1996 Collector Edition Corvette

[wxo]

I decided to do more investigation and in the process may have figured out why the hanger doesn't match the original attaching point.

Here's what I wrote to MagnaFlow:
Your request for photos from under the car, which is up on jack stands, leaves very little opportunity for accurate perspectives on this problem. There is just not enough room under there.
I decided to do a comparison of the old and new to explain the problem. In the process, I discovered the real reason for the mismatch of the hanger and attaching location.
I started by matching up the two cats like this:

In this photo, you can see the mismatch between the location of the original bracket and that of the new bracket position on the rear end of the cat.
There is at least an inch of difference between the two when the new bracket is positioned as far back on the cat as possible without falling off the end.

Then, looking everything over, I discovered that the new cat is shorter than that new cat by, maybe an inch. See photo below. This is bad because this end must meet the exhaust system perfectly when the exhaust system is installed in place. If you are unfamiliar with C4 Corvettes, the entire exhaust system from the cat back is removed in one piece.
Looking at this photo you can see why the hangers don't match. See photo below.

Here you can see that the first bend coming out of the exhaust manifold is different that that of the original cat system.
If the new cat had a shallow bend like the original, it would move the rest of the system, including the cat, further back so that
both assemblies are the same length.
By positioning the cat further back a sufficient amount, the mount would then be able to slide onto the cat and at the same time
match the original mounting location.

Here is another photo showing the difference in the two bends. Decreasing the severity of the bend on the new cat would serve to move everything back including the cat, and also even out the total length to match the original.

Let me know what you think.

[TireSmoker]

I think the 3rd photo makes your point clear. You can see how much further forward the inlet side of the cat is compared to the original.

[wxo]

After a few exchanges with MagnaFlow, they gave me a case number and told me go back to Summit and exchange this one for another one. I told them I don't trust that I will get a replacement that fits so I would like a refund for this one and the other one I bought. I told them that I'm going back to the original cats. They flow well and fit well.

[wxo]

With the Magnflow defective cat in the rearview mirror, I felt somewhat relieved to move on, so I started work on getting the old cats back on. I bought some really nice stainless exhaust header studs and nuts to replace the rusty studs on the manifolds. So out of 6 studs, the first three on the driver's side came out without issue, and the first one on the passenger side was a bit stubborn but came out. The fifth stud was tight and just broke off. The last stud was also, very tight, but I had learned my lesson on the previous stud and carefully worked at it and got it out without breaking it, too. So I'm faced with this:

As I see it, I have two options. 1) drill it out and try to work it out with an easy-out. (This option is very iffy. I've not had a lot of success with it in the past) 2) hold an appropriately sized nut over the hole and try to weld the broken off stud to the bolt without welding the nut to the flange (Considering my welding talents, this option is also very iffy). The beat goes on.....

[wxo]

Today, I decided to ignore the broken stud on the right side and work on installing the OEM cat on the left side. The first thing I had to do was reinstall the hanger with the inaccessible bolt that was such a pain to remove. After some careful thought, I decided that the bolt didn't need to be as long as it was, so I cut off about 1/4 inch. Wow! What a difference! It went right in without much of a struggle at all. Once the hanger was in and torqued, I installed the 3 new stainless studs into the exhaust manifold and with a brand new donut, in went the cat. Everything is snugged up now and, next chance I get, I'll torque everything and move on toward the rear end.

[wxo]

ANOTHER SNAG! This time on the other bolt on the same cat hanger where I had my previous struggle. This is really a stud and a most important stud. It serves as a grounding point for four ground wires. First, I torqued the stud in place and then attached the four ring connectors and then the nut. When I tightened down the nut, the four connectors rotated and ripped off three of the connectors. This is also in another inaccessible place! RATS!
I don't have a reasonable plan in mind on how to get myself out of this mess.

[wxo]

I got this book for Christmas.

It's really interesting, especially for a C4 owner. I'm about halfway through it and I've enjoyed reading about the development of ABS systems and the reintroduction of the convertible option on the '86 Corvette. I recommend it.

[wxo]

Today I repaired the wiring to the grounding point. Instead of adding new ring connectors to each of the individual grounds, I consolidated all three into one wire to the grounding stud. I also had to extend the length of the wire to reach the stud. Access to this wiring was quite restricted so the result, although satisfactory, is not something I am very proud of. This grounding point is used by the PCM, the ignition module and the wiper motor so I'll need to keep this in mind if I start having problems in those areas.

[wxo]

Since my last update regarding the ground connections, I have been inching my way toward the leaking pinion seal. Today, I have arrived!

To get here, I had to remove, first the drive shaft. That came out rather easily leaving the driveline support beam or “C beam” as the next battle. Once I removed the four bolts, the battle started. This thing is nestled in place between the Dana 44 rear and the ZF S640 transmission. There is little room to maneuver when it is also enclosed by the drive shaft tunnel. So here’s what I had to do to get it out:
The beam will come out toward the rear, but it must be moved forward as far as possible. It must go forward enough for the ends of the beam to move past the diff in a downward direction. I found that rotating the u-joint helped it to clear the diff entirely. During the process, I raised and lowered the trans to allow manipulating the beam in different situations while moving it forward and backward. Using a 2x4 to wedge the ZF toward the driver’s side, will provide the small amount of room needed to get the beam all the way forward. I found that removing the 13mm bolt on the mount for the parking brake on the passenger side allows the parking brake cable to be loose enough to allow the beam to be manipulated around it.

