1988 Canadian GMC C1500 305 TBI w/TH400HD going into 1973 C20 Custom Crew Cab

[dwmitchell61]

My gal has a 1973 C20 Custom Crew Cab Heavy 3/4 ton with Long Bed. It originally had a 454ci big block in it according to the VIN number. It currently has a small block 350ci & TH350 transmission. The transmission completely quit on her and the engine was getting tired.

She bought a 1988 Canadian GMC C1500 that according to the VIN has a 305ci TBI engine, the transmission is a heavy duty (HD in the bell housing) TH400 transmission with electronic speedometer.

My assignment is to put the GMC engine & transmission into the 1973 Crew Cab.

[dwmitchell61]

July 18 - Prepared for removals. Unbolted everything from both engines and transmissions for removal. Drained the fluids. Pulled the ECM/TBI/engine compartment wiring harness from the 1988 and researching necessary wiring.

[dwmitchell61]

July 18 - July 25
Unwrapped the wiring harness.
Cleaned out unnecessary/unused wiring from the harness. Labeled each sensor plug. Need to extend the harness as the best location for the ECM seems to be under passenger side of front seat. Cut each lead from ECM in a staggered pattern, labeling each end for ECM pin out and destination of the wire.

[dwmitchell61]

July 25 - Pulled engine & transmission from the 1988 donor truck. My mechanic friend noted the freeze plug overheat indicator shows no sign of overheating of the engine.
Set up on blocks for cleaning, started cleaning the crust from both engine & transmission.
Connected the sensor wires to the sensors, laid in the cleaned up harness on the engine.

[dwmitchell61]

July 25-27 - Laid in harness wiring in the firewall area, repaired some grounding lugs that had wire damaged near the lug.
Removed the heater control relays from the 1988 for re-utilization on the 1973. Will need a relay for the Park/Neutral signal to ECM. Another will be needed to kill the circuit for the downshift solenoid when the brakes are applied. I will use a third energized by the 1973 ignition switch RUN to power the distribution of power needed by the ECM and injectors during operation from the battery +.

[dwmitchell61]

[dwmitchell61]

Parts are in.

2 ea fuel filters for between the tanks and the tank selector solenoid
1 ea 6-port tank selector solenoid, Standard Motor Products part #FV5T
1 ea Carquest part #E2182 fuel injection pump
1 ea Champ part # G481 fuel injection filter

Cleaned the heavy gunk off of the transmission. Starting to de-gunk the engine.

Engine serial number is 14102058, has 5.0L G? in the block on the left, rear of the head. Says "Canada" in the block on the right near the rear of the head. It had a connector and the wiring for the air injection control valve, but it must have been unused. There is no air pump and no ports in the exhaust manifold to inject the air.

There is a "45" in raised letters on the left top of the bell housing. There is a "HD" in raised letters on the top right of the bell housing. The output shaft has 29 splines. The identification tag has "TurboHydroMatic LB 352 A" and the serial number is "87 LBA-1800".

Need to get a fill tube rubber grommet/seal. The transmission filter and pan gasket came in.

I have to strip as much of the fuel line form the 1988 GMC C1500 as possible, before we drop the old engine and trans in the back of it and send it of to anyone that may want to take it. It has some nice rims on it. Hmmm... maybe make a trailer out of the back half and scrap metal the rest?

[dwmitchell61]

I bought an Airtex ES2182 fuel pump for the engine/trans swap project. It produces 90-100psi output. Will that work with the 1988 305ci TBI system? Will the regulator handle that? From what I read the fuel pressure at the injectors is only 9-13psi.

[dwmitchell61]

Originally Posted by dwmitchell61

I bought an Airtex ES2182 fuel pump for the engine/trans swap project. It produces 90-100psi output. Will that work with the 1988 305ci TBI system? Will the regulator handle that? From what I read the fuel pressure at the injectors is only 9-13psi.

Damn... looks like I will have to order an Airtex E8094 pump. So much for reading the article from a TBI specific site.

[dwmitchell61]

The stripped down & extended wiring harness for the TBI & ECM





I have to tie it into the truck harness battery & ignition power, relay the brake signal and the Park/Neutral signal.

[dwmitchell61]

The TH400 transmission identification

[Katrina/10]

The e8094 is a good inline fuel pump for TBI. I could not tell any difference in idle speed using the park/neutral wire, so I didn't hook it up.

[Katrina/10]

Run better with more back pressure = NO.

A 305 pulling around a truck that big will have a lot of work to in any case.

Yes, the reluctor wheel is pressed on. I'm sure standard Turbo 400 gears will go in it's place, just make sure you can get what you need. The VSS is not horribly expensive, buy it and you will never have to mess with it again.

Hit the reluctor wheel with a big drift and hammer to knock it off the shaft (toward the trans). I then stuffed the trans with rags, and cut the wheel in two with a Dremel. Not too hard.

[dwmitchell61]

I bought a VSS DRAC/buffer for 1990-1993 with the DIP switches on it from Warr Performance. Bought a connector kit for the DRAC. Mounted it atop the EMC. Updated the TBI wiring harness for the VSS. I had to extend the wiring harness leads for the oil pressure switch; I moved it from atop the engine so I could connect the mechanical pressure gauge there, and installed it where the electronic sending unit was above the oil filter.
We stuffed the engine & transmission last weekend. Today we got the wye pipe in (with O2 sensor bung added) and plugged the O2 sensor port on the manifold. The chassis was interfering with the stock location of the O2 sensor. This afternoon I put the TBI wiring harness in the truck, threaded it where it needed to go and have most of everything connected.
Need to put a hole into the floorboard under the front seat passenger side for the harness. The EMC will go under the passenger side of the seat.
I have to remove the cover from the differential to identify the gear ratio. The tag is no longer on the case. I need that to program the VSS DRAC/buffer.
I found the throttle cable was too long on the old carb setup. I removed the throttle cable from the donor truck in the hope I can work it with that. I have to see what the '73 throttle lever looks like up top.
I may have to have the front driveline segment shortened for the TH400... That bites... Just don't have the funds at the moment for the cut/weld/balance job.

