Severe shudder when applying throttle
Thread Starter
Racer
Joined: Sep 2010
Posts: 325
Likes: 8
From: Princeton Jct. New Jersey
Severe shudder when applying throttle
I'm trying to get my '84 (automatic, Z51) back on the road after a few years of sitting idle. After fuel pump, tires, battery, etc., it runs relatively well except when moving. If I apply the throttle I get a very strong vibration or shudder which stops when I ease off on the pedal. She accelerates/runs ok up to about 30 mph and will be fine at various constant speeds (I haven't been over 50 in these 1st test drives), but will shake the whole car when accelerating from one speed to another above 30. I'm guessing it might be the torque converter slipping/engaging but not sure. There is also a fair amount of torque steer when I go on and off the gas so I suspect the rear alignment and thrust angle may be a bit off too. Any thoughts on what the cause might be?
Safety Car
Joined: Aug 2009
Posts: 3,752
Likes: 277
From: Melbourne, Victoria, Australia
The shudder is an indication its not running on all 8 cylinders.
Best way to narrow it down is from cold start the engine and idle for 20 seconds, then check the exhaust headers half inch from the head and make sure they are all the same temp.
Injector, spark plugs to be checked then as well as your leads measure resistance with a multimeter.
Compression loss in a cylinder from valves not closing can have the same effect a shudder, shake missing feel.
The torque steering can be a sign of worn bushings in the rear suspension?
Good luck
Best way to narrow it down is from cold start the engine and idle for 20 seconds, then check the exhaust headers half inch from the head and make sure they are all the same temp.
Injector, spark plugs to be checked then as well as your leads measure resistance with a multimeter.
Compression loss in a cylinder from valves not closing can have the same effect a shudder, shake missing feel.
The torque steering can be a sign of worn bushings in the rear suspension?
Good luck
Last edited by gerardvg; Sep 14, 2012 at 10:37 AM. Reason: more info
Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
You need to be clear on where the shudder is coming from...engine or drive train.
Engine gives the most dramatic feeling of something wrong. As someone else suggest, make sure its firing on all cyl, thats great for a shudder, pushing around a dead hole. Open the hood and rev it by hand...you can tell if its got dead holes.
Engine gives the most dramatic feeling of something wrong. As someone else suggest, make sure its firing on all cyl, thats great for a shudder, pushing around a dead hole. Open the hood and rev it by hand...you can tell if its got dead holes.
Racer
Joined: Jun 2006
Posts: 361
Likes: 7
You need to be clear on where the shudder is coming from...engine or drive train.
Engine gives the most dramatic feeling of something wrong. As someone else suggest, make sure its firing on all cyl, thats great for a shudder, pushing around a dead hole. Open the hood and rev it by hand...you can tell if its got dead holes.
Engine gives the most dramatic feeling of something wrong. As someone else suggest, make sure its firing on all cyl, thats great for a shudder, pushing around a dead hole. Open the hood and rev it by hand...you can tell if its got dead holes.
Thread Starter
Racer
Joined: Sep 2010
Posts: 325
Likes: 8
From: Princeton Jct. New Jersey
Thanks for all the replys. The engine runs at idle and up to full throttle smoothly and under load accelerates up to about 30 mph without any issue. The shuddering begins when attempting to accelerate from 30 to 40, stops when I back off the throttle, will run smoothy at a constant 40 and then starts again when attempting to accelerate from 40 to 50. Again, it will stop shuddering when running at a constant 50 mph. It does not feel like the engine is misfiring. The severe vibrations start when I apply the increased throttle pressure and appears to be coming from the drive train. I'm currently considering draining the transmission, flushing, and replacing the fluid and filter, although I'm not sure that will solve the problem. I'll also be checking the u-joints first to see if there was any damage from hauling the car up on a flatbed recently. I had asked the tow operator to use the body clevises but the hooks may still have been bearing on the half shafts on the way up.
Burning Brakes
Joined: Dec 2005
Posts: 805
Likes: 11
From: Hickory Flat Ga
Speed ranges won't change a misfire under load. You should put a scanner on it and drive it before guessing driveline failures. I bet it's a wire or plug or injector or in my case a head gasket trading compression between #6 and 8.
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Safety Car
Joined: Apr 2011
Posts: 3,660
Likes: 22
Did 84 have TCC ????????
seems like it did and IIRC there were service bulletins about ..the TCC solenoid going in/out.....
oh yeah..it was part of the wire harness rubbed thru on a casting seam on the trans housing that caused the elec problem with the TCC...
seems like it did and IIRC there were service bulletins about ..the TCC solenoid going in/out.....
oh yeah..it was part of the wire harness rubbed thru on a casting seam on the trans housing that caused the elec problem with the TCC...
Race Director
Joined: Aug 2007
Posts: 11,889
Likes: 8
From: Whitefish Falls Ontario
St. Jude Donor '08-'09
Yes the 84 has a TCC solenoid, located drivers side of the transmission just about 8" in front of the speed sensor. Three wire connector, purple from TCC brake switch (NC), lt. blue from ECM, and tan/black from ECM.. 
Last edited by ccrazor; Sep 16, 2012 at 10:24 PM.
Thread Starter
Racer
Joined: Sep 2010
Posts: 325
Likes: 8
From: Princeton Jct. New Jersey
Again, thanks to all for the input. I'm less inclined to think engine misfiring is the cause based on the severity of the vibrations (unless the engine mounts are loose or broken, which is unlikely). The TCC is a possibility I'll need to check, along with u-joints, differential mounting, TBI balance, ignition, and rear shocks (which are ~20 years old). The list of possible causes is growing.
Thread Starter
Racer
Joined: Sep 2010
Posts: 325
Likes: 8
From: Princeton Jct. New Jersey
Shudder resolved, but now a whine
Just to close the books on this one, I finally got around to checking the ATF level (probably should have been the 1st check -ah well-d8o), and needed to add 2 quarts just to get to a low reading on the dip stick. Another half qt. brought the level up midway into the cross-hatched range. Road tested it and no more shudder when accelerating. Of course now I'm hearing the high pitched whine from the rear end. Anyone using Dextron LS in their differential?