Help with 48re trans diagnosis

[BigFish]

I'm slowly working on figuring out what's going on with my trans. In each gear it feels like it's slipping until the torque converter locks. Once it locks it feels solid, but until it does, it feels like I'm powering through it with sufficient throttle. Just doesn't pull like it should.
When I look at the transmission pressure read out on my smarty touch, it's zero in park and in gear at idle. Once driving it come up some but not much... been a while since I drove it so I can't recall an exact reading.
The trans as roughly 30k miles on it, but it's never felt quite right and has become a worse with time. I assume it was poorly rebuilt.
Can anyone give me an idea what may be going wrong? Is it just toast and needs rebuilt, or is there a chance there's something in the VB, or elsewhere somewhat easily fixed causing it?

 

[Ozymandias]

I think you need to have it diagnosed hands on.
To many things can cause it and can't be pinpointed without pressure readings from the circuits.

But one simple thing can be - a disconnected or badly adjusted TV cable.
This you can check from the outside by yourself.

 

[BigFish]

I should have included a truck description, sorry. It's a 2006 so I don't believe it has the TV cable. Is there an equivalent adjustment on the later designs like mine?

 

[Ozymandias]

Okay, no there isn't, TV is controlled by the ECM then.

It seems that you have a problem with the line pressure as long as the TC isn't locked. And that makes sense as locking TC also raises the line pressure quite a bit, generating holding power to the rest of the Trans too.

I'm sure you can start throwing parts at it like pressure transducer, Governor valve and so on but it would really make more sense to diagnose it first with an external gauge and following the FSM and then fix what is broken.

Did your converter come with the Trans?
A bad converter would show very similar symptoms, powering through the converter generating heat instead of torque. I had that once with an aging TC and it felt weird.

But that guides us back to diagnosis the trans hands on.

 

[Ozymandias]

Unknowing who did the rebuild it is also impossible to tell you any pressures that show.
No pressure in P is totally normal.
Having it in D idling about 30psi can do, then steadily climbing according to throttle input.

My Suncoast shows 80 idling in gear up to 180 floored and locked.
Most of the time about 120 going down the highway.

 

[BigFish]

Understood.
Prior to baby number two, I had bought a list of parts suggested by a member here (Cerberus if I remember correctly) including a superior shift kit, gm style gps, maybe some servos and an accumulator... something along those lines. I have been tempted to start with installing the gps, maybe the rest of the parts and see of it helps. Lacking any intimate knowledge of auto trans inner workings has me wondering if any of that will make a difference.

 

[Ozymandias]

We don't know this before we diagnose it hands on. That's why I don't like the parts cannon.

Cerebrus is hands down very competent for Trannys but has the same problem as I have here - no hard facts to work with. With just a couple numbers we could be way more specific on the topic.

Like mentioned above, it could be as possible that with the transmission everything is perfect but the TC is not. And you don't want to tear a trnny apart only to find out the problem is somewhere else.

Who built your transmission?

 

[BigFish]

Unfortunately the guy I bought it from had his brother rebuild it when it let go not long after I got it in 2020. I haven't been able to get ahold of either of them when I tried. I'm afraid that's a dead end road and a lesson learned on me part.
Are the diagnostics you're referring to something that the average mechanically inclined guy could pull off, or should I be taking it to a shop and trusting their diagnosis?

 

[Timd32]

Can't help with the issue.

But Goerend is still one of the go to shops for parts and pieces for these rigs.

They don't do the work but if you read up on them you can get a back story of their business and support for the Cummins rigs.

https://goerend.com/p-35851-about-us.html

Then they have an installers page, which may help you find a competent shop to work with.

https://goerend.com/locator.html?geo=1

I've purchased a bunch of stuff for my 47RE from them.

 

[Ozymandias]

Unfortunately the guy I bought it from had his brother rebuild it when it let go not long after I got it in 2020. I haven't been able to get ahold of either of them when I tried. I'm afraid that's a dead end road and a lesson learned on me part.
Are the diagnostics you're referring to something that the average mechanically inclined guy could pull off, or should I be taking it to a shop and trusting their diagnosis?

I'd say any Trans shop with good reviews should be able to diagnose it properly.
We don't speak about a full rebuild here just basic diagnostic work.
But it needs someone that has the knowledge and the tools for it.

