Transmission Sliding Hub Plungers

[AUSMHLY]

What is the purpose for the plungers in the sliding hubs?

1) Why does 1st gear hub assembly have 2 plungers and they can slide out when the assembly is together on the bench. (Part #44)

2) Why does 3/4 hub assembly have one plunger and it doesn't come out when the assembly is together on the bench? (Part #29)

3) Why are the designs different?

Both assemblies have 3 ball bearing and 3 springs.
I believe the balls are in the center grove of the teeth when in neutral. (Photo attached.)

4) If the springs are worn, what effect would that have?

5) What's the purpose of the plungers when switching gears or when in a stationary position?

 

[AUSMHLY]

What is the purpose for the plungers in the sliding hubs?

1) Why does 1st gear hub assembly have 2 plungers and they can slide out when the assembly is together on the bench. (Part #44

1) CORRECTION, IT HAS 1 PLUNGER I FOUND OUT. MOSS'S CATALOG SHOWS 2 PLUNGERS. IT DOES SIDE OUT.

2) Why does 3/4 hub assembly have one plunger and it doesn't come out when the assembly is together on the bench? (Part #29)

2) CORRECTION, 3/4 HUB HAS 2 PLUNGERS AND THEY SLIDE OUT.

3) Why are the designs different?

Both assemblies have 3 ball bearing and 3 springs.
I believe the balls are in the center grove of the teeth when in neutral. (Photo attached.)

4) If the springs are worn, what effect would that have?

5) What's the purpose of the plungers when switching gears or when in a stationary position?

 

[AUSMHLY]

Here's an update with my hands-on learning with this rebuild.

Denis Welch sells an updated designed 1st gear hub assembly. The stock hub assembly has one grove in the teeth for the ball bearings for 1st gear. DW has two groves. One for 1st and 2nd which I assume locks the assembly in place. It's also lighter and some of the teeth are designed differently.

The plungers in 1/2 and 3/4 hubs go into cut-outs in the mainshaft.

There's no need to line up the plunger in the 1st hub assembly when sliding it on the mainshaft. The mainshaft appears to has cut out on all splines for that plunger

3/4 hub (I believe) should be lined up with the 2 cut-outs on the mainshaft. I'll post photos showing why I think that's so.
Photo showing the 2 cut-outs on the mainshaft.
Photo showing the 2 plungers positions in the 3/4 hub. I've pulled them out a little to show them.
Photo showing the assembly plungers lined up with the mainshaft splines that have the cut-outs, marked with a black marker.

If any information I've posted is incorrect, please reply.

 

[AUSMHLY]

Update 2.
The 3/4 hub plungers will automatically line up with the notches, for the hub can only go on one way.
Hey, I'm the only one commenting on my post, lol

 

[Jerry]

I remember struggling with the hubs but I only rebuild transmissions about every 5 years so memory is not reliable. I do know what happens if you pull the hub off and don't keep it together, springs and balls go everywhere!

 

[AUSMHLY]

I believe once the hub gear has moved from neutral to engagement position, the plunger(s) are then pushed out into the shaft cut out area to help keep it in place.

I find this post interesting because (I'm in the learning curve rebuild) I've asked a question about a part's function and I'm the one responding with the answer, lol.

So Dr. it hurts when I do this, then don't do that.

 

[AUSMHLY]

"For anyone that is following this thread"...I found this write up on AHX. Thank you Robert Hosking, aka Robxk120.

Mystery transmission part : The Sprite Forum : The Austin-Healey Experience

So this little "bean" was stuck to the magnetic drain plug on my transmission. I'm assuming I cant plant it in a pot and pour gear oil on it and grow a new transmission...

www.ahexp.com

Post #12

For anyone that is following this thread, these are using me considerable grief. They only exist in the BJ8 gearbox, and rebuilders (such as Welch) say they are unnecessary. Their purpose (I deduce) is to keep the central hub from engaging the baulk ring for the other gear before the original gear has been fully disengaged. they are operated by special ramped teeth on the outer hub, that depress them into the cut-outs on the main shaft as the outer hub engages the gear. While depressed into the cut outs, they then prevent the inner hub moving far enough to start the synchro engagement on the opposite gear. as the the Outer hub moves out of engagement, the plunger is released by the ramp, and the outer hub then enters the balls and presses the inner hub against the baulk rings, synchronising the gear, allowing the outer hub to engage the other gear and at the same time depressing the second Plunger in its corresponding cut out in the main shaft. (I note that the plungers can (and do) easily fall out through the central hole of the inner hub and into the cavity) of the gearbox when assembling on to the main shaft!)
So, to my issues. To me, the companies building the replacement hubs have not understood how these are supposed to work, and do not use the plungers in their gearbox rebuilds, as all gearboxes up to BJ8 do not use them. (I wonder if it has something to do with the movement from Bronze Baulk Rings to Steel Baulk Rings has any thing to do with the plungers inclusion)
(i) the hole that they fit in in the new synchro hub bought from AH spares was too small to take the original ones from my gear box. it was equal in diameter to the plungers themselves, when it needed to be slightly larger. Sent back , and ordered one from Dennis Welch. Asked them to ensure the fit was correct. Assured me it was. Of course, it wasn't. Both holes needed to be relieved. assembled gearbox. Would not go into 4th. Disassembled Gear box, and examined issue carefully. The ramps for the plungers on the original were at a constant angle up to the final flat. DW ramps have a hump before final flat (owing to DW design to slightly engage balls to help to provide positive hold in gear) and requires grinding down (but must be accurate and smooth as any imperfection may then prevent disengagement, as found by trial and error), to allow gear to engage when using the plungers.

