4000 rpm @ 55 mph

[wolfewerx]

Lots of guessin' goin' on. Jack the diff up and turn a wheel and DETERMINE the gear ratio. Measure your tire diameter. Get or borrow a handheld tach and compare rpms. Get or borrow a GPS and check your speedo for error. Have a look and identify your transmission. All this is stuff you really need to know about your truck. And if you are 4x4 you should check the front gears also. BTW- when you're under there check your diff levels.

At 4000 RPMs on a commuter - the wind noise should be fighting the exhaust burble and the hiway patrol should be droppin out of sight!!!

[bellemare_486]

Originally Posted by wolfewerx

Lots of guessin' goin' on. Jack the diff up and turn a wheel and DETERMINE the gear ratio. Measure your tire diameter. Get or borrow a handheld tach and compare rpms. Get or borrow a GPS and check your speedo for error. Have a look and identify your transmission. All this is stuff you really need to know about your truck. And if you are 4x4 you should check the front gears also. BTW- when you're under there check your diff levels.

At 4000 RPMs on a commuter - the wind noise should be fighting the exhaust burble and the hiway patrol should be droppin out of sight!!!

I'm doin 100 mph @ 4000 in my '70 but I think my walmart special tach in the '67 is suspect. The truck is definitely low geared and all of the drivetrain noise at 55 makes it hard to tell. I received many similar responces and by next weekend I should have it figured. thanx

[piecesparts]

SIMPLE---take your truck to the highway as noted above. Get your watch out or a stop watch and start down the highway, set the speed at 60 MPH and go through a couple sets of mile markers (THEY ARE NOT always set in 1/10 mile increments--so do more than one set). As you go through these sets check your time. For a 60 MPH speed, you should be right at 60 seconds. If not then calculate by taking the number of seconds, that you get in a mile, and divide that number into the number of 3600 (60 X 60 = 3600). You now have your speed that you were going. You now can work your speedo gears and rear end gears from this knowledge.

Also get a shop tach and check your tachometer in your truck. 4000 RPMs would sound really loud and harsh on an engine.

[DANTIP]

If you have ever driven your truck over 80 mph and your engine stayed together you are either getting false information or you have a really well built engine. Check your tach with a dwell/tach combo set to 8cyl. Speedo can be checked on highway with mile-markers as mentioned above.

Good Luck!

[chrislehr]

I have the same problem. I called it powerglide.