I'm Feeling Speed Bumps

[Ripp 73]

So here is my problem. As I am driving down the road I can feel something that feels like maybe a grind? Really it feels like I am running over those smaller speed bumps or rumble strips before construction zones. I do not feel it until I hit about 55mph, it becomes more prominent as I increase my speed and becomes closer in the feeling. That’s right, it is not a constant rumble but rather spaced apart. As I was saying the rumble gets closer together as I increase speed, also, as soon as I let off the gas the rumble seems to go away altogether. Push in the gas just a little and the sound and feeling comes right back. I do not feel the pulse in the pedal, but I can feel it when I put my hand on the park brake. I am hoping someone has had this similar feeling and could tell me what my problem is. Since the car is a winter project now I have time to dig into this. Thanks for any help. :confused

~Grant

 

[Vettehead Mikey]

U joints in the driveshaft or half shafts, or both.

 

[Ripp 73]

I have checked all three visually and they seem to be very solid. Do you think it has anything to do with rear differential? Are you speaking from experience on this one Mikey? Thanks for the quick reply as well. Hope you are having a good Turkey Day.

 

[JohnZ]

Check the upper and lower rubber snubber bushings where the diff nose bracket attaches to the frame crossmember in front of the diff; when they deteriorate, they allow metal-to-metal contact, which transmits diff noise directly into the frame, and it also upsets the operating angle of the rear U-joint, creating a driveline vibration. If the bushings are shot (very common issue), DON'T use the "poly" replacements - use the OEM GM rubber bushings; the poly bushings in the kits are made wrong, aren't thick enough, don't have the correct molded-in centering sleeve that aligns the upper and lower bushings, and they kill the isolation between the diff and the frame.

 

[Vettehead Mikey]

Are you speaking from experience on this one Mikey? Thanks for the quick reply as well. Hope you are having a good Turkey Day.

Yup personal experience. External visual inspections can be very misleading.

Thanks for the Thanksgiving wishes, but ours was on October 11th. I'm still digesting that giant turkey!

 

[Chas]

when my diff went..it changed the movement of my car...sounded like a ran over a cinder block and it rolled over under me...my ring gear bolts backed out and trashed the housing..so i had no core deposit returned...dont go to any trans shop...these rear ends are diffrent...good luck ...chas

I have checked all three visually and they seem to be very solid. Do you think it has anything to do with rear differential? Are you speaking from experience on this one Mikey? Thanks for the quick reply as well. Hope you are having a good Turkey Day.

 

[81 Corvette]

check the parking brake out as well.

I don't know if the diff was part of the cause or not, but my u-joints were shot and made a terrible clunk sound when leaving a light. I had the diff rebuilt and u-joints replaced and all is well. my diff had a spun bearing on teh carrier and the snub axles were worn. it be worth taking to a good shop to have it checked out.

 

[Ripp 73]

Thanks for all the info guys. I'll have to take a closer look at it this weekend. Might be awhile before I get to solve the problem, but it'll get there. As far as the parking break... that is one thing I have not been able to get around to yet. For some reason it looks like the previous owner decided to cut the brackets off at the back by both wheels and just tie-wrapped the cables up against the frame. I am thinking there is an underlying problem there and want to take a closer look at that this winter as well. Maybe they just got rusted and broke off? All part of the fun I guess.

 

[Chas]

I started at the brake

Mine is an automatic trans...the parking brake was toast so i had them just remove it....then we went to the U-joints...one side was factory original...and one side had been replaced....this is where i learned that this is a very diffrent rearend...this is a good trans shop, they have done work in the past with no issue. But he was sure the problem was fixed . it wasnt, so i found a shop that knows vettes....the owner has a pace car....this is where i find out it was the ring bolts backing out. i learned it is not uncommon either...this was a horrible sound...not the brake or joints....they would be a smaller metal to metal sound....this was a very hard clunk, and it changed the motion of my car....cinder block kind of sound....made me look for parts on the ground , kind of sound...so becareful and be persistant. good luck and let us know how you do.
Chas

Thanks for all the info guys. I'll have to take a closer look at it this weekend. Might be awhile before I get to solve the problem, but it'll get there. As far as the parking break... that is one thing I have not been able to get around to yet. For some reason it looks like the previous owner decided to cut the brackets off at the back by both wheels and just tie-wrapped the cables up against the frame. I am thinking there is an underlying problem there and want to take a closer look at that this winter as well. Maybe they just got rusted and broke off? All part of the fun I guess.

