1951 Dynaflow Park Pawl linkage

[Eric W]

I know park doesn't work on this transmission. The vertical piece with the "GM" part number is the park pawl. At the bottom of it are two sheet metal links. Anyone know what this is supposed to look like, or have a photo? There were no "extra" or loose parts in there, but park may have been broken before I got the car (I got it in non-running state).

[JohnD1956]

Looks like you are missing a shaft that goes through that empty hole and possibly a spring that goes on the shaft.  I have taken some pictures of my '61 parts manual, which is not the best, but I believe you can use these as a guide for what should be there. It does not show how it goes together.  Just the parts involved.  I'd be glad to try and get better pictures with some natural daylight which may be better, if you need them. parkingpawl.zip

 

 

[Eric W]

The figure looks similar in my many-generations-copied reprint of the '51 parts book - problem is, item "AS" is "lever and pawl" which is an assembly. What's in the transmission I have appears to be missing the rivet or pin that made it an assembly. I did take out the "AW" "rod", the lower end of which appears to line up perfectly with the hole in the lever behind it - to see if maybe that rod end was originally longer - maybe snapped off. It does not look like the rod end thread is sheared off. Maybe I'll take it off again and put a drill bit or something in there to link the pawl to the lever at that point just to see if the mechanism makes the necessary motion.

 

I'm not all that tempted to pull the rear housing (where I could possibly see these parts more easily), because that gets into disconnecting control rods that I can't even see - figure in the book shows pushing one loose with a screwdriver through a slot - how do you get that back together...

 

There's a vintage transmission specialist in town - I think this one will be headed his way. (This trans has another issue to be resolved.)

[JohnD1956]

Looks to me like you are missing part AT, the spring,  and AR, the shaft that holds the spring.  The diagram shows AR the shaft goes through AS, which is the Lever on your Pawl assembly. Then there should be a spring between the lever on the pawl, and part AU which is also called a lever.  AU is the lever where your rod AW is connected. 

 

All this sounds like weird science but looking at your pictures, if the lever from the pawl assembly was connected to the AU lever, then when activated it would appear the lever on the pawl rotates the parking pawl itself by a cam action.

[Eric W]

Finally got back to this. Part of it was I was put off by the shop manual, which went down a path of disconnecting linkages you can't even see in order to remove the rear bearing housing. Today, I decided I would try to fix the park linkage, and if it doesn't work, I'm not really any worse off. So looking inside the rear housing, there's just the shift rod itself that goes forwards. It's held on by a small pin that is held to the clevis by a spring built into the pin itself. So that just pops out. Then I pulled the 7 bolts holding the rear housing to the main body of the trans. I tapped the housing with a rubber hammer, and it started to slide back, and then off. So there's nothing else holding that on.

The pin for the park pawl just slips in from the front of the housing (held in by the housing being attached to the rest of the trans). This pin has a 1/4-20 thread in it. So thread a bolt into the pin and use the bolt to pull the pin out (it slides out easily). The pin that the other links pivot on is also only a slip fit into the housing, and I got that out by hammering the links forwards using a screwdriver through the main rear opening in the housing. Get that pin worked about 1/2" out, and can work it the rest of the way out by hand while working the links. Also need to loosen the link to the cross shaft, but that's a simple 3/8" hex. Then all the park linkage parts come out.

I did find half of the small pin that broke and fell out. I measured it, and it's right on .250" diameter. My initial fix was to use a .187 bolt, because I had one with about 3/4" of smooth shank. I got all this stuff back together, and was to putting the universal joint back on the output shaft, and the end of that is to hold the shift lever in park to lock the shaft to complete tightening the bolt that holds the u-joint to the shaft. Well, park didn't hold. The slight clearance of the .187 bolt in the .250 hole let the park pawl slide out just enough for it to not hold.

So I got a 1.5" 1/4-28 grade 8 bolt, even though it's too long. But this gives about 3/4" of shank, which just more than covers the distance through the 2 sheet metal links and the cast link. So bolt all the way through, then a washer on the other side (so the nut isn't bottomed on the thread), then a metal locking nut.

I had to shave down the head of the bolt for clearance to the other link, as well as grind down the other link a little to clear the bolt head. On the nut end, there's actually plenty of room in the housing, but I cut the bolt of close to the nut.

[Eric W]

Photo below didn't upload correctly in the original post.

[punisher]

hello everyone I use this topic because I am looking for a key with the whole with a little luck there is here a person who will be or find thank you to all and good day of France

[JohnD1956]

Do you also have a 1951 Buick? Or some other year?  They may be different