register1987

Just put a freshly rebuilt bench tramsmission in my 01dumsilverado. It shifts from 1st to 2nd just fine but will not shift into 3rd. It's not throwing any codes. I Took it to a shop and they put it on their computer. He said it was showing question marks for the mlps. So I bought a new one and had him put it on. It's still doing the same thing. He said he has never seen this before and neither has the guy who rebuilt the transmission

I know this isn't a chevy forum but there seem to be people on here that know a lot about the 4l60e transmission

coryforsenate

iTrader: (1)

What does it do when it tries to shift into 3rd gear i.e. rpm's jump up suddenly?

Can it go into manual 3rd?

Experienced folks, is it possible for one of the solenoids to be bad without throwing a code?

register1987

It doesn't even try to shift into 3rd. Acts like I have it in '2' rather then 'd'

No it won't go into manual 3rd

bbond105

When your shop had their computer hooked up to your truck did they look to see if the trans is being commanded to shift? If it is not being commanded to shift you most likely have a sensor or some kind of electrical problem. If it is being commanded to shift and it doesn’t shift then you have a problem with either a shift solenoid, valve body or the 3-4 clutches.

I will have to check my manual when I get home for which solenoid is for the 2-3 shift and get back with you.

coryforsenate

iTrader: (1)

Does it shift harshly into 2nd?

Do you know what the guy replaced when he rebuilt it?

What bbond105 suggested would really help narrow down electrical vs mechanical.

coryforsenate

iTrader: (1)

It's solenoid B, the one closest to the force motor.

register1987

He said that he couldn't see it commanding any shift changes. Not even the 1-2 shift it does make. As for it shifting harshly. I don't know cause I had him put it in and he is the only one who has test drove it.

bbond105

In 3rd gear both shift solenoids are off, so it’s not a shift solenoid causing your problem. Now you need to determine if it is being commanded to shift. You may need to take it to a different shop for this. It sounds like your shop maybe over their head.

register1987

He said that his scan tool shows question marks where it should show the mlps status and that it doesn't show a demand for 1st or for 2nd even when it shifts to 2nd.

bbond105

His scanner is not reading correctly or maybe your PCM or TCM, (which ever one you have), is bad. I would find someone who can diagnose your problem. Why was the trans rebuilt in the 1st place?

register1987

3-4 clutches burned up it would Rev like in neutral when shifting to 3rd and there was a lot of clutch material in the pan.

This is the third rebuilt transmission I put in it in a month. The first one did like this one and wouldn't shift out of 2nd. They swapped it out for another one. When they were taking the mlps off the side they broke it so they gave me another one off a different used transmission. My transmission guy claims that this transmission is currently in another vehicle working fine and that he didn't do anything to it. Claimed that it wouldn't shift due to a faulty mlps.

The seccond one worked great until it over heated and broke something inside cause I didn't get the cooler properly flushed and it was mostly clogged off.

When I got transmission number 3 I took the truck to a local repair shop and paid him to flush all the lines and install the transmission so I knew it was done right. When it wouldn't shift out of 2nd and he said he couldn't see the mlps I had him put a new one on but that didn't fix it so now I'm at a loss as to what to try next

mrvedit

First the MPLS (Manual Position Lever Sensor - I had to look it up) is not even related to trans operation; I don't even have one. It often acts as the Park/Neutral safety switch when starting, turns on the backup lights in Reverse, and tells the PCM whether you are in Park/Neutral or Drive for selecting slightly different Idle tables.

The Manifold Pressure Switch (MPS) inside the trans communicates to the PCM whether the shifter is in [D1], [D2], [D3] or [OD]. A good scanner can read this position.
From the descriptions and symptoms so far, I suspect the MPS is defective or has a wiring problem. It is relatively easy to replace. That would exactly explain why "Acts like I have it in '2' rather then 'd'".

IMHO a good shop should quickly figure that out.

Sometimes yes. The PCM mostly checks for electrical continuity, although it also checks for a change in RPM after the commanded shift.
The tiny filters on the shift solenoids can get clogged. Solenoids can stick. I recall a thread where the OP had dented oil trans pan enough to hit and affect a solenoid.
At $12 a piece, IMHO the solenoids should be replaced anytime the pan is off and they have more than 100K miles on them.

bbond105

You can try this to see if the 3rd gear clutches are working. Unplug the big wire connector on the right side of the trans and test drive. By unplugging this connector you will cause the trans to go into fail safe mode. When you are test driving it be gentle because the trans will start off in 3rd gear and will not shift. Once you get some speed up, around 35 to 40 mph, you can get a little rough with it. If it takes off and does not slip this will let you know that the problem is not with the hydraulics and 3rd clutches of the trans, this would point to something electrical.

As mrvedit and I have said a good shop should be able to quickly figure out what is going on.

mrvedit

Please explain.

bbond105

Sorry meant to say gentle.

register1987

Can I just take the wireing harness/mps out of the one that was shifting fine and put it in this one? Does it require more then dropping the pan and pulling some bolts?

Will this work even if my mps is messed up? And if it doesn't work would that point to a valve body issue or something else?

Also will the 3 led test for gear demand work on this transmission?

mrvedit

The MPS (Manifold Pressure Switch) is easy to replace.
The harness is a bit more difficult - you probably need to remove the 1-2 accumulator, the PCS (Pressure Control Solendoid) and then press and twist a large 1-3/16" (?) socket over the connector to release its tabs. Also unbolt the TCC solenoid.

I would just start with replacing/swapping the MPS.

I don't know the "3 led test for gear demand"; I've been fortunate to always have had HPT available for testing the trans.

register1987

The three led test is in the stickies on this forum. Basically you hook the negative lead to each wire for the two shift solenoids and the tcc solenoids. Then you hook the postive to a 12v source in the cab and watch the lights to see what gear the pcm is demanding.

Is there a way to test the mps?

How do i change the mps out?

mrvedit

I couldn't find it in the stickies, but see post #7 here:
https://ls1tech.com/forums/automatic...-into-3rd.html

Since that is a multi-hour project, I would suggest just borrowing a scanner or having a local trans shop check it out for you.

The MPS has membranes and o-rings; problems with those are often obvious. I suspect an ohm meter and pressing on the membranes with your finger would work for testing..

Pretty simple.
Drop the pan. (may want to first pump ATF out via the dipstick tube.)
The MPS has an electrical connector and is held in my 5 bolts (3 long valve body bolts and 2 shorter bolts holding it to the valve body.)
Swap in a new one and tighten/torque the bolts to 8 ft-lbs. (96 in-lbs)

register1987

I will be headed up to work on my truck probably saturday. And I was thinking about trying things out in this order.

1] unplug harness from trans and see if it starts in third.

2] if it does then change out mps.

3] if that doesn't work then start testing the wiring harness.

Does that sound like a good way to go or should I try something else. Radio shack is going out of business near me and I won't be able to buy any leds to do that test. And the only transmission shop in town is the one that can't figure it out.