Help! Thumping noise under my 98 vert

[XLR8]

After scanning 6 pages of search results, I still didn't come up with anything similar to a thumping noise which I can hear clearly at slow speed in my C5. I've heard it on both gravel and paved surfaces and there seems to be no rhyme or reason for it, such as bumps or potholes.

I took it to the shop and they checked everything they - or I - could think of... including the transverse spring retainer bolts, which I recalled from a past thread. They did find a bad tie rod end, and they replaced it. I also had a nail in the sidewall of the passenger rear tire, so they replaced it and did an alignment.

When I drove it on the gravel road leading to my driveway, about 5-10 MPH, I heard it again.
I'm going to take it back to the shop and make Kevin go for a ride with me until he hears it as well, but I thought someone else may have experienced the same issue and could make a suggestion.

TIA
Jane Ann

 

[gmjunkie]

My bet is on a wheel bearing or CV half shaft Jane Ann!
The heck of it is,It may have to get worse to find it without just throwing parts at it!~!!

 

[XLR8]

I hadn't thought of wheel bearings, junk. And half shafts I recognize, but ... CV? Not a term which springs easily to mind. At least not mine anyway.

I'm not planning to make any roadtrips in her anytime soon, and I agree about not throwing parts at it until I'm sure what it is. Will it be okay to drive her locally in the meantime?

 

[gmjunkie]

I hadn't thought of wheel bearings, junk. And half shafts I recognize, but ... CV? Not a term which springs easily to mind. At least not mine anyway.

I'm not planning to make any roadtrips in her anytime soon, and I agree about not throwing parts at it until I'm sure what it is. Will it be okay to drive her locally in the meantime?

C5's and C6's don't have U-Joints like earlier generations,they have Constant Velocity Joints!

Constant Velocity joints tend to last longer and run smoother than conventional U-Joints,But are not as user friendly as u-joints! It's more complicated to rebuild and messier than the BP oil spill! The grease thats in them sticks to everything and strings out like bubble gum!~!!

Just keep a ear open for the Thump to get Worse,Scraping Noise,or funky ABS operation!
If it's a wheel bearing it'll probly go from a thump to a rumbling and maybe throw a ABS,TC or Active Handling code!

If it's a cv joint,you may start picking up a little rumbling/viboration and maybe some cracks and grease leaking from the CV Boots as it gets worse!

If you don't have it figured out by the time Vett Boy and I run through on our 1st Annual Polar Vette Tour across the country in a convertible in winter,We'll put Vett Boy in the trunk and hit some interstate clover leafs,maybe he can tell where it coming from!~!!

 

[navy2kcoupe]

Jane Ann, how many miles on that lovely girl?
Shocks ever been changed?
On a lighter note........maybe it's the possum you hit a few weeks ago.
Junk had to go you one better and get a deer with his truck, but a possum
could make a thumping noise...........maybe
Andy

 

[LLC5]

After scanning 6 pages of search results, I still didn't come up with anything similar to a thumping noise which I can hear clearly at slow speed in my C5. I've heard it on both gravel and paved surfaces and there seems to be no rhyme or reason for it, such as bumps or potholes.

I took it to the shop and they checked everything they - or I - could think of... including the transverse spring retainer bolts, which I recalled from a past thread. They did find a bad tie rod end, and they replaced it. I also had a nail in the sidewall of the passenger rear tire, so they replaced it and did an alignment.

When I drove it on the gravel road leading to my driveway, about 5-10 MPH, I heard it again.
I'm going to take it back to the shop and make Kevin go for a ride with me until he hears it as well, but I thought someone else may have experienced the same issue and could make a suggestion.

TIA
Jane Ann

Is it a constant rotational type noise or a noise that happens very intermittently?

And does it only happen at low speeds and not faster speeds, what mph do you notice it at?

 

[XLR8]

Approximately 126,700 miles.
Intermittent only; not cyclic or rotational, at least not yet.
No scraping noise, just an occasional THUMP.
So far I've only heard it at low speed. And come to think of it, low FORWARD speed only, I think.
I haven't noticed it in reverse or at speeds over, say, 15 MPH.
I've never heard it at highway speed.
I don't think we've ever replaced the shocks since I bought it at 25,000 miles.
And no possum encounters. :L

 

[XLR8]

I had an opportunity to pull the codes too. All of them are H except for one C:
10-PCM - No Codes
28-TCS - 3 Codes - C1225 H, C1255 H, C1278 H
40-BCM - No Codes
60-IPC - No Codes
80-Radio - No Comm (I think that code is caused by my aftermarket Alpine Stereo)
99-HVAC - 1 Code - B0446 H
AO-LDCM - 4 Codes - B2282 H, B2284 H, B2272 H, U1064 H
A1-RDCM - 4 Codes - B2283 H, B2285 H, U1064 H, U1016 H
A6-SCM - 5 Codes - B0851 H, B0856 H, U1064 H, U1016 H, U1160 H
BO-RFA - 4 Codes - U1096 H, U1064 H, U1016 H, C2110 H C

Now to look up that CURRENT Code...

