1977 F350 not enough pulling power HELP
 

I am restoring my 6 cylinder 1956 Chevrolet truck and got myself a temporary replacement.

It is a 1977 Ford F350 that was originally a wrecker, or tow trucks as we call him here in Australia. It has a 351C and someone has recently converted from 4 speed to auto. It does not run on petrol anymore, it has a Liquid Petroleum Gas (LPG) system fitted.

My problem is that at a steep boat ramp, the truck will not pull out my 26ft powercat that weighs about 3500kg (7000 pounds?). The Chev had no problems, even with my bigger boat and even our automatic Range Rover has no problem getting it out of the water. Last weekend we had to use the boat motors to push the boat, truck and trailer out of the water. The truck just got to a point where it loaded the torque converter and wouldn't go anymore. No wheelspin, just no go.

Later it also boiled the coolant just maneuvering around the yard trying to position the boat. It doesn't overheat at other times and has a new heavy duty radiator, twin thermo fans etc. It tows great once going, it is just working way too hard trying to get off the mark.

I guess the questions are:

1/ Is this normal, do automatic F350's struggle of the mark?

2/ Any suggestions on what to do?

First off, the 351 wasn't anywhere near a powerhouse- but it should still get a boat moving up a ramp. I'd start with the basics- beginning with a compression or better yet, a leakdown test. Then I'd find someone knowledgeable with propane and have them make sure the equipment is working. If your mixer or regulator have issues, you could have flow restrictions to the engine.

Is there some reason you'd want to retain the propane?

I had an old F250 with the 351 auto and same problem. It was the tourque converter something to do with the stall speed. I traded it in on a new truck with the 300 6cyl and 4 speed, 4X4, just put it in 4 low and used the granny gear, could pull anything up the ramp.

Bowtie, I was thinking the same thing with the torque converter, maybe I should look at a higher stall speed.

Chris, to go back to petrol I need fuel tanks, lines, carbies, basically everything and with petrol prices are something like $6 a gallon, it would make this truck not usable on a day to day basis.

I am thinking that step 1 is compression/leakdown test.

Step 2 get the propane system looked at by someone who knows what is going on.

Step 3, investigate if a higher stall converter will get me moving

Step 4, see if diff ratio swap is feasible,

Step 5 get Chevy back asap.

Definately got me curious! What kindda ratio ya got in the rearend? I know propane cuts a bit a power but being a 350 the gearing(ie converter) should at least get ya boat outta the water! Does sound like a motor issue to me.

Not sure of the ratio, but turning the wheels 1 revolution, the diff yoke turns about 4 1/2 times, so I am guessing about 4.5 ratio.

No tacho on the truck, but the converter sure seems to kick in real early. Not sure if it is down on low end torque, or is a very low stall converter. I did chat to an automatic transmission specialist and he seems to think that I should be looking at the engine side.

Acceleration is not too bad, it can almost keep up to econo cars on a traffic light drag. Feels responsive too.

Are you SURE its taking off in 1st gear? Older Fords will take off in 2nd gear(AT)if your shifter is in 2nd or your linkage is inncorrectly set up

I'm kinda curious, our Toyota Forklift at the shop developed All the same symptoms as your truck over the winter this year. Its also ran on LP.

My thoughts too.

You are right, it does start in 2nd if in "2" and yes it does feel like it is starting in second but I have counted the gear changes and I get 3.

Maybe when at that particular angle at the boat ramp, it moves the linkage just enough to put it in 2nd. The shifter is something that was adapted to fit and the workshop that fitted the auto kept it there for a month until they 'got it right'.

It is Saturday midnight here, so I am going for a drive to count gears again but this time on a very steep hill. I will keep you posted. At least that is what I am telling the other half...

Getting first, second and third every time.

Come to think of it, the truck was also struggling in reverse, which is probably pretty close to 1st in ratio.

It is cold, wet and windy ... the streets are deserted.

What exactly happens when you attempt to pull up the ramp? DOes it bog? Is your foot to the floor and and just wont move? Sounds like something is wrong. Even thought the 351 was not a strong engine, it should have no problem pulling up that boat at the ramp.

Are you sure your trailer axle/s are not falling off the ramp under water? I dont know anything about the propane systems, but soemthing is definitly not right.

not motor....trans......check it out.

I have been on the Ford forums and one thing that may explain it is that the LPG we get here used to be all propane but is now a mix of butane and propane. As there is no Australian standard, it varies from supplier to supplier and from time to time. A few of the blower guys have learned the hard way. Maybe I am getting bad fuel.

As it is Easter weekend and there are no workshops open, I think I will drive around, empty the tanks and try a different fuel supplier. It is the cheapest simplest and only option at this stage.

Thunder, as you press the accelerator the revs rise normally to a point and then go no more regardless of how far I push the accelerator. It is as if I am pushing against a wall and have 100% traction. There doesn't seem to be a hesitation or a flat spot as such. If it was a manual, I would just slip the clutch some more, but being an auto it just doesn't go.

The ramp is one of the steepest I have seen, but a Range Rover will do it and a 6 Cylinder 1956 Chev that is pretty well worn will do it. Admittedly the Rangie uses low range and the Chev has a very low first gear. It was high tide, so the trailer was well on the ramp. It also had trouble in reverse pushing the boat up a steep driveway so I think we can eliminate the off the ramp theory.

Tblrklakemo, I went to an automatic transmission specialist and they said to look at the engine. It is not often a workshop doesn't want your money and sends you away. Having said that I think there may be some value in a higher stall converter.

Does anyone know if high stall converters work in towing situations?

The higher the stall the more heat the transmission creates. Then cooling becomes an issue.

Cooling is an issue at the moment but we can add more coolers, is it common for those towing to use higher stall converters?

I wouldnt think a higher stall speed converter is the answer. It sounds to me like the engine may be down on power.

Another option to look into is adding a transfer case from a 4x4 truck. At the ramp you can shift it into low, and then have a really low gear to pull up the ramp. Shouldnt be too hard to rig, since you wouldnt have to add the shafts and hardware to the front axle. Just transfer case, driveshaft, and linkage.

Like I said, sounds like a weak engine and not low enough gearing.

Did a compression test, was great.

Played around with timing, couldn't get it better

Beginning to agree with Mild Thunder. Probably just need lower gearing, need to look into the transfer case.

Just thought I would update this.

Quite a while ago we put in a C6 and 4wd transfer case to get low range gearing. The FMX didn't last long at all and was most unsuitable to the weight of the truck.

Now the truck has no issue with bogging down, just no traction. Changed tyres and dropped tyre pressures which helped.

Next step is to soften the rear suspension as there are a lot of leaves and/or add some weight over the back wheels. The truck has no overhang at all at the rear and is much higher at the rear than the lowered front. This may have been great in its previous life when it had to lift the front of vehicles it was towing, but trailers are not providing enough downforce on the wheels.

Throw a Vtech in there!