96 3500 4X4 4:10 rear end... . As I start slowing down I hit a point where the rear of the truck starts shaking/bouncing up and down. I thought it was the rear brakes but they are now new and the same problem is occurring. Front brakes are good and system is flushed/filled with new fluid. When I have some weight in the bed (my slide in camper), much less noticeable... I've looked at my service manual-- doesn't seem to address this issue to troubleshoot. Any ideas???
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Rear end bounces when braking
- Thread starter HomerDog
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Truck has been doing this since I've owned it (almost 2 years). No suspension mods except for new Rancho 9000's. I think I've read here before that there is a proportioning (sp?) valve or is that just on the newer trucks. Like I said earlier, with weight in the bed the back doesn't bounce. Overall the truck stops fine but the bounce is annoying, especially when people are riding with you (kind of embarrasing). thanks again...
Dave
Dave
I dunno..... tires?
you never know. I've had my truck since 94 and no brake trouble. Recently I put air bags on the rear which raised the back of the truck and then the brakes surged pretty bad. Then i replaced all shocks with Rancho 9000 and this helped, also leveled the truck. Recently read about the porportaning valve and this makes sense to me. Got to find time to get under my truck and see if I have some sort of control rod for this valve.
Michael
Michael
brakes
If the drums are new and not oversized and no oil or grease on the shoes, and the shoes are not made wrong( I have seen remain shoes that when installed into new drums that only had a small contact area). The shoes would have to bend to try to conform to the new drums until they wear in? Just a sponge brake peddal. Several years ago you could buy oversize shoes for worn drums and arc the shoes to the drum, I have got good brakes like that.
When I bought the 95 with a dissmal brakes I installed the larger wheel cylinder and got better brakes, however they will hop ever now and then. That is still better than it was no or little brakes in the rear. I will probably get caught in a cross fire But the ford that my father bought to replace the dodge is a hugh improvment in the brakes.
good luck Jimk
If the drums are new and not oversized and no oil or grease on the shoes, and the shoes are not made wrong( I have seen remain shoes that when installed into new drums that only had a small contact area). The shoes would have to bend to try to conform to the new drums until they wear in? Just a sponge brake peddal. Several years ago you could buy oversize shoes for worn drums and arc the shoes to the drum, I have got good brakes like that.
When I bought the 95 with a dissmal brakes I installed the larger wheel cylinder and got better brakes, however they will hop ever now and then. That is still better than it was no or little brakes in the rear. I will probably get caught in a cross fire But the ford that my father bought to replace the dodge is a hugh improvment in the brakes.
good luck Jimk
It sounds like you have gone through it: Checked the brakes, drums round and clean. Also checked the shocks.
What about tire pressure? What do the wear patterns look like on the tires? Stand at the back the look down low. Do you see any daylight around the tire sholders?
Over inflated for the weight you are carrying will cause this. I have see it on skid marks from the big rigs when they bounced while having at least one set locked up.
What about tire pressure? What do the wear patterns look like on the tires? Stand at the back the look down low. Do you see any daylight around the tire sholders?
Over inflated for the weight you are carrying will cause this. I have see it on skid marks from the big rigs when they bounced while having at least one set locked up.
brake problem
HomerDog,
Do you get any feed back thru your brake pedal? If so, does it progressively increase as you increase pedal pressure? If your brakes are surging for any reason, it could appear as a bouncing affect as the weight is transferred back and forward as the brakes surge... one possiblity, if so as JimK mentioned your drums to brake shoes may not be contacting evenly and may need arching of the shoes. Even if the brakes are new, the contact area of the shoes may not mate correctly with the drums.
It could also be the front disc, if you have too much run out, your disc may need to be turned to be trued up.
Another thought, do you have anti lock brakes. Early on there were problems with the brake systems. Anti lock brakes are actually designed to brake and release very quickly in order to prevent lock up. This by design could induce a surging affect.
Keep us posted and good luck
Chris
HomerDog,
Do you get any feed back thru your brake pedal? If so, does it progressively increase as you increase pedal pressure? If your brakes are surging for any reason, it could appear as a bouncing affect as the weight is transferred back and forward as the brakes surge... one possiblity, if so as JimK mentioned your drums to brake shoes may not be contacting evenly and may need arching of the shoes. Even if the brakes are new, the contact area of the shoes may not mate correctly with the drums.
It could also be the front disc, if you have too much run out, your disc may need to be turned to be trued up.
Another thought, do you have anti lock brakes. Early on there were problems with the brake systems. Anti lock brakes are actually designed to brake and release very quickly in order to prevent lock up. This by design could induce a surging affect.
Keep us posted and good luck
Chris
The rear wheel anti lock is pretty slow. I think the frequency is about 1-2 Hz. But if you are not used to it that might be what is happening too.
This sounds like a case for...
Steve St. Laurant's ladder bars in reverse.
