What RPM's do you hold at 70mph? I hold 3000 and thats not right.....

 

mine sits at 4500... needless to say none of our tachs are right, mine is about 1500 rpms off, compared to the ecm

 

I hope mines off, it should sit at 2100. So either my torque converter isnt working, or I have no 4th gear and the torque converter can only lock in 3rd. I just want to know whats wrong and thought that I would ask other people with V6 engines because I dont know how much different it is with a V8 hooked up to it like the people helping me or lack there of in the transmission/drivetrain forum.

 

my tach is screwed, but it should be around 21-2500....

you should be able to hear the engine strain to hear how hard it's working.

 

best thing i can tell you is drive it and listen to it shift into all gears and overdrive, more than likely your tach is just wrong. listen to it you should be able to tell.. im willing to bet at least half the people on here have screwy tachs, they show idle right or close to it and get worse as they go up.

 

How do I fix a wachy tech then? Because it really does feel like it shifts right....

 

i dont think they can be fixed but i could be wrong.. get an aftermarket of some sort and hook it up or get a scan tool and hook it up to check rpms. or do as i did and buy an aldl cable, tuner pro RT, and check the rpms that way, and now you have your own scan tool

 

The thing though is that when I drive at higher speeds you can hear the engine pulling hard, like it isnt in O/D or maybe its in O/D but it didnt lock in 4th gear. I'm so confused with it lately....

 

More than likely, a, your tach is slightly off, and b, your torque converter clutch isn't working. At 70, with a malfunctioning TCC, my car was puling around 2900 on the highway (and my tach is dead on). When the TCC worked, I was closer to the 23xx RPM I was supposed to be at (I have a 3.42 rear). If you know your rear gear and your tire diameter, you can plug the numbers into the Tech Equations on the TGO main page to help find where you should be running at a certain speed.

The TCC can be fixed, but it depends on what is wrong with it. Mine was a hydraulic malfunction. Sometimes it's bad wiring, sometimes the torque converter needs to be replaced. Simplest way to test the electrical is to get up to about 60 or so on the open road (above 45 at minimum), and put a switch between the top right and top left terminals of the ALDL, which grounds the TCC and should engage it.

Also, if you're not in 4th gear, your shift cable may need adjustment. Hold the shifter slightly towards Neutral going down the road above 35 MPH, and if the trans shifts again (into 4th, not neutral), your cable needs adjustment.

 

I suppose I'm going for a drive right now then! Thanks again MaverickH1L!

 

BTW, if you're not sure the TCC works, leave the switch or wire in the ALDL and drive anyways. The TCC should lock whenever there is sufficient oil pressure to do so, no matter the gear the trans is in (won't engage at a stop due to lack of governor pressure).

 

Yes, well that was exactly what I did, I got the paper clip ready to just push into the pin when I hit speed, but it was close enough to ground when I hit second gear. It locked at 1250rpm on my tach which is only god knows what for the actual engine speed. And it climbed pretty quick to 55, actually it climbed a lot faster than it does when its not in O/D. And while I was marveling in how good it was working, I didn't pay attention to the gear shifts.

But this is good, this means that the Torque Converter is in fact still there and in working condition. The thing that I'm wondering though is at what speed it actually first locked up at. It locked when I was moving about 20mph and it made the car shake really bad like I was driving a manual car and I was in a gear that was too high for the speed I was at, but it kept accelerating, and pretty nicely at that.

But When I was at 35mph it said on the tach that the engine speed was 1500rpm, but it was making the car shake and vibrate, like an engine does when its about to stall, so that tells me that it was actually locked right above my minimum air speed, or something very close......or thats what it makes me think, but it has to be.

So either my tach is wayyyy off like the majority of people tach's, or its just coincidence that the RPM it tells me for 70mph in 4th and O/D, is the same as the 3rd gear speed is, or should be.

Any thoughts?

 

For the tach fix hit the electronics board. There is a good thread on it that shows pictures of the driver board, where it is located in the cluster, and which resistor goes bad.

Note that the TCC gets power via a switch at the brake pedal. Pressing on the brakes drops power to the TCC solenoid forcing it to unlock. It may also be that the switch is intermittently bad or that it isn't adjusted properly. As mentioned on the tranny board, a code 24 will also cause the TCC to unlock.

