c4 tranny stall speed

[backrodebob]

coming to stop car stalls! thinking converter stall speed to low? has anybody run across this issue and how did you fix it?

[JayChicago]

Maybe just increase the engine idle RPM ?

[backrodebob]

i’ve done that to!

[paul2748]

Be sure you don't have a vacuum leak. had the same problem with a C-4 in back of my Y block. Found a small vacuum leak , fixed it and everything seems to be ok

[69a]

When up to temp. mine idles about 600-700 RPM stopped and in "drive" if i shift into neutral it's probably 1,000-1,100.

[5851a]

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Many different stall speeds on any automatic. Ford tailored the convertors to engine size/hp and vehicle weight. One thing in common was most auto cars of the day had a dashpot on carb. If you have a rough idling camshaft you may need to talk to a custom convertor builder. Stall speed is not idle speed. Not uncommon in the day to slip it into neutral at a stop light.

[backrodebob]

No leaks that I can find

[backrodebob]

what's interesting is that it doesn't do it all the time? rpm in gear 750
in neutral rpm 1000 and when i put it in reverse it BANGS?

[Zeke3]

1000 RPM in neutral sounds too high to me. I think idle sped in neutral ishould be around 650-700 RPM. Lowering the idle speed may reduce or eliminate the banging when putting it in reverse.

The "Stall" speed can be measured by holding on the brake, placing the trans in drive and flooring the gas pedal. The engine speed will level off at the point where the torque converter absorbs the amount of power produced by the engine. Do not hold this for more than a few seconds because all that power is going into the trans fluid as heat. This will give you an idea of the stall speed for the particular engine/torque converter combination.

[drolston]

I have a c4 in my '34 pickup with '53 Merc engine. If you put it in either low or reverse at 1000 rpm it will bang really hard. Mine actually broke the drive shaft, which had been welded very poorly when it was shortened. Fortunately it broke at the transmission end so I did not have a drive shaft flailing the undercarriage.


I lowered the rpm to fix that problem and always warm up the engine to get the carb off of fast idle before putting it in gear.



I am no C4 expert, but here is what I found: "In almost all cases, symptoms such as yours are caused by a vacuum leak. Look on the passenger's side of the transmission and insure the rubber hose from the steel transmission vacuum line and the tranny's modulator valve is intact and not leaking or slipped off. That small rubber hose is frequently compromised by transmission fluid, oil, and anti-freeze over time and becomes soft and stretched to the point that it is not getting a good seal."

[69a]

Originally Posted by backrodebob

what's interesting is that it doesn't do it all the time? rpm in gear 750
in neutral rpm 1000 and when i put it in reverse it BANGS?

Same revs as mine.
I've had my C4 for over 20 years, I don't remember it ever banging when I put it in gear.
I start it cold with full choke. And stick it straight into reverse, push choke in till I know it won't stall and reverse down my drive. I do have to pull the choke if I need to stop, or even get right off the gas, within the first mile or so to prevent it stalling. I love it! I have a 8" with around 2.74 gears. 2,400 RPM at 60 MPH.

[vilanar]

When I changed vacuum modulator on my ´50 to one that has black stripe on it , it made huge difference. And the length of the pin is very important ....