I am a newby and recently I purchased an XJ 1999. By driving (on a straight paved road) suddenly the front wheels lock/unlock by itself. It occurred 6/8 times, I was about 30 mph and I can say that it occurred all the time when I was going over a slightly uneven paved road surface. The issue starts by a little vibration of the steering wheel and then the front wheels loick/unlock.. Then in a couple of seconds everything goes back to normal. I bypassed ABS (by removing the fuses) but but it doesn’t seem to be the cause as it does again today.

Hoping someone can help me -thanks.

 

Perhaps worn front brake pads, worn to the point that they dont have enough thickness to keep them heldin place, and the bumpy road is jarring them loose from the calioer then they are jamming against the rotor. It happend on a dirt bike I had... not fun.

Do you hear any scraping or screeching noises?

 

Sounds like a wheel bearing is locking up.

That is not fun at 60mph

 

No, I never heard any scraping or screeching noises since I have been driving. Not before or during the event or even after. I'll check brakes anyway.

 

Which transfer case?

 

Check for worn steering knuckles where the ears of the pad hit:

 

Thanks - please tell me more

 

How's your arc welding skilz?

 

arc welding skilz ... ? nothing of course

 

Well, that's the cheapest and easiest way to fix that (if that's what it is, take a look). Just fill the voids with a little weld (even a 90 amp welder will do) grind it smooth and you're done.

 

When you're driving down the road and it locks up are one or both of the brake rotors hot ?(assuming you haven't used the brakes for the last few miles)
it would be a way to narrow down the possibilities

Folks are thinking it may be pads hanging up, if BOTH rotors are hot that would likely be a different diagnosis than if one rotor was hot... which would be different than if neither was hot

 

That's is a good point, however, it is not possible to determine as when it does happen I instinctively push the brake pedal to stop the vehicle immediately.

 

I hope you are not driving it since this happend.

 

Must be interesting for the traffic behind him.

Another question for the OP.
When you say both front wheels "lock up" I'm imagining tire smoke and skid marks. If that's the case you would accomplish nothing more by hitting the brakes.
What do you mean by "lock up"? I'm still trying to figure out if it's a brake problem or a drivetrain problem

 

I want to specify that this event is characterized by vibrations and fast lock and release of the wheels. I am sorry but I cannot find any proper word in english to describe that ... ...