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1947-55 Tech Talk

1947 – 1955 Chevy and GMC Technical Article Listings

Monday, April 2nd, 2018

 

 Accessories

Bed

Brakes

Bumpers

Cab

Door

Electrical

Frame and Chassis

Gas Tanks

Grilles

1949 – 1955 GMC Grille
1947 – 1948 GMC Grille
1947 – 1953 Chevrolet Grille Restoration Tips

Interior

Lighting

Mechanical

Mirror

Misc.

Paint

Panel Trucks

Radio

Running Boards

Sheet Metal

Speedometer and Gauges

Split Rims

Suburban

Suspension

Transmission

Trim

Wheels and Covers

Window

COE Shift Lever

Wednesday, June 18th, 2014

As vehicle owners begin to use their truck (cars as well) they report to local dealers of developing problems. Many things show up in long field use and not during short laboratory tests.
An excellent example is the 4 speed shift lever on the 1947-55 Chevrolet and GMC Cab over Engine “COE”. It was found that wear in the lower end of the vertical lever would develop. Even a little wear moved the top end of the lever closer to the dash until finally a drivers knuckle could actually touch the dash!
By 1950, a factory correction was made. The lever was shortened and moved away from the dash. Photos by Kent Zimmerman – Mesa, Arizona
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1947 – 50
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1951 – 55

Photos by Kent Zimmerman, Mesa, Arizona

The 20 Year Chevrolet Horn

Wednesday, April 16th, 2014


This new horn design was introduced in 1934. It is attached direct to the 207 six cylinder engine and was so successful there was almost no changes through 1952.
As shown in these photos this 1934-36 horn was attached to a flat foot that secured it to the center of the intake manifold. A long nose directs the sound to the area very close to the radiator cooling fan.
A slight change to the exterior appearance occurred with the new 1937 216 cubic inch engine. Possibly to keep it away from the high temperatures of the exhaust manifold, the horn was relocated. It now was attached to the forward leg of the intake away from engine heat.
The “bell” part of the horn was shortened to keep it the same distance from the fan. There, it remained on cars and trucks with the 216 engine through late 1952.
It was so well designed it rarely required attention. A single screw secures the rear half circle cover. When removed the inner workings are exposed for an occasional tone adjustment.
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1934 – 36
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1937 – 52

Short Shaft Water Pump Discussion

Monday, March 17th, 2014


The revised Chevrolet 235 and 261 high pressure inline six cylinder engine (1955 through 1962) was given a much better cooling system than prior years. This was due to a big change in the water pump and how it attached the front of the engine block.
The prior 216 and early 235 design pulled coolant out of the engine block through two quarter size holes, into an exterior pump, then forced it through the lower radiator hose and back into the engine block. This system worked well for millions of Chevrolet cars and trucks for at least 16 years.
One of the difficulties began to develop as these vehicles became older and were exposed to faster speeds of more modern roads and radiator coolant water contained a high calcium content.
Calcium started to slowly accumulate inside the block but even more in the radiator cooling tubes. The coolant temperature would rise in the block due to slower water circulation.
This was first noticed in the low geared 1 ½ and 2 tons, even with their extra row of radiator cooling tubes. Local radiator shops would remove the top radiator tank and “rod out” the cooling tubes to restore most of the original radiators ability.
With the introduction of 2 new Chevy six cylinder in 1955, General Motors made a change in the water pump that would at least postpone this over-heating problem for many more years than the earlier engines.
Now, the water pump propeller actually was inside a 4” hole in the front of the block. It could move a higher volume of coolant through the block. Chevrolet cars and trucks could now be used so many more miles before this rodding of the tubes was necessary.
With General Motors wisdom, they designed their new high pressure 235 and 261 engine to easily fit in the place of a failing earlier 216 engine. The main problem with this engine exchange was the longer length of the new water pump shaft.
Local mechanics would then either cut some metal from the upper and lower air dam to move this radiator forward a few inches or shorten the pump shaft to provide radiator clearance for the fan on a new 7” pulley.

