Engine/Transmission (1994 - 1998) lift Pump

[BTanzini]

I am having a vibration problem and it seems like it is comming from the engine at around 20-60 MPH. I have checked tires for balance, drive shaft u-joints, center support bearing and replaced front joint, rest are fine. My question is if the lift pump is not putting out proper pressure to injection pump(low pressure) would this cause the engine to viabrate at low speeds. 20-60 MPH?? Thanks for any help.

 

[Joe G.]

No. Mine ran smooth for a 100 miles with only 6 PSI when my overflow valve failed.

 

[hsmith]

Make sure the harmonic balancer is not starting to separate.

 

[BTanzini]

Have checked harmonic balancer and does not show any signs of seperation. Thanks

 

[Missouri Mule]

Have you checked tires for shifting belts. How about motor mounts and transmission mounts?

Is the vibration felt through the steering wheel, fuel pedal (front floor) or seat?

 

[BTanzini]

Missouri Mule- Have checked engine & trans mounts there o k. I feel the vibrtion through the seats. How can you check for tire belt shift ? I did have tires rebalanced and correct air pressure-I keep 80 psi rear and 60 psi front,these tires made today have weak side walls so I compensate with tire pressure. Thanks for reply.

 

[SRehberg]

How about the drive shaft(s) balance or out of round. Then there's the remote possibility of the companion flange at the rear end is slightly loose. I see you have an automatic, is the flex plate damaged or bolts loose? 20-60mph is a wide range. Is the vibration a higher frequency like a drive line or slow like a unbalanced tire? It might help everyone narrow down the culprit.

 

[Joe G.]

Does the frequency change when the transmission shifts?

 

[BTanzini]

O K guys, the transmission seems to shift fine in all gears and have not paid much attention to frequency but I will, how ever I think the viabration is beteewn the engine and transmission. I have heard a scuffing sound at times that sounds like its coming from engine or transmission and I noticed the engine loops sligtly today,the RPM is about 800? I will have to do a temporary shaft balance and get back to you on that. I may have to change the middle and rear u-joint and go from their. (SRehberg by companion flange do you mean Yoke?) Thanks

 

[SRehberg]

Yes, the flange that is on the rearend that the U-joint mounts into. The large nut in the middle may or may not be loose. It requires considerable torque. It probably isn't it, but it has happened. The frequency of the vibration would be helpful.

 

[HLEschenko]

Since you're looking at the whole drive train. I assumed you've verified the carrier bearing is good. Just a thought, I had one go bad and it sounded like something close to the engine/transmission.

 

[Missouri Mule]

BTanzini, tires are easy to check. Jack up one end look at tires make sure there are no bulges on tread (I have had two tires shift belts on me on the Mule, One tire shifted to the side the other tire shifted to the middle).



While ends are in air take a cement block put it close to tire and spin watch for a large gap between tire and block. Tires are not totaly even so there will be some small gaps.

My Freightliner original tires caused the truck to shake it got so bad I had them balanced but it still shook. My roving tire man jacked the liner up(font end) put a block in front of it found that the tire had a flat spot about 25% of tire (when they computer balanced them all they did was put extra weights on one side). Two new front tires(different brand) and truck was riding smooth.



If you feel it through the seat of pants it usually something on rear of vehicle.

 

[BTanzini]

Missouri Mule, I believe I have a rear wheel bent rim on the backside. Thanks

 

[Missouri Mule]

When my front tire belt shifted I took it to my mechanic they jacked it up an saw the bulge. I had been having a vibration around 45 so they jacked the back end up(felt it on my seat) started out slow about forty the right rear tire started to shake at 45 it almost came off the jack beyond that it was ok.

I put 4 new tires and 4 aluminum wheels on it, the vibration went away.

 

[BTanzini]

Thanks for all suggestions, it will take me a little while to check every thing out and I'll get back as soon as I can, about a week as i am tied up for awhile. Thanks again

 

[Ahopper]

not meaning to steal the thread but i have had a similer problem. at around 70-and up i get this vibration in the steering wheel. i checked the tire pressure and the tires are brand new. it comes and goes. i do notice if i let off the gas and the tourqe converter unlocks it goes away. it seemes perfectly normal around town. its just when im on the highway. and it doesnt to it if i rev it up in the drivway to around the same rps when its at 70mph. (~2000rpm) anybody have any sujestions? i just had the trannie serviced and i just did the kdp so the front of the truck (belts) was ok too. how can you tell if the harmonic balencer is seperating?

 

[BTanzini]

Well I guess the problem was with tire balance and U-Joints, so thanks for all input guys.

 

[jleons]

Hello

I had the same issue. At 55-60 mph, there was a vibration I could not find. Replaced all components and - no deal. I noticed a leak in a shock and replaced it. No problem with vibration after.

Check your shocks. Make sure you have even pressure to the road.

Good luck

JL