915 Gearbox advice

[davidbrown]

First Porsche and first post be kind.

Fortunate to find myself in the position to fulfil a lifelong dream of owning a Porsche. From the age of 10 I’ve longed for a classic black Carrera and after looking for a very long time finally found the car of my dreams.

A genuine and completely original 1984 Coupe sport, black on black with only 63K miles with a superb history file. It has had some renovation work done in the usual places to a high standard and is sound in all ways.

The only item that is niggling me is the gear change from 3rd to 2nd. The 915 box is fab, I take my time, let it get up to temp and it is sweet in all changes, isn’t like stirring porridge and is so engaging and satisfying to use. However, on occasions coming down from 3rd to 2nd it is a little strained and takes more pressure to ease it in to the gear. You lose flow, balance and rhythm in the drive and I know it would be dreadful on a track day.

I’m assuming the worse and it is synchros thus a rebuild but wondered if anyone could offer any advice. I’ve spoken to Tuthill and Cape International at Redditch are giving me a call Monday to give me some guides in terms of price and it is a little eye watering.

many thanks Dave

 

[IndischRot]

Is there anything in the documentation that indicates which oil is in the gearbox? The 915 box isn’t well suited to modern synthetic gearboxes oils and there’s a lot of empirical evidence that oils like Swepco 201 or Motul Motylgear 75w-90 work best.

The other thing you can do is to learn to double clutch on downshifts; once you get practiced it becomes second nature.

 

[davidbrown]

Many many thanks for the response.

I will definitely check on the gearbox oil and was thinking of having that changed and bushings swapped as well.

Will enjoy trying to master double declutching not any real experience of it. In terms of the lifting of the clutch whilst transitioning through neutral do you have to lift entire or just past the bite point?

 

[911hillclimber]

If I may..
had 915 boxes in my 911 for the last 34 years.
The current box is fully rebuilt and has been in the car for 1000's of miles.

sometimes the drop from 3rd to 2nd needs a little more force, but was perfectly sweet the similar changes before and after.
all box parts are perfect, all bushes are too and a stock gear shift.
any quickshift shifter will raise the effort to change gear remember.

I take it as all part of the 915 experience, get it right and it is a pleasure, bit wrong and a bit irritating.
So try harder! As you say, lovely when you get it right, don't rush a 915.
also, imho the best box expert in the UK is Mike Bainbridge, MB Motorsport up in the Lake District.
a no bs kind of specialist, done 3 x 915s for me.
He will tell you the right oil also, and do not try the evil Swepco stuff.
You need to keep it all simple, nothing fancy unless you have a plated lsd.

 

[chas3.2]

Something else to check Clutch cable adjustment
very important.
Also the Omega spring may be broken or just worn out.
If the clutch dose not clear poor gear change.

Charles.

 

[davidbrown]

Many thanks for the responses.

Swepco transmission fluid was last installed Sept 2019, less than 1500 miles ago.

Had a lengthy Sunday drive and really concentrated on my double declutching and it certainly seemed to help. I don't think I'm quite rev matching the drop to second perfectly just yet but I'll master it.

 

[911hillclimber]

Good on you to master that technique, but you shouldn't need to to peddle a 915 or other box with synchromesh.
the sweep o is a modern oil and well suited to modern designs, so today that means boxes with bronze alloy synchro rings , Borg Warner type, used my nearly all from the 60's onwards.
the exception is Porsche of course with their own designs which use steel dog blocks and taper rings to synchronise the gears.
The swepco oil is not too good, but the old oils are.

Doubt you will find many classic 911 drivers who double clutch everywhere.

 

[davidbrown]

Thanks for the response. Seems differing opinions on Swepco.

if I decide to swap the transmission oil to see how it helps what would you be recommending? You mention the ‘old oils’, could you offer us a little more detail.

Once again thanks for taking the time to offer some advice.
Much appreciated.
Dave

 

[911hillclimber]

I have 2 915 boxes, oneinafullspecracecar andone in my classic.
Bothhave Motul HD SAE 80/W90 mineral oil in them.
hope this helps.
Be sure your box does not have an old design plated limited slip diff first.