39 synchronizer question

34fordy

34fordy

Well-known member
I opened up a 39 3 speed this morning. All looked nice--except- the synchronizer did not have any springs or detent bars. Must be something I do not understand here.
 
No bars, springs or balls. Nothing laying in the bottom of the case. All very clean. The only wear is on the tips of low gear on the mainshaft.
 
A couple pictures
 

Attachments

  • IMG_0091.jpg
    IMG_0091.jpg
    81.3 KB · Views: 218
  • IMG_0090.jpg
    IMG_0090.jpg
    79.5 KB · Views: 216
There are variations in the blocker ring type synchronisers. The first type 91A-7124 assembly had two spring rings and little 91A-7116 metal plates that fit the hub and acted as detents to a degree but not by much. In 1940 for Fords, they went back to the 81A type hub that used the coil springs & ball bearings as detents as P/N 01A-7124. The Mercury number changed 09A-7124 for 1940 & 41 Later on after the war, they brought back the spring rings but the hub changed to a 51A prefix and they used little formed metal plates to act as the detents. They kept this set up well after the war in the 259 series, light duty pickup, and Mercury transmissions. The final style was the follow on replacement set up for all earlier blocker type synchronizers and was part number 8M-7124 assembly.

A person may find any of these in a blocker type cog box since many of them were overhauled with new or good used parts over the years. They are all basically interchangable.

The photo indicates the plates with the springs and balls should be in there. Someone must have liberated them.
 
Can you tell us a little more? Is this trans out of a car and bought as working or rebuilt?

I'm curious what MacVP thinks? I'm assuming they are essential and help to keep the synchro hub in it's forward or aft position.
 
Tim Ayers said:
Can you tell us a little more? Is this trans out of a car and bought as working or rebuilt?

I'm curious what MacVP thinks? I'm assuming they are essential and help to keep the synchro hub in it's forward or aft position.
Click to expand...

I just sent Mac a PM. The transmission has been sitting for many years so I do not really know the history. The outside was very dirty so I do not believe it had been apart for many years. The condition inside seems very good. I have not disassembled it yet. I posted some pics earlier in this thread.
 
34fordy said:
I just sent Mac a PM. The transmission has been sitting for many years so I do not really know the history. The outside was very dirty so I do not believe it had been apart for many years. The condition inside seems very good. I have not disassembled it yet. I posted some pics earlier in this thread.
Click to expand...

Does the synchro slide back & forth easily or does it take some effort and "clicks" into the forward and aft position?
 
Looks to me like somebody forgot to put the rest of the parts in . . . the little springs and balls. It would have synchronized fine (as these parts do not influence that), and I guess the shifter top could have kept the synchro ring centered when it was in neutral???

The gears and the interior do look very clean and in good shape . . .
 
I just disassembled the transmission. Lo and behold all of the pieces, 3 balls, 3 springs, and 3 plates were in the bottom of the case. The only reason I can see is that whosoever assembled it at some point in time did something wrong. I do not understand how the plates could have fallen out unless the ball and spring were reversed??? Amazing that the parts never got into the gears. Lucky me!
 
34fordy said:
I just disassembled the transmission. Lo and behold all of the pieces, 3 balls, 3 springs, and 3 plates were in the bottom of the case. The only reason I can see is that whosoever assembled it at some point in time did something wrong. I do not understand how the plates could have fallen out unless the ball and spring were reversed??? Amazing that the parts never got into the gears. Lucky me!
Click to expand...

Here's what happened. Somewhere in it's life. someone either forced the stick too far forward or back or had it apart and moved the synchro hub too far forward or back and they came out. The spring and ball type blockers can do this if the hub is moved past it's normal resting spot.

I'd assume it happened while out of the car at some point.
 
Yeah, I've had an issue before with this exact thing happening . . . usually because of very worn synchros and associated parts. I switched over from this style of synchro hub mechanism to the "chicklets with ridges" type of mechanism on all my recent builds (how is that for a description!).

I did have a transmission where the third gear synchro was very worn and the slider went too far forward and allowed one of the "chicklets" to pop up. This locked the transmission in high-gear.

Truth be told, I've had just about enough of 39 boxes . . . and I've done a lot of custom stuff to make them better than stock. With higher horsepower engines and my tendency to flog them a bit, I just beat these ole' transmissions up. I wish there was a good alternative for my 32 Cabriolet - but I do NOT want to cut the K-member. Arggggghhhh!
 
That is the 81A syncro hub and it should have three steel balls and springs. Mac sells a kit with the balls and springs for the syncro. The transmission has to come apart to install the kit. With the parts missing, taking the trans apart for complete inspection is important. The 1-R gear appears to have very little wear since both sides of the gear leading teeth are rounded from the factory.
 
You must log in or register to reply here.
Back
Top