It can be done from yourself but still needs some knowledge and tools to it.
Basic you need is a mechanical pressure gauge that you can see in real time while driving what the line pressure does.
Also you need to check the slack of the bands, the need to be set factory spec.
All of this you find on YouTube how to do it.

That it is a shade tree rebuild with unknown parts in it doesn't help at all so the pressures can be in factory spec or way above, we don't know.

Want to hear my opinion?

I'd give it a try at a shop to do it, no more then 500$ - if they can't figure it out for this amount I'd go for a full rebuilt Trans with core exchange from a reputable company.
Sure you can try around, put some money in, then put more money in it and in the end maybe it works, maybe not.
There are way to many question marks in this Trans you have.
Just tearing it apart to figure that all out costs a ton of money by itself.

...Heck maybe they put a high stall converter in the build and that's the problem, we don't know.

So depending how much the truck is worth to you, the decision is yours.

 

[Ozymandias]

One more question - how big is the rpm drop in 4th gear at 3/4 throttle input when the TC locks up?

 

[BigFish]

I'm trying to remember... I haven't driven it much in a while, but I remember a pretty significant drop of a few hundred rpm when the TC locks even under "normal" driving, let alone 3/4 throttle. Is that an indicator of anything specific?

 

[Ozymandias]

Yes, it indicates how "loose" the Converter is.
So it can give us at least a hint where the problem maybe comes from.

For example, I have a "thight" low stall Converter, my drop is more then often less then a 100rpm, going all in it can be 300rpm.
Factory Converter the number where like 300 on 50% throttle to 600 at WOT.

Sometimes people choose a high stall converter to get faster off the line.

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One more thing you want to look for, from a dead stop - you floor* it, whats the rpm you reach before the Turbo spools up and the vehicle really starts to move away from the line?
Mine barely reaches 1400rpm before the TC holds it back. Which means I'm slow of the line because the Turbo doesn't light up right away.

* I really mean pedal to the metal here.

 

[BigFish]

When it comes to the rpm drop as the tc engages, I would put mine in the loose as factory or worse category.
As far as pedal down off the line, I'd have to give it a try and see, but if I put it to the floor from a stop, I don't know if it would hold at a stall point like your saying or if it would just Rev until it started moving if that makes sense. It's really pretty slushy that way from what I remember the last time I took off in any kind of hurry in it.
I'll have to try to get a video of the guages when I try that the next time I fire it up and share it here.

 

[Ozymandias]

Yeah, the interesting point at which a rpm it stopps going any higher.
I don't think it will Rev up to 3200rpm red line.
Depending on what numbers you bring back we might have found your problem.

 

[Timd32]

Have you replaced the fluid, if a person was to cut corners paying for ATF+4 would be a low hanging fruit to mistakenly try to save a few bucks. It's always been a more expensive option vs other basic fluids since it's a full synthetic.

But you need the right qty of fluid, any fluid certified to ATF+4 is great stuff, all brands.

Some custom builders use specific fluid but they build the parts and VB to use the features of those fluids.

 

[BigFish]

So I went out and played around with the truck a bit since I got off work early.
Trans fluid is pinkish red, not brown or burned smelling.
Trans feels alot better than it did the first time I drove it a month or so ago after it sat for so long, but still not like I think it should necessarily.
I took a couple of videos of taking off from a stop, and the rpm drop when the tc locks. I took them close to home since tags are expired, so I used tow mode to make it lock in 3rd instead of 4th but hopefully it'll still five some info to those that know more than I do. I'll try to post them this evening.

 

[BigFish]

Ok Ozy. Here is a video of taking off from a stop, I didn't do full throttle from stop because to be honest I'm deathly afraid I'll break something, but I rolled into pretty fast in the short video.
The other is turning onto a main road and putting it probably close to 3/4 throttle and holding it there until the TC locks in 3rd.
I had to do it in a 45mph zone close to home hoping not to get ticketed for my expired tags lol.

 

[BigFish]

This is another one I recorded before backing out of the driveway. Someone mentioned that I could test the torque converter stall point to make sure it was functioning by essentially power braking it and see where the rams stop rising. I looked like the stopped close to 2k. I don't know what that tells us other than the stall point, but here it is lol.

 

[Ozymandias]

Oh well, that's not what I hoped for...
From the short snippets it looks almost like a factory Converter to me.
Which isn't great but works like it should.

So we are back to post #10 from me above. So sorry for that.