Revving 4000 rpms on the highway

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67Dart273 said:
Do you understand how to manually determine rear gear FOR CERTAIN?

If you don't know if it's limited slip, jack up one wheel with front safely blocked, and with transmission in neutral, see if you can turn the jacked up tire. If not you have limited slip and you must now jack up BOTH rear tires

With the one jacked up, assuming no limited slip, watch and count the driveshaft turns as you turn the tire TWO turns. This will give you the ratio

If it is limited slip, turn either tire ONE turn and count driveshaft turns. Same thing. You can easily estimate between 3.55/ 3.91/ 4.11 by being careful
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OK so tried this, i did two wheel turns and came up with around 7.5. So that should basically be 3.73, so i guess the tach is out.
 
If you suspect tach, I would do the back breaker slip & slide and try & get your head up behind the dash to see if anything was visible before pulling the cluster. PITA I know , but so is pulling the cluster especially if you can see a simple solution.
 
RogerRamRod said:
If you suspect tach, I would do the back breaker slip & slide and try & get your head up behind the dash to see if anything was visible before pulling the cluster. PITA I know , but so is pulling the cluster especially if you can see a simple solution.
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Great idea, I will give it a shot. At the end of the day a working tach is not important. Though it's nice when you have one to make sure it works. I also have a digital timing light that reads RPMS, so I can also compare the tach to that. My 80 roadrunner did not have a tach, either does my dodge ram charger.
 
Yes if you have a timing light that reads RPMs you can easily have someone inside and take it up to 3200 and hold it and ask them what their seeing?...
If you really had to get inventive you could tape your phone to the seat with it on video pointing at the tachometer and rev it up to 32 and scream out 32!...
 
trivium91 said:
OK so tried this, i did two wheel turns and came up with around 7.5. So that should basically be 3.73, so i guess the tach is out.
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Agree if you did as you think....You have limited slip then, and turned both tires?

Anyhow you will get it figured.
 
67Dart273 said:
Agree if you did as you think....You have limited slip then, and turned both tires?

Anyhow you will get it figured.
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I knew I have limited slip before, the two black lines behind me told me :rofl:. I was actually told its a Detroit locker since the rear end was rebuilt. I actually had a Detroit locker on my old 80 Volare Roadrunner aswell, when it was new the tires would chirp when turning. It managed to break in a bit and worked well right up until I sold the car.
 
RogerRamRod said:
If you suspect tach, I would do the back breaker slip & slide and try & get your head up behind the dash to see if anything was visible before pulling the cluster. PITA I know , but so is pulling the cluster especially if you can see a simple solution.
Click to expand...
One of those inexpensive USB or bluetooth snake cameras on Amazon that connect to your phone could save you a lot of discomfort.
 
I used to own a 64 Ford Fairlane that had 3.45 gears in it. 245/60R14 and at 4000 rpms it would sit right on 80 mph.

Like other mentioned a 4.30 gear would probably be taching 4000 rpms at 62 mph.

So you either have more gear than you think, or there is something wrong with the tach/ wiring.

Tom
 
Update guys, I used my timing light and the tach is out. The RPMS, im getting are right in line with what would be expected for 3.73 gears. I did pop my head up there but can't really see anything, even if I used a scope camera there is no way I can reach it if there was a switch back there without pulling the cluster out.
 
trivium91 said:
I knew I have limited slip before, the two black lines behind me told me :rofl:. I was actually told its a Detroit locker since the rear end was rebuilt. I actually had a Detroit locker on my old 80 Volare Roadrunner aswell, when it was new the tires would chirp when turning. It managed to break in a bit and worked well right up until I sold the car.
Click to expand...
A Detroit Locker should be a bit noisy in operation as the dog clutches engage and disengage.
 
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