 

[gmjunkie]

I had an opportunity to pull the codes too. All of them are H except for one C:
10-PCM - No Codes
28-TCS - 3 Codes - C1225 H, C1255 H, C1278 H
40-BCM - No Codes
60-IPC - No Codes
80-Radio - No Comm (I think that code is caused by my aftermarket Alpine Stereo)
99-HVAC - 1 Code - B0446 H
AO-LDCM - 4 Codes - B2282 H, B2284 H, B2272 H, U1064 H
A1-RDCM - 4 Codes - B2283 H, B2285 H, U1064 H, U1016 H
A6-SCM - 5 Codes - B0851 H, B0856 H, U1064 H, U1016 H, U1160 H
BO-RFA - 4 Codes - U1096 H, U1064 H, U1016 H, C2110 H C

Now to look up that CURRENT Code...

DTC C2110 Right Rear TPM Sensor Malfunction

 

[XLR8]

DTC C2110 Right Rear TPM Sensor Malfunction

Thanks junk.

Just looked it up in the CAC Tech Center: Corvette Action Center Knowledgebase :: 1997 - 2000: Diagnostic Trouble Codes

That sensor may be about to give up the ghost; even though all of them were reading pressure on the drive home last night, I kept getting intermittent "Serv. Tire Mon. Sys" messages.

 

[LLC5]

I had an opportunity to pull the codes too. All of them are H except for one C:
10-PCM - No Codes
28-TCS - 3 Codes - C1225 H, C1255 H, C1278 H
40-BCM - No Codes
60-IPC - No Codes
80-Radio - No Comm (I think that code is caused by my aftermarket Alpine Stereo)
99-HVAC - 1 Code - B0446 H
AO-LDCM - 4 Codes - B2282 H, B2284 H, B2272 H, U1064 H
A1-RDCM - 4 Codes - B2283 H, B2285 H, U1064 H, U1016 H
A6-SCM - 5 Codes - B0851 H, B0856 H, U1064 H, U1016 H, U1160 H
BO-RFA - 4 Codes - U1096 H, U1064 H, U1016 H, C2110 H C

Now to look up that CURRENT Code...

I think you may have found your THUMP. It is probably the EBTCM cycling or being inhibited by the PCM (C1278).

C1225 refers to the RF wheel sensor which is probably causing the problem, and can be a bad bearing, sensor, or more than likely a harness connection problem at the sensor.

C1255 is an intermal malfunction of the EBTC module and sometimes is caused by low voltage, don't worry about this one yet unless it is cleared and comes back consistentaly.

C2110 is a right rear tire pressure monitor code, have you been having problems with the pressure monitering system?

I would clear all the codes and see what returns after driving for a few different trips, if possible this time of year. Good luck with it.

 

[Hib Halverson]

This "Thump"....what's it origin?

Front, back, left side, right side, right under your seat? What?

I tend to think it's not a CV because they usually don't thump. They'll click, snap or vibrate and, even if it did thump it would be cyclical.

I tend to think it's not the EBTCM as that unit is up in front of the engine and it buzzes or vibrates when it operates. It doesn't "thump". Plus, you're hearing the noise when the brakes are not applied.

 

[XLR8]

I drove the Vette today to run errands, doctor appointments and a trip to the pharmacy. All in all, I ran from about 1 pm to 5 pm; highway driving as well as city traffic. I heard the thump after cold start and driving about 15 mph, but couldn't produce it again when I finally made it to the shop. Naturally. Kevin was out so I talked with the other shop manager and he said the only thump they heard while troubleshooting earlier this week, was the "body thumping". Those were his words.

It's hard to say where it originates, but it seemed to be coming from the right side rear. And a couple of times it seemed strong enough that I did feel it as much as hear it.

The right rear tire pressure monitor stopped working today. The other 3 were displaying normal pressure but the RR was X's all day.

