Transmission is causing engine to stall

[KnockingDiesel]

I bought this truck a few weeks ago and just started working on it. 1985 C30 3+3 dually 454 th400.

I got it started after replacing a bent fuel pump push rod and fuel pump.

I got it up to temp to check for leaks. All fluids were checked and ok prior to starting. I got warmed and checked for any obvious issues. Ran a little rough so I replaced cap, rotor, coil, plugs and wires. Also replaced all vacuum lines. Got it started up and runs quite a bit better but still not quite right.

So i decided to check trans function. I put in reverse and rpm’s drop to barely enough to keep it started but reverses under its own power.

I mine to neutral an rpm’s come back to idle.

Put it in drive and stalls. I start again and put it in drive and rev a bit, stalls again. It’s like popping the clutch at idle on a manual car, just jumps a bit and dies out.

Not sure what’s up, I’ve never had this happen before. It idles and revs ok. I’d say idle is 600-700rpm and drops to 300-400Rpm in reverse.

I’ve rev’ed it up to 1000-1200 and tried to go into drive but it just jumps and stalls?

Any ideas? Trans fluid looks good. I’m doing an engine oil change tomorrow. Should I do a trans filter and fluid change? I’d say it’s a bad trans but it works ok in reverse so I assume the torque converter and pump are working.

Thanks for any replies!

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[PrairieDrifter]

Bring the idle up to 750-800 rpm and check it.

 

[R Carnella]

I doubt it's the transmission causing this.

 

[Snoots]

Does it have a lock-up converter?

 

[KnockingDiesel]

I doubt it's the transmission causing this.

What else would cause and why in coward but not reverse?

Does it have a lock-up converter?

I don’t think so but that’s what it seems like, but only does it in D, 2 or 1 , not in reverse.

 

[squaredeal91]

Sounds like timing maybe??

 

[nvrenuf]

I agree, the issue is most likely not the transmission. I'd start looking for tuning related things (like previously mentioned timing) and vacuum leaks. If those are ok, run a compression test and maybe "T" in a fuel pressure gauge at the carb inlet.

I'm curious if you know the story behind the bent fuel pump push rod? That is something that really never happens short of a catastrophic failure. The arm on the pump isn't strong enough to bend that rod in the unusual instance the pump seized.

 

[QBuff02]

I'll throw a suggestion into the ring.. You gave it a tune up but did you check the condition of the advance weights and pins/bushings and springs under the rotor while you were replacing them? I have seen on several instances where similar conditions existed and the problem ended up being that the pins/bushings, weights and springs were worn and what actually was happening is when it was held at a higher idle rpm it was fine until you dropped it into gear and when the idle dropped the distributor weights traveled (basically over center the wrong direction) too far the other way causing a loss of correct timing and it just stumbles and dies out. If you had it in park or neutral you could rev it up enough to catch it and get it to stay idling, but as soon as you did anything to force a lower idle rpm, rattle rattle die. Usually for the price you can buy a complete distributor for these days I don't mess with caps and rotors and coils to tune them up, just buy a whole new unit and drop it in for pretty much the same money, especially on an older piece becuase it solves a lot of problems. But before I went digging too deep, i'd pull the top of the distributor back apart and take a close look at the distributor advance components to make sure that's not where your issue is.

 

[85K304SPD]

Probably timing and or carburetor related. Set it with a light, VA plugged. Check real good for vacuum leaks.

 

[KnockingDiesel]

I'll throw a suggestion into the ring.. You gave it a tune up but did you check the condition of the advance weights and pins/bushings and springs under the rotor while you were replacing them? I have seen on several instances where similar conditions existed and the problem ended up being that the pins/bushings, weights and springs were worn and what actually was happening is when it was held at a higher idle rpm it was fine until you dropped it into gear and when the idle dropped the distributor weights traveled (basically over center the wrong direction) too far the other way causing a loss of correct timing and it just stumbles and dies out. If you had it in park or neutral you could rev it up enough to catch it and get it to stay idling, but as soon as you did anything to force a lower idle rpm, rattle rattle die. Usually for the price you can buy a complete distributor for these days I don't mess with caps and rotors and coils to tune them up, just buy a whole new unit and drop it in for pretty much the same money, especially on an older piece becuase it solves a lot of problems. But before I went digging too deep, i'd pull the top of the distributor back apart and take a close look at the distributor advance components to make sure that's not where your issue is.

