Junk Yard Gems for GMCs

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GMC Western States
Motorhome Club

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:
Panels from ’70-’71 Buick Riviera will fit ’73-’76 motorhomes. Panels from ’77-’84 GM cars will fit ’77-’78 motorhomes. Vacuum select wafer is unique. Change wafer from original panel. (Don’t lose OEM wafer.)

A Arm/Frame (Upper and Lower Arms):
’73-’78 Olds Toronado and Cadillac Eldorado basically the same except reinforced torsion bar socket and lower balljoint mounting area and other welds. (Modifications can be copied by a good welder with the old A arm as a pattern.) Must use motorhome lower ball joint.

Air Compressor Electro Level II:
Available from most 70s and 80s Buick Riviera, Cadillac Eldorado or Seville, and other GM luxury cars with rear air suspension. Direct replacement without modifications. Mounted on left front fender.

Alternator - 80 Amp Delcotron:
Most 70s GM luxury cars have 80 amp Delcotron - Riviera, Toronado, Eldorado, Seville and others. The alternator capacity is metal stamped near the mounting ears. Larger GM trucks and school buses have 145 amp Delcotrons for folks who need lots of power!

Axles and CV Joints:
Axles will not fit! They are shorter and have a dampening device which is not compatible with the motorhome.
You can use the inner and outer CV joints from ’66-’78 Toronado and Eldorado if you thoroughly clean and inspect them before use.

Blower Motor (Dash AC):
Many GM cars may work. A variety of parts available, but some rotate in reverse direction. Take your old one along. Make deal to return if it won’t fit!

Brakes:
Calipers: ’71-’78 Toronado and Eldorado will fit. Rebuild kits are about the same price as rebuilt calipers.
Master Cylinders: Not advised.
Wheel Cylinders: Not advised.
Rear 75-78 Eldorado disk brakes can be modified to replace rear drum brakes.

Carburetors:
Not recommended unless you conduct trial and error tests with a pocket full of Rochester jets, metering rods, and lots of time. Best to leave this in the junkyard!

Throttle body assembly, cover, choke coil assembly, filter nut, vacuum breaker control, etc. can be used without problems.

Closet light:
Makes your wife or significant other happy! Car or truck dome light with built-in 3 position switch. Also find a pin door switch for automatic turn-on. Built-in switch can override pin switch.

Ignition Distributors:
Most Olds V8 large and small block distributors will work with modifications. Olds V8s have HEI. Auto distributor must be reworked to use on motorhome. Weights and vacuum advance requires changing. Upgrading from point type distributor to HEI is a major improvement for frugal GMC owners.

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
Black-red-white leads (White tach lead) Black connector body (or blue tie)
Black-red-yellow leads (Yellow tach lead) Yellow connector body (or yellow tie)

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 usually bad.)

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.
403 Olds engine - same comments.
Exhaust Manifolds: Olds 455 Toronado manifolds will fit 455 or 403 right side only! Left side has donut problem. Inspect for cracks and flatness. Resurface?
Intake Manifolds: 455 use ’68-’72 Toronado low silhouette. ’73-’76 Olds Toronado will also fit but have EGR valve (block off). Non-Toro manifolds will fit but require raising engine compartment lid. For the 403 - most 403 Olds will fit.
Light Lenses: Dome lights - Most 70s GM cars fit cockpit lights. Some Pontiacs have sunburst lenses like the ’78 GMC.
Tail light lenses - 70s Chevy and GMC vans are the same. '80s full size vans use new style that can be adapted to the motorhome.
Clearance lights and lenses - 70s GM heavy trucks.

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: ’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!

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.