The word spread quickly that the shaft could be cut and the 4” diameter pulley from a 1953-1954 would press in the proper position. (Most shops could find one of these pulleys on a nearby used engine)
All fit well but the rotating RPM speed of this small 4” pulley turned the fan and pump 20% faster at the same vehicle speed. Because of the low engine gearing of the larger 1 ½ – 2 ton trucks we have heard owners feel their water pump experienced “cavitation” (the fan is turning so fast water flow will almost come to a stop). It may not boil the coolant but it just might! At slower road speeds the water temperature returns close to normal. A small 18” fan from an early 216 donor engine was also required to prevent contacting the lower radiator tank.

NOW enters another modified water pump that has a much flatter 7” diameter pulley. This lowers the fan speed to the correct RPM that GM intended to be used on ½ ton up to the 2 tons. It was a one size fits all!
It is the other short shaft pump design! You can easily install this modified 235 and 261 engine in the 1953 and older truck (and cars). It is strongly recommended that you use this pulley pump for Chevy trucks rated over ½ tons!
It requires the correct wider four blade 235 fan, however the blades must be bent slightly forward to miss the lower radiator tank.

Therefore, if you want to operate your 235 and 261 engines water pump at a slower speed as GM intended, the 7 inch pulley design is the way to proceed. It will cool ¾ to 2 tons with lower differential gearing at high speeds with no boiling, just as the vehicles were designed. Yes, Jim Carter Truck Parts has the new updated pump assemblies available at a price of $159.00 (a used original wide blade fan is by another order).
A small 4 inch diameter pulley water pump have been placed on a 235 or 261 engine since they were first introduced. They usually work well with vehicles with clean radiators on cars and ½ ton light vehicles that have been given a higher speed differential. Not recommended for larger trucks as water temperature will raise at higher speeds! We have these that operate well (without add-on air conditioning) at our company at $130.00.
As the owner of Jim Carters Truck Parts, I can assure you we have sold over 500 short shaft water pumps with 4 inch pulleys in the last 10 years. Return rate is about 4%. I suspect it is rarely due to an inefficient pump but rather the new customer not aware of the difference between a 216 and later 235 six cylinder. Maybe a few were using them on a low differential ratio ¾ to 2 ton truck.
Does the 4 inch pulley cool as well as the 7 inch design? Probably not on larger trucks! In some situations, if your radiator has calcium build-up, the coolant flow can be so restricted, your temperature gauge will show an increase at highway speeds. The 4 inch pulley turns the water pump much faster than GM intended!
With the low differential gearing (as in the ¾ ton to a 2 ton) plus driving higher speeds, the increase engine RPM will definitely cause temperature increase. It can go so far at very high speeds causing the water to cavitate and the coolant circulation will almost come to a stop! It may not boil the coolant but it just might!

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4 inch pulley

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7 inch pulley

1954 GMC Deluxe Pickup

Friday, January 3rd, 2014



The Korean War has ended and copper used in quality chrome plating is now readily available at an acceptable price to commercial buyers. General Motors loses no time introducing a deluxe pickup in both their Chevrolet and GMC lines. Quality chrome plating was required for this project and was now in stock. Other metals have also dropped in price including stainless steel.

The new deluxe GMC pickup was far above the appearance of earlier years even though the mechanics were virtually unchanged. With more disposable income in the US, General Motors gambled that many buyers would purchase a new upscale truck even if they did not have immediate hauling needs.

Actually GM invested very little to make their top of the line pickup stand out above the crowd. Using their base model, the following made up much of this special pickup:

  • Grille, bumper, grille surround and hub caps are chrome plated.
  • The exterior side window and new one piece “panoramic” windshield is surrounded with high polished stainless steel.
  • Wing vents assemblies are combination chrome and polished stainless.
  • The end of the rolls in the bed sides have plastic reflectors (actually from a 1953 Buick) and held in place with a GMC only stainless ring. A small screw hole was in only the deluxe pickup bed side to secure this assembly. Not on Chevrolet.
  • Chrome tail light ring.
  • The interior upholstery consisted of cloth covered cushions rather than traditional vinyl material on trucks of all prior years.
  • The pleated door panels matched the material in the seats.
  • The unusual metal interior was painted the reverse of the deluxe Chevrolet colors. Thus, dark being the primary color. A lighter shade was the dash, steering column and steering wheel.
  • Driver’s side are rest.
  • Yes, like the deluxe Chevrolet, the running boards were the lower body color.M
  • A different contrasting color, not necessarily the body, is placed on the wheels.

