Cruising down the highway, this is the situation. I've verified the RPMs via a computer, and verified the rear gear by popping the cover and counting teeth. I'm about to go test my TCC lockup, but I'm fairly certain its working. What could this be? Can a transmission be constantly slipping on a high speed, low PRM condition cruise condition?

 

i would definatly say there is something wrong. i used to have the same setup and i would at times be around 1000 RPMs at that speed.

 

Sounds like your TCC isn't locking up.

It may be a variety of reasons for your TCC not locking. List includes: it's not wired, broken connection, eprom set too high/disabled or TCC is either not working or non-locking type.

 

i have the stock 3.23's with my 700r4 and im at roughly 2000 rpms at 60/65mph. your 2.73's like my 86 should be alot lower prob like 1500

 

I'm running a 700R4 w/ 3.23's and a 3600 stall and I'm turning ~2200 @ 60

 

700r4 with 2500 stall 3.23 and i only turn 2250 at 70 with stock 245-50-16's

 

Well just went out and tested my TCC. It's locking up fine. Tapped the brake at 65mph and the RPMs went up a bit for a second then went back down. Still turning ~1900-2000 RPM though at this speed. By these calculations I should have a 3.23 rear. However I counted the teeth and got 41:15 which means 2.73. What could possibly be happening??

 

65 mph with a 2:73 = about 2200 RPMs.... the stock tach is off by a couple hundred RPMs. My opinion

 

I'm not using my stock tach, I'm using my laptop which is plugged directly into my ECM. How do you figure that anyway?

With a 245/50/16 tire, 2.73 gears, and a .7:1 overdrive I should be doing 80mph @ 2000 rpm, NOT 65. Something is not right. My car is acting like it has a ~3.23 rear gear when it certainly does not.

 

Darkshot, i dont have solution or a theory yet, but i think some more information would help. How is your lockup designed? Is it factory, or custom? ie: only designed to come on in overdrive? And how is the car behaving in other gears. ie: if you are cruising in second or third, what sort of RPMS and speeds are you getting? Might help track down the prob. Maybe clutch pack probs, or probs with a gear? Or maybe torque converter is worn?

 

Maybe the speedo gear isn't correct.

 

Go to F-body.com and their Performance calulations and plug in your info....gear ratio/mph/od ratio/tire dia=RPMs
about as close as you can get. Do the math yourself or plug in the data and let the formula calulate it. Your numbers are incorrect in my opinion and it looks like everything is find. Another quick check is drive in OD at steady 40 MPH and your tach should read 1000 rpms.

 

sounds like your not in overdrive and in 3rd, i have 3.73s and am at 2000 rpms in OD with 215-65-15s on

 

man, 92 ta, 700r4 and 3.23's im at 1800 at 60 mph, and 2000 at 70 mph. could be the tach being off, but thats what i get.

 

in 3rd with 3.23 im running 2000 at 40mph roughly. i checked my tach through the comp and a code reader and my tach is dead on and so is my speedo. as i said before with 2.73 like my 86 tpi with 700r4 u should be running around 1500. u should not be near 2000 at 60/65 with 2.73's. how is ur trans shifting? does it shift good no lag etc, or is it slow into gear and when u step on the pass does ur RPM's rise but the car doesnt accellerate? if thats whats happening its ur trans plates are slipping, or torque converter,if not it could be the converter,speedo gears, maybe even ur rear is goin....

 

My TCC setup is stock, AFAIK. I'm riding around with a laptop on my passenger seat connected to my ECM running WhatsUp software, which has a TCC lockup indicator. It locks up at 33 mph (in 3rd) as I set in the PROM. My trans shifts into OD at 40. TCC stays locked through the shift and all the way up through 60mph, 70mph, etc. Wont unlock unless I tap the brake, or put my foot in it. At 65 mph I can tap the brake, and my RPMs will jump up slightly while the TCC unlocks. The TCC indicator on my laptop also shuts off when I do this, and comes back on then the RPMs go back down (This is how I varify the reliability of the TCC indicator on my laptop). I have varified my guages, both MPH and RPM, with the computer. They are accurate throughout the range and are NOT the problem.

Like I said, AFAIK, this is stock behavior. However the engine is still spinning many PRM higher than it should be. My transmission is known to have problems. It slips sometimes in first gear, always slips on kickdown to 2nd gear, it clunks, whines, and bangs, all internally (no broken external mounts or anything). My original question is can a transmission *constantly and consistantly* slip like this? I just always think of transmission slipping as random and erratic, not eating up 'x' RPMS as some function of vehicle speed.

 

A transmission that's slipping constantly like your considering wouldn't last long under those conditions. You figure your turning 6-700rpm more than you should be, it would heat up and destroy those clutch packs pretty quick. How does the car behave in overdrive under load? If you get on the gas hard enough, can you feel the TC suddenly unlock? Or, conversely, when you apply firm throttle after unlock the TC with the brakes, do the revs climb, and then fall as the TC locks up? You should be able to load the motor with some throttle, and hit the brakes while still on the gas and notice a pretty big, as in 500rpm plus change, at 60mph if your on the gas pretty good when you apply the brakes. IF you're confident of your rear end ratio, and that the transmission is achieving 4th gear, then you've gotta have a TC lockup problem. Either that, or you're calc'ing the rearend ratio wrong. If you're slipping that much, you'd be generating a LOT of heat, and things wouldn't last very long.

 

Well I only realized the RPM inconsistencies since I fixed my tach and started cruising around with a somewhat accurate tach. At first I thought my re-calibration of the tach was off, but when I connected the computer to it my guage I saw that it is very close. Accurate enough that at 2000 RPMs the needle is about one needle's worth of width below 2000. (does this make sense?) This means I only know for sure that its been happening for a month or so, but I have no reason to believe it hasn't been doing this since I got it a year ago. It gets about 30 highway miles (in 5 mile spurts between which it cools off), plus about 75 city miles each week.

This slipping and drag would account for my gas mileage problem which I have NOT been able to track down. The best I can reliably manage over time with the above distribution of miles is 12mpg. The best i've seen was one tank of 17mpg, which was surprisingly all city. Maybe things are finally coming together.

 

Problem solved. I just went out and drove on the highway alongside my friend's mom's 06 Camry....my 55 is the same as its 65.

 

Gauges will do it every time. Whats the fix for the speedometer - wrong gear in the tranny? Either way, it beats the possible alternatives you were facing.

 

What worries me is my ECM readout matches my guage, so the computer thinks I'm going faster than I am. Anybody know how to fix this?