I just got my new 408 buttoned up and running, took it out for a couple break-in runs and the car is back on jack stands!

Got around 40 miles on the car when I noticed a "loose bolt" noise under heavy braking/engine braking. The sound is definately coming from the center area under the shifter and the shifter starts to vibrate a little as well. Pretty much sounds like a bolt is bouncing around in the bellhousing when the cars weight shifts to the front.

I initially thought to myself that I must not have torqued a PP bolt and it has back out so I put the car on stands, dropped the exhaust and the inspection cover but they are all there.

Now I am thinking maybe a torque tube bushing is bad or a bushing bolt backed off. The car is still on stands and I will attempt to remove the TT this weekend but thought I would share my problem and see what others think or have learned from their experiences with these cars.

It really sucks to get a new motor in, get it running, then tear the car back apart!

 

I've heard that sort of noise on other cars and it turned out to be a loose heat shield on the exhaust.

 

I was hopefull that was the problem but everything was nice and tight, I initially thought it was an exhaust flange bolt that came loose but no luck. Torque Tube come out today..........

 

Found the problem, sure enough, a loose bolt! Well, I should really say a broken bolt. One of the bolts broke from the bushing and of course the noise I heard was it bouncing around in the TT. Just thought I would share the conclusion to my problem as too many posts on this board are not followed up.

 

Good fined and guess as to what the problem was!

The bad news, you had this issue to begin with, the good news, you found it before it became a major issue.

Best of luck with the fix and I hope it goes better than it all started for you.

 

So whats the recommendation for replacement TT bushing bolts? I know I have to get one for sure but do we re-use the others or replace with grade 8/ 10.9 equivelant?

 

Ok. something does not make sense here. 1 bolt out of 6 sheared?

 

The bushing with the broken bolt was very badly worn which may have aided in its destruction but I more than likely put too much stress on the TT when I removed the engine.

 

If that's the case, then you probably have bigger issues....than just a broken bolt. Check the bearings, drive shaft runout, input shaft, etc.

 

Sure hope not but will definately inspect as that is very possible...

Called the local chevy dealer and they wanted $7.50 ea for replacement bushing bolts!!! And they have to be special ordered!

I understand the originals are torx head bolts but I may just have to replace them with M10x1.5 (10.9) 6-point bolts as I have them on bench stock. Anyone see a problem with this or has done it before?

 

So does anyone know the torque specs for the bushing bolts?

 

See below. I believe what you are looking for is coupling to propellor shaft bolts.

Fastener Tightening Specifications
Application
Specification

Metric
English

Bearing Housing Assembly to Coupling Bolts
70 N·m
52 lb ft

Bearing Housing Assembly to Driveline Support Tube Bolts
65 N·m
48 lb ft

Clutch Actuator Cylinder Mounting Bolts
12 N·m
106 lb in

Coupling to Propeller Shaft Bolts
70 N·m
52 lb ft

Driveline Tunnel Closeout Panel Bolts
10 N·m
89 lb in

Driveline Support Assembly to Engine Flywheel Housing Bolts
50 N·m
37 lb ft

EBTCM LH Mounting Bracket Mounting Bolts
50 N·m
37 lb ft

Flexplate to Flexplate Spindle Bolts
50 N·m
37 lb ft

Hub to Flexplate Spindle Bolt (Automatic Transmission)
50 N·m
37 lb ft

Input Shaft Bearing Positioning Bolts
35 N·m
26 lb ft

Input Shaft to Coupling Bolts
70 N·m
52 lb ft

Negative Battery Cable Bolt
15 N·m
11 lb ft

Output Flange Bolt
50 N·m
37 lb ft

Propeller Shaft Hub Clamp Bolt
130 N·m
96 lb ft

Rear Exhaust Hanger Mounting Bolts
50 N·m
37 lb ft

Rear Shock Absorber Lower Mounting Bolt
220 N·m
162 lb ft

Rear Suspension Crossmember Mounting Nuts
110 N·m
81 lb ft

Shift Control Mounting Bolts
30 N·m
22 lb ft

Shift Control Closeout Boot Retaining Nuts
12 N·m
106 lb in

Transaxle Mount Bracket to Differential Bolts
50 N·m
37 lb ft

Transaxle Mount to Rear Suspension Crossmember Nuts
50 N·m
37 lb ft

Transmission to Driveline Support Assembly Bolts/Studs
50 N·m
37 lb ft

Transmission Oil Cooler Rear Pipe Front Fittings to Junction Fittings at Engine Flywheel Housing
27 N·m
20 lb ft

Transmission Oil Cooler Rear Pipe Rear Fittings to Transmission Fittings
40 N·m
30 lb ft

Transmission Oil Cooler Rear Pipe Front and Rear Retaining Clamp Bolts
12 N·m
106 lb in

Transmission Shift Control Cable Bracket Retaining Nuts
20 N·m
15 lb ft

Transmission Shift Rod Clamp Bolt
30 N·m
22 lb ft

Transmission Wiring Harness to LH Transmission Case Retaining Bolt
2.5 N·m
22 lb in

 

Thank you sir, that was very helpful.

Jerry