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Old 12-23-2007, 06:42 PM   #1
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Default How did I get 3.96 gears??

Since I got my new tranny put back in, I have been averaging about 11mpg. It was getting 19+ before the tranny build. I noticed 2 things tonight. First, it doesnt seem to be shifting into overdrive. It is turning 3000rpm @ 60mph in O/D and when i shift it into D the rpms dont change. Any ideas? Second, I have 225/60/R16 tires. And 3000rpm @ 60mph with those size tires in 3rd gear (1:1) yeilds a 3.96:1 final drive ratio. I thought a the 2.89 H-D diff swap into a 3.06 tranny yields a 3.29 final drive. My tranny guy had to swap different gears to get everything to work without a matching ring gear to thr 2.89 set. I wonder if this is what gave my the lower gear? Any ideas?
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Old 12-23-2007, 07:16 PM   #2
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There is no 2.89 diff.
A HD FDR is made up of 37/33 gears multiplied by a 3.33 diff which equals a 2.97 FDR.
A 3.06 FDR is made up of 35/35 gears and a 3.06 diff.
A 2.84 FDR is made up of 35/35 gears and a 2.84 diff.

So it sounds like you had a 3.06 diff previously and you put in a 4t60-hd diff. That means you have a 3.33 FDR and your shift points will be off..
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Old 12-23-2007, 07:54 PM   #3
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Evidentially you have no Overdrive...

Even with the 3.29 Gears you have I think you should be doing 2100-2200 at 70...


It seems to me that you have no 4th gear...


Now the question is does the PCM request 4th gear and it just doesn't happen? Also if there is an issue the PCM can command 3rd gear and lock you out of 4th gear...

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Old 12-24-2007, 02:21 AM   #4
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It still shifts at 5950 rpm. And sometimes it does shift into 4th, I think. Because a little later I was doing 60mph @ 2100 rpm. I did have some problem with the PCM this last sommer. My car would randomly shut off and lose power. It did it a couple of times, but has been fie for almost 6 months. I think I will bring the scan tool home during christmas and see if the tranny is being commanded to go into 4th. It does launch real hard out of the hole. The front end jumps up and it will leave 2 20ft black strips that curve to the right slightly. Major difference from before!!
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Old 12-24-2007, 03:18 PM   #5
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Quote:
It seems to me that you have no 4th gear

what do you call a 4th gear we have 3 foward gears and overdrive and a lock up
or am i mistaken are tranny does the 3 gear goes into lock up after it overdrive



what i think is that youre lock up not working and if the lock up not working youre tranny not going into overdrive
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Old 12-24-2007, 03:43 PM   #6
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Quote:
Originally Posted by firebuick
what do you call a 4th gear we have 3 foward gears and overdrive and a lock up
or am i mistaken are tranny does the 3 gear goes into lock up after it overdrive



what i think is that youre lock up not working and if the lock up not working youre tranny not going into overdrive
The trans has 4 gears and it locks up in 3rd and 4th. But if it dosen't lock up in 3rd, it won't see 4th.

I think you need a chip made with all of your shift points multiplied by 92%. (3.06/3.33)
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Old 12-24-2007, 03:47 PM   #7
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Quote:
The trans has 4 gears and it locks up in 3rd and 4th

what you call the 4th gear is the overdrive

overdrive is not what you can call a 4th gear because you can't go full throttle in overdrive overdrive is only there to cruise at a lower RPM
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Old 12-24-2007, 04:19 PM   #8
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Quote:
Originally Posted by firebuick
Quote:
The trans has 4 gears and it locks up in 3rd and 4th

what you call the 4th gear is the overdrive

overdrive is not what you can call a 4th gear because you can't go full throttle in overdrive overdrive is only there to cruise at a lower RPM
The transmission has 4 gears with 4 seperate clutch packs. It locks up the converter clutch in addition to these.

Pick up a ASTG manual..
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Old 12-24-2007, 07:17 PM   #9
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Yes the Trans has 4 Clutch Packs... It does have 4 Gears... Overdrive iirc is where you have more wheel revolutions than engine revolutions...

If you were to look at the 3T40 Trans you'd be 1:1 in 3rd gear... I think we are .7xx to 1 in Overdrive

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Old 12-24-2007, 07:21 PM   #10
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Do the T/C lock in 3rd? Because sometimes (notice it more when the tranny is cold) the RPMs will drop at 60mph from 3000 to 2100. Like its shifting another gear or the TC clutch engaged. I have a new torque converter and that Transgo Jr kit installed if that would make any difference. Is there any kind of anjustment that needs to be made after the trans is installed? Something I am missing here?
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