View Full Version : What's that "bump"?

08-10-2001, 07:32 PM
Wondered if anyone has experienced this. When slowing down to a stop, I feel a little "bump" under the truck. Like maybe the tranny or the drive shaft area. Or maybe the u-joint? It is not happening on every stop, but it is happening. It happens just after I have come to a full stop-within 1-2 seconds. Just had the tranny flushed and refilled,also.

John DiMartino
08-10-2001, 08:05 PM
If it has an automatic transmission,the bump is it downshifting into 1 st,as you get under 10 mph usually.GM's tranny goes to first,so its ready to accelerate strong if the need arises.That is my biggest gripe with Dodge,and Ford auto's,they stay in 2nd until you fully stop,so a rolling stop or plowing,you hit the throttle,and it bogs,then kicks down,then after all that it starts to accelerate.Gm's are in first,and quickly accelerate when you hit it.If you notice Ford's and Dodge's dont clunk as much as GM's,but they dont respond as quick either.

08-10-2001, 10:13 PM
With my Dodge, its the fuel in the tank sloshing back and forth, esp when between 3/4 and full.

08-12-2001, 01:56 PM
Well, my tank was full, so it wasn't that. The other idea sounds better,however, it is sometimes happening even as late as 2 seconds later! Sometimes it is very faint and sometimes it is a bit louder.

08-12-2001, 10:35 PM
Drive another 100 miles and see if the thump is still there. Ill put $$$ on the gas in the tank sloshing diagnosis.

08-15-2001, 11:17 PM
THELAWN GUY, I'll e-mail you my P.O. box so you can send the check. How much was that,anyway?

08-16-2001, 06:56 AM
So, wise-guy, tell us what the diagnosis was will you? :rolleyes:

08-16-2001, 07:48 PM
I can't. It is not the fuel,and the tranny shop says there is no problem.What is left? I have found the answer to a lot of tricky questions on posts. This one has not really been addressed.
Your idea was definitely a possibility and one I had not thought of, it just isn't the one.

08-16-2001, 10:33 PM
Check that the spare tire is secure, and there is nothing rolling around the cab, bed, under the hood, etc. You would be surprised what can come loose.

08-17-2001, 12:45 AM
Just got my 2000 C-2500 from the shop today for the same problem, clunk when you take your foot off the brake after stopping, then clunk again as soon as you hit the gas. Dealer technician said, "Oh yeah, I definitly feel that, we'll check it out." Well an hour later the service writer says, "It's normal." I still think it's either the anti-locks or the u-joint, but they are the "experts."

08-19-2001, 03:21 AM
Is your trailer connected when you feel this? If so I'll bet that your equipment isn't 100% secure. My equipment is never secured very well and I have just learned to live with the thumps.

Chopper Lover
08-19-2001, 11:25 PM
I have a K1500, same year as yours. Mine bumps after you come to a stop also... I have no idea why. After hearing you have the same thing I just figure it is a "characteristic of the beast".


08-20-2001, 09:11 PM
I have a similar issue with my ford F250... I have a convert a ball cushioned draw bar and it has give so for a while I did not know what was happening when I came to a stop and the draw bar slid in and then back out to take up the shock..

Also as for the trannys .. The Ford E40d downshifts too when slowing under 10 MPH but only seems to shift when your going slow to begin with not when doing 35 plus... But it's not a thump or bump its' just a shift ?? But the spare tire sound s like a definate possibility..

Do you by any chance have one of the shock absorbing hitch draw bars>>>????

Chopper Lover
08-20-2001, 10:08 PM
Mine does it mostly when it is empty with no trailer.

I come to a complete stop and SOMETIMES, about 2 seconds later, I get the "bump" that wants to push the truck forward but won't because the brakes won't let it.

I want to say that it may occur more often when I make an abrupt stop. I will try to pay more attention when it does it.


08-20-2001, 10:39 PM
My friend has a 2000 Chevy 2500 4x4 and is having the same problem. I have been in the truck when it has done "The Bump". I have never seen anything quite like it. He has had it to the dealer several times and they have yet to figure it out. He's disgusted and ready to trade it off on a new Ford Super Duty.:( ED

08-20-2001, 10:54 PM
Originally posted by Chopper Lover
I come to a complete stop and SOMETIMES, about 2 seconds later, I get the "bump" that wants to push the truck forward but won't because the brakes won't let it.