A few items in the attached GMC advertisement, placed in a major magazine. Were extra cost factory options:

  • Hydra-Matic transmission.
  • White top, to reflect sun.
  • Jet plane hood ornament.
  • Factory Clock.

Note: A rear bumper was always an option in 1954. Their problem: They prevented a pickup from backing close to a loading dock. When carrying merchandise or walking livestock into the pickup the gap caused dangerous falling problems for some owners. The beginning attached factory photo of this article shows the tailgate totally open and thus down vertically to eliminate the gap. This can only happen with no rear bumper.

Accessory GM Reflector

Thursday, October 24th, 2013

To add better night visibility to all trucks, Suburbans and panel trucks, General Motors offered a 4 inch diameter reflector as a dealer installed accessory.   With the single small factory taillight, seeing of these vehicles on the road could be difficult especially if their one bulb burned out.  To help correct this problem GM offered a larger reflector that could be attached to the rear license plate bracket.  It greatly improved visibility to others at the rear during night driving.

This was a time when town street lights were limited.  Of course, on the open road these were no lighting along the highways!  This simple GM reflector was offered by the dealers to prevent rear end accidents.  The customer could buy this dealer accessory from about 1940 through 1953. One of the attached photos is taken from a 1949 Chevrolet Truck Data Book. The 4 inch lens is a Stimsonite # 24 and the metal Guide ring has a stamping of X-19.

Jim Winters of Rochester, Minnesota has both a restored 1946 panel truck and ½ ton pickup.  He found these reflectors for both his vehicles at local swap meets.  Few people recognize what these reflectors were used for.   Jim found his in a box of miscellaneous unmarked parts.

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1947 Suburban

Wednesday, April 17th, 2013


If you like non-original suburbans, you will love this 1947. Seen in a recent advertisement at $115,000. Look at the large quarter panel window!

1954 Chevrolet Grille Guard

Thursday, April 11th, 2013


A nice dealer installed accessory in 1954 was the grille guard. It was easily installed by using the pre-existing bumper bolts.

A problem when installed was that it lessened the visibility of the front license plate. Therefore, another change was made during the installation. The license was moved to the center of the front splash apron from the factory position on the right side. In the kit were two small rubber plugs. These filled the factory license bracket holes that existed when the factory license bracket was removed.

Installing an Updated Duel Chambered Master Cylinder

Thursday, August 16th, 2012

Warning:  When installing an updated duel chambered master cylinder under the floor of an older GM truck, a brake line modification may be necessary.

It is not acceptable to allow the modified brake line to touch or be very close to the exhaust pipe.  During long trips, the exhaust heat can cause a rise in the brake fluid temperature to near boiling level.  Modern master cylinders do not have a vented cap to release line pressure so fluid will be forced out through wheel cylinders.  The early single chambered caps are vented to prevent this.

Check your brake lines on non-original trucks.  Do not allow a safer system to leave you without brakes.

An Inner-Line Oil Filter

Monday, October 10th, 2011

An Inner-Line oil filter from Long Island, New York!  Rarely seen today but a popular early aftermarket option.  It secures to the engine block after removing the oil distribution cover.  No oil lines.  No moving the horn forward to make room for the intake manifold mounted oil canister.

Inner-Line Oil Filter Inner-Line Oil Filter
Inner-Line Oil Filter

1954 GM Transition Year

Thursday, February 11th, 2010

This was one of the most unique years for Chevrolet trucks. The Korean War and some resulting material shortages were now history. The economy was growing and the average worker brought home more wages than ever before. Sales of luxury options on automobiles were showing definite increases.

To capitalize on this trend for transportation improvements, GM was fast working on total new automobile and truck models for the coming year. When introduced, the result would be record sales which put General Motors even further above it’s competitors.

But what about the 1954 year for GM trucks? Waiting buyers had the demand for a new updated truck but the tooling was not yet complete. Other competitive truck manufacturers were beginning to offer many deluxe features.

Therefore, General Motor’s 1954 answer to temporarily satisfy new truck buyers was a major facelift of the prior models. To keep costs down, GM continued to use the basic cab introduced in mid-1947. To update this seven year old design, an enterprising engineering department added items such as a modern one piece curved windshield, completely redesigned dash board, and created a totally different grill. All this while keeping almost identical hood, fenders, bumpers, running boards, seats, doors, etc.

