John in KC - Roadster Build Thread

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Originally Posted by cv2065

I guess you just have to remember that you are replacing all of these parts on the assumption that the kit supplied stuff is going to fail. Many have used the Wilwood stuff with no issues, including myself. As with any mechanical item, there’s always a chance of failure regardless of the brand.

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I try to analyze/research and make informed decisions. A lot of people on the forum advise to replace the gas tank fill pipe grommet with an authentic Ford one as the FFR supplied piece tends to leak. Same for the clutch cable if you're going that route, the FFR supplied cable is not nearly as nice actuating as the genuine Ford cable. For the master cylinders, the odds are on your side the FFR supplied Wilwoods will be just fine. To me, just the reported failure rate for this critical device is way too high for my comfort. And this has been known for decades. Not to mention the absolute PITA they are to change.

To me, a clutch MS failure means you're on a tow truck. A brake MC failure means you have very limited braking capacity (thanks Paul).

Of course everyone is free to make they're own decisions.

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Originally Posted by Mike.Bray

I try to analyze/research and make informed decisions. A lot of people on the forum advise to replace the gas tank fill pipe grommet with an authentic Ford one as the FFR supplied piece tends to leak. Same for the clutch cable if you're going that route, the FFR supplied cable is not nearly as nice actuating as the genuine Ford cable. For the master cylinders, the odds are on your side the FFR supplied Wilwoods will be just fine. To me, just the reported failure rate for this critical device is way too high for my comfort. And this has been known for decades. Not to mention the absolute PITA they are to change.

To me, a clutch MS failure means you're on a tow truck. A brake MC failure means you have very limited braking capacity (thanks Paul).

Of course everyone is free to make they're own decisions.

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Agreed. I changed my clutch out to the Tilton as it's the hardest to get to (thanks Mike :D). That said, I think a Tilton will be harder to replace than the Wilwood if it did happen to go out. I guess its 6 of one, half dozen the other.

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Originally Posted by cv2065

Agreed. I changed my clutch out to the Tilton as it's the hardest to get to (thanks Mike :D). That said, I think a Tilton will be harder to replace than the Wilwood if it did happen to go out. I guess its 6 of one, half dozen the other.

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You know, I'm sure Tilton has MC failures also but in over 30 years of using them I've never heard of one. If you watch the video in the link below there is quite a bit of difference between the two in both design and materials.

Rear Differential & Friction Modifier

I don't remember how I came across this, but I was watching a video about differentials on the Flyin Miata youtube channel (it has a ton of great content, a good bit of which pertains to cars like ours) and learned why my Traction-Lok differential chatters the inside wheel on tight turns.

On a tight turn where the outside wheel needs to go a much further distance proportionally than the inside wheel, it can cause the clutch pack to engage and try to mitigate the relative difference in wheel torque/speed. So it's basically engaging the differential clutch to drive the inner wheel while you want it to turn. This can cause the car to 'push' and the inside tire to chatter during a tight turn. This isn't right or wrong, it's just how it behaves in our cars with the standard 4 oz of friction modifier. But one thing you can do to help each wheel move more freely and get rid of the chatter is add more friction modifier to the diff fluid as that is what modifies the clutch engagement (hence the name).

I'm wondering if the much lighter weight of our cars makes a difference here. Perhaps much heavier cars like the Mustang need more clutch engagement, but lighter cars don't need so much?

The spec calls for 4 oz added to the diff when you fill up the fluid. I did that when I assembled the rear end, but it chatters under certain circumstances. It's ok to add more friction modifier so that the clutch plates can slide a bit easier, if needed. I read on an older post where Gordon Levy adds 6 oz instead of the standard 4 oz. (He's been tracking these cars for a long time...I trust his advice.) So I'm adding 2 more ounces. You want the clutches to engage and give you the limited slip, but you don't want them to engage so much that they inhibit the differential wheel speeds needed for regular driving. And if they engage too aggressively it can actually cause the inside wheel to try and speed up on a tight turn, which can cause the car to push as the rear tires are trying to go in a straight line when you actually want them to turn. So bottom line, limited slip is good for traction but there is such a thing as too limited of a slip that prevents the car from rotating and handling the way you want it to on the street. If you're a drag racer you want the clutches to engage aggressively, but for the street or road racing/auto-x not so much.

So here we go. Jacked up the back end, sucked out 2 oz of diff fluid:
Attachment 228513

Measured to make sure I was taking out the same amount as the amount of friction modifier I was adding. (I had the fluid level with the fill hole when I first filled it, so didn't want to over fill by adding more fluid.)
Attachment 228514

The fluid looked pretty good, which is should with only about 1300 miles on it. I thought about changing all of it, but really no need if it looks good:
Attachment 228515

Added half a bottle of friction modifier and done!
Attachment 228516

I should be able to feel the car more willing to rotate with less understeer under power in a tight turn now that the wheels aren't locking together quite so aggressively. These cars already tend to understeer with the stock suspension setup and I think this will help get more toward the neutral feel I'm looking for. One step at a time!