48RE shifting problems "start in 2nd"?

[Txcummins2013]

Hey guys Merry Christmas!!! I have a 05 48RE that got a high performance valvebody done recently and ran great for two weeks but now I am getting a strange intermittent shudder from a start off in "assumed" 1st gear. What the truck does is usually after warmed up when I come to a full stop and accelerate again it seems like it is starting in 2nd and has I continue to accelerate it has a "shift" then it accelerates smoothly. It shifts into 2 3rd 4th etc normally after this little "bump shift". It feels like it's shifting into first after power is being applied but I cannot pinpoint. It does it about 2-4 in 10 dead stop accelerations. I thought maybe after the valvebody was installed it started flushing out crap from the last rebuild where I believe it was not flushed which would make sense if there is crap in the trans still. The trans shop said it is probably some funk that will pass and make it back to the filter or pan magnet. I put some Lucas non-slip in it and it has descreased the firmness of the bump and decreased its frequency. What do y'all think?

 

[rrowdy]

Not sure of your mileage but it sounds like the Governor solenoid and pressure transducer. You might as well spring for the heavy duty
GM governor solenoid, replace the pressure transducer and while in there, adjust both bands. I'd replace the output speed sensor also.
Your looking at about $200 less the fluid and filter.

Good luck!

 

[Txcummins2013]

New sensor and transducer. All else was done when valvebody was done two weeks ago. High pressure flushing out old crud?

 

[cerberusiam]

Doesn't matter if it was done 2 days ago, those parts are known to be bad out of the box and have issues shortly after install. If it truly is starting out in 2nd gear, either the transducer is producing a false reading or the gov solenoid is failing to set correctly.

If they used the stock style gov solenoid there are known issues and random failures. Get the DNC aftermarket gov housing and bigger solenoid to at least eliminate solenoid and gov housing issues.

The ONLY time to use Lucas or any other additive is when you are trying to save a wounded transmission and limp it home. The snake oil is not doing the trans any good if it was in good shape. At the same time you change out the gov solenoid and housing flush the system of the additive and get good clean ATF+4 in it.

 

[Txcummins2013]

Right I understand. The solenoid that I replaced with transducer were BW specifically for that reason. I bought new fluid yesterday i got on the highway yesterday and wouod not go above second. Pulled over turned off truck and started up again and all was just fine. All symptoms cleared up. That makes me believe sensor was clogged or had trash in it. Im planning to put in new fluid and see what happens

 

[sag2]

Before you just start changing parts, you would be wise to get a scan tool that reads governor pressure (DRBIII) or put a mechanical gauge on it to see what is actually happening. Then you can diagnose and replace the correct part the first time. And I would get it done sooner than later. If there was debris left in the cooling system from a prior failure it will end up somewhere you don't want it. Get everything flushed out and if needed replace the trans coolers to get rid of the debris.

 

[cerberusiam]

The solenoid that I replaced with transducer were BW specifically for that reason.

It depends on what you actually got when you say BW solenoid. Both the stock solenoid and GM style are made by BW. The GM style is simply a lot larger and better able to handle higher pressures with less drift. Part of the problem with stock gov assembly is the housing, the DNC piece addresses a lot of the issues along with providing the larger solenoid.

As sag2 said, if you put gauge on it and a scanner you will see what is happening and where the issue is. Sometimes it is a lot easier to just replace the pieces than source the tools to check though.

 

[sag2]

If you want to just check the governor pressure this is an inexpensive tool. The 0-140 psi may not give enough detail down low, but you could also use the fuel pressure test kit in a pinch and use a longer hose. Most of the tools the dealers have are already equipped with long hoses, but they aren't $20 either.

http://www.harborfreight.com/engine-oil-pressure-test-kit-98949.html

http://www.harborfreight.com/fuel-injection-pump-tester-92699.html

 

[Txcummins2013]

Yea i guess I am going to take it back to the shop Monday to have them go through it. It does it intermittently not constant which tells me its a sensor problem vs a hard part problem. Fluid change did not fix it although it is much much softer and immediate right now

 

[Txcummins2013]

Well i went ahead and replaced the solenoid and transducer and it most fixed it for like a day. Now its back.

 

[sag2]

Well i went ahead and replaced the solenoid and transducer and it most fixed it for like a day. Now its back.

