C3500 Almost No Brake Pedal.

[BBslider001]

An update for you guys. Since I am currently without my own shop, I am paying a guy who has quite a bit of experience with the GMT-400 generation. He found some pretty shoddy work, to put it mildly. I hung out with him for a few hours on Saturday so I could learn the axle for the next time, if there is one. He used all AC Delco parts, seals, and cylinders. He found one spring on backwards and another not even atatched on the driver's side. Who ever was in there before did all cheapy after market shoes. The cylinders were both leaking, as you guys guessed, and the drums needed turning. The axle seals were trashed and whoever was in there before used silicone between the axle and hub instead of a gasket.....no bueno. Anyways, it'll all be good and right by tomorrow. I'll be stoked for a well maintained axle and rear brakes.

 

[BBslider001]

Well, another update. Trying not to be pizzed, but the truck vibrates now at 60 and above....bad. All new rear brakes, seals, and drums. It was smooth as a Cadillac before this job was done. Got the tires balanced. No joy. Getting worried this is going to be one of those issues that is a real pain to find. The mechanic said maybe the front tires have flat spots from sitting jacked up in the back for a week. Sounds like crap to me, but I guess we will see. I've never heard that in my life.

 

[Schurkey]

the drums needed turning.

the truck vibrates now at 60 and above....bad. All new rear brakes, seals, and drums.

Were the drums turned, or replaced?

If they were replaced with the usual Chinese junk, I'd suspect the drums are out-of-balance; perhaps out-of-round.



As for silicone on the axle shafts, that's what the manufacturer used for years. GM recommends a gasket, they claim that the silicone is degraded by synthetic axle lube.

A thousand years ago, tires made with Rayon cord were known to flat-spot in the winter. When it got cold out, folks would have to drive a few blocks to pound 'em round again. I don't think that sort of flat-spotting happens any more. I've got vehicles that are parked all winter, and aren't flat-spotted in the spring.

 

[BBslider001]

Were the drums turned, or replaced?

If they were replaced with the usual Chinese junk, I'd suspect the drums are out-of-balance; perhaps out-of-round.



As for silicone on the axle shafts, that's what the manufacturer used for years. GM recommends a gasket, they claim that the silicone is degraded by synthetic axle lube.

A thousand years ago, tires made with Rayon cord were known to flat-spot in the winter. When it got cold out, folks would have to drive a few blocks to pound 'em round again. I don't think that sort of flat-spotting happens any more. I've got vehicles that are parked all winter, and aren't flat-spotted in the spring.

Yes drums are brand new. Old ones were shot. I wondered the exact same thing though. They are supposed to be Centrics, but they do have China stamped on them. After driving on the interstate, vibration feels it's from the front. I have known for about 4 months that the front end needs to be completely rebuilt. After driving a little more, I began to think it is either ball joints or idler and pitman arm causing the vibrations.

 

[Nad_Yvalhosert]

High speed vibration (45 mph and faster) is 95% caused by whatever is spinning: meaning tires, and to a lesser extent rotors/drums/ driveshafts.

Of all those parts, the tires are the heaviest, so balance the tires. All of them.

A vibration under 45mph is usually caused by loose front end parts. So before you load up the parts cannon, refer to my second paragraph.

 

[Nad_Yvalhosert]

Now, IF (and only IF) you do have loose front end parts, DEFINITELY change them and get an alignment.

Though you need to realize that an alignment WILL NOT fix a vibration, it's gonna be safer and cause less tire wear, which wears tires unevenly causing high speed vibration... (viscious cycle)

 

[Pinger]

Yes drums are brand new. Old ones were shot. I wondered the exact same thing though. They are supposed to be Centrics, but they do have China stamped on them. After driving on the interstate, vibration feels it's from the front. I have known for about 4 months that the front end needs to be completely rebuilt. After driving a little more, I began to think it is either ball joints or idler and pitman arm causing the vibrations.

Confirm the theory by jacking the rear wheels clear of the ground and running them up to 60 mph?
(Gently - lest it is the rear that's out of balance and the vibes shake it off the axle stands).

 

[618 Syndicate]

Confirm the theory by jacking the rear wheels clear of the ground and running them up to 60 mph?
(Gently - lest it is the rear that's out of balance and the vibes shake it off the axle stands).

Ummmmm.....
Not recommended. Might not go wrong, but if it does it'll likely be catastrophic.
If you're bound and determined to do this make sure there's nothing in front of you for a hundred yards at least. (And video it for internet immortality...)

 

[Pinger]

Ummmmm.....
Not recommended. Might not go wrong, but if it does it'll likely be catastrophic.
If you're bound and determined to do this make sure there's nothing in front of you for a hundred yards at least. (And video it for internet immortality...)

It's not as scary as it sounds - I've done it before albeit on a smaller car. Providing there is no vibration, it's pretty straightforward. Just build the wheel speed very gradually and jump out of it if it starts shaking.
At worst, once it's shifted up through the gears, with the minuscule throttle opening, and low (vs total vehicle) inertia of the drive train, it won't go far if it does drop. Cars jump dyno rollers from time to time and more or less just stall. That said, approach with caution nonetheless. It does provide the fast-track answer to which end the vibration is coming from.

 

[618 Syndicate]

It's not as scary as it sounds - I've done it before albeit on a smaller car. Providing there is no vibration, it's pretty straightforward. Just build the wheel speed very gradually and jump out of it if it starts shaking.
At worst, once it's shifted up through the gears, with the minuscule throttle opening, and low (vs total vehicle) inertia of the drive train, it won't go far if it does drop. Cars jump dyno rollers from time to time and more or less just stall. That said, approach with caution nonetheless. It does provide the fast-track answer to which end the vibration is coming from.

It doesn't sound scary, it sounds like tempting fate. Cars on dynos are strapped down...
Doing this in a fwd manual trans vehicle with relatively little torque is one thing. Trying it in a 3 ton V8 auto truck is something else entirely. If your burb slips off the stands at 60 mph I promise it won't stall.