Are all of the U bolts tight? Grabby brakes (for what ever reason... those mentioned above) will try (and in this case succeed) to "wrap" the rear end around the spring. Do you have any kind of suspension lift kit installed that would make "this" problem worse?
Steve St. Laurant's ladder bars in reverse.
Are all of the U bolts tight? Grabby brakes (for what ever reason... those mentioned above) will try (and in this case succeed) to "wrap" the rear end around the spring. Do you have any kind of suspension lift kit installed that would make "this" problem worse?
Thanks for all of the responses. To answer Chee's question, there is no feed back what so ever through the brakes. The brakes as a system work fine, just the shaking/bouncing in the rear. The drums looked good, but maybe we should have checked them closer. We put in new pads and parts and the same thing happened. BTW, the old brakes were really bad and cracked. For Steve Campbell, no suspension mods except Rancho 9000 (no effect before or after). For Dan Gilson, I have 4 brand new factory size Michelins on the rear. I belive they are filled to the max for when I'm towing. I'll try to adjust the pressure to see if that changes anything. Again, thanks for all the help to everyone. If I solve anything, I'll post the results...
I think one question the was not asked is: Do you have this problem loaded or unloaded?
Some other general information.
If you keep the rear tires at 80psi when unload they will wear out real fast in the center. You will probably decresae the life by 10's of thousands of miles. Also you have reduced your contact patch on all of the rear tires such that yor braking will be probaby cut in 1/2 of that with a full contact patch. There is also a greater tendency to bounce. Bounce further reduces braking and handling. To make matters when loaded light you are already front heavy and hard braking will tend to greatly unload most of the weight off the rear. Worsening the tendency to swap ends.
Unloaded I run with around 40psi. I am currently trying 30psi but have found that it seems too soft. I am getting some sideways wiggle at times that make me think that there is not enough air pressure to keep the side walls stiff enough. The tires don't seem to have any of the other problems associated with under inflation though. They are not overly hot but are warmer than when I ran with 40psi.
Some other general information.
If you keep the rear tires at 80psi when unload they will wear out real fast in the center. You will probably decresae the life by 10's of thousands of miles. Also you have reduced your contact patch on all of the rear tires such that yor braking will be probaby cut in 1/2 of that with a full contact patch. There is also a greater tendency to bounce. Bounce further reduces braking and handling. To make matters when loaded light you are already front heavy and hard braking will tend to greatly unload most of the weight off the rear. Worsening the tendency to swap ends.
Unloaded I run with around 40psi. I am currently trying 30psi but have found that it seems too soft. I am getting some sideways wiggle at times that make me think that there is not enough air pressure to keep the side walls stiff enough. The tires don't seem to have any of the other problems associated with under inflation though. They are not overly hot but are warmer than when I ran with 40psi.
Well here are a couple easy tricks and some suggestions.
1) Drive down some patch of deserted road, about 35 mph, and slowly apply the emergency brake. Apply about a click every five seconds or so. See if you feel a wiggle or pull. This will tell you if your brakes are even or not, and where to look. Also check for your bounce condition.
2) Set complete rear on jack stands, and block front tires. Now put in gear and go about 35mph again. Apply the parking brake, and see if you get a vibration. This will take your suspension out of the equation and focus on your brakes. You can also apply your regular brakes and check for braking effect and vibration. You would want to be going about 60mph for this one. This will also tell you if the AWAL is working in the rear. This wll also let you check for trueness of rear rims and tires. Just look at them while they are spinning, but WATCH OUT FOR FLYING ROCKS!!!
If you have the limited slip rear, one side braking harder will cause a funny pull and some added noise/vibration from the rear. Remember, the limited slip slows the faster wheel.
Did you deglaze or turn the rear drums? If they not grooved and did not get turned, you may have burned or glazed spots that will affect braking.
Hope I could help.
1) Drive down some patch of deserted road, about 35 mph, and slowly apply the emergency brake. Apply about a click every five seconds or so. See if you feel a wiggle or pull. This will tell you if your brakes are even or not, and where to look. Also check for your bounce condition.
2) Set complete rear on jack stands, and block front tires. Now put in gear and go about 35mph again. Apply the parking brake, and see if you get a vibration. This will take your suspension out of the equation and focus on your brakes. You can also apply your regular brakes and check for braking effect and vibration. You would want to be going about 60mph for this one. This will also tell you if the AWAL is working in the rear. This wll also let you check for trueness of rear rims and tires. Just look at them while they are spinning, but WATCH OUT FOR FLYING ROCKS!!!
If you have the limited slip rear, one side braking harder will cause a funny pull and some added noise/vibration from the rear. Remember, the limited slip slows the faster wheel.
Did you deglaze or turn the rear drums? If they not grooved and did not get turned, you may have burned or glazed spots that will affect braking.
Hope I could help.
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Issue 128 – Digital Version
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Subscribe
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Back Issues
Subscription Status
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