tchernobog

Alright. I drive a '91 z/28, 305 TPI. 700r4 automatic. Car will shift into all the gears normally, but at 60 mph I'm at 25-2700 RPM. That seems excessively high, considering my old v6 700r4 cruised at sub 2000 at 60mph.

Running 2.73 gears currently.

Is this a normal RPM for highway speeds with a 305 TPI, or is something going wrong here?

tchernobog

Anybody?

91interceptorZ

iTrader: (3)

running stock tire size? Gotta check, but are you sure about gear ratio?? and is it shifting into 4th (overdrive) gear?? If so you convertor might not be locking.

tchernobog

Stock tire size, yes it shifts into all gears.

91interceptorZ

iTrader: (3)

maybe the convertor is not locking.....you can check by putting a switch connected with wires to both upper outside pins on your computer connector....when driving steady speed on interstate, flip switch to on position, if convertor locks then, it might be something wrong with computer....you should see a 200-400 rpm drop when covertor locks...

91 1LE

iTrader: (1)

You can test converter lock-up at freeway crusing speeds by touching the brake pedal enough to turn on the brake lights but not enough to apply the brakes. As long as you are still on the throttle at a steady speed the converter will unlock when the brake lights come on and the RPM's should jump by about 300. Release the brake pedal and the converter should lock back up.

tchernobog

Guess not...

tchernobog

On second thought...maybe it's not. I was cruising about 55, steady throttle, tapped the brakes to turn the lights on and the RPM's jumped about 250.

Is it possible my tach is off? I doubt it, though...There's a definite difference in sound between 16-1700 and almost 3000.

matj1990

my 350 cruises about 2300 to 2500 at 60mph but i only have a 3spd with 205/60/15 tires and 3.27 axel ratio

tchernobog

Um.

Ok.

tchernobog

Well. Pulled engine codes and got a low vacuum reading at the MAP sensor.

Might have something to do with it. Just maybe, though

Guess I'll be replacing that tomorrow.

91interceptorZ

iTrader: (3)

I have read many articles about how bad our tachs are off.....you might check in to that too...might not be a bad idea...

tchernobog

I hooked up a standalone tach. Surprisingly mine is only off by 20 or 30 RPM.

Oh well, I work at a GM dealership, a new solenoid is only $14 with my discount, and I can get free shop time. Might as well replace it, because the MAP didn't fix it.

91interceptorZ

iTrader: (3)

some of the tachs work okay....mine does too....try the solenoid and see what that does....maybe the speedo is off??

80schild

iTrader: (5)

My TC isn't locking and at 60mph my RPM's is around 2,000 (3.27 gears). If my TC were locking like it's supposed to the RPM should be around 1800.

2500 seems very high, even with the TC unlocked.

tchernobog

My speedo is off, but I run a GPS all the time, so I know how fast I'm going. The speedo being off wouldn't cause it to run so high, would it? It reads ~13% higher than it should (reads about 60 when I'm going 50ish). I'd think all that would do would make my converter lock sooner.

91interceptorZ

iTrader: (3)

True.....If your convertor is actually locking...then you shouldn't have any slippage....unless trans. is slipping badly.

91 1LE

iTrader: (1)

Sounds like the trans is still in 3rd gear. The converter locks in 3rd gear too and that can be what you feel as the 3rd to 4th shift. Have you tried adjusting your TV cable? The valve in the trans that controls the 4th to 3rd kickdown may be stuck which wouldn't allow the shift to 4th.

91interceptorZ

iTrader: (3)

I agree....I never thought of that....you might be in third....that would be a logical conclusion....

91 1LE

iTrader: (1)

And I'm guessing that you installed the 2.73 gears yourself? These are definately not the stock ratio for a G92/1LE with a 305. IIRC the stock ratio should be a 3.42 with the 5 speed. Your RPM's sound about right if you had 3.73 gears, though.

80schild

iTrader: (5)

I agree. Get it on the highway and drop it into 3rd, if it doesn't do anything you'll know.

tchernobog

This isn't my 1LE, that's running perfectly lol.

edit - I completely forgot, no, it does shift into 4th, I checked that last night. At 55mph, if I shift from o/d D (4) to regular D (3), the RPM's jump to about 4k. I'm thinking the solenoid just isn't working.

Darkshot

iTrader: (4)

I would bet strong money that your tach is off. I've owned 3 91 Camaros and every single one had a tach that read high.

If you search for 91-92 tach fix you will find a thread on how to fix it.

tchernobog

I said in a previous post that I hooked up a stand-alone tach.

However, I have made in interesting discovery. I have a feeling my TV cable is not the right size.

Piece of evidence one: Previous owner tied a knot at the end of it, to shorten it. Not sure how I missed that earlier, but I took the knot out...which made it waaaaay too long and I was getting red-line shifts out of first gear at light throttle.

I've tried 4 different lengths, I'm not really sure how to determine if I have the right length or not, though. Right now it's set to shift to second at 5k RPM's under WOT conditions. Have to admit, it makes the amount of rubber a stock 305 can lay a lot more impressive

Would an incorrect length TV cable keep it from locking up? It still shifts into 4th gear, I dropped it into third going about 50 and the RPM's jumped considerably, so I know 4th is working correctly.

tchernobog

Well, I just adjusted it properly (fully extended at WOT) and it still won't lock.

I ordered a TC lockup solenoid at work and a new gasket ($20 total, employee discount is pretty awesome haha) so I guess I'll replace that when it comes in.

tchernobog

Well, the solenoid did not fix it.

Suppose that means the clutch in the converter is dead?

tchernobog

Alright.

