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Old 05-19-2002, 10:15 PM   #1
72chevyLWB
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Post 700R4 ?

I have 27" tall tires. When cruising 75mph it runs around 3,700rpm. It should be alot lower than that. I have 3.73 gears. I am only getting 7mpg wiht it. What could be the problem? It has a 2400 stall on it and is lockup. It runs around 2,500 at 55

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Old 05-19-2002, 10:17 PM   #2
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have you corrected your speedo yet?

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Old 05-19-2002, 10:24 PM   #3
72chevyLWB
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yes I have and it is exact.

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Old 05-19-2002, 10:27 PM   #4
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My TH350 with 28-ish inch tires and a 3.07 gear does 3700 at about 95 MPH. (I have a pic of it on my digi-cam right now)
Is your ranny slipping at all?
That 2400 stall is probably killing you. You want your cruise RPM to be higher than your stall speed, or else you'll get tons of slippage.

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Old 05-19-2002, 10:36 PM   #5
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What kind of system do you have telling your converter when to lock up? Is it adjusted right? If it is, then you might have a bad converter. I can feel when the converter locks up on my S-10. It might now be locking up. If you have a trans. temp. gauge check it out and make sure your trans temp. is not way out of wack. You may have something slipping inside. If all that is good.....what kind of engine do you have? If its a low power engine it may not have the umph to push the truck at those low RPM's.

Thats all I can think of.

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Old 05-19-2002, 11:49 PM   #6
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Is the 700 in your truck right now? If so, your'e not getting lockup on the converter. There has to be power to the lockup solenoid or you have to bypass that hydraulicly. Those are the only two ways to do it. Jeff.

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Old 05-20-2002, 11:54 AM   #7
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lockup will only knock off a couple hundred RPM, not 1500. Look at his RPM's, that is WAY off!

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I've been dubbed the Longhorn Freak/Fanatic/Expert, I just hope I can live up to it.
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Old 05-20-2002, 02:00 PM   #8
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My 69 has 3.73 gears and 28" tall tires and in overdrive its 2000 rpm at 65 mph.
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Old 05-20-2002, 02:04 PM   #9
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By the way the lockup only drops the rpm 400. I have 12 volts going to the lockup all the time and it goes through my brake light switch so when I stop it disconnects the lockup.
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Old 05-20-2002, 06:09 PM   #10
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That's WAY OFF! I've got 255 70'x15's, 3:55 gears and with my 700R I'm doin' 2200 RPM in the Studebaker, doin' 80 MPH, and I'm calibrated correctly. With my 350 ci engine, I'm gettin' 23 MPG.

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Old 05-21-2002, 10:56 AM   #11
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When I am in overdrive (or I think it is) I can pull down into 3rd and nothing happens. Is the converter maybe just locking up and not even shift into fourth? And how can I get it to shift into fourth if it isn't. When I cruise down the highway and touch the brakes ( I have the painless kit with brake switch) I can't feel the converter unlock.

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Old 05-21-2002, 11:44 AM   #12
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It does sound like you're not getting fourth gear there. You're not above 3/4 throttle, are you? Stock 700R4's have a lockout so they won't shift into fourth above 3/4 throttle...

Then again, that's probably not the issue...

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Old 05-21-2002, 01:00 PM   #13
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It actually sounds right. Do the math (I wrote a program for my iPAQ to do it for me). I get that you should have 3483rpm @ 75. Are you sure the converter is locking up? If everything was locked tight, then you should be getting 80 @ 3700rpm

I also get that your rpm at 55 should be 2554. If it's right at 2500, it should be 54. That's a 2% variance, and with 2% at 80 mph, that would mean about 78mph on your speedo at 3700rpm.

It all sounds right to me. 7mpg has a lot to do with the high rpms. I think that with a good carb overhaul and/or rejetting, you could get 10. Taller tires would help with both.

All the above numbers are NON-overdrive. If you have an overdrive tranny, it's not going into overdrive.

my 2¢


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[This message has been edited by ckhd (edited May 21, 2002).]
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Old 05-21-2002, 01:06 PM   #14
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Duh, read your post 3 posts up.

You are definately NOT getting overdrive. Your tranny gets into drive and no further. How to fix it? I don't know. Check your throttle cable. If it's not right, it could think your throttle is at 75% or more and not allow 4th. I've heard the throttle cable on the 700r4s are sensy.



