Hey everyone, I’ve got an 03 Sierra 2wd 5.3/60e. The truck has 243k miles, I have no idea if the trans is original or has ever been rebuilt. I’ve only put about 20k miles on it.

When I bought the truck it had a pretty bad flare on the 2-3 shift. I knew going in I’d probably end up doing the trans eventually. I had a vette servo laying on the shelf so I put it in there. It helped out a lot but I still have some issues. I’ve done a lot of reading just trying to educate myself on these transmissions and from my limited knowledge it seems like the hard parts might be ok.

If I take off with light throttle everything is good. TC lockup is pretty soft and slow.

Moderate throttle I get a nice 1-2 and sometimes a 2-3 flare. 3-4 and TCC seem pretty good.

Heavy throttle is harder to describe. The 1-2 isn’t as crisp. It’s like it feels like it shifts good at first but then I feel a bump like maybe the band hasn’t applied all the way. The RPM never shoots up when this happens. I don’t go WOT often but it usually makes the 2-3 shift pretty decent when I do.

I may be way off here and you may say I need a full rebuild which is probably true, but does this sound like it could be a servo travel issue? I’m thinking about ordering the transgo HD2 kit and doing the fixes to the valve body in the common leak spots just to eliminate that potential problem. I’d also like to check the servo travel and I think that kit comes with shims if the pin isn’t long enough.

I hate to throw money at it without knowing it will help but I’m guessing if the trans craps out I can pull the shift kit parts out for the next one. It just seems like it might have a fighting chance because it never slips at all when it’s in gear, and the issue hasn’t gotten any worse in 20k miles. I appreciate your advice and hopefully I can squeeze a few more miles out of this thing.

 

Sonnax 77787-02K will help.
Sounds like band clearance too wide for you.

As for the shift kit, I would pass on the HD2 and do the following:
LB1 boost valve from Sonnax
Sonnax O-Ring End Plugs 77964-08K
Sonnax Abuse Valve bore plugs 77754-21 OR Transgo Abuse Valve Bore Plugs 4L60E-ABUSE-BP
Use a piece of brake line, cut to length, to block both the 3-2 downshift and 3-2 control valves inboard
for the 3-2 downshift, take the spring out, and place it INSIDE of the AFL spring
Throw away the 3-2 control spring
Remove the TCC reg valve lineup, take the inner most valve, flip it 180 degrees and re-install it backwards. Reinstall the rest as it came out. This will be ON/OFF TCC
Block the 4th accumulator with a 1/4" checkball driven into place OR my preferred method is to block with a 5/16-18 setscrew. Omit the piston. Take the 4th accum spring and put it on the opposite side of the stock piston for the 1-2 accumulator.

So, the 1-2 accumulator will go separator plate, spring, piston, spring, housing.

Drill the separator plate holes also.
I usually leave the 1-2 hole alone when changing the accumulator.
2-3 Drill .105
3-4 drill .093
Band release drill .085
Transgo shows two small holes in the bottom left of the plate...do not drill

 

You could have too much servo travel, a worn out 3-4 clutch, or both. If you do build the transmission, the above recipe is a pretty good one. Follow that and you'll be just fine.

One other thing that you can check, which I have seen a TON on Silverados/Sierras is to grab a scan tool that will read live data and check your long term fuel trims while driving. If they are running at a very high value (+18% , +19%, +20%...somewhere in that range), you likely have a dirty mass airflow sensor (MAF). This will affect your line pressure. The PCM uses the MAF signal as part of its load calculation to set line pressure. If your sensor is dirty, the signal will be skewed, and your line pressure will be lower than it should be. I see this a ton with K&N style air filters when the oil from the filter gets on MAF wires, which is immediately downstream of the filter. Cleaning the MAF is simple, but you need to be very careful. Those wires in there are tiny and easily damaged. Get some Q-tips and some isopropyl alcohol. Then remove the MAF sensor and use the Q-tips dipped in the alcohol to clean the wires inside the sensor. They will likely be very dirty on the upstream (thinking in terms of airflow) side of the wires. Carefully swab the wires until the Q-tips no longer come back dirty. Reinstall the MAF and drive the truck. It's kind of fun to watch the short term trims immediately start pulling fuel back out, and the long terms start clicking back down to where they're supposed to be.

 

Thank you both for the advice. I almost cleaned the MAF sensor the other day just for the heck of it. I doubt it has ever been done. The truck does have the stock intake with paper filter, but still at 20 years old and a quarter million miles I’m sure it’s due.

I do plan ordering HPTuners very soon so I’ll do some logging then. I’d like to buy a core transmission and build it myself. I’ve always wanted to try it and I think it’s something I could pull off especially having a resource like this forum. For now I’m going to take the advice here and see what happens.

Thanks again,
Joey

 

Indeed, be very careful with reusable engine air-filter oil treatments...

When in doubt, clean the MAF sensor after servicing the reusable engine air-filter with oil.

 

I cleaned the MAF yesterday. The q-tips had some black gunk on them so I figured maybe I’d get some results. Turns out it helped quite a bit. It seemed to clean up the 2-3 mostly and made the 1-2 a little firmer. It could be in my head but it seems to idle smoother. I’m interested to see if I gain any mpg on my next tank. I normally average right at 16mpg (hand calculated) which I feel is a little on the low side for my commute.

Now that’s out of the way I’m gonna check my band clearance. Do I literally just push the servo cover in until it stops and measure the distance?

 

That's how you do it.

 

Yup, just a ruler to estimate how much the cover moves in when pressed with e.g. a crowbar.
Spec is .075 to 0.125 (1/16 to 1/8"). Around 0.175 (3/16") you likely will start to have slippage. Around .250, the band may no longer engage.
Some people have successfully welded a blob on the end of their servo pin and gotten a useable amount of extra life out of their trans.
A longer servo pin (77964-08K) does the same, but might require more install/remove iterations as you will have to grind it down to the length you actually need.

 

Glad it helped. I clean the MAF on every Silverado/Sierra build that I do. You may not see much at the gas pump, though. As your MAF collects dirt during normal operation, and its signal slowly (over time) begins to skew, the ECM is also watching the O2 sensors and making corrections to its fueling maps via the short term and long term fuel trims. The problem for the transmission is that its calibrations do not get these same corrections, and you can end up with a normal running engine (via the fuel trim corrections), but a transmission that is running as much as 18-20 psi (or possibly more at times) lower than it should be for a given throttle setting. The fuel trims will continue to correct fuel up to somewhere in the 24% range (the exact threshold escapes me right now), where the ECM will finally set a lean code. But 24% ends up being quite a bit of a discrepancy at the transmission, and it can (and has many, many times) lead to operating issues and, ultimately, transmission failure.

Cheers!