Andrew91PGT

Will the supercharged GTP transmissions with tap shift interchange with ours? Are there differences?

This being grand prix specific of course....

DavidGXP

iTrader: (14)

no. Starter mounting is different

LS1 Racing

iTrader: (15)

LS4-specific transmissions also have an upgraded gear train, which is stronger than the all the others.

BlauGXP

I'm sure this has been covered before but I couldn't find it in my searching, that is why do the GTP and other Supercharged 3800 folks seem to not have as much trouble with their transmissions as the LS4-folk?? I mean it's not like the SC3800's are low on torque, especially after a few mods. It seems weird...

LS1 Racing

iTrader: (15)

The L67 cars have about 40 lb-ft of torque less than do our LS4s out of the box.

Also, the LS4's version of the 4T65-HD has different valve body calibration that is biased towards smoothness in the name comfort as well as supposedly enhancing durability. At least, on paper.

As it turns out the execution of those upgrades turned out to be substandard, and as a result, we get grenading torque converters and leaking seals.

The interesting thing is, the LS4 gear train and axles are stronger than those found in the SC3800's trans. And those items are never the cause of failure. It's usually the converter relief valve or an internal seal that puts an LS4 in the shop.

LS1 Racing

iTrader: (15)

I should clarify, its the converter relief valve that causes the TCC to fail.

BlauGXP

So to that end I must ask, is our TQ Convertor relief valve different than that of the Regular (GTP-version) of the 4T65-E? And is there anything, besides regular trans services, that can prevent the relief valve from failing? i.e. TCM reprogramming/shift kits, etc?

LS1 Racing

iTrader: (15)

I need to be a bit more clear about this. The converter relief valve does not fail. The problem is, the factory-equipped valve bleeds off at too high of pressure. The result is, the torque converter clutch engages with too much pressure. This causes extreme wear on the TCC, and it ultimately fails. When the TCC begins to fail, bits and pieces of it begin to circulate through the transmission. These pieces begin to wipe out the clutch packs and cause excess wear on all the other parts touched by the fluid.

Not sure what the part interchange on the converter relief valve, but the recommended one is made by Sonnax costs about $4.95. The problem is, the you need to drop the cradle and pull the trans down to access it.

If your trans is still in good shape and not exhibiting any weird behavior, AND there's no material in the pan, then it may be worth the $300-$400 in labor (if you don't do it yourself) to have the valve replaced with the Sonnax unit. This is the route I went, though I also upgraded the valve body, seals, and had some clearance taken out of the 2-3 clutch pack.

I have a couple of threads that describe the whole cause and effect, as well as what I did to upgrade. You may want to check them out.

06MonteSS

and no... even the LS4 gxp and monte/impala ls4 trannies are different... due to the tap-shift...

the ls4 gxp tranny is not the same as the monte/impala ls4 tranny...

there are different internals...