Is there a way of setting the gear linkage/stick?

[Chopperman]

I have the rubber gaiter off my gearstick and I have noticed, as well as felt it try and go into the reverse gear section when selecting from 4th to 5th. The toggle that is to the right to help select reverse/5th moves freely. Sometimes when selecting reverse, it won't go in as this toggle is blocking it. Is there a common fault?

[911hillclimber]

915 gearbox?
If so that all sounds like you need to adjust the linkage again.
Presuming all the bushes etc are in good condition in the whole linkage..

Get the box into 2nd before you slacken anything.
Release the clamp at the box connector so the rod is axial lay and radially free.
Move the gear lever into the 2nd gear slot BUT not hard onto the shifter slot,a low 1mm or so clearance. This allows the gear input shaft to alway reach and locate into the detent in the box for all gears.

Pinch the coupling clamp ring up tight.

Select all gears to see that the gear lever in in the slot and has some slack in the first 4 gears.
Check carefully that 5 the selects and then reverse.

Re check tightness of the coupling clamp.

Ps make sure the coupling taper grub screw is tight!

[Nick Moss]

It sounds to me as if the detent spring is broken.

[hot66]

have you checked the grub screw holding the socket to the gear rod ( under the shifter ) . These can come loose leading to problems

[Chopperman]

Thanks guys. I have been tinkering but I thought there must be a way.

It's a 915 with new bushes just before it passes through the rear bulkhead.

I have not yet checked the Grub screw.

Nick Moss. How do I check the detent Spring?

[Nick Moss]

You have described the symptoms above

[Chopperman]

By how do I check it, I mean how do I know what it should be doing? How do I sort it? I have not come across a detent on the gearstick before.

[911hillclimber]

A detent is a simple steel ball with a spring behind it, When a shaft has a shallow dimple (sometimes just a shallow drilling/tip) in its face the ball locates into the dimple so 'detenting' it into a precise repeatable position.
The depth of the dimple in the moving part is critical to ease of getting the ball to come out when the shaft is moved. The dimple is sometimes chamfered to assist this.

If the spring is broken or the dimple worn etc then the detent action will be lost or become very hard to move out of. Gearboxes rely on detenting positions.

If you have checked the alignment of the shift rod/gear leaver housing and 1/2/3/4 gears are good and the issue is still reverse/5th then it is a gearbox out I think, but...

I think on the 915 the detent spring/ball are behind external bolts in various locations in the main case, but maybe a call to gearbox man Mike Bainbridge (MB Engineering in the Lake District) could help.

[Chopperman]

Sorry, I thought it was to do with the toggle/lever on top and to the right of the gearstick housing?
The reason it won't go into reverse is because this little toggle is blocking it sometimes from moving rearwards as it also blocks it sometimes when I try to select 5th

[911hillclimber]

Yes, that is why I suggested doing the alignment routine to make sure the box was synchronised with the shift 'H'

The neutral position is between detents on the gear positions so should cleanly pass through the small blocker finger in the shifter (I am assuming you have the 'tall' tower type gear shifter) and up into 5th and its detent is located freely. Similarly to go to reverse.

I have learnt over many years that the shift lever must be accurately aligned, and you must be mm perfect.

I would still start there before delving deeper, but I have only experience of 2 915 gearboxes and about 30 engine removals/gear shifter re-alignments under my belt!

I would not doubt the more experienced people above, the box may need help in the end.

Bit like 'change the fuse before you change the power station' approach.

[Chopperman]

911 hillclimber. When you say 1mm clearance, is that both sideways and aft with no pressure on the lever?

What is the tall tower gear shifter?

Thank you for giving your time to explain to an experienced novice

Gary

[911hillclimber]

There are 2 gear shift designs in the early cars.

The cars up to 1972 have a small simple steel pressing and mechanism for the lever. Under the rubber boot the mechanism is very simple. My 1973 T with a 4 speed 915 box had one of these designs for example.

Later/1972 on some of the S and E cars had what is called a 'tall tower' shift mechanism designed to give a far better shift lever control.
The rubber boot is much larger and covers a tall (120mm ish) cast aluminium pot housing of about 70mm diameter.

In all my comments I have assumed you have a 5 speed 915 box with the pot shifter.

If this is so, then the adjustment is indeed trying to get the lever to have clearance when slotted in 1/2/3/4 gears.
The clearance ensures the box detent spring can fully locate and allow the shift forks to align the gears correctly.

The pot gear shifter has a bias spring for 5/Rev built into it but if you allow the correct alignment in 1/2/3/4 positions then (if the box is good) the 5/Rev will take their right position and work well.

It is a bit of trial and error to get the clearances but worth the effort.
I remove the passengers seat to make access easier.

Sometimes tightening the rear C clamp ring can just move the position enough to loose the clearance....start again!

The factory fit bushes in the rear 'UJ' on the end of the shift rod/gearbox. They have slots in them that allow considerable fore/aft movement. This movement ensures the detent can get into position and makes the setting of the lever less critical but induces a lot of slop in the change.

This setting is even more critical if a short shift mechanism is fitted.

Hope this helps.

[Chopperman]

Absolutely brilliant thank you. I think there are a lot of people who will see this and gain from your knowledge

[Chopperman]

Grub screw behind the joint before it passes through the bulkhead is tight.
New coupling was fitted by me.
Grub screw with Alan key and locking nut on the front of the tower shifter is tight.
But! The cage that sits in the longitudinal pin on the rear of the shifter and the grub screw and nut on the front of the shifter that allows the gear stick to rock either side has a small amount of wear.
Generally, there is a small amount of movement in both axis of the gearstick though nowhere as bad as an early Mini.

[Chopperman]

One thing that I have found that i did not notice as I was driving. The little flapper arm on the right prevent reverse being selected when changing from 5th, sticks across.
I am hoping this solves it.
Car off the road while I change it's rear end to the correct shape from impact bumper style.