LT1 guys, see anything strange in this picture?





How about now?




Yessir, that's correct. The accessory bracket snapped at the top bolt. It was all barely held together by the belt. I'm lucky it didn't come apart completely and make a complete mess of my entire engine, hood, and me.

The opti is toast, I don't know if this is the cause of it or not. I'm not sure how, but it seems quite coincidental that both failed at the same time.

 

Wow, you know I've personally broken a bunch of PS mounts off those accesory brackets. I guess hi revs???

 

The car died on the straightaway, I don't know for sure when the bracket actually broke. Certainly not before Saturday as I had it apart until Friday doing other work. You set the limit at 6700, I hit it occasionally but try to shift at about 6500. I guess that's a lot higher than the 5500 stock, and I'm above 3500 all day.

So do you know of a better replacement or a way to strengthen it?

 

Wow! if revs are doing it I guess I'll be looking for an underdrive damper, is the ASP945803 any good?

(It's 22% underdrive so an engine was running at 7K it would drive the accessories at the same belt speed as a stock engine going at 5460 right?)

 

I've never seen that happen before! Vibration induced fatigue from the high rpms?

I'm saving for a C6Z, but more and more I'm thinking an '01 or '02 C5Z would be a nice gap filler for a few years. I hate to say it but it's getting to the point that C4s just take waaay too much effort to put on a road course (and be able to run with the big dogs) short of turning it into a full-up gutted track car / spending Z money. It's the little stuff driving me insane...alternator a couple months ago. High pressure ps line (DRM ss braided line) a couple weeks ago. What's going to happen this weekend, I have no idea?!

 

96GS#007.....if you let up just a little on how hard you're punishing that poor GS - it might last a little longer between repairs

 

Bring it to a precission welder and beef it up a little.

 

I hear that! Just to keep it running within the last month I've had to do:

both rear wheel bearings (wear item)
right rear suspension knuckle (failure)
accessory bracket (failure)
fire damage (bad luck)
optispark (failure)
exhaust (failure, but it's aftermarket)

My competition brings their C5Z's to the track, put up similar lap times with the AC on and radio blasting, and go home. I gather up a group of people and push my damn car up on the trailer. Then I spend every night until 2 am fixing it while they cruise around town in their warranteed cars

 

Now that is surprising.....

 

 

Haven't seen that one before. I'd just put another one on there and call it a day. If if happens again, then I'd give it sme more attention.

 

In the post above I asked the rhetorical question "what's going to happen this weekend...?"

2nd session out on the track I got my answer.... wheel bearing

 

Is there any particular reason you're not using the factory flanged bolt in that location? Are the washers you're using there hardened? How many of the rear accessory supports are still in place?

 

Excellent question!

 

you obviously have a vibration problem or a bent pulley, or something in that realm. The best thing to do for the broken bracket in my opinion is:
1. obtain a dial indicator with the little wheel on the end of the stick,
(I think they make different feet for it)
2. do a runout on each pulley.
3. do a runout on your powersteering pump shaft.
4. Check each pulley before and after the powersteering for cracks
5. I would (don't laugh) try a modified frisbee to see if your harmonics might be affected by the belt screaming around the pulleys faster than it's design speed.
6. see if there's an opportunity to change out your belt tensioner for either a new one, or one with extremely low time. It could be that yours has crud in the pivot area, and the spring cannot react fast enough due to high friction losses.
7. try using something called dye penetrant on your brackets after your last race (every time) to determine the number of hours you are going to get out of a bracket, and about an hour before you suspect failure, change the bracket, and cut it up with a hacksaw in some manor to alert you that that bracket has about reached it's racing life.
8. try changing the pulley diameters on different things to ascertain if the current frequency of speed vs pulley diameter isn't setting up a belt flex motion that's resonating at the bracket's destruction frequency.

other than that, I have no clue

 

Geez Scary... that sucks. As far as the competitiveness of the C4, I think you still got a good car there. When I was doing autox, I saw some pretty serious guys do VERY well with C4 cars.

 

Mostly becaue I didn't know they weren't...guess I'll be making a trip to the dealership.

Additional information - upon taking the bracket off I noticed that there were only two bolts. This didn't seem odd until I looked into my FSM for torque specs and saw three. The middle bolt under the tensioner pulley was gone. I can't see how it could have come out due to it's position (trapped under the pulley) so at some point it didn't get put back in.

That could very well have caused extreme loading on the upper attachment which caused it to fail over time.

 

Good suggestions, thanks. The AC replacement pulley was slightly farther back than the WP and Alternator pulley, putting a cantelevered rearward load on the upper corner. Another possible contributing factor.

I put it back in position and will keep an eye on it.

 

Lucky you...at least your car didn't catch on fire.

 

Are you by any chance running FMRFST's AC Delete Bracket? If so I have found that you can either shim it with a washer to get the belt perfect, or in my case where I needed a smaller pulley, it came with an insert that I had to drill to fit diameter wise, but is also shimmed the pulley into the perfect spot.