TheAMCForum.com Homepage
Forum Home Forum Home > The Garage > Transmission & Drivetrain
  New Posts New Posts RSS Feed - Trans Repair-Park Springs? BW Iron Flash-o-Matic
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Click for TheAMCForum Rules / Click for PDF version of Forum Rules
Your donations help keep this valuable resource free and growing. Thank you.

Trans Repair-Park Springs? BW Iron Flash-o-Matic

 Post Reply Post Reply
Author
Message
RamblRumble_63_19 View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Apr/08/2019
Location: Boise, Idaho
Status: Offline
Points: 84
Post Options Post Options   Thanks (0) Thanks(0)   Quote RamblRumble_63_19 Quote  Post ReplyReply Direct Link To This Post Topic: Trans Repair-Park Springs? BW Iron Flash-o-Matic
    Posted: May/21/2022 at 8:07pm
Original 1963 Iron BW Flash-O-Matic 3 speed. Had a trans shop diagnose and fix it not holding the Park position. Trans would pop out of Park on it's own, especially on an incline/hill. Can anyone interpret/explain exactly what this means and where is in the TSM? The problem is fixed but I want to clearly understand exactly what they did/what their statement means and if it's in the TSM. 

They only dropped the pan, drain/refill fluid for this repair - 
"Removed part of the valvebody and detent combo, installed Secondary spring to assist the weak detent spring. Adjusted shifter and emergency/park brake. "

I found a brief section in the TSM that mentions Manual Shaft Lever Seal and detent ball and spring. Also Selector Lever Linkage Adjustment. 
Thank you!
Unique gearhead, overcoming life's obstacles.
'63 Rambler Ambassador 880 Original. 327 61k miles.
Link=> https://garagehotrods.com/2020/10/16/joey-shelbys-63-amc-rambler-ambassador/
Back to Top
Regamble1969 View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Dec/01/2021
Location: Boise Idaho
Status: Offline
Points: 204
Post Options Post Options   Thanks (1) Thanks(1)   Quote Regamble1969 Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2022 at 1:41am
So there are two parts to this, first the problem of it popping out of park and second the fix of putting in a second detent spring. Let's start with what's happening inside the transmission when you are in/out of park. There is a part inside called a park pawl. It is a finger that grabs one of a series of notches and locks it in place so the output shaft cannot turn this locking the driveshaft in one position.


Now the detent spring and shift lever. The shift shaft takes the linear motion of your shift linkage and turns it into rotational motion. This turns a piece inside the transmission that controls the valve body and the park pawl. To make certain that shift positions inside the valve body are kept exactly where they should be, and to keep the park pawl locked in place when on a hill, the shift shaft lever inside has notches where a spring pushes a ball or a pin or a roller (there are several different types) that locks this in place. If you've ever manually shifted a transmission from under the car without the linkage hooked up, you can hear and feel this action when the shift shaft positively locks into each shift position.




Here you can see two different types, the TH400 (second photo) was plagued by shift spring weakness and this is a very common thing to fix. Your transmission uses a spring and ball like this one though from the Ford FMX transmission. You'll see the spring and ball and shifter at the top of the diagram.



So the repair shop added a second spring to put more pressure on the detent to keep the shift shaft locked in the correct position and, most importantly, keep the park pawl fully engaged in park.

Whether this is in the TSM I would highly doubt. Though a common fix for a lot of older transmissions that parts are hard, if not impossible to acquire for, this isn't something that the dealer would put in a repair manual. They would advise either tear the transmission down and replace the park pawl, sprag, shift lever, detent ball, and detent spring or replace the transmission.

Hope this helps.
Back to Top
RamblRumble_63_19 View Drop Down
AMC Apprentice
AMC Apprentice
Avatar

Joined: Apr/08/2019
Location: Boise, Idaho
Status: Offline
Points: 84
Post Options Post Options   Thanks (0) Thanks(0)   Quote RamblRumble_63_19 Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2022 at 12:58pm
Thank you! That was very helpful, and makes a lot more sense now. 
It does seem to be an adequate fix, but I also wonder now if it is more of a "band-aide" fix to a bigger problem of the parking pawl, or if the spring fix will work just fine. Seems if it's been done on other transmissions and works, it should be okay. 
In hindsight, since I had some other communication problems and disagreements with this shop (the "right" ATF), I wish I had a lift and I could've looked at it and done it myself or likely looked harder to find a different shopConfused
Unique gearhead, overcoming life's obstacles.
'63 Rambler Ambassador 880 Original. 327 61k miles.
Link=> https://garagehotrods.com/2020/10/16/joey-shelbys-63-amc-rambler-ambassador/
Back to Top
Buzzman72 View Drop Down
AMC Addicted
AMC Addicted
Avatar

Joined: Sep/15/2009
Location: Southern IN
Status: Offline
Points: 2713
Post Options Post Options   Thanks (1) Thanks(1)   Quote Buzzman72 Quote  Post ReplyReply Direct Link To This Post Posted: May/22/2022 at 10:16pm
Springs weaken as they age. The spring over the detent ball has likely never been replaced, so increasing spring tension on the detent ball would probably keep it fixed for another 59 years.

But I doubt I'd guarantee it for more than 20 years, due to my age [I'm 67, so I doubt I'll be tearing into transmissions 20 years from now].



Edited by Buzzman72 - May/22/2022 at 10:20pm
Buzzman72...void where prohibited, your mileage may vary, objects in mirror may be closer than they appear, and alcohol may intensify any side effects.
Back to Top
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Forum Software by Web Wiz Forums® version 12.03
Copyright ©2001-2019 Web Wiz Ltd.

This page was generated in 0.125 seconds.
All content of this site Copyright © 2018 TheAMCForum unless otherwise noted, all rights reserved.
PROBLEMS LOGGING IN or REGISTERING:
If you have problems logging in or registering, then please contact a Moderator or