🚀 go-pugleaf

>   The automatic transmission of my '77 Plymouth Volare is producing a 
> heavy thump when shifted from Neutral to either Reverse or Drive.

A thump usually indicates "play" in the drivetrain.  The usual cause is
a worn universal joint in the driveshaft.  These are pretty easy to
change if you have access to a large enough vise to press the old
bearings out and a set of large sockets (you use them as "pressing
pistons").

	Steve Falco

> 
>   The automatic transmission of my '77 Plymouth Volare is producing a 
> heavy thump when shifted from Neutral to either Reverse or Drive.
> The harshness of the transmission engagement is roughly proportional to
> the idling speed. The thump can jolt the car at cold idle speed (1400 rpm),
> but is tolerable at hot idle (700 rpm). The level and quality of the 
> transmission fluid has been checked out fine, the idle speeds are 
> also alright.  Other than the stated problem the trasmission works fine
> (no delay, no slippage). I would appreciate any pointer
> to the probable cause of the problem. Thanks.
> 
> 
> Kaihu Chen
> {ihnp4,vonvex,pur-ee}!uiucdcs!chen

The problem may be elsewhere in the driveline.  Worn U-joints on your driveshaft, 
a worn differential, etc. may cause a clunk when the transmission is engaged 
from neutral or park into drive or reverse.  
-- 
______________________________________________________________________________

Earle A. Sugar
Disclaimer:"I doubt anyone else here agrees with me."
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> /* ---------- "harsh transmission engagement" ---------- */
>   The automatic transmission of my '77 Plymouth Volare is producing a 
> heavy thump when shifted from Neutral to either Reverse or Drive.
> The harshness of the transmission engagement is roughly proportional to
> the idling speed. The thump can jolt the car at cold idle speed (1400 rpm),
> but is tolerable at hot idle (700 rpm). The level and quality of the 
> transmission fluid has been checked out fine, the idle speeds are 
> also alright.  Other than the stated problem the trasmission works fine
> (no delay, no slippage). I would appreciate any pointer
> to the probable cause of the problem. Thanks.
> 
Check your universal joints, if they're loose (loose bearings) they could
cause the `thump' you describe.  The thump would be proportional to the
engine speed.  An easy way to check it out is to reach under the car
and twist the crank shaft (make sure the car is not running and that it
is in Park).  If there is play (slop) at either the front or rear U-joint,
I would suggest that both joints be replaced at the same time.

If it's not the universal joints, you might want to also check the motor
mounts (loose or broken), however, this is more of a wild guess.

		Good Luck.

    Scott @ {convex!smu, rice, texsun}!tilde!tifsie!sat

In article <1336@jhunix.UUCP> ins_aeas@jhunix.UUCP (Earle A .Sugar) writes:
>> 
>>   The automatic transmission of my '77 Plymouth Volare is producing a 
>> heavy thump when shifted from Neutral to either Reverse or Drive.
>> The harshness of the transmission engagement is roughly proportional to
>> the idling speed. The thump can jolt the car at cold idle speed (1400 rpm),
>> but is tolerable at hot idle (700 rpm). The level and quality of the 
>> transmission fluid has been checked out fine, the idle speeds are 
>> also alright.  Other than the stated problem the trasmission works fine
>> (no delay, no slippage). I would appreciate any pointer
>> to the probable cause of the problem. Thanks.
>> Kaihu Chen
>> {ihnp4,vonvex,pur-ee}!uiucdcs!chen
>The problem may be elsewhere in the driveline.  Worn U-joints on your driveshaft, 
>a worn differential, etc. may cause a clunk when the transmission is engaged 
>from neutral or park into drive or reverse.  
>
>Earle A. Sugar


This may also be normal. Automatic transmissions can object to being put in gear
at 1400 rpm (a little high). The cold idle speed can be adjusted but stalling 
problems may result. If it was my car I would adjust the cold idle down to about
1000 and try it. If stalling occurs tweak it back up. Anyone know what the 
service manual says the cold idle speed should be.

the slower the idle speed the smoother the engagement.


					Billj

> 
>   The automatic transmission of my '77 Plymouth Volare is producing a 
> heavy thump when shifted from Neutral to either Reverse or Drive.
> The harshness of the transmission engagement is roughly proportional to
> the idling speed. The thump can jolt the car at cold idle speed (1400 rpm),
> but is tolerable at hot idle (700 rpm). The level and quality of the 
> transmission fluid has been checked out fine, the idle speeds are 
> also alright.  Other than the stated problem the trasmission works fine
> (no delay, no slippage). I would appreciate any pointer
> to the probable cause of the problem. Thanks.

One thing you might want to consider is to check the universal joints on the
driveshaft itself.  If you at times hear a metallic like "klink" when the 
transmission engages, then it probably is your universal joints.  To roughly
describe what is happening, imagine two of those trick rings that a magician
uses.  Imagine them interlooped, with the plane of one ring perpendicular to
the other.  Now hold one ring steady with one hand and give the other ring a
sharp 90-degree twist.  Notice how it contacts with the other ring?  This is 
what happens when your universal joints are worn.  I would suggest having it
checked out as soon as possible, because even though you may not notice it while
you are driving, the same thing is constantly happening as you drive, and
accelerate, decelerate, stop, start, etc.  Eventually you will actually break
the universal joint and/or drive shaft, and if it is really bad, you could even
drop the driveshaft itself (it happened to me!).  Good luck and let me know how
yo made out...
-- 
     Adrian Zannin
..{bbncca,decvax,dual,rocksvax,watmath,sbcs}!sunybcs!ugzannin
CSNET:    ugzannin@Buffalo.CSNET
ARPANET:  ugzannin%Buffalo@csnet-relay.ARPA
BITNET:   ugzannin@sunybcs.BITNET

  I received many responses regrading the harsh (automatic) 
transmission engagement problem I posted sometime ago. Most responses
I received suggest worn-out u-joints, but the u-joints were replaced 
to no avail. Upon careful examination of the drive train, I found out 
that most people were at least partially right - the problem is  
indeed caused by excessive play in the drive train. However, in my  
case the source of play seems to come from BEFORE the transmission output 
shaft (not BETWEEN the transmission output shaft and the drive shaft).
I was able to turn the drive shaft clockwise/counterclockwise
almost a full half inch before hearing a slight click.
There is also slight, probably ignorable, play in the differential as 
another response has predicted. As the problem has turned out
to be much more expensive than I am willing to pay for an old car,
I am most likely going to leave it alone. Thanks again for all of you
who suggest a fix.



Kaihu Chen
chen@uiuc.arpa
Department of Computer Science
University of Illinois at Urbana-Champaign