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 transmission was 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, the exhaust 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 the transmission 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.

ohyeahjay

Great post just wished I had this before I did mine over the summer.

LS1 Racing

iTrader: (15)

You have a slip off the line? Or can it be described as a slip-then-catch? This would be a situation where the engine would rev when trying to pull away from a stop, but the car doesn't move for a split second or so. Then it catches with a bit of a thud.

2005gxp

holy burnt fluid in the 2nd pic.

GXP25

iTrader: (3)

Good information and great pictures!

SigmaX6

So what basically this says is the magnet looses its magnetic pull and so forth the PCS solenoid collects the dirt and then transmission bombs later on?

I drop my pan once a summer and change the fluid and clean the magnet/pan and inspect what I can.

Couldn't hurt to install 2?

LS1 Racing

iTrader: (15)

This is a good precaution, however, the material we generally find circulating through our trannies is from the TCC. A Sonnax converter relief valve (about $5.00) cures the problem altogether. Unfortunately, you gotta drop the cradle to get to it.

EmersonHart13

iTrader: (3)

Drop the cradle? Yuck, is there a more info on that valve?

Clean94Z

iTrader: (5)

Do you have to flush the trans to clean put the solenoid?

GXP25

iTrader: (3)

If you want beaucoup problems, go ahead and flush that transmission.

LS1 Racing

iTrader: (15)

Well, the converter relief valve bleads off pressure so you don't engage the TCC too hard. The problem with the factory unit is, it bleads off at too high of a pressure, which causes the TCC to wear faster and fail, which is what usually wipes out our transmissions and shows up in the form of other problems.

As I mentioned in the earlier post, the trans needs to come out to get to it, according to Dave @ TEP.

DrJesus616

so what you guys are saying is that with any kind of slippage, or messed up engaging in the tranny ... ( like i just had )

there are really no simple fixes other than a fluid change, and hoping for the best ? because when i checked my fluid levels the other day after i got my first revvv....clunk ... it was a little darker than normal ... at 55K miles and ive had the car since 35K

man this winter is gonna kill my car ... i really need to find something else to drive and park her til it gets warm

Ill_Born_ss

Just so you know... I power flush my tranny every 25k, 18 qts,new filter,use only Mobil (blue container)specifically for our GM`s. Clear the TCM`s memory and dirve normally for the next week.
With more than 30 years experience, never had problems with a complete flush, if it is done correct and with a clean machine.
The WYNN`s kit for flush and conditioning is a must! Be sure they follow the instructions and theres enough gas in the car to complete it.

Clean94Z

iTrader: (5)

I dropped the pan yesterday on my 07 impalas ss with 36k. The magnet was solid covered with metallic slug. I cleaned the magnet and add the new magnet with a new filter. It took just over 7 quarts to fill. I will keep you updated if it happened again

LS1 Racing

iTrader: (15)

The metallic slag is most likely from your TCC. It's only going to get worse, too.

You may start to notice the torque converter locking and unlocking while cruising. Or, you might see the rev-and-clunk when trying to pull away from a stop.

Sucks, but it's only a matter of time.

ls4door

So if you have a constant locking of the tcc and unlocking of the tcc and its under warranty try and grenade the tranny right?

LS4_SS

i hate this transmission

LS1 Racing

iTrader: (15)

Actually, if the dealer can reproduce the lock-unlock problem they should rebuild or replace the trans under warranty. That's what happened my first time.

bxd20

Sorry for resurrecting an old thread, but the symptoms here describe what I'm going through with my 4T65E. Off the line, there is slip and then it catches with a thud and takes off.

No other shifting problems. And so far, I have not had TCC lock and unlock happening.

The other thing is, my "slip then catch" happens very sporadically. I drove a lot of miles on Sat, Sun, Mon, and 40 miles so far today. Sat was bad, happened numerous times. Sunday and Monday and so far today, not once. Similar load, driving, and temperatures outside.

I did my first pan and filter drop at 50,000 miles (Dex VI - this is a 2007 Buick Rendezvous), then again at 75,000, and about to hit the 100,000 mark at which point I was going to do one.

The problem started years ago at around 65,000 miles. So 30,000 miles ago.

It's kind of rare but annoying and definitely worries me.

I tried one bottle of Lubeguard Red, didn't make any difference.

Are line pressures the root problem? If so, would a trans tune to keep pressure at idle around 120psi be all I need perhaps?

Thanks.
Brian

91parkave

iTrader: (4)

Tuning and a shift kit take care of most of these issues