Open Road

So I was complaining at Frenzy that the 86.5 928S was shifting hard and someone reminded me about the pressure valve that has the vacuum line. Sure enough there is no vacuum on it at idle, and the line at least back by the regulator is old, crappy, etc....

Time to replace. However:
1) What do I have to remove on the back end to get to the metal line interface? Is it just the driver's side tin over the exhaust or more stuff? And where is it again, any photos so I know where to stick my hand?

2) On the front side of the engine, where does the metal line terminate? Driver's or passenger side of the transaxle to engine interface? Can it be reached from the top (air filter now out) or do I have to do it from underneath?

3) What's the best vacuum line to use these days in terms of size and such?

I did check the fuel regulators and such and all have sold vacuum, so that should not be a problem.

Thanks!
Chris

The hardline terminates at the upper hell housing exactly where the clutch release arm ball stud would be on a 5-speed.

You'll need the exhaust and heat shields removed to get fingers to it. Minimum.

I've seen on many occasions, where other shops have just run a new vacuum line from the modulator into the engine compartment rather than attempt to fix the factory-original setup.

Tons of good choices for vac hose. This is close to the original:

https://belmetric.com/cohline-series-31 ... stic-hose/?

Thanks Worf! Trying to google stuff like the hose inside and outside dimensions is pretty useless, so do you know those off the top of your head?

I thought I could get to the front metal hard line from the engine compartment, but maybe not. Now I know it's on the driver's side I'll have a look with the boroscope to see what's going on down there. Just a real pain, but if I decided to say fuck it, can one run a tape over the drive tunnel from the back to the engine compartment and follow it with a long length of hose?

ChrisZ wrote: ↑Sun Oct 05, 2025 12:19 am ... but if I decided to say fuck it, can one run a tape over the drive tunnel from the back to the engine compartment and follow it with a long length of hose?

I've seen evidence that tells me yes.

But first I'd make sure that the existing line is not holding vacuum.

ChrisZ wrote: ↑Sun Oct 05, 2025 12:19 am Thanks Worf! Trying to google stuff like the hose inside and outside dimensions is pretty useless, so do you know those off the top of your head?

It's the same as all the other semi-rigid vacuum line. Just pick one in your engine bay. IIRC its 4mm.

Suggest running a second line, leaving the original disconnected in place. That's what I did. Much easier that way.
Can clean it up later when you have access for other reasons. Agree on testing it first, to ensure it really needs replaced.

I've changed this vacuum line, dropped the exhaust and heat shield, and it did nothing for the hard shifting. Even put a vacuum gauge on it afterwards.

Just an observation.