I want to say that it may occur more often when I make an abrupt stop. I will try to pay more attention when it does it.


I'll say it again; its the fuel in the tank. Been round and round with this for years on my Dodge after much experimentation thats what ended up being the cuprit. That long polyethylene tank builds up quite some wave action, no internal baffles.

Run the truck almost empty; you will find no thump. Same when topped off; no room for the fuel to slosh.

Chopper Lover
08-21-2001, 06:19 PM

Been There, Done That, No Change...

The fuel was my first thought also... It has "bumped" when the tank was full, empty or anywhere in between. I would be more inclined to agree more with the idea the transmisson is shifting into first gear than anything else I have heard to date.


I think it is just a characteristic of the beast....


PS. I have been thinking about going with a Ford Super Duty myself... But not because of the transmission "issue".

08-24-2001, 04:23 AM
When you go to the dealer ask the service advisor to check for
TSB`s, campaigns or silent campaigns. These are all advisories of common problems a manufacturer has with particular vehicles they send to all their dealerships.

They may say that the problem is normal, but at least you will know. Sometimes a less than honest mechanic may be just blowing off a job that does`nt pay very well or just is too lazy to do.

No offense to those honest mechanics out there. The bad ones give us all a bad rap.

There are websites you could check for TSB`s(technical service bullitins) ,but I cant think of their address.

09-07-2001, 06:56 PM
It is the nature of the beast, my old 88 chevy 1500 did it and I went through all of the trouble of having ujoints changed and everything checked. Almost everyone I know with a chevy has the drive line clunk, there is no fix unless you replace everything. My next door neighbor owns a transmission shop and he gets people in the shop all the time with the same problem. It sucks but you get used to it.


09-07-2001, 09:24 PM
Just remembered another thing, my truck didn't start bumping until around 8000 miles. Then, all of a sudden, it started. It wasn't a gradual thing. It has to be the anti lock brakes in the back, 'cause if your not moving at all, it can't be the u joints or the rear end gears. Also, why would anti lock brakes LOCK UP in the morning when you first hit the brake when it is raining? Hmmmm
This problem has to be with the brakes. If it were fuel sloshing around the tank, it would rock you back and forth a couple of times, these bumps only happen ONE time when you come to that final stop, and then ONE time when you first hit the gas. Never in between. You guys who carry big spray tanks know what I'm talking about with 180 gallons sloshing back and forth. It'll make you sea sick almost.

09-24-2001, 01:01 AM
I talked with a client who rebuilds tranny's. He mentioned the fact that the bump normally will happen after running over 40mph for a couple of miles then coming to an abrupt stop. Yes! That's it.
He says it is the torque converter and that is an early sign of failure. I must note that the symptom has not happened as often since I had the fluid flushed and replaced.

09-25-2001, 03:09 PM
Check the slip yoke where the rear driveshaft slides into the trans.The yoke gets dry and cause the symptoms you are describing.GM had a TSB on it a while back,which requires a special lube from GM.I have used regular grease,which works OK,but the problem may come back after a while.

I have seen the same thing happen on some two-piece drive shafts,when the splines get rusted up.On some 4WD models,if the front driveshaft slip yoke siezes,it will cause a pull under hard braking or over large bumps.

10-02-2001, 12:21 AM
Wyldman is right on the money here. My 2000 Silverado 4X4 had a service bulletin on this problem. A service bulletin is not a recall so to speak, but rather an advisory.

This same problem showed up on mine at about 6 or 7k miles. I thought at first it was a u-joint, but I slid under it and found the u-joints to be fine. So I sheduled it in to service. The dealer said something about grease in the driveshaft drying out. They took care of it, and I have not had the problem since.

On my 98, I had a noise somewhere near the passenger side footwell. It would clunk after driving just 15 or 20 feet after initial startup. Never figured that one out. It was almost like an emergency break was released on the passenger side. :confused:

Hope these posts help.