915 trans - stiff shifting after hamfisted driver

[jwasbury]

Last day of the track season I made the mistake of letting a guy take a few laps driving my 911SC based racecar without first observing him driving his own car. This guy was an absolute spaz with the shifter, slamming the hell out of it, and in about 2 laps it seems something got screwed up. I yelled at him to take it easy, but the damage was already done.

Moving the shift lever either front to back, or side to side became very stiff, and shifts were not very positive feeling so it became very easy to miss them or hit a wrong gear. Initially I thought it was damage to the Hargett shifter, but upon removing the shifter I found that mechanism was smooth and supple. The binding/stiffness is apparently the shift rod itself, so the problem internal to the transmission.

I've got the box out of the car and my current plan is to take it to Gary Fairbanks, have him look it over and fix whatever is needed and perhaps some other 'while you're in there" stuff. I've been inside 911 engines several times so I am pretty comfortable how they work, but the gearbox is a thing of mystery to me. Any ideas what is likely to have been damaged by my hamfisted friend?

[JohnJL]

Your friendship.

Sorry, I am in the same boat as you...good working k owledge of the sparky bits but the gears are a mystery to me...

[jwasbury]

Originally Posted by JohnJL

Your friendship.

funny

I can only fault the guy so much. He'd never driven a vintage 911 before (currently tracks a 997 street car) and I encouraged/pushed him to give it a try. My excitement to share the joy of the aircooled 911 got ahead of me.

[Nick Triesch]

Yup, I learned my lesson a long time ago. If anyone asks if they can drive my 3.2 I just say "No".

[dicklague]

I am surprised that he could not sense that he was forcing things!!

[sc_rufctr]

Ask your mechanic to check the shift fork inside the trans. A loose or misaligned one can cause these symptoms.

This was how mine looked when I first opened up the trans on my 78.
I also had other issues but as you can see one of the studs was broken and the other two were loose also. I've always driven and shifted my car sympathetically.

Apparently this is a common problem. Your "friends" ham fisted efforts could have dislodged yours.

[Matt Monson]

I was thinking the same thing. Either it came loose or a finger broke. Nice thing is you can check and repair it with gearbox in car. Just drain the oil first.

[OsoMoore]

I encourage you to take a look at this yourself. The transmission seems like a crazy thing, but inside it isn't that complex. The same mechanism is just repeated 3 times, once for each gear pair.

Definitely start by taking off the inspection port, hopefully it's just the fork. If not, there are lots of great threads here about how to dissasemble and repair a 915. I did so with my own a few months ago. I haven't taken the engine apart - it was my first time dropping it. So if you can do significant engine work, a 915 teardown is definitely within your skill range.

Can't Shift Into First

[Walt Fricke]

Like Oso, I was fearful of transmissions for more years than their design called for. They aren't that complicated, you can make up or fake most of the special tools which are helpful, you can have a shop do things which really are tricky (like setting up a replacement ring and pinion), and when it comes to replacing the dog rings on the gears you can give those to a shop also.

Checking the fork shown in the picture is dead easy. About the only trick is to remove the transmission oil filler plug first. Why? Because if you drain the oil, and then can't get the filler loose, you are in a bit of a pickle.

If the fork is tight, you might look at how the shift forks attached to the two sliding shafts align. One of these is built into its rod, but the other is clamped on. The "finger" parts which engage the shift sleeves and move them are also clamped onto their rods. If any of these clamped parts move on their rods you have troubles. Unfortunately, I don't think it is possible to realign any of these without disassembling the transmission pretty significantly.

By jamming shifts it is possible to bend the clamped on slot part on one rod. You will see how the rounded end of the dongle which is attached to the shift rod itself rotates up and down to the three gear engagement planes, and lines up with one slot, then the next slot, and for 5th/reverse, is out in thin air outside of both of these slots (because shifting for these gears takes place elsewhere). You can see that if the shift rod is rotated so that the dongle end is placed right between the two slot pieces, and then shoved forward or back, it can try to spread the two apart. One isn't going to budge, but the other one can be bent. I am certain of this because I did just that trying to get into 1st when angry. As it turns out, what is bent can be bent back, and externally to boot. Not likely this is what happened to your 915, but if it is you will know how to spot it and how to fix it.

