Thread: Transmission slipping from stop?? Read this

I found an article on the dreaded banging from a stop delayed engagement issue. I figured that since there are numerous posts about this I would post the link here.

http://ls1tech.com/forums/ls4-perfor...ement-fix.html

Here is the text from the article. None of this is mine, it is all borrowed and credited to Boattail455.

"A little while back I posted that I noticed the transmission in my Buick slipping off the line. Being a mechanic I did some research and dug up several different causes for the scenario.

The Super's transmission shifts very smooth from the factory, almost unnoticeable. From what I've read, to achieve a smooth shift the line pressure is reduced. Sometimes a waveplate just isn't enough to cushion the engagement of a clutchpack. Naturally I wanted to check the line pressure in my trans so I can continue onto pinpoint diagnosis. First I checked the line pressure with the Tech 2 at work.

Minimum line pressure in P R N is 79-101 psi. The scan tool will show this value in amps. 1.0 amp is the spec for minimum line pressure in all gears. D4 D3 D2 line pressure is 74-86. D1 is 146-187. If you have the opportunity, you should take the Tech 2 with you on a test drive and try to duplicate the problem. I didn't have time so I just recorded D1 line pressure @ .78amp at 93*F. I really should have taken it out on a test run to watch the values through all the gears once the transmissionwas warmed up. But you'll see later on why I didn't need to.

If you don't have a Tech 2 or access to one, there is a pressure test port on the case of the 4T65. On v6 cars its easily accessible. On v8 equipped cars, theexhaust pipe that crosses over the trans blocks it almost entirely. You could probably get the plug out, but there isn't enough clearance to thread a pressure gauge fitting in.

I continued to dig and found several TSb's. The TSB that best fit my problem is bulletin no: 08-07-30-040B. The summary is that a new transmission pan magnet was released because the old magnet can become "saturated" with metal shavings. Once "saturated" it can no longer collect metal shavings and the shavings go to the PCS solenoid. The solenoid is magnetic and thus will collect the shavings, this throws off the readings and decreases line pressure. "When checking PCS line pressure and it shows that the line pressure is lower than required for a given current at the PCS or the transmission oil pan was removed, only then should thetransmission oil pan magnet be upgraded."

My Super has 71K miles on it and I planned to do a transmission service anyway so this worked out. I called up the local Chevrolet dealer and ordered eight (8) quarts of Dexron VI and a filter. I talked to a service writer about my issue and asked if I did the work will GM still send me the new magnet free of charge. The dealer was more than helpful and ordered the magnet free of charge aswell. For reference here are the part numbers and price.

Filter kit #24227477 $32.23
Dexron VI #88861003 $6.47 (each)
Magnet #29535617

Start by dropping the pan, I removed all but a 2-3 bolts towards the front of the pan. It wasn't really messy but it will take a couple minutes to drain out of the pan. After dropping the pan I inspected it for burnt fluid, clutch material, how much metal is on the magnet, etc. The fluid was burnt and the magnet had an average amount of metal on it. After a quick trip to the parts washer I was ready for reassembly. For the 4T65 the TSB will have you keep the original magnet in it's "corner", behind the raised portion of the pan. The second magnet is installed on the new filter assembly. See photo for location. The gasket is reusable, just rinse and dry. Pan bolts torque is 13 ft lbs. Refill with Dexron VI, mine took just over seven quarts. I used GM Dexron VI. Its been over a month and 1,700 miles without any slipping.

Just a heads up, the dealer won't perform this TSB under warranty unless you request a transmission service where the pan gets dropped. The TSB was very adamant about this. The magnet should only be replaced if the pan is being dropped under normal maintenance or diagnosis of a customer concern requires it.

Hope this helps someone else out. I'm by no means an expert but stuff like this interests me alot."