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post #1 of 10 Old 04-08-2012, 11:43 AM Thread Starter
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Identifying auto transmission

How do I identify which transmission I have in my truck? I have a 2002 7.3, which I hear should use a 4R100, but I can feel distinct shifts for five gears.

I bought it a few years ago with 100k on it, and the dealer I bought it from didn't know what the previous owner did to the drivetrain (but it's noticeably more powerful than stock). I'm wondering if it's possible that the previous owner pulled an Allison out of a F650 and put it in there? Maybe even the whole engine and transmission, together (that would seem to eliminate the ECU compatibility problems)?

How do I find out what's in there? I'm having some troule with Park (ie, some teeth are missing, so it will sometimes roll a bit before it finds one that stops it - only a matter of time before that becomes a critical problem), so I really need to track down which transmission it is. I'm hoping there's something simple that I can look for to identify it...
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post #2 of 10 Old 04-09-2012, 12:02 AM
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It's all in your mind... What you are likely feeling is the TC lockup. The factory options were a ZF6 6 speed manual and a 4R100 4 speed auto. I doubt anyone went through the trouble to do a swap but post a pic and we can tell you.

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post #3 of 10 Old 04-09-2012, 03:50 AM Thread Starter
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Quote:
Originally Posted by JSchuricht View Post
It's all in your mind... What you are likely feeling is the TC lockup. The factory options were a ZF6 6 speed manual and a 4R100 4 speed auto. I doubt anyone went through the trouble to do a swap but post a pic and we can tell you.
Wouldn't the TC only lock up when there would be little impact on RPM's? The tach drops substantially at each of these points, which is another reason I'm assuming they're legitimate shifts.

I'll see what I can do about getting a picture.
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post #4 of 10 Old 04-09-2012, 11:57 PM
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The TC lockup can cause a few hundred RPM drop.

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post #5 of 10 Old 05-24-2012, 06:46 AM Thread Starter
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My camera died, so I'm still working on pictures.

Where is the TCC supposed to lock? Because it's locked in the two higest gears. So, if it's a four-speed and I'm feeling the TCC lock as a shift, then it would need to be using the following shift pattern:
First
Second
Third
Third+TCC
Fourth plus+TCC.

However, I was thinking that the RPM's/speed might nail it down, depending upon the ratios that are calculated...

I have stock tires, and a 3.73:1 rear. With a 31.7" outside tire diameter, that's 99.59" circumference, so 636.2 revolutions per mile. Multiply by 3.73, and that's 2373 revolutions per mile at the output of the transmission.

At 50 miles per hour (0.8333 miles per minute) I'm running 2000 rpms with the "Overdrive off" option activated and the torque converter locked.

At 70 miles per hour (1.167 miles per minute) I'm running 2000 rpms with the transmission in its highest gear and the torque converter locked.

50 mph should be 1977 rpm at the output of the transmission. 70 mph should be 2769 rpm at the output of the transmission.

So, that gives ratios of 1.012:1 for drive, and 0.7223:1 for overdrive. There are some variations in speedometer readings and tire diameters, and we know that drive is 1:1, so we can use that to find a correction factor of 0.9881 based upon the deviation between the calculated and known drive ratios. Applying that to the calculated overdrive ratio, corrects it to 0.7137:1

And that's a lot closer to the 4R100's claimed 0.71:1 overdrive ratio than to the Allison's 0.74:1.

Still too close for comfort, though, unless someone can confirm that the shift pattern is as I described at the top of this post. I definitely want to get a picture.
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post #6 of 10 Old 05-24-2012, 07:18 AM
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Mine shifts as such:

First,
Second,
Third,
TC-lockup in 3rd,
Fourth (with TC locked)
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post #7 of 10 Old 06-15-2012, 11:40 PM
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4R100 is four speed with OD. IE: a fifth gear as I understand it. I can count five distinct shifts and TC lockup. I don't recall if I have actually tried it, but disengage the OD button and count from a standing start. Bet you will count four shifts. If I am climbing a steep hill in OD and click it off RPMS will increase by almost 500, far more than TC unlock would be, but never counted down shifts from there. Never needed to.
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post #8 of 10 Old 06-15-2012, 11:53 PM
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Nope, 3 with a OD. Your just imagining a 5th gear.

2.71 - 1.54 - 1 - .71 and a 2.88 reverse

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post #9 of 10 Old 06-16-2012, 05:36 AM
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You have a 4r100 3 speed with OD. What you feel is Converter lockup.

That point varies with ECM programming but its generally anywhere from 46-60mph

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post #10 of 10 Old 06-25-2012, 06:05 PM
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tc can come on in every gear , 1st thru 4th, depending on load. It is a 4 speed with 4th being od plus tc lockup, makeing it feel like a 5 speed.
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