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Old 05-21-2002, 01:17 PM   #15
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How can you tell if the torque converter is locking up? Do you feel it? Does it lockup only in fourth?

I have 12 volts to it and am running about 1400 RPMS's @ 55 with 3.07

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Old 05-21-2002, 01:30 PM   #16
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Dude! your stuck in the 3rd gear. I put in your numbers except I told prestage.com to give me the transmission ratio with those numbers and I got 1.06. 3rd gear in a 700R4 is 1.00. So now we know what is happening, just need a tranny guy that can figure out why.

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Old 05-21-2002, 02:29 PM   #17
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You are NOT in overdrive. Your 700R will give you a 30% reduction in RPM when in overdrive. Specifically, that 3700 will go down to 2590. Have a reputable tranny specialist check it out for you.
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Old 05-21-2002, 02:39 PM   #18
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What tranny did your truck have originally? Your indicator may be off. When you take off what position do you shift to? Drive? Nuetral? What ever it is, put it in one position higher and see what it does. I think your shift indicator might be off and your in a gear lower than you think you are.

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Student at the University of Kentucky.
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Old 05-21-2002, 07:40 PM   #19
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What do you guys know about the servo's in the tranny? I heard there is a 2nd and 4th gear servo. Could the 4th gear servo be bad? If wires go to it or something? And thanks alot to all of your input also

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Old 05-22-2002, 12:15 AM   #20
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no overdrive dude.cuz with those r's u should be doing at 107 mph if u were in od

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Old 05-22-2002, 02:05 PM   #21
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Guys,
Go to www.700r4.com and take a look at the rmp calculator. At 75 mph you should be turning 2438 rpm with 27 inch tires, in overdrive.

If the tv cable is not adjusted properly, It will shift very badly IN ALL GEARS. In other words, the 1-2 shift can occure extremely soon (like almost immediately) or after the engine revs beyond what makes sense. It doesn't just control shifting into overdrive.

Electronics don't have anything to do with shifting into overdrive, but they do control lockup. Most trannies are not set up to lockup in any gear but overdrive. It is possible to wire it up to go into lockup in any gear. Most common way is to use a vacuum signal combined with a signal from the tranny that it is in overdrive to control the electrical signal for lockup. You can feel (but mostly hear) the lockup if you pay close attention and know roughly where you are based on gears. Best test (again assuming wired correctly) is to tap your brake at cruise speed. The lockup should disengage when you hit the brake. If it doesn't, I hope your insurance is paid up, because your destined to drive right through the guy in front of you.

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Old 08-29-2002, 04:57 PM   #22
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About your trans, well I don't have much knowledge in them, but I got off the phone with this trans builder (cause i want to do the swap), and he told me he has a 67 c10 with the 700r4. he told me about the 4th gear lockup. he said all you needed to do for the lockup was to run 12V (he's running it to his ignition key) to the trans, and the rest of the shifting into overdrive would be done internally (no selnoid).
He said he somehow grounds something inside the valve body that'll triger 4th gear to come on. now as far as what he does to it internally (he builds transmission)for this to happen, i don't know. let
me know, and i can give you his phone # if you have question....
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Old 08-29-2002, 07:57 PM   #23
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I just talked to a guy last week and he said that if there was only 1 wire going into the tranny the ground was gone. He said there must be a way to ground it internally.
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Old 08-30-2002, 12:13 AM   #24
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If your converter is not locking up, if I were you I would quit driving it till I founf out the problem. The converter has got to lock up on the 700r4 if not it will burn it slef up. I agree with longhornmail, if your conerter is 2400 stalh and your driving 55 and the rpm is at 2400 to 2500 you are getting a lot of slipage, and this is going to build extra heat, and the 700r4 do not like heat, it will burn it self up this way also. So, my 2 cents is you have got to have these trannys just right, or you will be putting another one back in there.
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Old 08-30-2002, 07:29 AM   #25
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I finally got mine out of the shop. They put what they called a "dummy" converter in it so it does not lock up. I really like it this way. I have more control over it. In drive it is a 3 speed and in overdrive it is a 4 speed. It seems that I am only turning 300-400 more rpms at 60 mph without the lockup.
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