The 700R4 can lock in 2nd, 3rd, and 4th. It can not lock in 1st. So with the TCC ALDL pin grounded it will lock as soon as it up shifts into 2nd. And slight pressure on the brake pedal will unlock it.

RBob.

 

Mine is somewhere around 3200 at 70, 2900 at 60 and 1500 at idle after it warms up (and it sounds like it's about to die). Cold idle is around 1900 and it sounds much better.

When I floor it, it will go past the end of the tach before it shifts, so I know mine is off.

 

Ok my tach is definately off, and I know by exactly how much....

Ok so my tach should read 2100rpm for 70mph, and mine reads 3000/3100.

So if I take 2100 and divide by 3100, I get .6674.

So then I take all of my RPM's and mulitply them by that figure, and I get the RPM's that the car should be holding. Now, all I have to do is fix the tach, and I will be golden, nothings wrong with my transmission.

Here is what you plug in:

Wheel radius:13 inches
Rear end Ratio:3.23
Transmission gear ratio(4th): .7


So before, heres what it would read in O/D:

40mph=1750rpm
45mph=2000rpm
50mph=2250rpm
55mph=2500rpm
60mph=2600rpm
65mph=2750rpm
70mph=3100rpm
75mph=3250rpm
80mph=3400rpm
85mph=3750rpm
90mph=3900rpm

And here arre the new values in O/D:

40mph=1184rpm
45mph=1354rpm
50mph=1523rpm
55mph=1692rpm
60mph=1760rpm
65mph=1862rpm
70mph=2099rpm
75mph=2200rpm
80mph=2302rpm
85mph=2539rpm
90mph=2640rpm

And here are the calculated values by the calculator right here on TGO:

40mph=1168rpm
45mph=1314rpm
50mph=1460rpm
55mph=1607rpm
60mph=1753rpm
65mph=1899rpm
70mph=2045rpm
75mph=2191rpm
80mph=2337rpm
85mph=2483rpm
90mph=2629rpm

So as you can see the new values and the calculated values are very close, and the differences could be explained by me rounding .6774 instead of the whole value of .6774193548.

So I've never had a problem with my transmission, but a problem with the tach. Problem solved, but now I have a new one! Go figure....haha.

So this could also account for my idle problems, I could never get the car to idle where it should (600rpm-800rpm), but now with the tach revealed as being incorrect, then I can also take my current idle speed of 1000-1100 and multiply it by the same ratio as above. Sooo.....

1000x.6674=677rpm
1100x.6774=745rpm

And now that is right on as well. Woohoo! Now I just need to get that damn tach fixed.

 

I'm not too worried about the tach being off on mine, I just go by the sound of the exhaust for a general idea of if the rpms are too high or low.

 

Well, at least the tach is a cheap, easy fix. I do have a spare if interested, it's not in the cluster at the moment, but I'm sure it's accurate (was in my old cluster before I swapped to the 120 MPH cluster and I verified that with a scanner).

 

What do you want for it?

 

I'm thinking $20 shipped if interested, but I'll test it first and make sure it's still good (been in the basement in an open shoe box for almost 2 years) and then I'll have to find a box (shouldn't be too hard but it's an odd shape).

 

Alright, that sounds great, PM me or something when you have it tested and everything that its good to go, and I'll send a money order to your address! Thank you so much!

 

Hit the Tach thread in the electronics forum before you do anything. It isn't the tach that you need. It is the driver board that is located in the cluster below the tach. And it is an easy fix. Snip a pin on a chip, solder in a small resistor, done.

The thread is near the top now. Look for the one with the 20-thousand-some hits. Can't miss it. Only need to reference the first 2 pages of the thread. The remaining pages are thanks and messages from the many that fixed their cars tachometers.

RBob.

 

At 70MPH i turn 2500 RPM. So you are in the ballpark. If the TCC isnt locking up, perhaps 3000 is where it is.

 

In OD, about 2k-2100 depending on the weather. My car has a hell of a time in high humidity.

 

Well I'm sure that I could solder on a new resistor, but I would feel much better if I just plugged in a new tach chip into the underside of the dashboard. And if the soldering job is easy and requires the same thing as getting a new chip and replacing it, then I would much rather just get a new chip for it, take out the old one, plug in the new one, and roll.

Plus, knowing me, I would get the wrong resistor and mess it up even worse haha.