You know I was thinking about this. I did the tune up on it to get it running and change the oil. The distributor is 100 degrees or so from where it should be and I need to pull it to set back so I’ll look at it.

I agree, the issue is most likely not the transmission. I'd start looking for tuning related things (like previously mentioned timing) and vacuum leaks. If those are ok, run a compression test and maybe "T" in a fuel pressure gauge at the carb inlet.

I'm curious if you know the story behind the bent fuel pump push rod? That is something that really never happens short of a catastrophic failure. The arm on the pump isn't strong enough to bend that rod in the unusual instance the pump seized.

This was strange to me as well, as I have never had this happen. I did some research and it’s somewhat common if a fuel pump is installed in correctly. Apparently if the pump lever is on top of the rod and not at the end of it. I don’t see how it could do it but I have come across a few posts about it. The only evidence I have to support this is the first 12/-3/4 inch of the rod is badly scored.

I still don’t see how the stamped steel lever can Ben a solid 3/8 rod. Mind you it’s not bent an angle but still curved enough to be stuck.



My guess is that whoever owned this truck had no idea what they were doing.


I have it running good enough to where I can get it warmed up and now that there’s fresh oil in it I’ll let it warm up to temp and do a compression test on it.

 

[rusted nuts]

What else would cause and why in coward but not reverse?

I don’t think so but that’s what it seems like, but only does it in D, 2 or 1 , not in reverse.

 

[rusted nuts]

I bought this truck a few weeks ago and just started working on it. 1985 C30 3+3 dually 454 th400.

I got it started after replacing a bent fuel pump push rod and fuel pump.

I got it up to temp to check for leaks. All fluids were checked and ok prior to starting. I got warmed and checked for any obvious issues. Ran a little rough so I replaced cap, rotor, coil, plugs and wires. Also replaced all vacuum lines. Got it started up and runs quite a bit better but still not quite right.

So i decided to check trans function. I put in reverse and rpm’s drop to barely enough to keep it started but reverses under its own power.

I mine to neutral an rpm’s come back to idle.

Put it in drive and stalls. I start again and put it in drive and rev a bit, stalls again. It’s like popping the clutch at idle on a manual car, just jumps a bit and dies out.

Not sure what’s up, I’ve never had this happen before. It idles and revs ok. I’d say idle is 600-700rpm and drops to 300-400Rpm in reverse.

I’ve rev’ed it up to 1000-1200 and tried to go into drive but it just jumps and stalls?

Any ideas? Trans fluid looks good. I’m doing an engine oil change tomorrow. Should I do a trans filter and fluid change? I’d say it’s a bad trans but it works ok in reverse so I assume the torque converter and pump are working.

Thanks for any replies!

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Just jumps a bit and stalls,, Well I'm thinking that jumps a bit is Tranns working but engine stalls for some other reason than the tranns Might want to look at brakes and rear end also

 

[MikeB]

Could it be a vacuum leak? What is the manifold vacuum at idle in Park, and in gear?

I've seen a tight stock converter cause this when a way too big cam is added, but sounds like your engine is pretty much stock.

And, wow, a bent pushrod is something that I've never heard of.

 

[Bextreme04]

What else would cause and why in coward but not reverse?

I don’t think so but that’s what it seems like, but only does it in D, 2 or 1 , not in reverse.

You need t oset your base timing, then adjust your idle mixture on your carb, then adjust idle RPM. If your timing and mixture aren't right, it will not idle well under load.

 

[Bextreme04]

Also, mine is a 350/TH400 and it will definitely clunk hard and load up in drive and reverse.