2nd Gen Non-Engine/Transmission Hopping when stopping

[gwalloch]

My 96 2500 4x4 has a braking problem that started about 25,000 miles ago. As I slow to a stop, passing through 20 mph, I get a terrible "hopping" from the rear end. I can feel it cycling through the brake pedal.



My tires were worn, so I got new ones about a month ago. It still hops. I had the rear drums turned and new pads put on over the weekend. Guess what, it still hops!!!



What next??? Any ideas?



96 2500 4x4 105K

 

[Pit Bull]

Have you ever flushed the brake fluid?

 

[gwalloch]

Good idea. thanks. I haven't changed it yet, or for that matter, ever. I guess I'd better do that tonight. Does brake fluid lose something over a period of time? I know it's hygroscopic, but I wasn't aware it lost any of its fluid properties.

 

[illflem]

How much pressure you running in the rears, it should be about 10 psi less than the front. My 2500 rears do best at 45 psi empty. Throwing some secured weight in the back will also make a big difference in overall ride and eliminate the hop. After all it's a truck, made to haul things.

 

[gwalloch]

Yep. They were dropped to 35 over the weekend after being at 50. It was suggested to add 400-500 pounds in the back.

 

[mberry]

Originally posted by gwalloch

Good idea. thanks. I haven't changed it yet, or for that matter, ever. I guess I'd better do that tonight. Does brake fluid lose something over a period of time? I know it's hygroscopic, but I wasn't aware it lost any of its fluid properties.

Over time the brake fluid will absorb water. This lowers the flash point of the fuild meaning it could vaporize with much less heat than fresh fluid. It will cause corrosion on the inside of the metal brake lines and cause wear to the internals of the brake system components. Imagine having rusty oil in your engine.



I would carry a little weight in the back also. That will definitely help the ride and braking. If I'm off somewhere, somebody please correct me.

 

[Sticks]

Originally posted by mberry

Over time the brake fluid will absorb water. This lowers the flash point of the fuild meaning it could vaporize with much less heat than fresh fluid. It will cause corrosion on the inside of the metal brake lines and cause wear to the internals of the brake system components. Imagine having rusty oil in your engine.



I would carry a little weight in the back also. That will definitely help the ride and braking. If I'm off somewhere, somebody please correct me.

Sound about right to me. I have seen rust/nasty corrosion in reservoirs and calipers. Takes forever to flush it all out.

 

[Pit Bull]

Originally posted by gwalloch

Good idea. thanks. I haven't changed it yet, or for that matter, ever. I guess I'd better do that tonight. Does brake fluid lose something over a period of time? I know it's hygroscopic, but I wasn't aware it lost any of its fluid properties.

WOW, that means your fluid has been in there for 7 years. It might not be the old fluid causing the hop but it might be what that old fluid did to the brake system that is causing the hop. Good luck.

 

[gwalloch]

7 years!! Not very smart of me. I am religious about oil, filters, and other stuff. Brake fluid did not occur to me. Thanks, I'm changing it out tonight and I'll give you an update.

 

[SMorneau]

It the drums

Your drums have warped. There are several threads where other members including myself sorted this, or at least a similar problem, and it always came up drums. I finally drilled a hole in the backing plate pulled the shoes out and put an indicator through from the backside to check for the runout... it was there.



They don't always warp right away and turning them will not cure it for long. The best fix is to get new drums. As I recall NAPA guaranteed theres but I don't know for sure because I got the best price from Dodge (about $75 each). I am on my third set and these seem to be ok. You may only have one that is warped



Do a search...

 

[gwalloch]

Even though I had them turned, it won't remove the warping?

 

[illflem]

The warp usually comes back soon if you turn it out due to unequal heat transfer though the rotor due to it being different thickness after turning. That's the same reason rotors will warp after hard or long braking then coming to a stop and holding the vehicle in place for a long period, the temp is different under the pads. Big cause of warping is while towing at interstate speeds then slowing down on a downhill or short offramp to be greeted by a long red light at the bottom. Best to use the parking brake to hold it after sustained braking.

To buy new rotors doesn't cost all that much more than to have them turned correctly.

 

[gwalloch]

illflem,



Yep. You were right. The left front rotor was 45/1000th's out, and the right was 10/1000th's out. It was sending a pulse through the entire brake system that caused the rear brakes to act as they did.



New rotors next time as this is the second turning.



Thanks for the help.

 

[Pit Bull]

I never turn rotors. Find it cost less to just replace the pads more often. That is why I think it is better to use a softer pad. JMHO

 

[HomerDog]

I had the same problems you describe and posted the same type of question about the rear "hopping" that you describe. I had the rear brakes done, new shocks, front end, etc. with no luck. To make the story short, I replaced the FRONT rotors and pads and the truck never has since tried to hop the minute I drove away. That was the last thing I considered but it was the culprit.

I never thought the front brakes were causing rear end hopping. Search my name and you'll see the post. Hope this helps someone,



Dave

 

[KFroese]

an easy way to see where the pulsation is coming from is ... ... put a line clamp on the rear brake hose. by locking off the fluid you could tell if it's from the front or rear. just remember you won't have full breaking power on the test drive.



when i worked at a brake shop we would do it all the time. you could narrow down the problem with out pulling a wheel.



if you can't find line clamps. just grind the teeth off a small pair of vice grips to lock the line off.