Help! Gearbox Stuck!

Post by MattA24 » Subscribing Member » Mon Jan 14, 2019 9:21 am
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 213
Howdy,

I took my '78 van for a nice long drive along the motorway this morning and it behaved itself very well, right up until I went to reverse into a space in the works' carpark.

I went to engage reverse, and I didn't notice the gearshift acting strangly, but when I lifted the clutch the engine spun free as if I was in nutural.

So I tried to move the gearstick but it's stuck fast in roughly the reverse position. I gave it a tug, but any more force and I would worry about breaking it.

Does anyone have clues on the cause, and on getting it unstuck tonight so I can drive home? I've got some tools in the van. If I have to drop the bottom off the gearbox, that should be possible although I don't have my RTV to stick it back on with.

The van has the vauxhall 4 speed with overdrive. Appart from been a bit growly in first the gearbox had behaved perfectly nicely until now...

Many thanks,
Matt

Re: Help! Gearbox Stuck!

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Post by Phil Bradshaw » Club admin » Mon Jan 14, 2019 10:10 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3791
Um.

Check inside the turret for the rocker arm stuck on its shaft, when the gear shift lever will seem stuck almost solid.

If there's movement in the lever and rocker arm still then first guess on balance of probabilities is a broken dowel pin in the selector cross shaft, probably the pin for the 1/2/R striking lever but a wobbly 3/4 lever could jam up the cross shaft just as well.

Other than that there could be a problem with the 1/2 synchro sleeve which carries the mainshaft reverse gear, or the synchro hub, but usually there's some warning (e.g. mashing synchromesh, jumping out of gear) before either goes terminal.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Help! Gearbox Stuck!

Post by MattA24 » Subscribing Member » Mon Jan 14, 2019 10:31 am
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 213
Phil, I wont lie - I'm sitting here at my desk with my fingers crossed that one of your beautifully annotated pictures is about to turn up...

:shock: :o :? :cry: :wall:

First port of call then, I'll take the side off the the turret in my lunch break to take a goosey in there.

Matt

Re: Help! Gearbox Stuck!

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Post by Phil Bradshaw » Club admin » Mon Jan 14, 2019 12:04 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3791
Inside the turret -

Image

If the shaft is bright with no lubricant near it then apply engine oil to un-stick the rocker if it won't move easily fore and aft.

With the bottom cover off -

Image

And what to look for -

Image

1/2/R or 3/4 striking lever (or both) moving independently of the shaft is a sure sign of a dowel pin problem.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Help! Gearbox Stuck!

Post by MattA24 » Subscribing Member » Mon Jan 14, 2019 12:39 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 213
Thanks Phil, I just popped out for another wobble of the gearstick. There is little bit of fore-aft play, perhaps as much wobble as exists when the box is in gear, but without disengaging the gear in the process of wobbling it. Beyond that it's like trying to push it somewhere it wasn't designed to go.

Feels ominous that it would get stuck with the lever in the "in gear" position, but spinning like it's in neutral :?

I'm just looking at potential local sources of dowel pins, just in case I'm going down that route. Do you know what diameter I would require?

Cheers again,

Matt

Re: Help! Gearbox Stuck!

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Post by Phil Bradshaw » Club admin » Mon Jan 14, 2019 1:17 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3791
3/16-inch Sellock roll spring pins for earlier transmissions (like in the photos) which are the ones that break for fun; Spirol coiled roll pins for later transmissions which pins I think are 4.5mm and can fall out when not fully driven home, e.g. when cross shaft and levers are not kept as a set and holes don't align during assembly.

Standard length pins have to have a bit ground off the length to fit snugly in the striking levers; grind a lead-in taper at the cut end before fitting.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Help! Gearbox Stuck!

Post by MattA24 » Subscribing Member » Mon Jan 14, 2019 2:30 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 213
Okay, thanks Phil.

As for the early/late gearboxes, I presume we're talking about vauxhall 4-speeds either way? The van is a '78, but the overdrive has a sleeve-type output so I'm guessing it's actually come from another vehicle. I think I remember reading somewhere that the CF laycock had a flange type output? This means the gearbox could be from a vehicle of any old age I guess!

Matt

Re: Help! Gearbox Stuck!

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Post by Phil Bradshaw » Club admin » Mon Jan 14, 2019 3:53 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3791
Earlier and later Vauxhall transmissions, yes.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Help! Gearbox Stuck!

Post by MattA24 » Subscribing Member » Mon Jan 14, 2019 6:24 pm
Joined: Wed Jan 15, 2014 9:06 pm
Posts: 213
Quick update cos I'm on the mobile (with oily fingers):

Opened the turret - not much greese but didn't feel like it was the problem. Slidey thing was sliding back and forth a bit, the jam felt like it was further in the box.

Reluctantly dropped the box bottom and managed to catch the oil in a bin bag (only got half a litre spare so this has to go back in).

With the bottom off, I wiggled the bit of the 1/2/R mechanism that hangs low and engages with the bit on the lid itself. It sort of pinged slightly like it has been caught and suddenly all gears engage.

Now to try and understand what it was caught on, and find something to stick the lid back on with!

Matt

Re: Help! Gearbox Stuck!

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Post by Phil Bradshaw » Club admin » Mon Jan 14, 2019 6:57 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3791
Check for any slop between the 1/2/R lever and shaft; if it can be wobbled, or levered along the shaft with a screwdriver or similar, then the dowel pin is broken.

Requires a 3/16-inch parallel pin punch to drive out the remains (once all the holes line up...) and then drive in a new pin once the pin punch passes through the lever boss and shaft.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

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