As this problem does not seem to have been identified before, can only assume that the plungers can be left out without any noticeable effect. The main issue would probably be wear in the Baulk Rings, which would not affect race cars (as gearboxes regularly rebuilt) or our cars (as no longer used for regular transport).

 

[Bob_Spidell]

I can't offer any help, but I installed DWM 1/2 and 3/4 hubs and synchros in my BJ8, using the plungers from the OEM hubs and have a properly functioning gearbox. No mods to the DWM hubs required.

I can't imagine how changing from brass synchros to steel ones would have an effect elsewhere. I've heard over the years that some aftermarket synchros didn't perform properly, but IIRC it was from the ridges in the synchros not being machined properly causing premature wear.

 

[RobXK120]

Just to be clear:
here is a quick description of the operation of the Synchro.

1.0 The gears are always in mesh, but spin freely in relation to the main shaft. They are selected by the dog clutch operation of the outer ring grooves sliding over the inner protrusions (“dogs”) On the gear itself. The inner hub is locked in step with the main shaft and the outer ring by the grooves. With no synchromesh, you would have to match revolutions (double de-clutch) to smoothly change gear, as you do in the non-synchromesh first gear.

2.0 So, synchromesh system A. A cone was added to the gear, and a matching inverted cone was added to the inner hub. As well, the inner hub had the spring loaded balls that engaged depressions in the outer hub, which was moved by the selector. As the outer hub was pushed towards the new gear, the outer hub engaged with the spring loaded balls, and pushed the inner hub + cone over the corresponding cone, before the dog clutch could engage. This bought the gear Protrusions and the outer ring up to the same speed, and allowed a crash less engagement of the dog clutch. BUT:

3.0 It was still possible to push the outer ring quickly enough to push the dogs together before the synchro had fully synchronised the gears (CRUNCH) (Hello, pre 4.2 E-Type Jaguar Moss boxes!). Hence the introduction of the Baulk (Synchro) Rings. Their purpose is to ensure that the full synchronisation has happened BEFORE the dog clutch engages, and hold out the outer ring until synchro has happened. The ring now sits between the inner hub and the gear, and has protrusions that prevent the outer ring sliding over the dogs, as it is twisted slightly out of synch with its matching slots on the outer ring, until the dogs and slots are in synch. (isn’t that a boy band?).

4.0 (and this is where I get into surmise, as I cannot find any literature on this) All well and good, but a slight issue, probably arising when the same gearbox was used in commercial situations. If the hub went one way for one gear, and the other for a second gear, it was possible that as you move the outer hub out of engagement, the springs and balls, although not in their true depressions, can take the inner hub towards the other gear, effectively trying to synchronise the other gear before the first has been disengaged. (another possibility I need to look into is if the outer hub is also redesigned to use the spring and balls to keep some pressure on the outer ring and in gear, the inner hub must be stopped from pushing the Baulk/synchro rings against the other gear, effectively wearing them out very quickly). Hence the ”beans”. Each bean is pressed into its matching slot by a ramp on the outer ring, stopping the inner hub from moving towards the other gear until released by the ramp once the gear has fully disengaged. As this effect would not be noticed in normal driving with out the beans, it is entirely possible for a bean to drop out to the bottom of the gearbox during assembly, and not be missed.

5.0 In order to get the beans working properly with the Dennis Welch hub, I first relieved the holes for the beans slightly, using a drill bit the same size as the Welch hole and working it back and forth a bit (air didn’t take much relieving, and then carefully ground down the ”hump” on the two ramps with a Dremel bit, followed by 1200 grit wet or dry, and finished with polish, to achieve a smooth surface. My tulip gearbox is now working beautifully!! As the three day Jaguar Mountain Rally over last weekend proved. A great test of one‘s relationship, if your partner is the navigator!
The one night stand that went wrong … 42 years later!

 

[AUSMHLY]

Thank you RobXK120