JWise

Background - In my quest for wider than OEM Cup II rear wheels, I purchased a set of Mille Miglia Cup II replicas which included 18x10 rears (I'm using OEM 17x9 ET70's up front due to their more suitable offset than the replica fronts). These are outfitted with 265/40/18 tires which were a factory spec size for this dimension of wheel. That said, it's one of the narrower tires one would put on a 10" rim. More on this later...

I knew going in these particular wheels had a reputation for being soft and susceptible to bending and cracking. Indeed, the set I bought exhibited all of these issues. I had the rears professionally repaired including having cracked sections cut out, new sections welded in, followed by having them straightened and refinished. They came out looking great.

The PO had an issue with one of the rears exhibiting a slow leak in cold weather, going flat over a period of a week or so. I had hoped it was from one of the cracks and that my repairs would correct it. The problem remained but was much improved and manageable as it generally only showed itself when temps dropped below 50 degrees and I'd only have to top it off every month or so rather than it going absolutely flat.

Yesterday, I noticed the one wheel was very low on pressure, much more so than usual. No problem, I'll just air it back up. However, after doing so, I could hear air hissing so I started looking for the leak. I isolated it to a spot along the bead seal. Hmmm, well it was fairly cool in the garage so I brought the wheel inside and warmed it up. Afterwards, I aired it up to 34psi. No more hiss was detectable, but when I checked it this morning it was already down to 26psi so the leak is still there and now it's happening even at room temperature and at a fairly rapid rate.

So, what to do? I've thought about the following options:

1. Shoot it full of Fix-a-Flat and hope it seals it
2. Remove the tire, thoroughly clean the bead seal area for proper adhesion and re-mount. Note: I thoroughly cleaned it prior to mounting the current tire.
3. Install larger 285's on the theory the wider tire will produce a tighter fit and/or alter the angle of the bead seal for hopefully better sealing (I suppose it could also possibly make it worse)
4. Dump 'em, and move on to Carrera III's

I love the look and would like to make it work. As previously mentioned, up until now it's only been a minor annoyance - but if it won't hold pressure at room temp I'm going to have to take some sort of action. What are the collective thoughts of the forum? Thanks in advance!

jpNcos

I doubt options 2 or 3 would work. Try 1 if that don't work move on to 4.
Good Luck. No matter what you decide that is one beautiful 928.

jcorenman

Jarrod,

We recently found a set of the same 18" wheels and had them checked and refinished, we got lucky as all four were straight and true-- and hold air. (We're running the 18x8" fronts with 235/40 tires, ET52 IIRC, handles fine but prefers to be aligned to the toe-in end of the spec'ed range).

On our car, there is no room for anything wider than a 265/35 rear tire on these rims (PS2's in our case).

I vote for #2-- mark the leak location as best you can on tire and rim, then have the tire removed and carefully examine wheel and tire at that location. I bet you will find something.

Cheers,

Glen McCartney

Jarrod, I had a bead leak issue on my wife's AMG. Took to my friends shop, broke the bead, it looked OK. Then they showed me a trick they have been using for years and it worked. They reseated the bead pouring brake fluid around the bead. Sealed perfectly, said it is a trick hey've used for years. Just make sure to clean all excess off so it doesn't damage paint.

blown 87

Wow, that really sounds like a very bad idea.

Glen McCartney

Been fine for 3 weeks, brake fluid softens the rubber to get better seal, they only used a small amount. Said they been doing it forever. Talked to another guy at a tire shop, said same thing.

blown 87

Yea, it swells the rubber, turns it to goo in the long run.
Not something I would consider doing even on a lawnmower.

Lizard928

I'd be less concerned about the effect on the rubber as suppose to the effect of the brake fluid corroding the alloy rim.

JWise

FIFY, lol.

Keep your thoughts coming, everyone! I must say I'm wondering if there's some sort of spot sealer that I could use to seal the leak itself. I'm not crazy about putting a whole can of Fix-a-Flat in there when it's such a small leak, but if there was a viable option for a spot seal I'd be open to it.

Speedtoys

FIND THE LEAK.

Manage what makes it leak.


spray bottle of water with a tad of dish soap in it...patience, just do it.

jpNcos

Throw the wheel in a kiddie pool to isolate the leak.

JWise

Guys, I know right where the leak is - I'm just trying to figure out what to do about it. Punctures are one thing, but I've never dealt with a bead seal issue before, hence the thread. I appreciate everyone's input!

Speedtoys

Then I dont see the problem..you KNOW where the leak is at.

..fix it.

you may have air leaking out through the porosities in the cast aluminum alloy. GM has a published repair procedure for this problem: Inflate the tire to 40 psi or more and immerse the wheel/tire in a dunk tank. If you see bubbles, mark the rim with a grease pencil where the bubbles form.

Then pull the rim out of the water & demount the tire from the rim. Scuff the (inside) of the rim area marked (an inch or so from that area), with 80-grit sand-paper (or say 3 M Roloc™ Bristle Discs) and clean with brake cleaner. Dry the area and cover it with a thin layer of silicone gasket sealer. Allow the silicon to cure for a few hours, and then remount the tire & balance.

JWise

Thanks for the specifics, that's exactly what I need! I found one other thread on this issue. It referenced a similar repair using Permatex Indian Head Shellac Gasket Compound. Duly noted, gasket sealer will probably be my first choice, but I appreciate all input. Isolated use of brake cleaner to swell the rubber intrigues me as well, though I wouldn't want to do the whole bead seal with it for the reason Greg stated.

Speedtoys

The brake cleaner is to CLEAN the area for the sealant. Not to use as a sealing agent.