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Old 05-31-2009, 10:02 PM
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4l60e - No reverse after rebuild - Low line pressure?

Good evening all! I'm crossposting this from another forum as I've seen a lot of transmission questions answered here.

First of all, a 'cliff notes' since this may get long: Had transmission rebuilt, installed it, car has slightly slugish shifts through the Drive gears, but DOES shift, however I have no reverse. Is a 2wd 4l60e inside a 1996 Impala SS.

Onto the long version...

I pulled the motor and transmission due to a pretty nasty grinding noise in 1st and Reverse, had the transmission rebuilt with new clutches and steels, Beast Sun Shell, and replaced (with new) a few planetaries that were chewed up. I got everything installed, and after getting the fluid poured in and whatnot, going through the proper transmission initial startup guide in my repair manual, I took off. The transmission shifted pretty slugishly through the 2-3 gears. Also, upon returning to my shop (only drove around the block) I find I have no reverse (car just acts like it's in neutral, just revs).

So, I've been researching and I read that it may be caused by low line pressure and a quick test is to unplug the Throttle Position Sensor and take the car for a short quick drive. I unplug the sensor, and sure enough, reverse works great, shift through the gears (only got into 3rd) and it's pretty damned firm, but it does shift quickly and well. Obviously though, I can't drive around without a TPS, so that doesn't fix it.

Another test I've read was getting the car into about 20 mph then shifting into low/1st and see if theres signifigant engine braking. Now I'm going to go out and test this myself tomorrow, but my father drove the car and said he shifted into 1st and there was some pretty good engine breaking. So this should signify that the reverse clutches are not dead correct?

Follow up question to that, what's the best way to do this 'engine braking' test? Just get to 20mph in overdrive and shift all the way into 1st? Should I go through the gears? I don't want to mess up the transmission (anymore than it already is).

I'm stuck right now since it's 10pm, but I'm going to buy/borrow a scan tool and see if there's a 'low line pressure' code thrown on the PCM in the morning, but all these symptoms should signify a low line pressure correct?

Now, I know for 96 and some 97 4l60e transmissions there was a wiring harness upgrade/retrofit (GM Part# 12167310) required due to a faulty ground, but I'm under the impression this fixes soft shifts in the forward gears, would this fix the reverse at all? Also, the car (before I ran into the transmission problems) drove and shifted fine it seemed, just seems strange that out of (seemingly) no where the wiring needs to be fixed after being fine all these years, or is it possible the rebuild process 'broke' that ground and NOW needs to be fixed? (Ok, actually I think that's exactly what happened, but if you could answer, that'd be great, settle an argument/bet between me and my father haha)

All fluid levels on the car (engine and transmission) are correct, no leaks.

When the transmission was rebuilt (and assuming that my rebuilder is telling the truth) it was actually rebuilt into a 4x4 4l60e case (why, I'm not entirely sure, I'm still bugging the rebuilder to tell me why). He claims he used every single nut, bolt, wire, etc, and that the two cases are identical (except the 4x4 being a little 'beefier'), however I'm curious if this would cause any [additional] problems assuming that he is correct in saying every part was swapped over.

The only other thing I think is worth noting is the fact that if I put the car into reverse, let it sit (with my foot on the brake) for a minute or two, then let off the brake, the car will very VERY slowly move backwards (like, at a [small] fraction of the speed it should be moving). Along with the fact that reverse worked when I unplugged the TPS, this does mean that reverse WORKS, just not being engaged for some reason right?

Terribly sorry this got so long, just want to cut down on "did you try this?" posts and save everyone some time hopefully. Thank you all for any help you can give, I'll try just about anything I can.

