ODD rod knock sound.....

[mrvette]

'72 vert, 200 4r auto, '89 truck 4 bolt 355, L98 heads, Injection, closed loop/headers serp drive, electric fans 336 rear,

I have a very strange problem, I already replaced the mufflers on the car, because if I pounded my fist into the left rear muff, it rattled but good, and that's what I thought it was.....so 100 bux later, two new tight stainless muffs in place, and I even bought new sleeves to wrap/patch the two pipes just after the headers...they are solid now....

When pulling in the garage, and hit the brakes, the engine sounds like a rod knock, but it's not, under no other circumstances does the car make that sound....it's equal from both sides of the car, it's not the brakes, i'ts not the differential, car drives normal, no brake pulling or other issues....

If I coast the car down hill going any decent speed, hit the brakes with engine in neutral...no noise....put car in gear, uphill or down hill or on level ground, hit brakes and no noise, UNTIL just before car comes to a stop, those last few feet sounds like pinging/rod knock.....car comes to a stop and the knock disappears, in gear or out.....pull it into gear with car stopped and no knock ease forward, no knock, go to stop and the knock is back...

frigging weirdest symptom I have ever had....

I just jacked the front WAY in the air, and inspected the converter/flex plate with a good flashlight up there and even prying around it seems solid as hell...

I jacked up the rear, spinning wheels in the air, no go...no sound...

WTF???:shocking::hissyfit:

Oh, I have had no lockup on the converter for some time now, down to maybe that O ring on the shaft, or the converter itself, so there something going on with the converter, but that knock?? it would think it would be much more rapid or even louder if it was the converter at speed, being unlocked especially....

front balancer/belts all LOOK fine....

:banghead::hissyfit:

 

[SmokinBBC]

Check to make sure you have no loose bolts in the steering or arms. That last bit of pressure right before you stop may be stressing something up front.

 

[mrvette]

Check to make sure you have no loose bolts in the steering or arms. That last bit of pressure right before you stop may be stressing something up front.

Car stops straight, no pulling, steering tight....I kinds wondering about brake pads....

anyone??:crutches: they are kinda thin, not down to rivets, rotors are good and smooth...:suspicious:

but if it was the brakes, why not do it on a downhill coast?? it ONLY does it in forward gear at the end of the stop, maybe1-2 mph, the speedo even on zero it's so slo....

 

[SmokinBBC]

Reason I mention steering is that I had a very similar problem. Idler arm bolts were loose and the braket banged against the frame when coming to a stop.

I know you have R&P, so just thinking.

 

[bobs77vet]

is there much of an apron on you garage with a height differetntial from the driveway? maybe the suspension is getting loaded as you pull into the garage and you are hearing it "unload"

 

[mrvette]

is there much of an apron on you garage with a height differetntial from the driveway? maybe the suspension is getting loaded as you pull into the garage and you are hearing it "unload"

NOPE, on the slab edging forward, REALLY hear it off the block walls....

does it in the street too, but ONLY when in forward gear, not neutral or reverse.....:goodnight:

 

[bobs77vet]

it may just be reflective noises that are always going on......i hear them when i go to the driveup window at the bank and the curbing and brick walls give a different sound perspective. the car is the same you just hear it differently

 

[mrvette]

it may just be reflective noises that are always going on......i hear them when i go to the driveup window at the bank and the curbing and brick walls give a different sound perspective. the car is the same you just hear it differently

OH, sure, but what is this 'rod knock' sound? it's NOT normal, and didn't used to be there....only in the last couple months....I hear it easing up on traffic to a stop, I hear it going uphill or downhill but ONLY in gear...

:sweat::hissyfit:

 

[Twin_Turbo]

Do yoy feel the knock? Almost sounds like your lockup is engaging. Did you wire the brake release switch properly?

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[mrvette]

Do yoy feel the knock? Almost sounds like your lickup us engaging. Did you wire the brake release switch properly?

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NO feel to it what so EVER, nothing, not steering not brakes, not vibration even, just sounds like a freeking ROD knock...like one hell of a ping on acceleration because of too much timing/too lo octane....