Another big first for 1954 Chevrolet truck cabs was the optional color coordinated interior and the two tone exterior. This had never been offered before by GM on truck cabs. Advertisements defined it as “The Bold New Look”. For an extra cost (only on cabs with rear quarter windows), the customer could order interior color combinations including two tone blue, gray and maroon, two tone green, plus dark and light brown. Each of these four base color combinations were harmonized with the headliner, floor mat, door panels, windlace, arm rest, and interior sheet metal. Pearl beige was the standard color on non optioned cabs.

This deluxe two tone interior package was introduced in mid year. Therefore, it is not shown in early 1954 Chevrolet truck brochures and many perfectionists do not know it was available later.

The above mentioned colored floor mats also added little to GM’s investment when they produced quantities.  These have never been reproduced.  Note:  For the perfectionist that requires all extras for the 1954 deluxe pickup, we have heard that a restorer spray painted his new black floor mat with flexible rubberized paint used on newer automobile exterior front and rear bumpers.

Here is another very exclusive item on the 1954-55 deluxe pickup were their armrests: These were not found on other GM vehicles. The more basic pickup still used the arm rest introduced in 1947. See our tech article & photos on these arm rests. They came in the four door panel colors so both could be correctly coordinated.

The two tone exterior paint option included a white top only (shell white) and only on the deluxe cab. For the short run in 1955 of this body design (first series), the two tone was still with only a white top but the shade was changed to Bombay Ivory.

Another very unusual feature, that cost GM no extra, was colored running boards.  They matched the lower body color.  On standard and prior years, the boards were black.

With fears of Korean War shortages now over, chrome and stainless steel could now be offered again as part of a long option list. On the deluxe model this included stainless exterior window trim plus chrome hub caps, grill and bumpers.

The option list also increased greatly for the 1954 year with new items available not offered during previous years. Examples were full wheel covers, electric wiper motor, automatic 4 speed transmission, ride control seat, day-night inside rear view mirror, etc.

It is also important to remember that for 1954, Chevrolet chose to introduce two major items and not wait for the totally new later 1955 models. This was the high pressure insert bearing six cylinder engines and the deeper restructured pickup bed. Thus, the 1954 shares both the early and late features and is a true “transition truck”.

At present, the 1954 GM light pickups, particularly the deluxe models are showing a fast increase in popularity among restorers. They stand out as a unique transition truck having various characteristics not associated in total with any GM commercial vehicle. It is felt their future pricing will also stay higher than either 1947 to 1953 or the 1955 to 1959 models in equal condition. Of course, all older GM trucks are on their way to the top in popularity and value. They are to restorers “the Model A’s of a New Generation”.

1954 gm transition

Early Chevy and GMC Engine Trivia

Thursday, February 11th, 2010

Though the major cab and fender sheet metal change began in mid 1947 (Advance Design), both the Chevrolet and GMC trucks kept their same proven six cylinder engines as used in prior years.

The base engine in GMC light trucks was the 228 cubic inch inline six cylinder introduced in 1939. This overhead valve unit had a full pressure oil system with its rod and main bearings lubricated from drilled lines within the crankshaft. Their high oil pressure is reflected on the dash gauge reading 0-50 pounds.

This family of engines during the Advance Design years also produced the 248 and 270 cubic inch units. The cylinder diameter in their main difference. They all share the same overhaul gaskets, water pumps, oil pans, distributors and side plates. On GMC, not Chevrolet, the cubic inch is the first three digits of the stamped serial number on the flat surface behind the distributor.

Chevrolet’s six cylinder used during most of the Advance Design years was very different from the GMC. Its standard 216 cubic inch engine was a result of continual improvements since the first Chevrolet six cylinder began in 1929. The 1940’s 216 truck engines were almost identical to that in the Chevrolet car. Therefore, millions of 216’s were on the road by the beginning of 1947. Their basic design and easy maintenance made them one of the greats in lower priced vehicles. When used on the roads of that era, they provided dependable service both on the farm and in the city.

