knocking noise from transmission and stalling

[santon]

Hello guys,
I purchased a new to me 2005 Trailblazer about a month ago. The previous owner told me that the transmission was overhauled recently. Indeed, the transmission operates quite good. However, there is a slight knocking sound from the bellhousing. I think that the flexplate is broken, probably during the installation of the transmission. How can I diagnose this? Also, is it possible to replace the flexplate without removing the transmission? For example, by supporting the transmission and using a pair of long bolts instead of the original bolts that connect the bellhousing to the motor? Could it be done with a jack and some jack stands?
Another problem that I discovered - the truck stalled several times. A couple of times it happened when I put on the reverse gear, and about 3-4 times it happened on the street light, when I removed the foot from the brake pedal and pressed on the accelerator pedal. It seems that it happens only when the A/C is on. I disassembled the throttle body - it was not so dirty. I cannot replicate the problem since then, but I am not completely sure that the cleanng of the throttle body solved the problem. There are no fault codes. What it could be and is there a possibility that the problem of stalling is somehow related to the knocking noise (potentially broken flexplate)?
Thanks!

 

[Mooseman]

I suppose you could pull the tranny back enough to access the flexplate, like you suggested, using a couple of long bolts to support it. You'd still need to disconnect both drive shafts.

Here's a post that gives a good idea of what to expect.

<FIXED> Lifter noise & dull knocking (bottom end?) troubleshooting

And I also forgot to mention, there's a second crack opposite of the one... @Sparky will do man, may end up asking Brandon's father to borrow his extra truck until I can install the flex plate next weekend. It'll arrive Wednesday apparently. Kinda nervous now seeing how it has two cracks. Also...

gmtnation.com

Before committing to replacing it, you should confirm first using an endoscope or just looking through the inspection holes. This post shows it in-situ:

<FIXED> Lifter noise & dull knocking (bottom end?) troubleshooting

Sound anything like this @Capote

gmtnation.com

Lower in that thread shows a video demonstrating the noise.

There was mention of failed trannys that may have caused the destruction of flexplates. In that thread's OP, he did replace the tranny after a catastrophic failure. So it's quite possible that when yours failed (by the PO), it was damaged.

 

[Mooseman]

As for the stalling, try resetting the PCM by disconnecting the battery or pulling the PCM fuses for 30 minutes. Stalling/rough idle with A/C on is a classic symptom of either a dirty throttle where the battery was disconnected or a cleaned throttle that wasn't reset.

 

[mrrsm]

The ATSG Comprehensive OBD2 Diagnostic Guide for The 4L60E,65E,70E & 4l80E,85E Trans

This is a VERY comprehensive 185 Page PDF Service Guide covering the OBD2 Diagnostics for The GM 4L60E, 4L65E, 4L70E, 4L80E and 4L85E Transmissions. It contains a great many contributions from the Members of the GM Automatic Transmission Service Group (ATSG) imparting arcane knowledge, tips and...

gmtnation.com

THM 4L60-E – ATSG (Automatic Transmission Service Group) – PDF Download

THM 4L60-E – ATSG (Automatic Transmission Service Group) PDF. This booklet contains general description and the procedures necessary to repair, overhaul, or

procarmanuals.com

 

[santon]

@Mooseman, mmrsm - thank you for your suggestions and the links. It seems that the problem of stalling is gone after the throttle body cleaning. Tomorrow I am going to check the flexplate.

 

[santon]

An update- I went to two different shops that specialize in transmissions. In the first shop, the mechanic does not think that the noise that I am hearing is related to the flexplate. He thinks the torque converter is bad. In another shop, the mechanic told me that this is probably the flexplate. I am no sure about their "diagnosis" since they did not try to see the flexplate visually. Both mechanics suggested to leave this problem as is. They say that I can drive for years with this noise. I don't like this and I would rather fix this issue. It seems that it's time to buy an endoscope to check the flexplate.

 

[Mooseman]

In either case, it's not a good idea to just keep driving it. A broken flexplate could all of a sudden leave you stranded. This is a pic of a failed 4.2 flexplate. It was just a matter of time before it completely let go:

If the torque converter is failing, you don't want to keep driving it. It will send shrapnel through the tranny and destroy it. Inspect the pan and fix it ASAP. I've seen enough tear downs to know what it looks like when a converter grenades and destroys the tranny however they were mostly the later 6 speed.

Pull the tranny and inspect the flexplate. If it's OK, run the engine without the tranny to make sure it's not the engine itself. I'd replace the torque converter if everything else checks out but check the pan for forbidden glitter and chunks of metal.

 

[santon]

Pull the tranny and inspect the flexplate. If it's OK, run the engine without the tranny to make sure it's not the engine itself. I'd replace the torque converter if everything else checks out but check the pan for forbidden glitter and chunks of metal.

Well, I am preparing myself to pull the transmission. Never did it but I may give it a try. If it is a torque converter, what is needed in order to replace it? Any special tools required?

 

[Mooseman]

Nope. Just pull it out, however you have to be sure the new one engages the pump tangs properly. While gently pushing on the converter, turn it until it bottoms out and the tangs are in the converter's notches.

If you don't, this can happen:

07 TB torque converter

So i just changed my torque converter on my 07 4.2 TB got everything back in and buttoned up but when i went to put it in gear the shift column moves but the truck doesnt. Cable also moves at the linkage underneath.. any ideas? Thanks in advance

gmtnation.com

Found this video that can be helpful and also shows how to install the TC:

This shows the entire operation of pulling the tranny out of a TB:

While you have the tranny out, check your cooler lines if they are rusty and could possibly spring a leak, it would be a good time to replace them.

 

[mrrsm]

However... There ARE Some "Special" Observations that need to be made:

What is WRONG in THESE Pictures?

Observe that there is a Pair of Aluminum Metal Tangs that encircle and elevate the Rear Heater Feed Pipe leading from the Driver's Side of the Coolant Outlet to the rear Passenger Side Firewall after moving UP and OVER the back of the space between the Firewall, the Rear Engine Block Face and the INSIDE of the 4L60E Bell Housing where there are Two out of Eleven 10.9 Long Bolts that marry the Transmission to the Upper Back of the Engine Block.

Look Closely at what happened here... Notice how the Tangs are Stuck IN BETWEEN THE OUTSIDE OF THE BELL HOUSING AND THE OUTSIDE OF THE ENGINE BLOCK? Once this occurred, it becomes IMPOSSIBLE to join those Two Surfaces together AND maintain a Proper Relationship between the Flex Plate at the Three10.9 Contacts Pads bolting it to the Torque Converter. Under the Stress and Load imparted by the Engine Crankshaft Torque and the actions of the Massive Torque Converter...The Thin Metal Flex Plate became DOOMED.

In the case of THIS Trailblazer, it meant BREAKING UP AND SHATTERING ONE FLEX PLATE INTO PIECES AFTER ANOTHER ... PER WEEK. Observe how the Right Hollow Guide Pin is MISSING and that at least THREE Bell Housing Bolts are NOT Installed!! The Bell Housing Flange became Dangerously Mis-Aligned as a result. Those Two Aluminum Heater Pipe Support Tangs MUST be situated on the OUTSIDE of the Bell Housing Buss Points where the Two Top Bolts can then pass through them both FIRST.

These images Illustrate What Can Go Wrong during the Transmission Installation if caution is not taken to Carefully Guide those Two Tangs OUT from in between the Front of the Bell Housing and the Rear of the Engine Block BEFORE Installing ALL (11) Bell Housing Bolts: