Clunking noise in Rear End. Sounds like I was rear ended.

[2madrns]

I have a 96 Astro. Sometimes when I come to a stop and keep my foot on the brake, I get a Clunking noise. One single Clunk. Sometimes it freaks me out and I look behind me to see if I was rear ended by a vechicle. Also notice that the van engine revs and the van tries to surge forward. I have had it in the shop 3 times. No one seems to know what it is. I U-Joints are in perfect shap with no play in them. Anyone have any ideas.

Tom

[candiver]

Originally Posted by 2madrns

I have a 96 Astro. Sometimes when I come to a stop and keep my foot on the brake, I get a Clunking noise. One single Clunk. Sometimes it freaks me out and I look behind me to see if I was rear ended by a vechicle. Also notice that the van engine revs and the van tries to surge forward. I have had it in the shop 3 times. No one seems to know what it is. I U-Joints are in perfect shap with no play in them. Anyone have any ideas.

Tom

Sounds like your idle is too high, and this causes your transmission, which is also computer-controlled, to downshift at the wrong speed. Your idle is controlled by the Idle Air Control valve (IAC), and this is monitored by your computer...if your IAC is acting up, you should be seeing your check engine light coming on, especially at idle. If not, there was a dealer memo regarding some driveshaft problems, in some cases, the driveshaft yokes had to have grease injected into them to prevent clunking on acceleration and deceleration.

[masterblaster1811]

I have a 98 Astro. The same thing happeneds to me but only after a long trip (when the transmission heats up). Also the exhaust system as a loud rattle that goes away when the when I shift into neutral.

[SeaBuzz]

I have a 2001 AWD Astro van, and had clunking sounds in rear-end. I drained all fluids, refilled with new and added a positraction additive. I also added the additive to the tranfer case and the frontend. After 50-60 miles it started to work and it's getting better each day. I'll do it all again just before winter. Remember drain all, and refill.
Hope it helps

[yoslick]

Just be careful which fluids you are using as the transfer case calls for synthetic fluid only.. Check your manual for your individual model/application.Mine was doing the same thing and it ended up being the trasnfer case was shot. Ouch!! luckily it was still under warranty, but the dealer said that there had been a notice sent out stating to be sure they were using the right fluid as some shops wern't and they were causing the problems.

[tableman]

I have a 1996 Astro, that had a loud clunk when I came to stop, only happened sometimes, and the fact you said your noise comes with your foot on the brake makes me think it is the same noise as mine. What I found was causing mine was the left rear brake cylinder was ceased. But only one side, so when the brakes were applied all the fluid being sent to that cylinder only pushed out the front brake shoe, forcing it to move out and down at the same time, (over travelled) the shoe would get caught on the lip on the backing plate, then when you let off on the brake a little bit while the van is still in motion the over stretched springs would slam the shoe back into place, Since I replaced the rear cylinder no more problem. As far as your surging, it could be cause by any number of those sensors, a scan tool is needed. Hope this helps

[SeaBuzz]

The last few days I hear a clunk in the rear when I start the van. I haven't even put it into gear, I just start it. It sounds like someone hit it. It doesn't do it everytime nor does it do it with I'm driving just when I start it and only one clunk, and only when it sits for a while. Other then that the fluid change works.