1997 Volvo 850 - two loud bangs...

[Ben850]

Which mount did you replace before? That has the indicating noises of the front, lower right mount by the balancer.

[xHeart]

Which mount did you replace before? That has the indicating noises of the front, lower right mount by the balancer.

Yes, aka motor mount. It is Bilstein.
For reference only http://www.ipdusa.com/products/5930/108177-engine-mount-right

[xHeart]

The jack-hammer is most felt at the shift-knob (not steering) and clearly heard during the first 15 minutes each morning while idling at stop-light in D with foot on the brake pedal.

Present at D, 3, or L.

After getting home last night, I found the air-intake tube was off. Looking closer, the shroud appeared few inches lower than usual. The torx screw holding the shroud was all the way out. Confused with the situation, scratching head, pulled car over the cn90 pairs-of-ramp. Soon it became clearer that the bolt holding the radiator was missing. The radiator and cooling fan were at odds.

The radiator was replace with Volvo's some two year ago with coaching from our MVS folks.

Two hours later, it was back to normal, used blue thread-locker this time... hoped that it would solve the mystery of jack-hammer. Nope! It was there this morning.

I will check the motor mount tonight, FCP receipt shows it is Lemförder, not Bilstein.

[xHeart]

The motor mount is firmly in place. I ran the engine while front raised and wheels off, the belt over oil pump/crank rotated smoothly. Idling in N is usual and familiar, love it.

Looked closely at the front brake calipers, pads and rotors. No obvious problem at a glance, rattle spring tightly on the caliper.

It was a wet morning with temperature above 46º. The jack-hammer was not frequent at each stop. I am starting to suspect colder temperature, but why jack?

Few earlier responses to this topic pointed at parking brake cable. I will search the forum for removing the center console next.

[abscate]

I think its in your transmission - the noise is changing on shifting from D to N, right?

If you have ruled out motor mounts, trans is left..

[xHeart]

I think its in your transmission - the noise is changing on shifting from D to N, right?

If you have ruled out motor mounts, trans is left..

:-(

Don't say that Michael.
I am planning on replacing subframe bushing this holiday. Can't retire it yet.
It only jack-hammers in D while idling at stop-light with foot on the brake.

[socompsp]

i dont think its the tranny, the bang would happen during gear shifts while driving forward, typically from 1st -2nd gear. honestly you have to look farther then the 9 or so motor and trans mounts. if the car shakes at idle and in drive you could have bad suspension component bushings. does the vibration decrease as you let off the brake? if so thats what happening, while on the brake all forces from motor vibration are sent through cv shafts into the brakes which is gonna send that energy straight into the strut and spring mounts/seats. as you let off the brake that energy is slowly allowed to bleed into the tire, and pass to the road. but your sub frame bushings will contribute to vibration substantially if they are bad.

[xHeart]

i dont think its the tranny, the bang would happen during gear shifts while driving forward, typically from 1st -2nd gear. honestly you have to look farther then the 9 or so motor and trans mounts. if the car shakes at idle and in drive you could have bad suspension component bushings. does the vibration decrease as you let off the brake? if so thats what happening, while on the brake all forces from motor vibration are sent through cv shafts into the brakes which is gonna send that energy straight into the strut and spring mounts/seats. as you let off the brake that energy is slowly allowed to bleed into the tire, and pass to the road. but your sub frame bushings will contribute to vibration substantially if they are bad.

Feeling better after reading your note.
After the radiator bolt falling off, there could be any fastener, I say.
I am going out to drive a little to explore the source of the noise.

Thanks!

[xHeart]

The search of jack-hammer made me look closely at the vicinity around the cat. What is obvious but many not be the cause, the two bolts fastening the pre-heat plate #8 to exhaust manifold #2 are no longer at work. The bracket on the exhaust manifold is rusted and separated, a gap of 1/4".

Any ideas on clamping it back together? Here is a relevant diagram...

[xHeart]

A photo...

pre-heat plate screws on the exhaust manifold

MVS_0962.jpg (331.91 KiB) Viewed 893 times