-An extremely impatient young'n who just wants his fun cruiser back

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Last edited by reddeth; 05-31-2009 at 10:07 PM.
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Old 06-01-2009, 12:43 AM
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Quote:
Originally Posted by reddeth
Now, I know for 96 and some 97 4l60e transmissions there was a wiring harness upgrade/retrofit (GM Part# 12167310) required due to a faulty ground, but I'm under the impression this fixes soft shifts in the forward gears, would this fix the reverse at all?
It fixes 'erratic pressure rise', which is consistent with the sluggish shifts AND lack of reverse. It takes a lot of pressure to engage reverse. It's a shift also.

Tap on the car's ECM and see if it changes anything.

Was the pump rebuilt along with the rest of it?

Has anybody checked the pressure in all ranges with a gauge?

Was the EPC solenoid replaced? Some call this a 'force motor'.

That's all I got.
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Old 06-01-2009, 12:52 AM
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First of all, thank you for the reply.

Second, when you say the cars ECM, I just want to make sure, you mean the cars 'brain' under the hood? Not anything on the transmission right, but the actual cars computer that all the wiring harnesses get routed into? I just want to make sure I'm on the same page here, no sense in beating on something that doesn't need it haha.

The pump should have been rebuilt, I'll check with my rebuilder when I talk to him tomorrow.

I'm trying to acquire a gauge, but the scan tool did register a low line pressure. So I'm not sure what pressure it's at, but it's low. It's high enough to shift through the drive gears, but not high enough to shift into reverse I guess.

I've no idea even WHAT an EPC is, I'll ask tomorrow.

As for the wiring, I believe it can be done in the car with the pan dropped correct? I may wind up just trying the wiring first, since it should be done anyways. If that doesn't fix it, I'll drop the transmission and take it to the rebuilder, thank god for warranties.
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Old 06-01-2009, 08:33 AM
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Quote:
Originally Posted by reddeth
Second, when you say the cars ECM, I just want to make sure, you mean the cars 'brain' under the hood? Not anything on the transmission right, but the actual cars computer that all the wiring harnesses get routed into? I just want to make sure I'm on the same page here, no sense in beating on something that doesn't need it haha.
It has the blue, red, clear and black connectors. That part number you posted contains a jumper lead and instructions that fixes a grounding problem between the boards internally in the module. Not sure where this 'VCM' is located on the Impala. (vehicle control module)
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Old 06-01-2009, 02:08 PM
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Ok, just a quick update. I had to move the car out of the shop to get some room to change the chain on my supermoto. Anyways, I figured I'd start the car up, help get some oil through it and having power steering is nice on a car that big. So I start pushing and figure "Why the hell not?" and try putting it into reverse, surprise, it moves!

Excitedly I took it for a test drive (just around the block), at first it shifted perfectly, then it started to shift softer and softer, by the time I got back to the shop I had no reverse again. I'll test later when I have more time, but it almost seems like there's plenty of line pressure at startup but once the car shifts a few times it looses that pressure?

That, or it really is intermittent and I do need that wiring fix. My rebuilder mentioned that he will try to come down to my shop and take a look at the car (as I don't really trust driving 30 minutes down a free way with line pressure issues) tomorrow, I'll see what he says, but I'll probably try the wiring fix and see if it works.

Last edited by reddeth; 06-01-2009 at 05:51 PM.
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Old 06-03-2009, 09:12 AM
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Alright, probably the last post till it gets fixed, since I'm out of ideas. I think I may have a bad pump, in that, it was never able to pump enough to get the line pressure built up to shift into reverse. I say this because slowly I've lost all drive gears to, and even now when I unplug the Throttle Position Sensor (which should put the pressure control solenoid to allow max line pressure) I've still got no reverse or any drive gears.

I also did a quick test of checking the transmission fluid with the car off, then while the car is running, fluid level didn't seem to move a bit.

I've got a code scanner that I'm borrowing tonight and a line pressure gauge is ordered, so we'll see if that does it. Just sucks if it is a pump, was kind of hoping it would be a wire I left unplugged or something

And sadly that service bulletin about the bad ground didn't fix anything, though I'm glad I did it.
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