Once out, I examined the bolt holes and could see evidence of movement. I found several bolt holes that were oblong and a bit larger. I don’t know if the enlarged holes will contribute to movement again or if the new mounting plates will hold it into place sufficiently to prevent movement under hard acceleration. I’m considering getting another used replacement C beam with normal sized holes.

So now I’m at the objective.

I’m waiting for the correct 1 5/16” socket to arrive so that I can test my strength against the pinion nut. It should be here in a couple of days.
In the mean time, this afternoon, I decided to change the tail shaft seal in the 6 speed. The old seal came out without a major struggle and I unboxed the replacement seal I had ordered from Amazon.

This seal is unique in that it has a dust boot to keep dust, dirt, and other debris off the main seal. The original seal didn’t have this dust boot. It seems like a good idea so I’m going to go with it.

[GMJohnny]

I would consider drilling out those oblong holes and inserting bronze
bushings in the holes as an option depending on cost of the new part.
McMaster Carr might have what you need. Just a thought.

GM

[wxo]

I have considered this option, BUT the top and bottom holes must be very accurately drilled to match each other. I don't trust myself or any shop to get this right because a problem-free assembly depends on it. The beam is attached to the trans and the diff by very long bolts inserted from the bottom. The top of the beam is about 1 3/4" from the floor pan. There is very little room to access the top to get the nuts started let alone hold them with an open ended wrench for torqueing. Since now that I've bought these beam plates for the top and bottom, the accuracy of these holes is even more necessary because the top plate holds captured top nuts, precisely spaced to match the bolt holes, into which these long bolts must enter when inserted from the bottom. All this would be much easier if there was room to work, but easy access is not a feature of the C4 Corvette. I've located a nice beam on ebay for just a little over $100 plus shipping. I've asked for photos of the bolt holes to verify if they are not worn like mine. They look good in the photos presented in the ad, but I want to be sure before I commit to it. I'm always hoping that I'll never have to do this job again, so I always try to get it right the first time. If you read back in this thread, it's a long involved process to get here since I first started by removing the entire exhaust system. And I still haven't fixed the pinion seal leak.

[MostMint]

I would use an impact wrench on the pinion nut for removal.

I trust you can tell those holes have been oblonged by the piece moving around - as opposed to being cut that way from the factory. I can't tell from the pics if there is evidence of rubbing on the flat where it would have been rocking back and forth, or evidence of the threads grinding on the side of the hole. Are other C4 owners having this problem?

[wxo]

Andy, I've been soaking the pinion nut with Deep Creep for a couple of days and I will try both a breaker bar and secondly, an impact wrench if needed. We will see how that goes.

Regarding the elongated holes in the C beam, here is information about the C beam plates that addresses that:

1. Advantages of C4 Beam Plates.
a. The C4 Beam Plates tie together each pair of bolts (Transmission pair and Differential pair) with a SS Plate.
b. Each C4 Beam Plate also offers a larger contact area of the tensile bolt loads onto the C-Frame. This eliminates the wear on the "C" Frame from a smaller original washer and resulting release of bolt tension.
c. The C4 Beam Plate also acts like one big washer wherein the tensile load from each individual bolt is now shared a bit between bolts (minimum effect).
d. The C4 Beam Plates correct the condition caused by the bolt holes in the Aluminum C-Frame getting bigger or elongated with wear or the thickness of the Aluminum C-Frame from top to bottom between the original bolt two washers becoming worn so that thickness is less releasing bolt tension.
The C4 Beam Plates are definitely worth it if only for the Bolt Load Distribution (Two BIG SS washers on each end) on the C Frame and Ease of Installation. Take Note of the additional Stiffeners on each C4 Beam Plate (The BIG H). There is a BIG Difference between a Clamping Load distribution by two washers and the Clamping Load on ONE BIG PLATE on the Transmission Yoke as well as the Differential Housing.

[wxo]

OK, I've spent too many hours searching and researching the web to find a C beam better than mine. It appears futile, so it's going back together as is.
I expect it will be fine with the addition of the beam plates for added support at the connecting joints. Now on to the installation of the seals.

Just additional info from designer of the beam plates:
Driveline Support Beam, Differential Carrier and Cover Beam - are responsible (for) torsion rigidity of torque delivery aft of the transmission, isolating the counter force from twisting the chassis/suspension planes. We at ZR51 Performance have found that the quality or degree of joint compliancy at both ends of the Support Beam directly affect the quality and level of vehicle acceleration handling. For example, a conventionally set up C4 driveline allows for a slight amount of flex to occur in the beam ends right around the fastener bolt and nut areas. This slight amount of flex at the beam contact planes propagates an undesirable effect know as driveline lateral deflection. The most prevalent affect of this phenomenon is the tendency of the rear end wanting to kick out to the right when aggressively shifting at higher RPMs. By using ZR51 Performance C4 Beam Plates, your C4 Corvette will benefit from higher levels of predictability and smoothness of directional tracking with respect to more intense levels of acceleration handling.

[wxo]

A small, but satisfying step today. I installed the tail shaft seal in the ZF.

It went in fairly easily. First, I prepared the bevel that guides the seal into the hole. With a stone, I removed the burrs, etc inflicted by removing the old seal and then took my time to make the bevel as smooth as I could. In addition, I lubed it with RTV to give it the best chance to slip in easily. Then I gently and carefully tapped it using a small hammer and flat nosed punch. Once the seal was started, I tapped around the flange little by little and I could see the progress as I went. I'm happy with the results.