Avant shudder.

[A83]

Now my 83 Avanti shudders when driving.  No problem when I rev the engine in neutral or going in reverse.  Only when in gear. It is like I am driving over railroad ties.  Sometimes real bad sometimes not as severe but dreadfully noticeable.

Any ideas? 

 

Thanks A83

[studegary]

Can you narrow it down as to coming from the engine, transmission, suspension or elsewhere?  From the very little information given, I would guess a failing transmission.    

[Bill Hanlon]

I had a mustang with this issue, it ended up being the torque  converter. See attached article http://www.agcoauto.com/content/news/p2_articleid/203

Edited April 2, 2020 by Bill Hanlon

[A83]

Thank you both - near as I can tell when I put it in neutral and rev the engine while driving the car, it does not happen.  Seems to be when I have it in gear (automatic transmission) starts at about 15 mph.  Not sensing anything from the suspension.  Wondering if drive shaft might also be a possibility in addition to the torque converter.  I have been having problems going through several new brake boosters and each one keeps hissing  as the current one is / also new brake lines out in recently.  Could the brakes be engaging due to the brake booster?  

 

 

 

[studegary]

No the brakes are not engaging.  With the bad booster, you would just lose boost and perhaps some vacuum in the engine (that could make it run strange).  There isn't anything to apply the brakes, like with an ABS system.  I would say no to the driveshaft.  It could be the transmission itself, as well as the torque converter.    

[wwundt]

My '82 Avanti-II shuddered  like I was driving over railroad ties, especially noticeable under acceleration.  I suspected the U-joints and had them replaced. That didn't cure the problem.  When the starter went bad, the mechanic who removed the old starter found that the plastic cover under the bellhousing was pinched by the starter and rubbing against the teeth on the ring gear.  A Dremel tool relieved the interference on the plastic cover and that fixed the shudder.   

I  experienced a similar "driving over railroad ties" sensation driving my Wagonaire home from a tire shop where I had just had a new set of tires installed.  Popping the hubcap on the drivers side front wheel I discovered the lug nuts were on finger tight, just started but never tightened down.  It ruined not only the studs, but wallowed out the bolt holes on the wheel. 

[A83]

Thanks will check that out 

 

A83

[A83]

I found some loose lug nuts and tightened them up.  Took for a test drive and the railroad tie feeling diminished but not gone.  When I came back from the test drive, one lug on rear driver side wheel was loose and retightened.  Now it seems to vibrate at around 20 miles an hour when I accelerate but shudders noticeably when the car starts to decelerate at around 20 miles an hour.  Did not highway test it yet.

Any more thoughts?

Appreciate any help.

 

A83

[Avanti83]

As said before, the next easiest thing to check is the u-joints on the driveshaft. Issues on deceleration are one sign of that.

Edited April 3, 2020 by Avanti83

[wwundt]

You may also want to have the driveshaft balanced.

 

[A83]

Thanks again 

[A83]

Looks like the shudder problem was a combination of bad plugs and a worn control arm bushing.  Engine runs fine but detect a shimmy in the front end when  driving which gets worse when I decelerate  especially in the low gears (auto trans).  Does this week plausible? 

[studegary]

2 hours ago, A83 said:

Looks like the shudder problem was a combination of bad plugs and a worn control arm bushing.  Engine runs fine but detect a shimmy in the front end when  driving which gets worse when I decelerate  especially in the low gears (auto trans).  Does this week plausible? 

These items could cause problems, but not what I would describe as a "shudder".  A vacuum leak due to a defective brake booster can also cause an uneven running engine, but I didn't mention it because that also would not be a "shudder". 

[A83]

Maybe I am using the wrong terminology but am using the term shudder to describe the feeling of driving over railroad ties.  That feeling is gone now and I felt it pretty much under the seat/ transmission area.  But still do get a vibration when driving and more when decelarating.  So will l have the control arm checked out next.  Not sure of anything until this is all over so also made a list of all your recommendations for another hot rod shop I am taking it to this week and I thank you all for your help. 

[A83]

Update - control arm bushings replaced and the U joints on the drive shaft replaced by a mechanic - car running nice - thank you to everyone for your  help and advice. Always appreciated.

 

A83