Get carbon filter.