Sylvain951

I have had the weirdest thing happen to me twice in 2 days. My wheel bearing dust caps came off while driving DE events. The grease made a mess of the wheels and ended my day after about 20 minutes.. I went to my favorite shop mid Friday and they said the bearings were fine But I needed a cap.

I found one used locally and went back the track the next day. same thing happened.

I wonder if the heat from the hub is releasing the cap?

I am sending the car back to my shop to replace the bearings.

also on the cool down laps my brake pedal nearly hits the floor from brake pad knock off. A couple quick pumps and all is fine.

Anyone else that tracks an '86 small Brembo brake 951 have this happen?

Lemming

Drill a 1/16" hole dead center to relieve pressure, if that doesn't work, use a bit of metal tape.

Sylvain951

I thought of drilling the cap. Wouldn't the grease just ooze out? I may try that.

Jamesr6967

Your brake issue makes me think that your rotor could be moving side to side (lateral run out), due to loose or bad bearings (you should feel this on the track tho...) Which would also cause pressure under the cap due to excessive heat.
Or , you have created so much heat from braking that you are essentially boiling your brake fluid and blowing the grease caps as well.
Large trucks have a small pinhole in the center of the cap to release the pressure (I own a 'semi' as well)
You could insulate the pads from the pistons, I have seen aluminum pieces in one of the Porsche magazines specially made to help dissipate the heat.

Van

Some people drill a hole in the cap as Tim suggests; some use a set screw like the Racer's Edge hubs; and some use metal tape.

If your front wheel bearings are tight, than a rear one is causing your pad kick-back. Do you notice it more after a turn in one direction or the other?

VaSteve

They have been blowing off my S2 for years. I drilled the holes and it didn't help. What I did do, was to mount the wheels and mark where the cap ends with the wheel on. Take the wheel off and put three blobs of red RTV on the wheel where the marks are. When it hardens, the cap will press against the RTV and not come off. Works great.

Sylvain951

I do get pad knock off. On the cool down lap I never use the brakes. The first time I go for the brakes at pit in the pedal goes nearly to the floor. A couple quick pumps and it comes right back. At speed with regular braking points the pedal stays firm.

That said the brakes do no pulsate in the least. I run Frozen rotors and Cobalt Friction XR2-3 pads. Best combo so far over non frozen and PAGIDS blacks/orange & Hawks HT10's I've tried.

The car is getting new bearings at all 4 corners and new dust caps with locktite.

Next event in 4 weeks.

Oddjob

Dust caps are a chronic problem. I have had better luck w/ new caps staying on, but once the caps have been pried off a couple times, they coin enough that they no longer hold in the hubs very well for track use. Heat is the issue. Therm expansion of the cast alum hub is greater than the steel cap, so it gets loser the hotter it gets. And there may be something to the grease outgassing and building pressure at high temps, but that would be a high enough temp to be thermally cracking the grease, so it would need replacement at that point. Certainly if the bearings are overpacked w/ too much grease, the problem will be worse.

Some wheels have lips that retain the caps if they fall out (phone dials for instance). But some factory wheels (Fuchs) and most aftermarket wheels do not. So I have used a lot of alum tape over the wheel center opening to keep from losing caps. And have also used RE hubs w/ the set screws on two cars now. That seems to work well, or well enough. I would consider drilling and tapping factory hubs to hold the caps if you have a lot of problems and don't like to deal w/ the tape.

Wheel bearings will grind when going bad. If driven on long enough, a bad wheel bearing can cause a rotor to wear uneven, so it will pulse/vibrate like its warped.

I have never had significant pad knock-back. Never found it to be a problem on 944 brembo calipers. Rough track surfaces may make this more of a problem.

Sylvain951

I have multiple sets of rims. It first happened on my 17" CCWs Classics with RA1's. This has a wide open bearing area. The next day I used 951 Fuchs with R6's and still lost a cap. I have a set of 8" phonedials I was thinking of using for this very reason and wanted to try running the same size tires at all 4 corners so I can rotate them front to rear. I wear fronts faster than rears at the track.

I don't mind using tape. My mechanic seams to think new caps and Loctite should be enough. This is the first time this has happened in 4 years of owning this car doing 8-12 DE days a year. The caps were removed 3 times this year so they could be loose. Maybe this becomes part of the scheduled maintenance when I swap out front rotors I swap out caps?

Lemming

Jim,

Do you know what acceptable rotor runout is on these cars?

Edit: looks like < 0.002" is acceptable for most cars

Chipster

Apply a small amount of RTV to the caps as mentioned above.

I was losing a couple caps a year, tried tape and drilling and they still came loose. I started using the RTV a couple years ago and haven't lost a bearing cap in over 20 track days since.

Sylvain951

What is RTV?

Lemming

http://www.permatex.com/products-2/p...-gasket-detail