[dwmitchell61]

Engine is in...

Fuel pump mounted. Need clamp for filter. Need to connect harness to fuel pump. Mounted it on the outside of the frame, away from exhaust heat.

[dwmitchell61]

Got the exhaust plumbed in and hung this morning. had to put two 45's in to drop the wye pipe outlet down to where the 1973 exhaust was. The 1973 was routed under the transmission cross member. The wye pipe outlet was just above the cross member.

We are now working the shift linkage. That from the 1973 TH350 didn't fit into the yoke on the TH400 transmission properly. So we are using the longer bell crank from the 1988. We ran it through the chassis where the parking brake cable goes through. We relocated the pivot from inside the chassis to a frame member on the cab floor. We are also using the link rod from the 1988. It has a bend the wrong direction. So my friend is taking it to the shop and using an inductive heater to heat it and get it formed right.

The drive line DOES have to be shortened 3". I will first look for a front drive shaft segment for the TH400 for that year 3+3 truck first. If the wrecking yards can't help, then I will have to have the machine shop shorten it. We replaced the front u-joint this morning.

[dwmitchell61]

Driveline has been dropped off at Six States Distributors driveline shop. Will have it back today, maybe tomorrow. Shorten 3".
My mechanic friend reshaped the shift rod from the 1988. It shifts marvelously! We found the distributor had been stabbed 180 degrees out by a PO. We re-stabbed it... It fired right up... But we still missed by a tooth. It was loping at idle and it seemed to have a leaking TBI gasket. I will buy the gaskets for the TBI & air cleaner and the spacer that has the crankcase ventilation air hose attached. When we change the gasket we will deal with the distributor being a tooth off.
Other than that, the engine runs smooth & sweet. No oil smoke or coolant steam in the exhaust. It has a barely visible "soot" when the throttle is "blipped".
The throttle linkage from the 1988 was too long, But I can swage on a new stop in the cable to "shorten" it.
The gear ratio options that were available for this truck seem to have been 4.10:1 & 4.56:1. I programmed the DRAC/VSS buffer for the 4:10 ratio and the 30" tire diameters she has on it.

[dwmitchell61]

She runs! For the most part...

The truck runs well with no load. HOWEVER... it overheats when one tows a two horse trailer....

So I installed the SES lamp... BUT, should have unhooked the battery.... AAagghhh.... The battery power lead to the SES accidentally shorted when I was trying to connect it to the LED lamp...

Now no power at all. The BATT PWR lead to the SES lamp was connected to the BATT FUSED. Looking at that, there is something like a rectangular can in the position rather than a fuse. Is this a circuit breaker or a large fuse? It doesn't seem to unplug like a fuse.... Ugh... Pleas help!

I need to get the codes from the computer to see if there is a sensor or computer related issue, or if it is fan clutch/radiator issue. The thermostat is new and works.

Thanks in advance,

Dave

[dwmitchell61]

Originally Posted by dwmitchell61

She runs! For the most part...

The truck runs well with no load. HOWEVER... it overheats when one tows a two horse trailer....

So I installed the SES lamp... BUT, should have unhooked the battery.... AAagghhh.... The battery power lead to the SES accidentally shorted when I was trying to connect it to the LED lamp...

Now no power at all. The BATT PWR lead to the SES lamp was connected to the BATT FUSED. Looking at that, there is something like a rectangular can in the position rather than a fuse. Is this a circuit breaker or a large fuse? It doesn't seem to unplug like a fuse.... Ugh... Pleas help!

I need to get the codes from the computer to see if there is a sensor or computer related issue, or if it is fan clutch/radiator issue. The thermostat is new and works.

Replaced a 30A fuse in the main battery lead under hood with a 30A resetting breaker. that fixed the power issue I caused.


Thanks in advance,

Dave

Truck over heats when towing a two horse trailer empty up an incline, under load.

Jumpered A & B on ALDL and only code I received was 12. The BATT + on the TBI harness IS connected on the truck BATT + so I am assuming there were no codes stored.

So it looks like a cooling system issue.

1. Fan clutch maybe. The one from 1988 has clutch and 5 blades. I have an non-clutched flex fan with 6 blades that was mounted on the original engine.

2. Pressure cap. I will buy a new one. reads 15PSI on the current one.

3. Radiator may have passages clogged. The fins are all clear.

I may buy a new radiator as it could be clogged in some of the passageways.

Dave

[SkinnyG]

If everything else in the cooling system is fine (cools fine any other time), look for plugged system either internally or externally, or both.

[dwmitchell61]

Forgive the lateness of my post. I have been very busy as of late. I am now working on putting a new axle under my brother's utility trailer.

The truck runs real well. Starts right up (after replacing an aged battery). SOunds just as awesome on the single exhaust rather than dual exhaust.

The over heat problem was caused by using the clutched fan from the 1988 serpentine belt system on the 1972 belt system (rotates the other way).

I am going to buy an aluminum 3 row radiator, a fan thermo-clutch and the proper fan for it before summer hits us.

The other problem is that the auxiliary tank filler neck is nearly horizontal and the return gas leaks out the cap. So I will see if a new cap might rectify that issue, suspecting the rubber seal is aged and dried/shrunk.

but it runs great and has plenty of power. The engine has a factory re-manufacturing metal tag attached to the block up in the area of the power steering pump. It seems to have plenty of power, does not burn any oil at all.

My gal is a happy camper.