Idles good but dies when in gear...complete engine rebuild

[Florian]

Just bought my ´71 F100. On the way home we first recognized the problem.



It´s a 71 F100, engine is either a 289 cui Mustang or a 302 cui, 3 speed manual shift.

The sparkplugs dont look too good anymore, the airfilter is in good condition, gas consumption is good, fuel pump and fuel filter are both brand new, clutch has been renewed by previous owner last year. It doesn´t seem that the truck has been driven a lot over the last years. Was imported from California, was a yard-driver at a steel-yard there.


Now the problem: The truck starts good when in neutral and also idles good in neutral, but as soon as you press the clutch and shift into any gear it starts to stumble and dies if you don´t push the gas-pedal. This happens while standing still and also during driving when you press the clutch but don´t shift back into neutral. After it died it starts good again when in neutral.


What to do?

Thanks guys!

[Florian]

No idea?

[R.Smith]

Ich habe kein Anun.

If it's happening while you're driving but only when you push the clutch pedal and shift then maybe it's some sort of electrical problem with the neutral safety switch...if it even has one. I've never fooled with a 3 on the tree setup.

[Dragon]

No neutral safety switch. I saw something similar once. The thrust bearing in the engine was shot on the rear side and when the clutch was pushed down the crankshaft moved forward and met increased friction.

Easy to spot have some one push in the clutch and hold your hand on the timing wheel you would feel it move. Increase your idle speed. My 390 hates 800 it will stumble and idle die below 800 so most time I Idle at 900.

[cdeal28078]

That is a bit strange unless there is a vacuum hose that is being acted upon by the clutch linkage and causing a leak when the clutch is pushed. Dragon's idea sounds likely.
What is the idle speed? Except for the white roof reminds me of my truck. Mine was a 302 3 speed when new
clint

[70_F100]

No neutral safety switch. I saw something similar once. The thrust bearing in the engine was shot on the rear side and when the clutch was pushed down the crankshaft moved forward and met increased friction.

Easy to spot have some one push in the clutch and hold your hand on the timing wheel you would feel it move. Increase your idle speed. My 390 hates 800 it will stumble and idle die below 800 so most time I Idle at 900.

That's what it sounds like to me.

When you push the clutch in, there is some additional load placed on it by the release bearing, but that is negligible.

However, if the crankshaft is being loaded by the internals of the engine, it could be enough to cause the idle speed to drop and the engine to stall.

I've seen that happen quite a few times over the years, especially if the clutch is hard to depress. That creates extra loading on the thrust bearing, like Dragon stated in his post. The result is usually wear on the thrust surface of the crankshaft, rather than on the thrust bearing itself. Once the wear on the crank begins, the thrust bearing then wears to match.

Does the engine sound like it's being "loaded" when you push in the clutch?

[fordman]

does it do it when you release the clutch to go? i mean can the truck creep forward or backward by itself without pushing the gas. after it is in gear and the clutch is released?

[Florian]

Thanks for all your replies so far!

Easy to spot have some one push in the clutch and hold your hand on the timing wheel you would feel it move. Increase your idle speed. My 390 hates 800 it will stumble and idle die below 800 so most time I Idle at 900.

Where is the timing wheel? Do you mean on the front of the timing cover?

What is the idle speed?

I don´t know, my truck does not have a tachometer...maybe I should get one?

..especially if the clutch is hard to depress...Does the engine sound like it's being "loaded" when you push in the clutch?

I haven´t got a comparison, but the clutch is really hard to depress. I gotta listen again and find out.

does it do it when you release the clutch to go? i mean can the truck creep forward or backward by itself without pushing the gas. after it is in gear and the clutch is released?

I don´t know, I always reved it up a bit before putting it into gear so that it wont stall. I´ll try it today, but I don´t think that it will work well, will likely be to stall before moving..




I did some research on the internet, and one word occurs very often in this context: vacuum leak. Could it also have a vacuum leak and stall in gear because of this? Remember the car has not been moved very much over the last years, so a sealing could be dried out. Does this sound logical? What is it more likely, thrust bearing and similar or vacuum leak?

Anyways, I´ll check the spark plugs first today and take photos of everything!

Florian

[Florian]

I forgot to mention one thing I noticed: the day before yesterday after I came home from a short ride I let the engine run and tested if there were any differences in the gears. It stalls faster in reverse than in first gear or the others. So reverse seems to be the worst.

[70_F100]

It also sounds like your clutch may be dragging just a little bit.

Do you get any grinding when you try to put it in gear?

[Florian]

When the clutch is depressed and you put in a gear there is no grinding. But when you want to start driving and let the clutch go it makes noise. This is only in first gear. Shifting in second and third is quiet.

I tried it and yes you can drive with only the clutch, without touching the gas pedal. The engine also stays okay when you just let off the gas in 2nd or 3rd gear and let the car roll.

[fordman]

The engine also stays okay when you just let off the gas in 2nd or 3rd gear and let the car roll.

ok thats what i was aksing i just asked wrong.

[Dragon]

More likely a vacuum leak of the two. But since you said it happened when you pushed in the clutch I went to other way. If the plugs don't look good change them to eliminate any hassle they might cause. 1st gear noise is the nature off that tranny. It gets louder over the years until it becomes obvious. Reverse is a lower ratio gear than the others so when you engage it it loads the engine down more.

The timing wheel is the crankshaft pulley.

[cdeal28078]

If the engine is off and you push the clutch in how far will it go before you feel significant resistance? IN other words how much free play is in the clutch peddle? How far can you push in the clutch before all of the slack is taken out of the linkages?
When the engine is running and tranny in neutral and you just push in the clutch what happens. Don't put it in gear just push in the clutch.
clint

[Florian]

Okay then I guessed right on the timing wheel, it does not move when you press the clutch.

But if it has a vacuum leak, why does it idle normally in neutral position? It must have to do something with the clutch or?