 

[JohnZ]

For some reason it looks like the previous owner decided to cut the brackets off at the back by both wheels and just tie-wrapped the cables up against the frame. I am thinking there is an underlying problem there and want to take a closer look at that this winter as well. Maybe they just got rusted and broke off? All part of the fun I guess.

99% of the time, when you find the brackets cut off, it was done to provide clearance for extra-wide wheels and tires.

 

[Ripp 73]

Well that would have been kinda fun.... *imagine wider tires*... however, I just replaced the original rotors a couple weekends ago. Major pain in the @$$ seeing as how I had to drill through each rotor to pop the rivets out. These wheels are proper size and I do not believe anyone put wider tires on this car in the past. Still playing though. I actually just gave her a bath and a quick run, she was happy to run around real quick.

 

[ernie d]

Hey Ripp,


Don't give up on the half shaft U-joints too easily. I had the same problem as you describe. Joints looked OK, and when checking shafts for looseness at joints, it seemed solid. However, when you pull the halfshaft, it was extremely hard to articulate and was very rough. Replaced the joints and all is well.

Just make sure you use a ball or u-joint press, particularly on the outer flange, otherwise it can get distorted.

Ernie

 

[curtis]

that rumble was a broken belt in one of my tires several years ago. It sort of reminded me of the lane seperators along the highway. Jack up the wheels and look for a high spot or a ridge across the tread of the tires.

 

[Culprit]

I had the same sound from a broken belt in my Firestone Wilderness tires also. There was also a nasy bulge on an inside firewall. It's definitely worth a look like curtis said.

Culprit

PS - Ford bought me 4 brand new tires. I just went to a tire shop, waited an hour, and drove off. No paperwork, no pay now and mail in a reimbursement form, nothing. I was quite impressed. (And Ford was probably just happy that I didn't sue like many of the rest).

 

[ruby76]

intermittant rumble/vibration

I had this same problem on my 68 chevrolet truck. Turned out after replacing all of the u-joints and harmonic balancer etc that the real problem was the flywheel. The higher RPM the vibrations would get closer together, when let off of the gas they would pretty much go away. (this is for an automatic mind you) The torque converter is connected to the flexplate/flywheel via three bolts. I simply unbolted the flexplate (you can do this without removing tranny/engine) and rotated the flexplate 120 degrees or one bolt. I rebolted and the vibrations were gone. Im not sure if the flexplate was slightly warped or not, but since the vibration went away, I didn't care any more.

I knew the vibration was engine related, as you could somewhat feel the vibratios at idle - but very slightly. It was exagerated when a load was present.

Hopefully you'll find that vibration.

See if it is completely RPM related by slowly going through RPM range in idle. that will let you know whether or not it is engine related or if it is originating further back in the drivetrain.

 

[curtis]

If you put the car in neutral at speed would that eliminate the possibility of drive train components (except rear end and driveshaft) and engine speed if the vibration stops?

 

[ruby76]

It would probably eliminate the problem, sometimes you need to have a load on the drivetrain to fully diagnos, but I've heard of folks doing that. On my truck, when I put in nuetral, the vibrations did go away.

See if it is completely RPM related by slowly going through RPM range in idle. that will let you know whether or not it is engine related or if it is originating further back in the drivetrain

My previous post said "in idle" but I meant in nuetral. I did this in the driveway, start it up, put in park or nuetral. Slowly give gas and pay attention to any vibrations, i went up through about 3500 rpm and noticed the vibrations. As you slowly let off of the gas the vibrations went away. If you don't notice anything with the above test, then you can ignore both of my posts and look further into U-Joints, driveshaft balancing etc. Your symptoms just sounded alot like the ones I had on my truck.

I some folks mention tires, I don't think a slipped belt or cupping etc would speed up or down in frequency as you described from your symptoms.

When I was troubleshooting I even tried re-phasing my driveshaft to eliminate that as well. (rotate either the tranny yoke or rear end pinion yoke 180 degrees in relation to the rest of the shaft) I guess the half shafts could have the same thing done.