Horrible Exhaust Leak

[Alan]

For the past month my car has been suffering from a progressively worsening exhaust leak. Figured it was the manifold leaking, so I patiently wait for my manifold to finish being built.

So the other day I'm poking my head around under the hood while the car is running, and notice a hair dryer like stream of air coming from the firewall/exhaust area. Under further inspection, it is leaking at the joint where the downpipe meets the exhaust discharge elbow.

Under even closer inspection, I realize one of the studs missing a nut. It is an easy fix, I just need to know what size nut to use. Can I use the nut from any Mustang? The stud looks to be about the size of the collector studs on any Mustang. Is this the case? Anyone know the exact size I would need...perhaps I could pick up a grade 8 stainless nut at the hardware store as a temporary fix.

[Philc]

I dont know what size, but...

the housing might be warped. one of mine was, I took it to a machine shop, and they re-surfaced it.

I've heard dont run stainless bolts in an exhaust application. dont exactly know why, possibly wrong coefficient of expantion, might cause cracked housings??

[Pat_in_L.A.]

7/16" coarse thread. Same as most any mustang out there. It should be on any Ford dealer's shelf.

[Alan]

Seriously...you guys are lifesavers. I'd buy you all a beer if you lived in town. Thank you greatly for your help.

[Alan]

Out of curiosity, what is Grade 8? I was always under the impression that was a grade of stainless bolt.

[Pat_in_L.A.]

The "grade" designation indicates the hardness of the bolt as well as determining the torque to which it may be tightened.

Here's a printable chart. Notice the difference in torque specs as the grade number increases:

http://members.aol.com/pullingtractor/torque.htm

[Eyelawdoc]

In terms of strength rating, a stainless fastener is roughly equivalent to a Grade 5 steel fastener. The stainless fasteners are also somewhat more brittle than steel. They should be put together with locktight, oil or antiseize to prevent galling of the threads, to which stainless is prone.

[notopstang]

I'm confused... Eyelawdoc states that SS is equivalent ot a grade 5 steel, but Pat's link shows that the SS torque settings are at least as high if not higher than the grade 8 fasteners...

what part of the equation am I missing here?

Thanks
--Javier

[Eyelawdoc]

Torque settings are not equivalent to bolt strength ratings. You are comparing apples to oranges.Stainless torque settings are higher because there is more friction between the threads of stainless fastners. When torquing stainless fasteners one should always use loctite, antiseize or oil on the threads to keep them from galling and binding up.

Beware of using stainless fastners in high stress locations. They are more brittle than regular steel fasteners. Those of you who have tired to bend 304 stainless tubing for exhaust pipe, fuel, or hydraulic lines know what I mean!