Drive train clunk over bumps causing ABS to engage

[07keo02]

As the title states, when coming to a stop and I hit a few repeated small bumps sometimes I feel a "clank" in the drive train (also felt through the shifter). Usually when this happens the ABS engages it's anti-lock system. The clank and ABS engagement definitely seem related. I am wondering if this is a transmission (ZF-6) or transfer case issue. I know on some vehicles, speed is calculated from the transfer case so I thought some "slop" in there was a possibility. I have no signs of pump rub or adverse sounds during normal driving.

 

[TeaBagger2006]

I would think it's got something to do with you going over the bumps makin the wheels loose contact. Check your u joints aswell

 

[DAVe3283]

I drove a '97 chevy that was very light in the back. If you were stopping, and the pavement was the least bit rough, it would lose traction and the ABS would kick in. Even then, it wanted to get the back sideways. So, if the back end of your truck is light, it may just be doing its job. The clunk could be the slop in the drivetrain as the wheels instantaneously stop for a sec before the ABS kicks in.

Like Joe said, check your U joints. Might want to check for play in the transfer case output as well.

 

[NC-smokinlmm]

Scan it for codes with a V2 or techII....

 

[07keo02]

I will scan with my v2. I was kind of wondering about the ones transfer case output bushing and slip yoke as i have a little drivetrain clunk. I just never heard of it causing an abs issue.

 

[Chevy1925]

I will scan with my v2. I was kind of wondering about the ones transfer case output bushing and slip yoke as i have a little drivetrain clunk. I just never heard of it causing an abs issue.

the reluctor wheel spins on the output of the t-case. if you have a bad bearing or something going out or even a bad connection on the VSS back there, it can cause a bunch of issues.

Monitor both front and the one rear speed sensor and re-enact what causes the issue. then see if there are any hiccups in the log for any of those wheel speed sensors though im not 100% sure EFI Live can monitor front wheel speeds

 

[07keo02]

Thanks, I will see if I can log that, if not I may just end up buying a pump rub kit and checking it all out during install. The pump rub fix will be a worthy install regardless if I find a problem or not.

 

[07keo02]

The only thing I can find in the PID's is "Transfer Case Ratio" and "wheel acceleration/deceleration". I am not sure these will give me what I am looking for. Can anyone confirm?

 

[07keo02]

Update for additional info. I put in a one piece driveshaft with new slip yoke and all. Drive shaft is nice in tight in the transfer, but I still get a clank over choppy bumps, as well as an occasional abs engagement. I guess it could be just the choppiness affecting will speed readings. The only place I do see some play is the front driveshaft out of the transfer. I can get radial play on that an 1/8 inch or so. Some have told me this is normal and others said it is the bearing. Anyone experience an issue with that? Btw, when I replaced my clutch I never could get that front shaft to come out of the transfer.

 

[chevyburnout1]

My truck does this with moderate stopping when hitting like bridge serrations or concrete edges. Felt it happen in three other trucks as well. It sounds like normal operation to me.

 

[Harbin_22]

Are you leaving it in gear on decel? If not see if it does it in neutral.

 

[Dozerboy]

Sounds normal to me too.

 

[Darius6t9]

Could a front wheel hub going bad cause the ABS light to come on maybe? That would be one of the first things I would check. Even if they are new, you might have gotten a bad one or installed it with the bolts not quite tight enough.

 

[07keo02]

Could a front wheel hub going bad cause the ABS light to come on maybe? That would be one of the first things I would check. Even if they are new, you might have gotten a bad one or installed it with the bolts not quite tight enough.

The front left one is a new timken, but it did this before and after that. The light doesn't even come on which is weird, just an engagement of the abs momentarily. I would feel it was pretty normal if it wasn't always associated with a clanking sound from underneath. If I leave the transmission in gear and try to twist the driveshaft back and forth it is tight. Would this confirm the drive train slop is not coming from the trans/transfer? If it is in neutral, it twists back and forth a good amount before the rear diff engages. I checked out a buddies cummins like this too and his seemed the same way so I think the diff is good. I'm going to try and get a pump rub kit here soon, will I be able to do a full inspection of the diff while installing? The front drive shaft does have some radial play but I have had inconsistent opinions on that.

 

[07keo02]

Forgot to mention, I think it does it in neutral and in gear as long as I'm applying the brakes over the bumps. I will confirm tomorrow though.

 

[Harbin_22]

What size and what air psi do you run for the rear tires?

 

[07keo02]

265-75-r16 on stock rims. 65 psi. I went over the same bump today in neutral, still did it a little bit. I guess its not too big of a deal and could be normal. I wouldn't think much of it if it was for that clanking sound.

 

[Dozerboy]

Sorry if I missed it but have you dropped the rear drive shaft and greased it? Us with the autos get a clank when going from D to R if we don't.

 

[07keo02]

Yeah its a brand new aluminum shaft swap, new yoke and all. I lubed it just a week and a half ago when I installed it. I've had the driveshaft clunk, this is not the same. Southbend told me the clutch I installed can make a noise when blipping the throttle at low speeds etc. Maybe it is just that happening in coincidence when the abs engages over choppy bumps. I reckon the truck is driving all good and everything so I shouldn't worry about it. I'm just a little investigative with my vehicles and try to make everything as perfect as I can. I guess I shouldn't be wasting money on whats not broke though. Thanks for the replies and ideas.

 

[heymccall]

I'd be looking at the RF WSS for signal fallout in the 3-10 mph hour range. With no light, there'll be no codes. If it were the VSS in the transfer case, the speedometer would be erratic at higher speeds.

The WSS's will send incomplete data at lower speeds (under 10mph) if the sensor has been lifted out of range by corrosion, or the bearing assembly is worn out (wobbly wheel). And, it'll activate the ABS on that corner, and, never illuminate the ABS lamp, or store a fault code.