GM transmission shudder?

My 99 GM shudders when it shifts into the overdrive gear. IT has approx. 84000 miles. At first I thought the engine was missing, but a machanic told me it was a tranny problem I could fix (at least for awhile) by adding some no-slip fluid. My questions are these: Do I have to drain some fluid out of the trans first? Is this really a good idea in the first place? And how much might this cost me to fix properly

To properly repair the shudder, the torque converter needs replaced. You might buy a lot more time by completely flushing the transmission fluid. What has happened is the dirt has gotton into the torque converter and the slippage is in the converter. It will eventually cause transmission failure and a rebuild will be needed. The anti-shudder is a friction modifier and is a short term fix.

Thank you! Is just replacing a torque converter cheaper than a complete rebuild?

Yes it is. You should still have all the old fluid flushed out to remove as much dirt and grit as possible.

Try replacing the fluid first. Drop the pan, drop the valve body, and drain the torque converter. You should need around 14 quarts to refill the transmission fully.

Use ONLY Mercon V transmission fluid. Never use anything with the words "Dexron III/Mercon" or "universal" in the name.

"...drain the torque converter..."

I need to do this. How do I drain my torque converter?
Thanks.
John

There is a little plug on the converter. Remove it and sit a while. It takes a long time to drain 8 quarts through the tiny hole.

msvatora---when the fluid is drained, you can purchase a can of transmission flush. You need to flush the transmission cooler and lines also. Most converters you get will be a rebuilt one. If you have someone rebuild it, it takes a lot longer than replacing it.

I own a 1999 GM with the same shudder. I first experienced the shudder when I drove a 1997 Ford Crown Victoria Police Vehicle. It seems that some of Ford transmissions for the CV and GM have this shudder. I dont know what the best fix is, But the mechanics at my former department (retired) used a substance or additive in the transmission fluid and it cured the problem, until the next time the transmission was serviced. I have now had my GM for about a year and can live the the shudder since I havent called over to my former work and found out the additive they used. There are no more early model vehicles of that year in the fleet. So the cheapest way to do this might be with this additive rather than a major repair job. Perhaps a Ford dealer may have known what the additive was that was used back then. Best wishes all.

The additive is called Dr. Tranny Instant Shudder Fixx (product page (http://www.lubegard.com/%7E/C-230/Dr.+Tranny+Instant+Shudder+Fixx)). Most people that use it have success. It is simply a concentrated friction modifier. This product will only work if the shudder is caused by worn out ATF friction modifier, and a fluid flush is the recommended way to cure it.

Remember, MERCON V ONLY! Never use Dexron III/Mercon or anything with "universal" in the product name.

There is a little plug on the converter. Remove it and sit a while. It takes a long time to drain 8 quarts through the tiny hole.

msvatora---when the fluid is drained, you can purchase a can of transmission flush. You need to flush the transmission cooler and lines also. Most converters you get will be a rebuilt one. If you have someone rebuild it, it takes a lot longer than replacing it.

My question is, how is this done "...flush the transmission cooler and lines..." ?
thanks.
john

The cooler you can't flush unless you can heat fluid to about 160 degrees F and pump through the lines, which will open the bypass valve and flush out the old fluid with new fluid. The lines will be flushed for the most part as they will back-drain into the transmission pan.

Don't worry about the cooler. The insignificant amount of ATF in the cooler will be mixed into the new stuff without issue.

The transmission flush is also sold in aerosol cans and attach to the cooler lined at the transmission. Just attach can, spray until clear liquid comes from the other line. There will be enough burnt and dirty fluid in the cooler that it needs flushed also. It will keep the cooler from functioning as it is designed and the problem will re-occur earlier than it should. The cooler is there to decrease the heat in the transmission. This comes from experience on over 400 Crown Vics.

Hmm I never heard of the aerosol flush cans. I trust your experience, but how do they bypass the temperature regulator valve on the ATF cooler? I imagine that without it being hot enough, it will flush the lines, but never go through the actual cooler because of the bypass valve.