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Old 01-07-2010, 04:48 PM   #1
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Default rough shifts

I was driving down the road the other day very low rpms barely on the gas and it slamed into 2nd gear really hard and the again into 3rd not so much 4th its only done this 4 or 5 times but worse everytime,the fluid is full and good the tranny has 25000 miles on it so my question.Is there a sensor that could be going bad or should i just change the fluid and filter and go from there
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Old 01-07-2010, 04:55 PM   #2
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Well, let'* start with the easiest to check.

Have you checked to see if your front motor mount has a lot of play in it?

If that'* not it, then your PCS may be sticking.
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Old 01-07-2010, 08:05 PM   #3
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If your mounts are good. I would think a sticking shift accumulator. This is a easy fix and can be done in under 2 hours with basic tools. The only special tool is a inch pound torque wrench.
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Old 01-07-2010, 09:22 PM   #4
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thanks guys i will be sure to check those things
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Old 01-07-2010, 10:28 PM   #5
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Scan for codes!

Changing the fluid is maintanance, not a repair.
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Old 01-12-2010, 10:23 PM   #6
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the bonnie i cuurently have, the trans locked up at exactly 25001 and it was shiftin hard intermittently just before that.


bad thing was..... the trans was covered up to 25,000 miles.....it was one mile over
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Old 01-13-2010, 08:14 AM   #7
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The most common issue with these transmissions is the EPC or pressure soleniod. One of the ways many have found to bandaid the issue w/o pulling the trans out to swap the soleniod is to add a shift kit and a quart of Lucas stop slip with a new filter and refilling the fluid.

The codes that usually are posted from an EPC soleniod would typically not be stored. Therefore once a restart has occurred the car will usually shift fine the first couple times. Once it shifts hard again, look for a max adapt shift code w/o turning the car off.

Due to the pressure going through the shift accumulators, I can't see one sticking in the bore. When your trans slams into gear this way, it'* seeing 96 lbs of pressure.
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Old 01-13-2010, 11:36 AM   #8
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I am not an transmission expert, so please take my comments as coming from a Bonneville owner that had the same issues as you, and found a potential solution.

I think the PCS is a symptom, not a problem. As the transmission gets older it starts to slip, the slippage results in delayed shifts, and the PCS compensates by boosting shift pressure. The result of the higher shift pressures is harsh shifts, which is what you are experiencing. I could be wrong and the PCS could be malfunctioning, but I think the PCS is doing its job and is not the problem.

I had the exact same symptoms with my 2001 SSEi and fixed it by installing a shift kit. The shift kit provides crisper shifts so the PCS does not detect the conditions that cause it to boost shift pressures. No more harsh shifts with the added benefit of crisper shifts than the car ever had, even when new. I recognize this may be a band aid, and not a long term fix. If my transmission is worn to the point where shifts are delayed (without the shift kit) eventually it will wear to the point where it needs a rebuild. I may have just put off the inevitable, but in the meantime, the harsh shifts are gone.

I bought the shift kit from BillBoost for $50. It was pre-assembled into the accumulator and made the installation one of the easiest repairs I have ever done. You will want to do a fluid and filter change at the same time, but the whole procedure can be easily done in half an hour. You will need an inch-pound torque wrench to install the accumulator and the pan bolts (10 mm socket for both). If BillBoost doesn't have a shift kit for sale, try Danthurs. If neither of these guys has one available, you can get a kit on-line from Intense or ZZP but the kit will not be preassembled into the accumulator.

BillBoost, Danthurs and Purplehazier know far more about tranmissions than I do, so if they weigh in here and say my comments are full of the stuff grass turns into when it comes out the other end of the bull, listen to them, not me.
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Old 01-13-2010, 12:03 PM   #9
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Pretty close Roy..

Transmission experts and GM have determined the PCS to be the common failure. Something with it causes the pressure to be an issue and then you get the P1811.

I'm uneducatedly saying that it probably fixes the harsh shift because it limits the movement of the accumulator. A place where the fluid accumulates to then perform the shift. With a shift kit..the pistons are not allowed as much travel and therefore can't fill as much and slam the shift through. I'm learning and have rebuilt a couple so far..but I'm far from an expert.

for expert advice I call Dave Norris at Triple Edge Performance. He'* a great builder, has been doing high HP 4T6X transmissions for years, and is currently the outsoured builder for all Intense-Racing transmissions.
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Old 01-13-2010, 12:40 PM   #10
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Not to thread jack, but im wondering when Bill will have some more of those famous shift kits?

Last edited by Nobotada84; 01-13-2010 at 12:41 PM.
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