99 Burb Drive Train Shake Problem

do not run it in overdrive unless you are in a nearly flat long stretch. the overdrive clutches are the weak spot in that 4l60e transmission. soon you will face a 2300 dollar rebuild. old john

Hello, ! You wrote on Mon, 3 Sep 2007 00:02:24 -0400:

MM> Thanks,

With best regards, snipped-for-privacy@comcast.net. E-mail: snipped-for-privacy@comcast.net

It is not so much the 4L60 being a weak design as it is as they ship them with too tall of gears in drive axles for false high EPA MPG ratings that do not pan out in real world and that strains OD badly at times. A 3.42 is pretty tall for a heavy burb with a SB and it has to strain a lot at times to maintain headway and hunts around. THis is also compounded by GM's knock sensor that retards spark to control knock before you hear it which reduces availble power in OD in warmer weather which can also make engine ruff at times under times a severe knock control. (the knock sensor masks true octane requirements at the expense of power and MPG) Make no mistake that without a knock sensor and ECM retarding spark that engine would rattle like it was full of marbles with 87 in it in summer. Retarding spark does stop knock but it really hurts power too. BTW, I have a old 89 burb that I bought new and I have run it for years on 93 and it runs sweet even after 180k plus miles. It has 3.73 gears and stock type tires and it pulls OD really well rarely downshift and will step right out in OD too when called on to do it. I averages 17 MPG or better on trips too using A/C.

----------------- TheSnoMan.com

The Dealership is adamant that the transmission is not causing the shake. I have the trailer package with the 3.73 gear ratio so the OD doesn't really strain at all. Code the service code reading of 5th cylinder missfire be caused by a sticky valve?

Mike

There's a lot of homework that can be done before teardown.

Generic list:

Swap injectors. See if the problem follows the injector. Do a compression test. Make sure all electrical connections are clean and solid Make sure the injector is receiving electrical pulses Pull all the spark plugs and compare their appearances

Thanks for the list of things to check before spending the $ on a tear down. One other item I forgot to mention earlier is that this shaking appears to occur when there is high manifold pressure.

Mike

Not so very likely, but, better check for a broken engine mount as well. And as the engine rocks in the direction opposite torque, make sure electrical connections aren't affected.

This could all be a wild goose chase, but these are easy compared to a tear down and you'd sure kick yourself if there was an easy fix discovered after a major expense.

Yes, a sticking valve could cause a missfire in cylinder #5. Easy 5 minute diagnosis with a labscope and a vacuum transducer.

More common would be failing intake manifold gaskets, a plugged injector or crossfiring in the distributor cap.

Tends to suggest a plug or injector misfire. Plug inspection is warranted and maybe new wires for plugs if they have never been changed.

----------------- TheSnoMan.com

Yeah yeah 93 octane - Oh Brother!

Have you changed the pinion seal on the rear diff lately?

Is this diagnosis with a labscope and vacuum transducer something I could do, or should I ask a garage to do it. I have access to an oscilliscope, if that is the same as a labscope, and could alsways buy a vacuum transducer. Just need to know what to hook it up too and what to look for.