It sounds like you have debris going through the system. Most of the time it comes out of the cooler(s) but if the transmission failed before and was not completely disassembled and cleaned it may need that now, along with cleaned or replaced coolers.

 

[Txcummins2013]

I replaced cooler due to leaky thermostat about 6 months ago. Got new fluid and filter shortly after that. Since then i have changed fluid and now custom valvebody went in so got new fluid. The fluid is pretty damn clean i do not see it as a debris issue. I think it is related to the higher pressure valvebody. Just changed the solenoid and transducer last week to fix and both were clear of material on exterior. Pulled apart transducer and was clean inside. Believe with circumstances solenoid gets flooded with pressures related to new valvebody. If problem with actual valvebody then as soon as installed should have done what it did correct? Is my logic sound right to yall?

 

[cerberusiam]

You need top check actual versus electronic pressure readings to see what is going wrong. Watch actual with a gauge and see what the transducer is telling the TCM it is seeing

Typically it is the transducer and the normal fix for that is replacing the VB harness. If you got a new VB that should have been done but don't rely on it. If you used the DNC piece with the GM style solenoid pressure should not be an issue. The OE part can have issues with higher pressures hence its removal.

Since it works for a day or so then back to same problem, it sounds like you have a wiring issue somewhere.

 

[Txcummins2013]

Understood Cerb (kudos to you btw, whenever i have problems i longingly wait for your oversight lol ) but when the valvebody first went in it took about a week to manifest the problems. When the transducers go out my ubderstanding is the computers chips or board inside burn out...when i pulled open the most recent transducer it was perfectly fine. I did order the GM solenoid to install cause I know it needs to be done.

 

[cerberusiam]

In that case you need to check the readings and see what it is doing setting gov pressure and what the computer is seeing. A lot of times unless you have a dead short they won't show burn marks but still won't work correctly either. They really are one big POS on an otherwise pretty decent transmission.

 

[Txcummins2013]

Understood. I know the transducer and solenoid work in conjunction to give the TCM the majority of its info to shift with but which does what specifically. I have trans temp lockup and slip monitored if i know which tells the computer that will help to tell me which is fried. I know the gm solenoid will fix my flooding solenoid problem which I think is the issue because pre valvebody i did not have these issues at all. But clarity of fluid and the truck shifting awesome for about a week leads me to exclude the idea of a sticking valve in the valvebody and no pre-existing condition makes me believe that the wiring harness should be fine. Is this also sound logic or not?

 

[cerberusiam]

Actually, the TCM sets the gov pressure for the hydraulic shifts. It is a feedback closed loop system, the transducer reads gov pressure the solenoid sets on command from the TCM. The TCM is reading the pressure and adjusting the solenoid to match. The transducer pressure sensor messes up and tells the TCM incorrect info to set gov pressure. The most common failure is it doesn't read bottom end pressures correctly, it tries to set gov pressure to its pre-set curve. You end up with 50 psi actual gov pressure with 0 mph wheel speed while the transducer reports 0 psi to the TCM, result is 2nd and 3rd gear starts.

The other way it reports high gov pressure so the TCM keeps backing off expected pressure and you get sticking in 1st gear until you wrap it way up and lift off the throttle.

You have to put a gauge on the gov circuit and a scanner on the OBD port and watch what is happening to see where the issues is. Both the OE transducer and solenoid are junk and have not gotten any better with production switching to lowest bidder now the transmissions are 8 years old. The DNC component at least takes the solenoid problems out then all you have to do is worry about the transducer. Might want to consider the BD transducer that is supposed help with life expectancy and flooding the gov circuit with pressure.

 

[Txcummins2013]

Oh wow ok. all that considered what are the dangers/damage associated with that little start in second? I assume its super hard on first gear? What about the rest of the gears? Is it ok to manual shift through first and then drop into normal drive for now?

 

[cerberusiam]

Automatic first is a sprag clutch on a planetary gear, starting in 2nd had no impact on 1st. However, 2nd gear is front band and that is another story. With a high TQ engine that translates to accelerated wear and stress on the component, front band, due to the lack of leverage in the ratio. Starting in drive is even worse as it really messes with the direct clutch pack which is border line anyway.

Manually shifting starting in first negates the potential for damage.

 

[Txcummins2013]

Ok thats what I wanted to know.