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Engine rpm's?

T

Terrific

NAXJA Forum User
Location
Brooksville, FL
I'm running about 2800 rpm at 75 mph. I have 4.09 gears, and 31"MTZ's. The true diameter, of the tires, is a little less than 31"'s tall, maybe 30" (8" wide rims). I have the AW4 transmission and 4.0 litre engine. Is 2800 rpm excessive, or about what I should expect in overdrive?
 
McQue said:
Use this site's calculator...your AW4's final gear ratio (Overdrive) is .75

http://www.offroadexchange.com/RPM_calcutator.htm

your RPM should be around 2575 with the figures you gave
Click to expand...

as long as your speedo is corrected for the tires and gears, going by this it sounds like your torque converter may not be locking up, when driving at constant throttle on a level road you should feel the tranny shifting like this:
1st>2nd>3rd>lock>4th>lock
each lock will drop about 200rpm and when it is locked you should be able to lightly tap the brakes while still maintaining constant throttle and it should unlock and rise about 200rpm
 
Is this the 1997 XJ in your profile? Just asking since the early Renix AW4s with the 21-spline output had a 0.705 final ratio. The later models with the 23-spline output had the 0.75 ratio.

As a test, while your driving along on the highway at an even pace, tap the brake pedal with your left foot. That will cause the t/c to unlock and you should see a few hundred rpm jump.
 
Does the engine have to be at a certain RPM before it unlocks when you tap the brakes while steady on the gas? On my '98 w/30's and stock gearing I noticed it would kick out of lockup, but w/the '01 I just bought that has 33's and stock gearing haven't had it do it yet? Perhaps because of the lower revs I'm now running at speed?
 
I always get my XJ to do that between 45 and 55 MPH. The breakes need not be applied firmly only enough to activate the break lights. It also do that frequently if I release the gas pedal and press it again more often if it is climbing a hill.
 
lawsoncl said:
Is this the 1997 XJ in your profile? Just asking since the early Renix AW4s with the 21-spline output had a 0.705 final ratio. The later models with the 23-spline output had the 0.75 ratio.

As a test, while your driving along on the highway at an even pace, tap the brake pedal with your left foot. That will cause the t/c to unlock and you should see a few hundred rpm jump.
Click to expand...

It is a 97. The tc definitely locks at the top end of 3rd gear. I don't know about 4th. I'll pay attention tonight, and try the brake pedal gimmick too. Thank you.
 
Weird not to threadjack or anything but mine shifts just fine through all gears and downshifts as it should. Just doesn't unlock the tc when I tap the brakes. It will when I let off and reapply the gas. Maybe the gearing and large tires has something to do with it on my application? Didn't have this feature in 01?
 
Last edited:
The stop light switch works fine. It has a disabler if the brakes are tapped with out the key in the ignition. Idk the PO did a lot of things I'm having to clean up after.
 
mrtosh said:
Weird not to threadjack or anything but mine shifts just fine through all gears and downshifts as it should. Just doesn't unlock the tc when I tap the brakes. It will when I let off and reapply the gas. Maybe the gearing and large tires has something to do with it on my application? Didn't have this feature in 01?
Click to expand...

the reason for the tc unlocking when the brakes are applied is that if you went into a panic stop and locked up the rear wheels it would stall the engine if the tc stayed locked, just like a manual rig if you didn't hit the clutch. every vehicle that came from the factory with a locking tc, be it ford, chevy, jeep, etc. will unlock when the brakes are tapped for that reason
 
Did some investigating with mine yesterday. If I pulled the brake pedal towards me with my foot while driving the cruise would work and when I let go of the pedal it would unlock the TC. Got playing with the brakelight switch and noticed it was barely touching the pedal.
 
mrtosh said:
Did some investigating with mine yesterday. If I pulled the brake pedal towards me with my foot while driving the cruise would work and when I let go of the pedal it would unlock the TC. Got playing with the brakelight switch and noticed it was barely touching the pedal.
Click to expand...

That would do it.
 
isnt that bracket adjustable so you can just move it away from the pedal
guess youve been driving with the brakelights stuck on for awhile?
 
kennzz05 said:
isnt that bracket adjustable so you can just move it away from the pedal
guess youve been driving with the brakelights stuck on for awhile?
Click to expand...

...and burning extra fuel because the TC remains unlocked...
 
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