engine/transmission bumping?

OK. this isn't exactly a tractor question but the guys on this forum know more about engines etc. than any other forums i have tried.

I have a ford ranger truck. When I drive lately, there is a "bump" sensation. Not really a hesitation. I'll be going along and "bump"- maybe two in a row. Then nothing. Some trips it doesn't do it at all. The engine doesn't seem to misfire, the tach does not jump. No noise associated with it. just a bump bump, then a minute or two later -bump --. Any ideas?

I'll take a stab in the dark and suggest that it might actually be a mis-fire. Spark plugs, plug wires, just guessing at this point.

Could be a loose motor support.

Manual or automatic?

If it's an automatic it could be the lock up torque converter coming off and on.

If it is an automatic transmission, when's the last time you changed the transmission oil AND filter? I had a Taurus that would jump in and out of OD while highway driving. Changing the transmission oil and filter solved that.

Check into your radius arms on the front end. These arms control the radius of the arc the wheel travels over a bump. The front of the radius arm is like a "Y" that attaches at the axel. The back of the radius rod is a large bolt which passes through a bracket rivited to the frame. On the bolt, on both sides of the bracket are some heavy rubber or nylon "doughnuts" and washers, held tight with a big nut. I believe your doughnuts are worn or missing.
CNJ

I bought a new chevrolet van and it bumps all the time,dealer says its normal,ive got a 2003 F150 that has wore out tires and 130,000 miles and it is quieter and rides a lot better,probally the last chevy van

jimmy

More information is needed to give a better idea of the issue/causal factor(s). Taking your statement that "the engine doesn't mis-fire - the tach doesn't jump" then it cannot be an issue with the torque convertor locking/unlocking (assuming it is an automatic; we need to know manual or auto also) as any misfire/lean burn issue or convertor lock/unlock would be noted by a change in engine RPM.
It's hard to diagnose also as a better description of what you mean by a "bump bump" and then another "bump" is in order.
Here is what you need to do to enable a better understanding of the issue and what may be at fault: (1). does the "bump bump" occur when on a straight and level road surface driving at a constant engine load torque/speed (i.e. steady state drive with minimal engine torque to maintain a constant speed) on a smooth road or (2). does the "bump bump" occur ONLY when the vehicle hhits a tar strip or other transient road condition? (3). is the "bump bump" associated with a condition like the tires hitting a tar strip on the road - i.e. there is a tactile vibration as well as audible noise occurring with the issue? (3) does the "bump bump" occur when you to thru a torque reversal - that is, when you just back off the throttle slightly (when travelling at a constant speed on a level surface) and then tip back into the throttle? This condition is most likely to occur on a manual when in top gear (5 assuming a 5 speed; what is the make/model of the vehicle also). (4) what road speed and under what road conditions does this issue occur in? Can you get this issue at the same engine RPM regardless of the gear it is in or does it occur at a given road speed regardless of the engine RPM?
If you can better describe the issue with regard to when/where it occurs, what make/model and powertrain (engine and transmission) it has, many more and accurate diagnostics can be made. Look forward to your reply.

It is a manual trans. At first it felt as if i was hitting tar strips on the road --the same sensation --but not its not that. I paid attention once it started occurring. I occurs at both high and low speeds and when i am traveling at a constant speed. I can take it out and drive 80 miles. the next trip go 5 miles and feel it every minute or so.
There is no sound associated with it, like i would expect if the engine misfired or something -- just that sensation of a slight bumping.

I know what to do on my old tractor and jeeps, but this is beyond my ability.

thanks to all who respnded.

The next time the problem occurs, note the engine RPM (hopefully you have a tachometer), road speed and the trans gear you are in. Then shift down a gear (say from 5th to 4th) and then maintain the same road speed of the problem. If the issue goes away, then decelerate to the RPM of the issue and see if the problem comes back. This will tell you at least if the problem is associated with engine speed (RPM) or road speed. If engine RPM sensitive, look for something with the engine - if road speed sensitive, look for something in the driveline or (potentially) the running gear (wheel tires, suspension) or the like. Too hard to diagnose otherwise without experiencing the problem first hand or a better description.

Good Luck