To all 915 experts, can you help me diagnose my issues?

[kamaro]

My car is a 1976 911S with complete original drivetrain. everything in this car is running perfect except the 3rd and 5th gears, it will grind slightly when I put it in 3rd and its very hard to put it in 5th (no gringing when it goes into 5th, though), I need to push the shifter real hard forward to make it engage into 5th. what do you think is bad? syncro? dog teeth ring? I fit a new clutch cable and its adjusted properly, so I think the issue is internal into the transmission.

[Flat6pac]

Just a thought, did you check the swivel in the back seat for breaking down?
Next, I would pull the side inspection plate and make sure the attached fork is firmly attached.
If it’s not, don’t try to repair, get a good one.
Bruce

[Trackrash]

+1 on Bruce.

Make sure all the shifter bushings and the coupler in the rear of the tunnel are perfect.

I would also make sure the clutch is adjusted correctly.

When is the last time you changed the trans oil?

[kamaro]

Originally Posted by Trackrash

+1 on Bruce.

Make sure all the shifter bushings and the coupler in the rear of the tunnel are perfect.

I would also make sure the clutch is adjusted correctly.

When is the last time you changed the trans oil?

The previous owner changed the trans fluid a year a go, I also checked it and it looks/smells new. The shifter coupling between the rear seats looks new as well and its firm and looks to be working good, as well as the front shifter.

Do you have any picture showing what I will find behind the inpsection plate? I never worked on any of the porsches transaxles and I need to carefully find my way through.

[RDM]

What Bruce and Gordon said.

If the clutch is correctly adjusted, look at the shift linkage next.

[mikedsilva]

sounds like worn syncro on 3rd... Does shifting slowly, or double clutching help?

With regard to 5th, I had a similar issue on a car a few years ago.. the guy that sold it to me said it was a 4 speed manual.. All 4 forward gears worked perfect. I got it home, and adjusted the shift linkage alignment, and had 5th gear ever since.. true.

[snbush67]

When you drain the gear oil you should be able to tell if it’s regular gear oil or swepco, whatever it is it should be replaced with Kendall 80w/90 GL5.

Swepco is too slippery, the synchros need more friction, could be your issue.

[DRACO A5OG]

Plus 1 check Coupler for slop and then try double clutching to see if that will slow/stop down 3rd and 5th

[Matt Monson]

Originally Posted by snbush67

When you drain the gear oil you should be able to tell if it’s regular gear oil or swepco, whatever it is it should be replaced with Kendall 80w/90 GL5.

Swepco is too slippery, the synchros need more friction, could be your issue.

Rubbish.

It sounds to me like 3rd gear synchro is worn AND 5th is likely a shift linkage adjustment issue.

[snbush67]

Originally Posted by Matt Monson

Rubbish.

It sounds to me like 3rd gear synchro is worn AND 5th is likely a shift linkage adjustment issue.

Likely it’s worn synchros, but don’t discount the swepco in a 915, I’ve personally experienced it, and it presents itself with the symptoms described.

But, I’m not an expert, just limited personal experience.

[Trackrash]

Yes Swepco is slippery. But once the trans is warmed up, the shifting should improve if Swepco is used.

Here is the description of the bottom plate. AND the Bible on 915s thanks to Pete Z.
How-To: Porsche 915 Transmission Repair Tutorial Part 2 - Porsche Wiki

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