So...the previous owner installed a stand-alone fan controller, which works correctly (I'm assuming, turns the fans on/off dependent on how hot the engine is) but, and yes I know this makes me stupid for not checking, disconnected the coolant temperature sensor. Reconnected it, temp. gauge works now (2 of my others had bad gauges, I assumed this was bad as well) temp gauge is working correctly.

Now when I hit 50 mph, I'm still turning just shy of 2500 RPM's, which is exactly what I was before. However, since I've replaced the solenoid, the converter now locks up (steady throttle, tap the brakes enough to turn the lights on, the RPM's will jump about 200).

Car is entering 4th gear.

Here's where it gets interesting haha. My tach is very, very slightly off. less than 100 at 5k RPM's. Converter is locking up correctly, but my tach is still reading high, and the engine sounds like it's spinning higher than the 1500 or so RPM's I should be at.

What's going on here? Because honestly...I am completely stuck. I suppose I'm going to pull the negative cable and reset the ECM, because that's about the last idea I've got.

Could, possibly, the stand-alone fan controller be affecting it at all?

IROC-Z Forever

Not to bring back up a dead thread, but did you ever figure out the problem? Mines doing the same as yours, but a lot higher rpms at 65, right after I replaced the transmission so really hope I didn't screw anything up.

IROC-Z Forever

Anybody? Pretty stuck here.

jmd

iTrader: (4)

​​​​​​what tooth count speedometer gears were in the old, and in the new transmissions? That's the only relevant thing that changes when the trans. is replaced. And it's pretty easy to check when .

paulo57509

Alternate "nerd" method:

Mile markers and a stop watch. Hold a steady speed and measure the time it takes to travel one or more miles.

Do some simple math and confirm you're car is traveling at the speed indicated.

IROC-Z Forever

I'm not sure the count of the teeth on the new transmission, but I believe it was the same as my previous since I reused my old speedometer gears, but my speedometer quit like 2 years ago now I just use my gps. On that note would a faulty VSS cause the trans issue?

If not I was wondering if maybe the transmission I got was geared really low, but my main concern is the possibility of the torque converter bad or shot? Although it locks up, goes into fourth and RPM's will jump up when I shift out of overdrive so I'm scratching my head. Btw, if its relevant the converter is a low stall (got it from monster).

Thank you for the responses too I have classes until Thursday so I probably won't get to anything before then, quick question the speedo gears if you take them out the trans fluid will come with it? if not I'll pop it out real quick and see how many teeth it has.

Thanks, Chris.

Abubaca

iTrader: (3)

Keep in mind that overdrive and torque converter lockup are different. You could be in overdrive and still not be locked. OD is physically a gear. Converter lock up is like having a slipping clutch (unlocked) or having the clutch fully engaged (locked). That's how you can be in gear, yet NOT moving, like at a stop light. Converter is NOT locked, and is kinda "slipping". Not exactly the same, but for this conversation....same thing. Anyhow....While at cruising speed in OD (or in third too), either way......VERY lightly tap the brake, doing so will automatically unlock the converter, and you should be able to feel and see the RPMs jump a little, -WITHOUT the trans actually shifting gears.

What RPMs at what speed are you seeing?

LT1/TA

This thread is 8 years old and the OP has not logged in since 2013

Abubaca

iTrader: (3)

....yes but someone else had a similar problem and we're discussing that now. All good!?

dlinger

iTrader: (4)

You can also download an app for your phone. I have digihud.

LT1/TA

I am not trying to stir things up.

I just thought it would be better to start a new thread with his specific problems since the op is not likely to respond and tell us what he found.

IROC-Z Forever

Yeah LT1 I had considered that as well and it is a good idea but since someone else had the same issue I figured that a little background with my same issue might help filter out some possibilities idk.

I did drive yesterday and when I tapped on the brakes I noticed no change in RPM's like Abubaca suggested. Btw, thanks for the info, it was very helpful I always thought if it was in forth then torque converter was working like one in the same. Which leads me to believe it is the Torque Converter, now since the thing is brand new I would like to think it's not shot, but I won't keep it out of possibilities.

I see the rpm's at about 4000 and when I let off the gas the rpm's drop down when I'm going 65ish and as for the speedometer I have waze (great app for avoiding speeding tickets on the highways) and its very consistent, rpm doesn't jump around or anything. I'll give digihud btw a try like finding new things like that.

The wiring that tells the converter to lock up, I know has to get info from ecm and tps and maf, i have replaced maf and tps this winter, and the only thing that doesn't work is VSS (code is thrown I don't know if its actually faulty or just speedo cable). Any possibility of being the culprit in your opinion?

Thanks! Chris

LT1/TA

I used a Gear Ratio Speedometer Calculator and I put in
tire diameter 25.6
rpm 4000
speed 65mph
final drive 2.73 and then 3.08
700r4 gear ratios
------------------------- 2.73 rear end gear -------3.08 rear end gear
1st gear ratio 3.06 ------36 mph ----------------------- 32 mph
2nd gear ratio 1.62 -----69 mph ----------------------- 61 mph
3rd gear ratio 1.00------112 mph ---------------------- 99 mph
4th gear ratio .70--------159 mph -----------------------141 mph





It sounds like the trans is in second gear if the Tach is reading correctly.
The Vss will proably effect the Tcc from locking but it should not keep it from shifting into 2nd,3rd,or 4th.

paulo57509

Thank you. I'm an old guy and GPS isn't in my vocabulary.

Shakenblake

Doesn't vss. Affect tcc? I have same issue and hoping once my speedometer gets fixed my rpms will drop at highway speed and hopefully better highway mpg. I tearing into it this weekend. Mines an 1988 305 700r4. Speedo works top cable is good so I know my issue is on the bottom end toward trans