Alright, time to ask for Help. I just had my transmission rebuilt (700r4), it has 166,000 miles on it, never been touched. It had a delayed shift into reverse, rpms were running really high and it over-reved when you smashed the throttle while already rolling.

Transmission shop said everything looked pretty good in general. So now, the engine still seems to run really high rpm and it still over-revs when you stomp on it while rolling. I have counted the gears and run the manually and counted them while in over drive, looks like its hitting all 4 gears. I have shifted from over drive to drive while running on the highway and the engine speed jumps up, so it looks like its going into over drive. I have also tapped the brake while holding a steady throttle and seen the engine speed jump up a few hundred rpm, so it looks like its locking up.

While running on the highway at 80 mph, the engine is turning 3,000 rpm. The car has a 2.73 rear end. at 60 mph I am running in the 2200 range. Much higher then I recall it used to run. (haven't driven it much in the last year or two).

I ran some numbers through the calculator on the tech page and it should be running much lower than this. what gives? Is this just in my head? 3,000 rpm at 80 just seems way to high for 2.73 gears, plus it could barely keep cool running like that on the highway.

Any suggestions?

 

I collected some data while on the road a few minutes ago. below is what I have from the tech calculator and what I saw on the highway. I have to be making a mistake somewhere.

Gear MPH RPM(Calc) RPM (Actual)
1 20 2200 4000
2 30 1750 2900
2 40 2330 3900
3 40 1440 2400
3 50 1800 3000
3 60 2150 3500
4 60 1510 2500
4 70 1760 2800
4 80 2054 3250


The calculated numbers seem a tad low and then my actual numbers seem high.....

 

No; actually, sounds pretty normal.

The issue at hand is, you have NOT THE VAGUEST CLUE what your engine RPM is, REALLY; all you're doing, is looking at that wavy pointy thing in the dash that goes up and down when the engine speed does, and you're making the mistake of believing that the numbers it is pointing at, are in some way "real".

They're not.

That thing in the dash is just a trim piece like the raised white letters on tires or the GFX on a 6-cyl car or a brightly-colored paint job with lots of high-tech-looking "codes" in stickers, designed to exude an "image" of "sporty"ness without actually contributing in any way to any actual "performance" of the car. At best, it is only loosely connected to reality; at worst, it is random. They left the factory somewhat close, but as time goes on, they fail. They fail by reading high.

I have a PILE of them. The one in my car only reads about 5% high. I have at least one that reads DOUBLE reality, and I have seen some that read TRIPLE the actual engine RPM.

Ignore it.

If you really want to know what your engine RPM is, hook up a piece of actual test equipment, such as a tune-up analyzer. Divide the one by the other to find the conversion factor to get from fantasy land to the real world (i.e. you'll know that you have to divide the dash trim "number" by 1.8, today, to derive actual engine RPM... tomorrow it will probably be a slightly higher number, and the day after that, and the day after that, and .... ). It won't necessarliy be "accurate" for very long, but at least you'll have the comfort of knowing that there's nothing wrong with your transmission, only the car's "sport" trim has broken.

There's an artice on this site somewhere about "repairing" it, but evidently it's wrong. It talks about a capacitor according to people who have found it. The REAL problem is the thick-film resistor that is trimmed at the factory to make it "read" "right". It burns up and changes value.

 

I assume the computer is still reading it correctly..... I'll see if I can get my hands on a scanner and see what it reads there.

 

Right; the computer is actually functional in regards to operating the car, and as such, is more rigorously designed than the interior trim option. They are not connected in any way except that they both get 12V from the ignition circuit.

Yerbasic aftermarket tach is usually far more accurate than the factory dash trim.