I even dropped the timing back this morning, just in case...but it's the 20 years old standard TPI speed density system with L98 cam in there....I dropped timing back to 6* methinks 8-10 is more normal....and readjusted the idle....

no real change, engine don't pull as hard now, but knocking persists, and stops when car is totally still....

why ME Lord? WTF did I do???eh?? damnit!!@#@!!:hissyfit:

 

[Twin_Turbo]

Does the knock relate to vehicle speed or rpm?

Weird fricken prob indeed

Got a way to shoot a vid?

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[Twin_Turbo]

Maybe it's the hydrobooster

In gear, engine lugs down, with booster more load on p.st. pump.....

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[mrvette]

Does the knock relate to vehicle speed or rpm?

Weird fricken prob indeed

Got a way to shoot a vid?

Sent from my GT-I9000 using Tapatalk

Maybe it's the hydrobooster

In gear, engine lugs down, with booster more load on p.st. pump.....

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I wish I could do a vid....but all I got is a still cam....got a cphone, but dunno how to do any vids off it....no clue, never needed...
engine at idle stays same ~650-700 rpm HB feels same coasting downhill for a ways in neutral, I have maybe 500' to coast and reach maybe 10 mph...hit the brakes and no sound, no matter how hard or soft on the pedal...

engine mounts....hummm. causing the exhaust to clank against the cross support....but engine don't turn backwards in reverse, so why not backing up the hill?? and hitting brakes? :hissyfit:




nutty, I know full well, otherwise I not be asking....guaranfuckingTEE I WILL find this MFer and when I do, it will be posted, but I getting sorta to end of solutions...

 

[big2bird]

Knock, or a "crack."

My list?:

Check a arm shaft bolts.

Tranny yoke to spline

U-joints

Pinion gear slop

Cracked spring pocket

Maybe cracked rad support.

Something else stupid like that/these items.

 

[mrvette]

Knock, or a "crack."

My list?:

Check a arm shaft bolts. Not a single knock, a high rate of speed knock

Tranny yoke to spline OR U joints?? why not in reverse??

U-joints on the drive shaft, is my next exploration...maybe tmrw after a couple cups of coffee.....

Pinion gear slop forward or rear I would have to hear some whine...nothing and no clunks either.....

Cracked spring pocket UP FRONT??

Maybe cracked rad support. it's new to the car and a few years ago it was out, and fine....but it IS a replacement ...electric fans and I can't see how

Something else stupid like that/these items.

OH, believe ME, it's STUPID..... :crap:

 

[big2bird]

Knock, or a "crack."

My list?:

Check a arm shaft bolts. Not a single knock, a high rate of speed knock

Then it's engine.

Rear main thrust bearing

Water pump/fan

Cam sprocket

Accessory engine bracket cracked

Rad support rubber/electric fan blades

Oil pan/crank scraper/windage clearence issue

 

[redvetracr]

Knock, or a "crack."

My list?:

Check a arm shaft bolts.

Tranny yoke to spline

U-joints

Pinion gear slop

Cracked spring pocket

Maybe cracked rad support.

Something else stupid like that/these items.

you forgot the loose nut

























































behind the wheel

 

[mrvette]

That was a shot.....but U missed....

 

[turtlevette]

My way of diagnostic testing, keep driving it until soemthing breaks. About 10 years ago i had a noise on the vette that sounded like a rod knock but some other times it didn't.

Kept driving it and it finally threw the rod through the side of the pan on route 3 about 6 miles from the house. And it kept running good enough to get me home. The dude following me a bit closely on route 3 put his wipers on a few seconds after it blew. At least i got a good laugh out of it.

 

[bobs77vet]

i was thinking water pump also....although i cant tell you why under only those conditions it does it.

 

[1Michel]

If I coast the car down hill going any decent speed, hit the brakes with engine in neutral...no noise....put car in gear, uphill or down hill or on level ground, hit brakes and no noise, UNTIL just before car comes to a stop, those last few feet sounds like pinging/rod knock.....car comes to a stop and the knock disappears, in gear or out.....

Have you tried stopping the engine when rolling and then brake to stop the car without the engine running?

