MarkBytes

my 1986 951 appears to have the original rubber "elbows" and thin nylon vacuum lines. I suspect some leakage and have had at least one (known) occurrence where the "elbow" fell off a fitting.

Question #1: I'm thinking replacement would be easiest if I dumped the elbows and thin nylon tubing and replaced with simple silicone vacuum line. Make sense?

Question #2: Any suggestions on finding the Silicone vacuum line? Vendor? Size?

Question #3: In my old "british" days I used to coat vacuum line connections with a bit of gasket shellac to keep them from coming off. I've never used silicone lines, but any reason I shouldnt do this?

Gracias!!! Mark

IceShark

This place has about the best prices on the net:
http://www.hosetechniques.com/

Good luck on the various sizes and lengths needed. I still haven't found a materials list for the 951. I'm waiting for the local Pep Boys or someone to start carrying the hose so I can start replacing and run back and forth to get what I need.

I believe 4mm hose is the most used as it will stretch over the 5mm fittings but is tight enough for the slightly smaller ones.

I don't know about using shellac but have seen plastic tie wraps used on lines that undergo positive boost pressure.

If you start replacing, keep track of the lines and sizes so we can get a materials list together.

MarkBytes

Anybody out there have a "micrometer" in metric that could "mike" the nipple for a typical 944 T vacuum line?

Seems they sell silicone vacuum lines in 3mm, 3.2mm, 3.5mm and 4mm. Not sure what to order.

Thanks!

IceShark

If you look around the common hardline of black plastic is 4mm O.D. while the nipples they connect to are somewhere around 4 to 5 mm O.D. depending on the nipple. So you would want 3.5 or 4.0 mm I.D. to replace that plastic hardline. It also depends on how good the hose barbs are and whether the line also goes into positive pressure under boost. Not sure how much the silicone will stretch. I'm guessing heavy wall tubing at 4.0mm I.D. would probably do the trick for most.

Then there are some 8mm O.D. fittings and the biggest one is the brake booster which is up somewhere around 13.5mm. You would probably want to go to a 1/2" I.D. line for that if you are going to bother and replace. I didn't notice any 6.0 or 10.0mm fittings in my casual inspection.

In summary it is a real grab bag and who knows the total length needed until you actually pull them.

If you really want to get going get some short samples to test for size, block off a week to not use the car, take them all off (after well marking where the heck they go) and get an idea as to length required, then order the hose. Oh, and I think you might have to remove the intake manifold to get at all the lines under there.

MarkBytes

IceShark,
Thanks for the good info. I plan on keeping a log of all the vacuum line used and posting to RennList when done.

IceShark

Well, I'm glad someone is going to take the plunge first and start to sort this mess out.

What I discovered so far:

Hose Techniques seems to have some of the best Silicon Vacuum Hose (SVH) around, but I'm starting to feel like it is a RiceBoy marketing scam like SuperIonWhiteBlowAwayTheDarkElectricBlueMagicILookKewl headlight bulbs. Its big benefit being the thick wall in small 3.5 and 4.0mm size. High temp is ok at ~ 350F, but that can't be the best silicone in the world as they claim as I know the big Magnecor silicone jacket plug wires will take double that laying down. But 350F should be more than enough as long as you don't lay it across headers or something dumb. HoseTech only makes the full color lines up to 10mm so would be tough to match colors on the larger sizes if you are into looks and want anything outside of red.

Burke Industries (Purosil) also makes it but from what I've been able to figure out it is much thinner wall tubing so I don't know how well it will take vacuum or pressure. Specs on the tubing are hard to come by, no doubt due to their being in Chapter 11 and not spending a lot of money on web pages. But their trademark blue sure would be easy to match.

One big thing we want to avoid is smaller hoses blowing off nipples on boost without relying on hose clamps as much as possible. Boosted RX-7s apparently have this problem in spades. So that is why I'm not sure if 3.5 or 4.0mm would be the best for the 5mm and slightly under barbs. The local PepBoys had some Asian thick wall hose kits in stock today and I went over this evening. The smallest they had was 4.0mm which seemed to fit pretty tight on an old 5.0mm blow off valve, but they didn't have any 3.5mm hose to compare to. And the colors were pretty strange so I didn't buy any to experiment.

The other issue is the larger unreinforced hose like 8mm up collapsing under vacuum (not as thick walls % wise as smaller tubing). Would probably have to use clamps on those bigger lines in any event for boost. And pure silicone would require a special hose clamp not to cut it.

Final issue is oil from the turbo system air lines. Oil will eventually ruin standard silicone. The first sign is oil bleeding through the walls. I think that is one reason Pursoil has that red rubber layer on the inside of their larger turbo connection hoses, but I'm not sure.

I'm thinking just replace the small plastic (4.0 to 5.0mm) vacuum line with this scam and see how it goes. All the bigger stuff seems to be pretty beefy, no plastic or cheap rubber and not in leak failure mode.

You would think this would be a simple deal, but for some reason it isn't.