Technical Determining if I need a different stall speed TC or a different rear gear

Hi,

I'm back again after giving more thought to finessing the driveability of my slightly OT 40 Ford pickup.
The issue is that same as I mentioned in past posts...lurching from a standstill.
Here's what's in it:
4.3 Chevy V6
700R4
3.45:1 rear gear
225-70 R 15's
Weight (approx) 3000 LBs

Ever since it was assembled, the truck exhibited a fondness to lurch from a stop making smooth acceleration very difficult. To "band-aid" the flaw, I modified the accelerator pedal ratio so that the lower part of the pedal (below the pivot) is now longer, requiring more foot travel to obtain the same throttle opening. This made the truck much more driveable but it's not a real fix. Watching the tachometer, I can see that the truck never gets anywhere near the supposed stall speed of roughly 1800 RPM before it's seriously underway. Also with anything short of stuffing the pedal, it's in 3rd by 20 MPH so I'm thinking that the engine is nowhere near a good RPM for developing any torque when I launch so with a low RPM and a 1st gear shift point of about 10 MPH, the truck hits 2nd and feels really doggy.
So, I'm wondering if I need to go to a numerically lower rear gear to present more of a load to the engine, letting the TC start too hook up at a higher RPM or if I should change to a higher stall speed TC. Any suggestions? BTW before we go down the TV cable rabbit hole, the cable is set correctly, and the entire throttle linkage is bone stock from the donor truck. The truck has been driven for 7 years like this so I'm not concerned about the tranny burning up due to a mis adjusted TV cable.

Thanks in advance

 

I’d start over.
Shit can that v6
The 1-2 shift on a 700 sucks
And double check that tv cable because you’re describing one that’s set too tight.

 

TV cable adjustment comes to mind. It’s critical to get that right. If needed, check here for some good info: http://purplesagetradingpost.com/sumner/techinfo/700R4p1.html

You might also check Hot Rod magazine about a year ago for a good article about it.

 

I have the same basic setup and it doesn't do that,do you have a carb on it and if so do you have the tv cable mounted correctlly

 

3rd gear at 20mph ? Transmission problem.

 

TV Adj or geometry

 

Is the converter lock up used?

 

There you go,,,
That’s what he said and look at this thread so far

 

Most of these were TB he said the linkage was bone stock he didn't say the fuel system was. I will shut up now.

 

How many times have we seen everything is perfect but it doesn’t work?


Oh I vote tv cable as well


Sent from my iPhone using H.A.M.B.

 

If the motor and transmission came from same donor and never separated, then converter should be right for V6 and transmission. What did it come out of and what gear ratio did the donor have in it? Its already geared about where you think an overdrive setup would be and the tires are fairly short at 27.4", so either the transmission is acting up, first gear is really low, or the shift cable is wrong not holding it in gear long enough.

 

Agree with a few things, but with a 3.45 rear and the low 1st of the 700, it should take off very smoothly.

What I'm saying is the T V cable being right or wrong, the tranny will still start off on low/1st, Shouldn't lurch. I'm thinking what's on top of the engine is the issue.

 

Thanks for the information. I only mentioned the TV cable because everyone tends to throw it into the mix. Even if it were mid-adjusted, can that cause the truck to get underway with an apparent “flash” stall speed of about 1100 rpm, regardless of shift points?

Additional information... the 4.3 came from an 89 S-10 and the transmission came from an 89 Safari the Safari was equipped with a rear gear of about 3.23:1 if I remember correctly.
The truck is OT TBI, I’m not expecting the H.A.M.B. to embrace it, I just know that there are plenty of really smart guys here who have many years of experience. Where else would I ask a question like this, on a gardening forum


Sent from my iPhone using The H.A.M.B. mobile app

 

I use to go to thirdgen.org, it's a lot slower there now days. But should be some help or at least a place to search forums for answers/help.

 

I would think a good transmission shop could sort it out for you.

 

Safari is a big Pontiac wagon, yes? I thought they came with 200 4r's. So where did the converter come from?
Also , the 3.06 low gear would make the converter act tighter, not looser.
You can't determine stall speed by part throttle driving and your particular tune up. You have to lock the brakes down hard and floor it and see where the rpm's stop climbing. Then you'll know what you're working with.
The TB could have problems with the TPS or the IAC but we don't talk about that stuff here.

 

What Mark said.

 

Okay, on normal acceleration you won't get anywhere near max stall speed. You will only get it to full stall with the brakes locked and full throttle. It does seem to be shifting at a low speed, but if we are talking mild acceleration, they are only slightly low. The throttle cable controls both shift points and operating pressure. If you adjust it for later shift points it will shift at a higher working pressure. What I don't understand is the lurch from a stop. Is it possible that the torque convertor is locking up on initial acceleration? Is the idle speed real low? I'm leaning toward something in the engine management rather than the torque convertor.

A torque convertor is fairly simple. You have a pump, turbine, and a stator. However, yours does have a lock up clutch. If the pump or turbine fail, the vehicle won't move. The stator is on a one-way clutch and it can fail. If it locks up, the vehicle will takeoff okay, but feel like something is dragging once you get a little speed. The convertor will also get very hot. If the one-way clutch won't lockup at all, the vehicle is very doggy on takeoff, but is okay once you get to speed.