Transmission & Drivetrain - Car slamming from park to reverse

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Car slamming from park to reverse

Printed From: TheAMCForum.com
Category: The Garage
Forum Name: Transmission & Drivetrain
Forum Description: If it's between the engine and wheels, it goes here
URL: https://theamcforum.com/forum/forum_posts.asp?TID=115945
Printed Date: Apr/23/2024 at 10:02am
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Topic: Car slamming from park to reverse

Posted By: 65ramwgn
Subject: Car slamming from park to reverse
Date Posted: Jun/21/2022 at 7:30pm

My 1965 rambler American with a flash o matic transmission is having an issue. When the car is running if will slam out of park and the really SLAM when reverse engages. The shift is pretty typical when going from neutral to drive, however the huge BANG returns when going to neutral. The u joint feels pretty solid (although there is a bit of play in the rear end) as well as the motor mounts look good. I couldn’t see the transmission mount from where the car was sitting. Any ideas?

Replies:

Posted By: Heavy 488
Date Posted: Jun/21/2022 at 7:46pm

What rpm is the curb idle set at?

Posted By: 65ramwgn
Date Posted: Jun/21/2022 at 7:56pm

It seems a bit high, however would high rpm cause it to seem to slam right out of park immediately even before reverse engages?

Posted By: purple72Gremlin
Date Posted: Jun/21/2022 at 9:04pm

Heavy 488 wrote:

What rpm is the curb idle set at?

Posted By: purple72Gremlin
Date Posted: Jun/21/2022 at 9:08pm

65ramwgn wrote:

It seems a bit high, however would high rpm cause it to seem to slam right out of park immediately even before reverse engages?

yes it will. If your choke works properly. It will idle fast. Then once its running smoothly lighty press the gas pedal and you should have the fast idle off the high step. It should slow down some, then shift in R or D. Shouldnt be harsh. And when its at curb idle...which means choke is fully open and idling like 600rpm or so

Posted By: wittsend
Date Posted: Jun/22/2022 at 10:25pm

A car doesn't "slam" out of Park or Neutral. In those positions there is no application of clutches or bands. Therefore there is nothing to come out of. What you are experiencing is slamming into Reverse which you need to pass through to get to (or back from) Neutral or any forward gear.

While a high idle can be a contributor internal valving might be putting a higher than normal pressure to the clutches and bands. Is the throttle valve cable that attaches at the carburetor hooked up and adjusted properly? That controls the internal pressure. You might also have the gear selector lever out of adjustment. Thus what seems like slamming out of Park or Neutral is actually going into or out of Reverse though it does not appear that way on the lever display because of mis-adjustment. Internal clutches and band servo applicators often have springs to cushion engagement. When these break the cushioning effect goes away and the application can be quite abrupt.

As mentioned ensure the idle speed is correct. When moving the gear selector do it as s-l-o-w as possible and note where the indicator is pointing when the selected gear engages. Check that any rubber bushings on the lever mechanism are intact and firm. Oil can soften and deteriorate rubber over time. Adjust the lever as per the manual if needed. Check the throttle valve cable at the carburetor. A manual should be use to test and adjust as necessary. If none of those have any positive effect the problem is likely internal.

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'63 American Hardtop

Posted By: george w
Date Posted: Jun/24/2022 at 6:16pm

Sounds like too high throttle pressure at idle. Check the kick down linkage to make sure it’s in proper adjustment. Idle speed needs to be in the right ballpark as well. If all checks out then you may have a broken spring in the rear band servo.

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Long time AMC fan. Ambassador 343, AMX 390, Hornet 360, Spirit 304 and Javelin 390. All but javelin bought new.