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The PCM nor scanner can read pressure No feedback from trans exist for this . What the scanner programmer sees are what the pressure should be in the AFL circuit not what the actual line pressure actually is , You can only get that info with an actual gauge
So I played around with the ATD-5550 and following this document, it seems my pressure in each setting are in check, so I guess that would mean it's not an electrical problem I am having...
Where do I go from here? I know I am taking it off again, but should I just go straight for a new (re-manufactured) input drum (since I won't be able to fix mine on my own)? Would I be better off buying a pre-assembled or should I take out my parts that I know are in order and put them in a new input drum/shaft?
Also, is there anything I should be worried about on the valve body? Should I/do I need to do the SONNAX upgrade? At that point, if there is already some damage there, should I just go ahead and get a new valve body?
I really don't want to take everything off a third time, so let me know if you guys have any suggestions for this second "rebuild." Thank you.
I'll give you a more detailed answer later this weekend, but in the mean time please post the pressures your found for:
* Idle in Park
* Idle in Reverse
* Idle in Drive
* Blip the throttle in Park
I hope you don't feel like I wasted your $35 and hope you at least finding this educational. If the pressures is OK, this helps us concentrate on the correct area of the trans. A pressure gauge is to a trans the way a volt meter is to the electrical system - you cannot really cannot diagnose one without its critical tool.
I can't remember the exact pressures, but I know from that chart that they were closer to the lower end of the spectrum for all tests that you told me to do. So for drive, park and neutral, they were a little higher than 55 psi. When we shifted from drive to 3, 2 and 1 and back up to drive, the pressure reading stayed the same. When we put it in reverse, the pressure shot up past 64 psi, maybe 75 psi at the max. Also, blipping the throttle in park had a slight increase in psi, but nothing huge.
They all fall in the range, so I assume it's not a solenoid I should be worried about. Should the pressures have been varying more, or is it normal for the transmission (as I had the truck running for only two minutes to do the test) to be at the lower end of the pressure measurements?
I have only tested transmissions with either the Transgo or Sonnax Boost valve installed.
I get 75 psi at idle in Park or Drive, but 150+ in Reverse and 200+ when I blip the throttle.
I suggest you try driving with the gauge attached and hanging e.g. from your outside mirror. A WOT acceleration should give you close to 200 psi.
If you don't get that, you might try replacing the PCS (Pressure Control Solenoid). If that doesn't do it, you might have a worn out pump.
Also, if it is easy to disconnect the trans connector, that will max the pressures at all times to see what the max pressure is.
Perhaps PerformaBuilt or one of the other pros can chime in here, but since you didn't get even 100 psi in Reverse or throttle-blipping, I think your pressures are low.
Last edited by mrvedit; 02-27-2017 at 08:52 AM.
Reason: Typo
Thanks for the input. I'm currently away from the truck until Friday and I know no one else is going to do these tests for me. Once I get back to it on Friday, I plan on taking things apart again. If I were to drop the pan and change the PCS, would that make a difference in the pressure if I tried it again the same way I did before?
At this point, everything seems like it would point to the seals on the input drum aren't working properly or the input drum itself isn't working. I know when I initially wrote this thread, I had said that the forward sprag must be faulty. It could be possible that I might've put the sprag in backwards when I took it apart, which is why it must not be shifting into 3-4.
I don't know, what would you recommend if I am just going to take it off and look through it all again? I am having the leaking problem again, so there's all the more reason for me to give everything a second look.
I don't think that worn seals on the input shaft would give you very low pressures; maybe if they weren't installed at all, but then there would be no forward motion at all.
If the forward sprag is installed backwards (as a bunch of people have done here), you have no forward motion in OD; you only have forward motion if you manually start in D1 and then manually upshift as the car speeds up.
We can give you a better idea of the problem once we know the max line pressure from either disconnecting the harness to the trans of a WOT run (however brief).
How many miles are on the trans and therefore the pump?