If the noise is reproduced just before you stop like the other times, then it's not the engine.

 

[mrvette]

I gone ape **** on this bitch over the last several hours, wife driving forward and back in the garage, on the brake easing forward and me under the hood with the open tube stethoscope, and even with the probe on the suspension and control arms, much less engine, heard absolutely NOTHING....

in back I could hear it, jacked the POS SOB MF'r up in the air, rested on stands, and with and without wheels, got wife to do the same, but really land on the brake in gear but heavy so to actually stop the rotation....as it came to a halt, I could hear that damn tapping noise....I got under that car and pried/wiggled/jiggled every possible point that made any sense....listened again with open tube scope, and found the only thing making any sense was the brake pads....they are worn but still only 1/2 gone.....so lifetime warranty to Auto Zone and tmrw around 2pm maybe I can trade them in....

last purchase was '03.....so I guess I had my use....

still UNsure it's the pads, and they seem to mimic a rod knock SO well, I have had clicking sounds in the past, turned OUT to be a ****** RETURN on a rotor, without surface grinding, so the pads could clunk and click like a olde tyme needle scratching over a record....at this point, I got no where else to go....so 4 wheels with pads, and see WTF....:crutches::huh2::bonkers:

 

[big2bird]

I gone ape **** on this bitch over the last several hours, wife driving forward and back in the garage, on the brake easing forward and me under the hood with the open tube stethoscope, and even with the probe on the suspension and control arms, much less engine, heard absolutely NOTHING....

in back I could hear it, jacked the POS SOB MF'r up in the air, rested on stands, and with and without wheels, got wife to do the same, but really land on the brake in gear but heavy so to actually stop the rotation....as it came to a halt, I could hear that damn tapping noise....I got under that car and pried/wiggled/jiggled every possible point that made any sense....listened again with open tube scope, and found the only thing making any sense was the brake pads....they are worn but still only 1/2 gone.....so lifetime warranty to Auto Zone and tmrw around 2pm maybe I can trade them in....

last purchase was '03.....so I guess I had my use....

still UNsure it's the pads, and they seem to mimic a rod knock SO well, I have had clicking sounds in the past, turned OUT to be a ****** RETURN on a rotor, without surface grinding, so the pads could clunk and click like a olde tyme needle scratching over a record....at this point, I got no where else to go....so 4 wheels with pads, and see WTF....:crutches::huh2::bonkers:

Broken parking brake springs sound like that. Sometimes pads on a "turned" rotor, or a pad that came off the backing.

 

[Twin_Turbo]

If the parking brake retainer pins allow the spring and cup to go too far they hit the back of the wheel studs. Bent backing plate? Something loose in there?

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[mrvette]

Well, I changed the pads, and guess what?? the sound is not nearly as pronounced and the rep rate of the sound is much faster.....like a 1200 rpm rod knock, instead of a 600 rpm rod knock....it don't sound like a rod knock now....

what's strange why the rep rate changes, IF the rotors were cut like a funny graph record, the pads tend to rattle in/out on circumference....these are totally still in that regard.....used to have some old rotors on there that gave me that rattle sound....

methinks Turtle has the right solution, drive it till it brakes.....

:club::hunter:

 

[big2bird]

Well, I changed the pads, and guess what?? the sound is not nearly as pronounced and the rep rate of the sound is much faster.....like a 1200 rpm rod knock, instead of a 600 rpm rod knock....it don't sound like a rod knock now....

what's strange why the rep rate changes, IF the rotors were cut like a funny graph record, the pads tend to rattle in/out on circumference....these are totally still in that regard.....used to have some old rotors on there that gave me that rattle sound....

methinks Turtle has the right solution, drive it till it brakes.....

:club::hunter:

Okay Gene. Jack stand the rear, remove wheels and re-lug. Run a dial indicator, and check the runout.
OR, run it till it breaks.

 

[Twin_Turbo]

it's a bomb.... tickity tickity means run your ass outta there

 

[mrvette]

it's a bomb.... tickity tickity means run your ass outta there

:yahoo::devil::flash::bomb: