P51 Hard to get into 4th, Likely cause

[RT104GT]

G'day. I just swapped over my P51 boxes and am disappointed to find that the so called low KM's box has a spongey feel when selecting fourth gear.
Apart from the usual slow syncro's in this model (which I was well aware of) the main problem is 3rd to 4th, it feels STIFF and slow to go in as though something is bent.
I remember this in happening in my 1900 SL gearboxed car after we hit a rock in a creek bed in a rally and bent a shaft but all the gears were stiff and we had to replace the shaft (side shifter) but P51 is top shifter and it has three rods to control the gears, the centre rod being the 4th/3rd gear.
Its smooth into and out of 3rd but stiff into 4th, (Not stiff out) in fact it almost tends to try to jump out and doesn't feel as though it has located properly, but I dont think its the lockout devices unless they are really full of gunge, or the spring loaded ball bearings are goo'd up.



A P51 Cluster,

Can anyone point out which is the 4th gear mechanism thanks??
Is it the locking mechanism next to the the front input shaft that locks the shaft in 4th. (^^HERE^^^)

CONFIGURATION LEFT TO RIGHT

5th Gear and Bearing REVERSE || 1st 2nd 3rd 4th + Input shaft and bearing.
Counter shaft 5th gear. ||


It is feasible that the shaft pictured has some rust on it or something else that is causing the stickiness, possibly in the brake band if it uses one for 4th??
Does anyone know what the brake bands are made from? It feels like a soft alloy, so I will have to watch additives. Has anyone used molyslip its about $20 for a small tube of white paste.


I used VBX80 oil so its as thin as.. Maybe I should try the recommended for this box LSD or ATU oil.
Or run it hard and flush it out and put some fresh stuff in once all the gunge is gone..

[RT104GT]

Thanks for comments about the front main bearing and possible misaligned due to wear.

So in the pic below when you select 4th which way does the selector band move left or right?
(Band is shown in what I think is 3rd gear transferring thrust to the transfer shaft.
In 4th it would lock the whole main shaft and no gears would access the rev idler shaft?)



INPUT SHAFT BEARING AND NEEDLES OF P51

If the front main is collapsing (worn) then that means the input shaft is running eccentricly and can wobble.
So what you are saying is that the higher force needed to select 4th is realiging the input shaft up straight?
And if the centre main bearing is also worn (probable seeing the input is worn) then the whole shaft is mis-aligned out-of whack?
And possibly the reason it is easily dropped out of 4th is the band slides off the three tapered pieces on that triangular device in front of 3rd gear??

The only thing countering this is there is no gear whine in the intermediate gears and if I remember correctly once the centre main bearing fails the whole gearbox screams and it is hard to go in and out of gears as they drag due to the sloppy thrust action of the failed main bearings.



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I had to put it in a run it to see what it was like, there is no other way.[/B]
Trouble is like in 1980 only 4 of the 6 bearings are currently able to be sourced.
The counter open roller idler bearing is n/a. and the opposite end idler shaft bearing. n/a.