If it turns out that clamped pieces were moved, I would have the transmission shop you involve, if you do, knurl the shift rods in the area where the pieces clamp. Won't cost much extra, and will pretty much preclude it happening again. If you do the work yourself (there is a super tutorial you can find here on Pelican by a guy who has a lifetime of professional work on these transmissions), you could take the shafts, with the areas you want knurled marked, to any machine shop to have that done.

997s are so easy to shift I am a bit surprised that would lead to ham handed shifting. Longer throws, sure. A bit more pressure needed, sure. Less certainty what gear you were about to engage, that too. But jamming it?

[dicklague]

you might want to look into the WEVO internal shifter gate. I have one in my 915 and love it.

[Trog]

Originally Posted by dicklague

you might want to look into the wevo internal shifter gate. I have one in my 915 and love it.

+1

[911pcars]

On a more basic level, I'd take a look at the internals. A gearbox in good condition should shift fine. Add the Wevo item afterwards.

Sherwood

[KTL]

Check out the 915 wiki by Peter Zimmerman. It's a very good tutorial on 915 teardown, inspection & rebuild.

List All Pages - Porsche Wiki

[mussberger]

You're lucky he didn't buzz the motor as well. I talked to Fairbanks once. Bavaro has done mine since then.

[dicklague]

Originally Posted by 911pcars

On a more basic level, I'd take a look at the internals. A gearbox in good condition should shift fine. Add the Wevo item afterwards.

Sherwood

++++that is what I meant. Looking at the parts in the photo reminded me of the WEVO.

I have had the internal gate shift if my 915 for a few years and maybe 10K miles and love it. Makes things really positive.

[jwasbury]

Bumping this back up. I finally have had the chance to peek inside my 915. The fork on the cover plate appears to be intact, so my problem isn't there.

The shift selector rod is noticeably stiff when trying to rotate between 1-2, 3-4 and 5-R planes in the neutral position.

I removed the nose cover and the shift selector rod is much easier to move around with the cover off. As an experiment, I bolted the nose cover back on and observed that the shift selector rod was stiff again. Then I loosened the nose cover bolts so it had some wiggle room, tapped the perimeter slightly and allowed the cover to open up just a bit from the gear case. That little extra room makes the shift selector rod much easier to rotate. Wondering if this is an indication that the selector rod is bent somewhere? I can't see anything obviously bent or out of place. All gears can be selected, just a huge amount of effort to move the shift selector rod around.

I am all ears to ideas to what else I should look at.

Thanks...

[911SauCy]

You're quite graceful in taking this as you are.

I understand the guy wasn't used to shifting a 915 but no matter my relationship to someone, I'd never take their car out and just smash it around...if I did and the result was similar, I'd expect to receive the repair bill.

Good luck as I couldn't tell you my arse from my elbow which bits that should or shouldn't be inspected.

[Matt Monson]

That sure does sound like a bent shift rod.

[jwasbury]

Originally Posted by Matt Monson

That sure does sound like a bent shift rod.

^this was my novice diagnosis based on the test performed. I'm struggling with how that part could be bent by beating the hell out of the shifter?

One other question: when you rotate the shift selector rod to access the 5-R plane, is there supposed to be a noticeable detent that wants to push the rod back to the 3-4 plane? I thought there was some spring loaded "feedback" when going for the 5-R plane, but perhaps that's built into the shifter and not the gearbox itself.

[jwasbury]

Originally Posted by 911SauCy

You're quite graceful in taking this as you are.

I understand the guy wasn't used to shifting a 915 but no matter my relationship to someone, I'd never take their car out and just smash it around...if I did and the result was similar, I'd expect to receive the repair bill.

I will see the perp again, and when I do I am going to mention the fact that I believe he damaged my gearbox. My purpose is not to shake him down for money, but to educate him that if he persists with the hamfisted/spaz shifting technique, his track car hobby is going to be more expensive than it needs to be.

I'm not too fussed about my car because I was planning to drop the engine and do some upgrades anyway. I wasn't planning on opening the gearbox but its not hard to do at this point anyway. The cost of fixing this is a squirt of piss in the grand scheme of my race/track hobby. I chalk it up to a learning experience for me: from this point forward, I will observe a person driving their own car from the right seat before I invite them to test drive mine.