Can I try that test in the same spot that it's in right now? If so, I can see if someone will be able to take care of that for me at some point this week. All it requires is unplugging the green connection?
As far as I know, this transmission has been on the truck since it came out of the factory. We got it from the previous owner at around 150,000 miles with no transmission problems. I don't know if the transmission has ever been rebuilt before (I would hope the previous owner had gotten some work done on at 100,000 miles).
If you unplug the trans connector and fire up the engine, the trans will immediately go to max line pressure even in Park.
Unless there is a major problem, it is unlikely the trans was opened at 100,000 miles.
Assuming the pressure is low, there are several rebuild mistakes that others have admitted to which resulted in very low pressure:
* Forgot the filter and seal on the side of the pump (#231, #232)
* Forgot the o-ring seal under the pump slide
It is also possible that the pump surfaces are simply worn and are leaking pressure.
I know for sure I replaced everything inside the front pump. However I will post pictures of it again if and when it comes off again.
I've been having a leaking problem at the back of the transmission where it connects to the transfer case, could something be going on with the rear of the transmission where the leak is also causing pressure to be released I should let you know that this leak started up, at least I noticed that it did, in the summer, however the truck was driving fine until the fluid was dangerously low. I thought I had fixed this leak since the old piston towards the back had a crack, so I replaced it with a new one. It showed up again about two weeks after I rebuilt and started the truck up again.
It would say that it good news - your trans is able to make high pressure.
A little curious that blipping the throttle lowered the pressure - I would have expected it stay right at 190-200 because the PCM is not connected.
Next I would suggest re-connecting it and then driving around with the pressure gauge attached and recording what pressure you get under moderate and WOT.
(Unless PerformaBuilt or other pro has other suggestions.)
I hate to jump to conclusions, but wouldn't proper pressure readings lead me away from a potential electrical problem? I asked my brother if he could drive it around tomorrow with the PCM disconnected and let me know if it gets to 30mph or above since it would be in 3rd gear.
I am still skeptical of my input drum, I know that you had said it looked like it was fine, but with the grooved spots where the 3-4 clutch was, I was thinking that maybe the clutch is just simply slipping or not applying in the spot that it is because it's not a "tight" fit. I was thinking that as the fluid warms up, it might just seep around the clutch pack and through these grooves instead of applying the clutches as the air test did.
I just wish I had the parts in front of me or the truck with me in order to do the tests on my own. I'm just really anxious right now because I want to get the transmission off the truck before I get back for spring break so I can do the second rebuild within the few days I have and get it back on again.
Again here is the picture of concern, it's not very obvious, but there is some slight wear that I thought was concerning when I had first seen it. I marked it so you could take a closer look, I wish I had a better picture of it.
Actually an easier possibility might be the TPS. I never actually did check it since you first brought it up to me a while back. Would that be the problem that's still holding my truck back?
It sounds like from what I've read elsewhere that a bad TPS can keep GM trucks from shifting out of 2nd and have really low power. I know that the MAF went bad last year and sometimes that might go hand-in-hand with the TPS.
We now know that your trans can produce high pressure.
As I mentioned before, now re-connect the trans harness and monitor pressure while you drive. If it stays low, then mostly likely the PCM is commanding low pressure; and the most likely cause of that is a bad TPS or MAF.
I'm still inclined to believe the PCM is commanding low pressure and this caused your 3/4 clutch to fail prematurely.
There have been plenty of posts about people having premature 3/4 clutch failure even with sponsor built transmissions. They usually continue the "4l60e is crap" message even though they never checked their line pressure under acceleration.
I still stand with you have a pressure issue no line rise on acceleration or a leak in the 3-4 clutch or drum. The marks / scars on the drum would not cause your issue . And as mentioned no or low line rise due to a host of issues is a common cause of 3-4 clutch failure though the trans itself is generally blamed,
02-19-2017, 01:23 PM