The 216 engine was the standard power plant in the 3000 and 4000 series trucks. Its big brother, the 235 was optional on the 4000 series and standard on the 5000 and 6000 series. It is almost identical to the 216 but the increased displacement gave the needed extra power to work trucks. The 235 truck engine was not used in pickups, however, was matched to the Powerglide transmission cars with some modifications between 1950-53.

These 216 and early 235 are designed to operate without oil lines drilled in the crankshaft to lubricate their bearings.

The early 235 should not be confused with the more famous later 235 full pressure engine first introduced in Powerglide Chevrolet cars and the Corvette in 1953. During this transition year trucks continued to have the lower pressure design. By 1954 the full oil pressure 235 became the standard of the Chevrolet fleet. It was modified for trucks by using solid valve lifters in place of the hydraulics in cars. The camshaft gear was changed from fiber to aluminum.

Battery Shields

Thursday, February 11th, 2010

As time progressed, GM realized their under floor battery position needed extra protection. The battery on the 1946 and older trucks were only protected by their partial tray. No doubt some hard working vehicles in rural areas lost their battery from fractures.

Thus, the 1947-1955 trucks were provided with a front vertical metal shield. The attached photos show a bare frame with this shield still in place.

battery shields 1

battery shields 2

1947-1948 GMC Grille and Bumper

Thursday, February 11th, 2010

Used only the first 1 1/2 years into this body style, these GMC grilles stand out for their different shape and very heavy duty construction. Because of it’s weight this assembly, it sets on the frame and is given extra support by a pair of steel rods extended at an angle to the frame rail.  See photo.

The grille has three horizontal bars and uses a heavier gauge metal than the four bar grille introduced in 1949. This same unit is found during 1947 and 1948 in all 1/2 ton through 2 ton GMC trucks.

On these early 1/2, 3/4, and 1 ton trucks the splash apron from the grill to the bumper is even different. The front bumper is the most unusual. It is rounded much like an automobile and has three bumper bolts on each side.  They all have the small grill guard on the 1/2 and 3/4 ton.

Some suppliers of 1947 – Early 1955 bumpers and grilles state they are all the same.  But, they are not.  The 1947-1948 stands alone!

1947 1948 gmc grill 1

1947-1948 “3” Bar (above)

1947 1948 gmc grill

Note the 3 bumper bolts.  The center secures the front splash apron and securing braces.  The other two are used by the dealers to attach GMC accessory larger grille guards to the bumper.

1947 1948 gmc grill 2

1947-1948 “3” Bar (above)

1947 1948 gmc grill 3

1947-1948 Angle Grille Support (above)

1947 1948 gmc grill 4

1949-1955 “4” Bar (above)

1947 1948 gmc grill 4

Safety Treads

Thursday, February 11th, 2010

Without the rubber covering over the metal running boards like GM cars, trucks immediately show scratches from the driver’s shoes. This is frustrating to the restorer who has placed so much effort in repairing and painting these boards to pristine condition.

Fortunately, a solution exists! The original running board safety treads have been reproduced. These treads were a GM accessory and available from the dealers. They were marketed to help prevent a person from sliding off the running board if their shoe or the metal surface was wet. No doubt legs and arms were occasionally broken in this hazardous area.

Today, these safety treads still help prevent falls but also stop the unsightly scratches that occur during normal use. Most all full stocking dealers have them including Jim Carters Truck Parts.

The following is from a 1954 GMC accessories catalog. Their wording also tells the story in a full page ad.

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1954-1955 Radio Blank Out

Thursday, February 11th, 2010

All 1954-1955 Chevrolet/GMC trucks came from the factory with a blank-out plate to cover where the radio would be installed. As this accessory was dealer installed the plate could be removed (probably thrown away) and the new radio added.

This blank-out plate and its two special clips has become very rare in recent years. They are not being reproduced. The enclosed photos show an original painted plate. The Chevrolet unit is the interior cab pearl beige color with a stamped bow-tie in black. GMC chose to not add their logo. These plates are just like Chevrolet except have a smooth surface with no trade letters.

1954 1955 radio blank out 1
Chevrolet (installed)

1954 1955 radio blank out 1

Chevrolet (above)

1954 1955 radio blank out 2

GMC (above)

1954 1955 radio blank out 3

Back View (above)