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Topic: Hydraulic Pump Noisy (Read 491 times) previous topic - next topic

Hydraulic Pump Noisy

Dear Forum - I have a 1997 U270 with the C8.3 engine. It has 85,000 miles and 3,100 hours on the engine.

I returned from a trip a week ago and noticed an unusual noise coming from the engine bay. It sounds like really loud crickets. I rolled up a newspaper to make a mechanic's stethoscope and identified the hydraulic pump as the noisy component. I took the pump belt off and started the engine momentarily - no more noise. With the belt off, I turned the pump pulley by hand. It does not turn freely, it take a decent effort to turn it. I also noticed that it clicks when I turn it. If I turn it 180 degrees, it clicks about four times. I checked the hydraulic fluid - it's full.

Are these the tell-tale signs of a failing hydraulic pump? Should the pump turn freely by hand?

I took a closer look at the pump and saw that it was a Sauer Sundstrand with the number 40998 stamped into the pump body. I looked around on the internet and it seems like this is not a commonly available part. I looked through the posts on the forum where members have had issues with their pumps. Thank you to those members who have shared their pump stories. I believe my options are ...

1) Order a replacement from Foretravel
2) Find a shop that can rebuild it

Guidance from those who have traveled this road would be appreciated. Thanks, Eric
Eric Pressey

Re: Hydraulic Pump Noisy

Reply #1 –
I'd suspect the idler pulley before the pump.  Or possibly just a squeaky belt.  You might try some belt dressing to see if that stops it temporarily.

Re: Hydraulic Pump Noisy

Reply #2 –
Yes the idler. The pump does not turn freely. Run the engine and squirt some WD into the center of the idler and see if it stops. The belt squeals, the idler chirps.
1994 U280, Build 4490
Deming, NM.

Re: Hydraulic Pump Noisy

Reply #3 –
Thanks for the advice - you have given me hope. The idler is brand new. I installed it yesterday, so I think we can rule that out for now. But the belt making noise as it slips around the pump pulley - that's certainly possible.

I read somewhere that the pump should turn freely. If that's not true, then maybe my pump is OK and it's just the belt slipping.

I'll get some belt dressing on there and see if that helps.
Eric Pressey

Re: Hydraulic Pump Noisy

Reply #4 –
Quote from: EricFromPA –
Thanks for the advice - you have given me hope. The idler is brand new. I installed it yesterday, so I think we can rule that out for now. But the belt making noise as it slips around the pump pulley - that's certainly possible.

I read somewhere that the pump should turn freely. If that's not true, then maybe my pump is OK and it's just the belt slipping.

I'll get some belt dressing on there and see if that helps.
If it's the belt, you can press down with some object while running to increase pressure to see if the squeal changes. The pump is an actual hydraulic pump and does not spin like a water pump (impeller).
1994 U280, Build 4490
Deming, NM.

Re: Hydraulic Pump Noisy

Reply #5 –
If the pump turned freely it wouldn't be pumping, and it wouldn't be drawing the considerable amount of power that it draws from the engine.  It should take some force to turn it by hand.  Your pump is most likely ok.

Re: Hydraulic Pump Noisy

Reply #6 –
Thanks Twig, thanks bdale ... I started it up and increased / decreased the tension on the belt using a 1/2" socket. That definitely changed the sound. Then I pushed IN on the tensioner arm and it went completely quiet. Looks like I need to shim the belt tensioner so it tilts more towards the front of the coach. Boy am I glad that's the answer. Thank you both for helping me.
Eric Pressey

Re: Hydraulic Pump Noisy

Reply #7 –
What tensioner are you using and what belt part number?Check the forum,most of us are using the Gates tensioner,there are indicator marks on the tensioner 2 spacer marks and when running the third mark should be between the 2,your belt could be a size too big or small.
96 U270 BUILD 4810
85 380SL
Drummonds TN.
 

Re: Hydraulic Pump Noisy

Reply #8 –
If your idler uses a serpentine belt, you will also need to make sure all the angles are the same. Crank pulley, idler and pump. Easy to do and covered in several old posts. If the angle is not the same, the belt will wear on the edge and have a short life.

Our idler was 3 degrees off and failed twice after we bought it before I figured it out. Coach does not have to be level. Just an inexpensive angle finder.

Pierce
Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)