High RPM at relatively low speeds

[Dale Lucy]

So, new to me '69 GTX conv, 440, 4-speed, Dana rear with 3.54 gears, 15 inch tires all around. Driving to the gas station today, and to the local body shop, I was seeing approx 4000 RPM @ 60 mph in 4th. I can easily take off at a stop sign in 3rd.
Just the way it is? Could someone have re-geared the 4-speed (is that even possible)?

Dale
SW MI

 

[Don Frelier]

Likely your 3.54 gears are more like 4.56.
Probably didn't change the little stamped tag.

 

[69sunfireGTX]

I am guessing your Tachometer is not reading correctly. Sometimes mine gets a little wacky and does the same thing

 

[vance.dykes]

Likely your 3.54 gears are more like 4.56.
Probably didn't change the little stamped tag.

if you take and mark the tire to a fixed spot and the drive shaft yoke to the housing turn the tire and count how many times the yoke passes the mark then you will know a 3.54 will go 3 and 1/2 times and a 4.56 will go around 4 and 1/2 times then you will know with out taking anything apart. this is for the poster and to support Don

 

[Fran Blacker]

One of the 2 above or your clutch is slipping? Maybe gears were changed, time to jack it up mark d-shaft and tire and count the turns.

 

[gkent]

He wouldn't be able to easily take off if the clutch is slipping.

 

[33 IMP]

If it's an aftermarket tach, set to 6cyl, wouldn't it read about 33% fast?
Otoh, if he can leave a stoplight easily in third, it sure sound like it has a LOT of gear in the back (not in the trans). 4.56-4.88?

 

[PRHeads]

As has been mentioned already......
First step should be to verify the rear gearing.

“If” those are determined to actually be 3.54’s, the tac is off(or you have really really short tires).
For example: 60mph, 3.54’s, 26” tires = 2745rpm driveshaft speed.

On the other hand......
60mph, 4.56’s, 26” tires = 3536rpm
And 4.88’s would be 3785rpm.

 

[Dale Lucy]

Verified the rear end; 3 and a half turns plus a smidge for every turn of the rear wheel
Rear tires are 225 60R15's
In-dash tach doesn't work, car came with an aftermarket one
Dale

 

[33 IMP]

So either your clutch is almost non-existent , or your tach is way wrong. I know which way I would bet.

Take a look at the back of the tach, look for a switch for 4/6/8 cylinder. Or just get a new tach.

 

[PRHeads]

If it has a normal-ish ignition, you should be able to evaluate/verify the tac with a tach/dwell meter.

225/60R-15’s are about 25.6”.

Driveshaft rpm at 60mph would be 2790 with 3.54 gears.

Either the clutch is slipping like crazy, or the tac is off.

 

[Cranky]

If it has a normal-ish ignition, you should be able to evaluate/verify the tac with a tach/dwell meter.

Was just about to mention that! My old Sears and Roebuck engine analyzer from the 70's is still pretty accurate.....

 

[PRHeads]

I think those work with the OE electronic ignition, right?

I don’t think I’ve tried to use mine in nearly 20 years.

 

[Cranky]

I think those work with the OE electronic ignition, right?

I don’t think I’ve tried to use mine in nearly 20 years.

I checked output voltage recently on my mid 90's pickup but didn't even think to see if the tach on it would work and can't remember ever trying. Heck I've owned my 95 since 98 too lol

 

[Kern Dog]

He wouldn't be able to easily take off if the clutch is slipping.

Not necessarily true.
A clutch can grip with the mechanical leverage of first gear but is more likely to slip in the high gear.

 

[PRHeads]

Well...... I have no idea about newer ignition systems....... I meant more like an “orange box” type of thing.

I don’t think they work...... well, I don’t think mine works...... with an MSD.

 

[dvw]

Not necessarily true.
A clutch can grip with the mechanical leverage of first gear but is more likely to slip in the high gear.

If the clutch is really toast, rpm would rise immediately with the slightest hint of throttle in high gear. No way anyone could mistake it. Steady state speed on a level road it wont slip. Tach is off.
Doug

 

[Cranky]

Well...... I have no idea about newer ignition systems....... I meant more like an “orange box” type of thing.

I don’t think they work...... well, I don’t think mine works...... with an MSD.

Seems like I used it on a drag car with a high performance Mopar ignition chrome box.....iirc. Dang, that was 36 years ago. The thing saw 7300 in the traps every pass! It had a mechanical tach drive set up and wanted to make sure it was reading right. My next car had an MSD but never even tried using the analyzer on it.

 

[PRHeads]

My tac/dwell meter doesn’t have a “power” lead.
There’s only two wires...... the one that goes to the coil “-“ and the other to ground.

There isn’t any standing voltage at the coil with an msd...... and I “think” that’s why mine doesn’t work with that type of ignition.

 

[Cranky]

My tac/dwell meter doesn’t have a “power” lead.
There’s only two wires...... the one that goes to the coil “-“ and the other to ground.

There isn’t any standing voltage at the coil with an msd...... and I “think” that’s why mine doesn’t work with that type of ignition.

This is the one I have....only much cleaner!
https://www.ebay.com/p/1523031169
And got rid of the magnifier a long time ago.