I didn't think to check the codes again when I got home, but I'll check them tomorrow and clear them afterward.
Jane Ann

 

[LLC5]

I drove the Vette today to run errands, doctor appointments and a trip to the pharmacy. All in all, I ran from about 1 pm to 5 pm; highway driving as well as city traffic. I heard the thump after cold start and driving about 15 mph, but couldn't produce it again when I finally made it to the shop. Naturally. Kevin was out so I talked with the other shop manager and he said the only thump they heard while troubleshooting earlier this week, was the "body thumping". Those were his words.

It's hard to say where it originates, but it seemed to be coming from the right side rear. And a couple of times it seemed strong enough that I did feel it as much as hear it.

The right rear tire pressure monitor stopped working today. The other 3 were displaying normal pressure but the RR was X's all day.

I didn't think to check the codes again when I got home, but I'll check them tomorrow and clear them afterward.
Jane Ann

Just throwing it out there since it is so intermittent - could it be an amplifier popping through the speaker from your aftermarket stereo system? Or something loose in the cargo or cubby hole areas? Your antenna is in the right rear area, was it worked on during the stereo install, or something could be loose and banging around in that area.

The EBTCM on a '98 is mounted next to your rear differential and when they are not operating properly I have heard them make more of a "THUNKING" sound noise when they try to work and stop, not saying that this is your issue but it's not impossible. You state right rear which is a good start, have someone (Kevin?) check the wheel and tire thoroughly in that area including all suspension bolts and muffler mounts. If he dismounts the tire to install a new TPM sensor have the inside of the tire and wheel inspected thoroughly for any deformations. Good luck with it.

 

[Hib Halverson]

(snip)
The EBTCM on a '98 is mounted next to your rear differential and when they are not operating properly I have heard them make more of a "THUNKING" sound noise when they try to work and stop, not saying that this is your issue but it's not impossible. (snip)

Any car built after 16 Dec 1997, has the EBTCM between the radiator and the engine, so about half MY98 production and all 99-up have it in front. Only 97 and about the first half of MY98 have it at the rear.

Jane Ann...help us out here...do you hear that "thump" when you're on the brakes?

 

[LLC5]

Any car built after 16 Dec 1997, has the EBTCM between the radiator and the engine, so about half MY98 production and all 99-up have it in front. Only 97 and about the first half of MY98 have it at the rear.

Jane Ann...help us out here...do you hear that "thump" when you're on the brakes?

I wasn't aware of the production date split on '98 model year for the EBTCM location.

The "THUNKING" noise that I am referring to does not require the brakes to be used and happens at low speeds, and the only time I have heard it there was a problem with the system and had stored codes for either ABS or TC. Since she has multiple history codes relating to the EBTCM system it was just something to keep in mind.

 

[Hib Halverson]

I hadn't heard of EBTCM's making noise like that when the brakes are not applied, but I 'spose anything's possible and I don't have enough depth-of-knowledge on EBTCM faults to say, "It can't happen."

That said, my gut feeling is this noise is not related to the brakes.

Boy. Would I like to road test this car.

What might be a bit unnerving is if this car "...goes 'thump' in the night." If it was a moonless night, it'd be even more scary!.

 

[XLR8]

All good suggestions and questions guys. And thanks for your patience.

Hib... mostly when I've noticed it I've been driving slowly up the gravel road in front of my house and though I don't ride the brake, it is possible I've applied the brakes. As to whether I'm braking when it makes the noise, I can't say but I will pay attention to that tomorrow when I drive it.

I don't think it's popping in the speaker because I actually did have that issue a little over a year ago after a driver door repair and Kevin found the problem and fixed it. It is possible that something in the trunk is thumping but doubtful... but I'll check that too. Antenna is good... no problems there, I think.

BTW... my 98 replica build sheet from the NCM is dated 10/27/1997.

I wish you could road test it, Hib. :L I hate chasing an intermittent noise.;squint:

Kevin will be back at work after the holidays and I'll probably take it to him to put up on the rack and go over the entire underside with a magnifying glass.

Thanks again guys!

 

[LLC5]

I hadn't heard of EBTCM's making noise like that when the brakes are not applied, but I 'spose anything's possible and I don't have enough depth-of-knowledge on EBTCM faults to say, "It can't happen."

All I can come up with is that the system was possibly doing a self test and it aborts immediately because of the multiple fault codes, causing a thunk noise. This happened on two different vehicles (one of them being my own), the noise was intermittent and I was only able to hear it at slow speeds. I do know that after repairing the faults the clunking type noise was gone.