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Topic: Shredding HYD belt, Bad Pump/Bracket?? (Read 898 times) previous topic - next topic

Shredding HYD belt, Bad Pump/Bracket??

New to us May 2017, U270. 32,000 miles. PO purchased coach new and never had any HYD belt issues whatsoever. Nothing questionable found in our pre-purchase inspection nor in the "pilot" logbook for the life of coach. Coach had been in storage for some time.

After purchasing coach, approximately 3000 miles ago, the HYD belt started slowly shredding. Would gradually eat thru one belt groove over 1000-1500 miles. Rudimentary square check on alignment, (photo) showed HYD pulley out of alignment 1/8" from the engine crank pulley! Truck repair shop said this was no surprise, bracket was bad design by coach manufacturer. (FOT says they assemble this, apparently it is not a Cummins part). Repaired by shimming the bracket/pump. I'm told there are no adjustments to the bracket or HYD pump for alignment. I've read on the forum this "shim" is a valid repair. Also, the second opinion I sought out confirmed this is how they would have fixed it. Unfortunately, I don't understand yet why no shredding occurs for 29K miles and then starts happening. My newbie opinion is that correcting this with a shim/washer where there was none needed before doesn't address the underlying cause. Am I thinking too hard?

1. Does the HYD pump produce enough torque to deform these brackets over time?

2. If the HYD pump were failing, would it put additional stress on bracket? Both shops that looked at this said the bracket has no cracks in it. How does one inspect/test the pump?

3. What is the proper torque for the tensioner? (I doubt the tensioner could cause the HYD pump to be misaligned.) BTW: The Cummins shop says replace it but they can't find the right part, (I'm not going back to them!). My chassis guy says it doesn't need replacing.

It makes me want to borrow Clint Eastwood's famous question from the Dirty Harry movies, "Do I feel lucky?, Well, do ya, pump" Truthfully I'm not sure how I should feel about this. Help!


2002 U270, 36' WTNS, Build # 6030, Cummins 400 ISL.
Wheelchair accessible modifications by ForeTravel, Braun UVL lift.

2001 Dodge IMS RampVan, M&G tow brakes, Sterling tow bar.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #1 –
I doubt your hyd pump is bad, or worn enough to cause an issue if so it would be leaking. Alignment is a major issue 1/8" out over that short of distance would be a problem I would imagine.

Mine went through that a couple of years ago replaced both tenisoners and belts with Gates (green stripe belts), I'm going to jinx myself but no problems last 20k miles.

Also a hint, make sure you have the correct belts, the tenisoners should be running in the middle of their indicated range.

Bruce, Linda, and Macy
Zoey RIP 1/20/19
1999 U295 40' build #5400
2017 silver Jeep Wrangler, 1260 watts of solar on top
Moving around the country

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #2 –
Maybe the belt was new at time of sale and doesn't match the pulleys.
Does everything match up rib for rib?

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #3 –
Looking at your picture,at the harmonic balancer,are you missing the rubber insert part or does it just look that way?
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #4 –
Quote from: John44 –
Looking at your picture,at the harmonic balancer,are you missing the rubber insert part or does it just look that way?
Agree - that does look kinda strange.  For comparison, see photos below of our C8.3 balancer.  The 400ISL must use a different type of balancer.  If the rubber insert was totally gone (like it appears) that outer ring would be making a heck of a racket with the engine running.
1993 U280 SE 40' WTBI, Build: 4359
C8.3 300hp, 6-Speed, Exhaust Brake
960 watts on the roof (6 x 160)
Sorento (or BOLT) on a Kar Kaddy SS
"Nature abhors a vacuum"

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #5 –
Good catch...anxious to see resolve.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #6 –
From what I can see, the drive pulley looks like mine.  The inner disk on mine appears to be smaller in radius and about 1/2"thick.

Rich
Rich and Peggy Bowman
2002 U270 3610 WTFS, build #5939--"Freedom"
2022 Jeep Grand Cherokee Summit 4xe
SMI AirForceOne brake system
PakCanoe 15

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #7 –
Also from Clint,get back to us Mike "We gots to know"!!!!!!
96 U270 BUILD 4810
85 380SL
Drummonds TN.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #8 –
Our U300 also would occasionally eat the hydraulic belt on the way across the U.S. after purchasing it in N.C. The PO had described waiting for the tow truck driver to arrive in the middle of the night a long way from civilization. Our Detroit's DDEC went into half power for 30 seconds to allow us to get to the side of the road.

Everyone said it was the tensioner and I did notice how it jumped up and down while idling. Even the videos seemed to fault the tensioner. I watched the tensioner for a long while and realized it was not the tensioner spring but the fact that the tensioner's pulley was out of line with the crank pulley and the pump pulley. I used an angle gauge to compare any differences and found the tensioner's pulley was 3 degrees off. I added a shim behind the tensioner to bring all three into perfect alignment. I took the old OEM pulley, spun it and determined that nothing was wrong so just turned it on it's side and oiled it a bit to make sure. Tensioners should last a very long time. Our RAV4 tensioner is going toward 300,000 miles and working fine.

So, what happens is the belt tries to move sideways on the flat tensioner idler pulley and as it does, it pulls the tensioner arm down. Once it moves over a fraction of an inch, it jumps back to the normal position and then repeats the cycle several times a second. This is what make the tensioner jump up and down and not the fault of an internal failure or wear.

Since my "fix", the new belt has worked flawlessly for 45,000 miles and is showing no wear on the edges. The OEM tensioner is also quite happy. Here is my documentation from an old post:

Belt tensioner on 6V92TA

Use Gates Green Stripe Fleet belts and make sure if the crank pulley and the pump pulley have 8 ribs, you use an 8 rib belt instead of the 6 rib that Foretravel recommends. Foretravel never updated the belt information when they went from a one fan system to the two fans we have on our 1993. Buy the Gates belt online as they are MUCH less expensive that way. Since we don't have another belt to remove, the new belt can be installed from no belt to ready to run in 7 seconds if you practice a bit.

Cummins or CATs will have the same fraying on the edges and failure problem unless all angles are the same. Our problem started with a poor installation at the Foretravel factory and was delivered in this condition.

Pierce

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

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #9 –
No one should be towed for a problematic belt.  Carry a spare and if a tensioned belt, wrench against the tension spring, and swap belts.  Towing is harmful to the coach and should be avoided at all cost.
If not using Gates sealed tensioner, swap out before it needs to be changed to a Gates.  This also can be done without going to a mechanic.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #10 –
Hi all,
Coach in shop today to straighten out a wiring miscommunication between it and the toad. Be back on Wednesday if all is well. I will check the balancer and post a better picture specific to that. Sorry John, and others, you'll have to wait for that news.

Barry, Pierce, (thxs P for the post link!), Regarding idler/tensioner: Our belt never did jump around as I recall, (can a short video be posted to forum?) I did originally investigate the idler but focused on the alignment once I saw how far off it was. Will look at idler more closely and check the range of movement again. I have looked at Gates idlers online and couldn't tell which one would be correct for the ISL 400 we have. Anyone know the Gates part number to use? Would FOT tell me? [We absolutely carry spare belts, green stripe, I have two of each, plus an airbag, fluids, filters and more. PO had coach fully outfitted for us]

Wish my posted picture of alignment was better. I couldn't get a clean pict from above but I can tell you the pulley alignment was way off. Looked like HYD pump was pivoting away from engine block as if the belt was pulling it forward. Weird angle. Now with the shims/washers under HYD Pump, the pulley grooves all line up. Have only put 950 miles on coach since repair. New grade 8 bolt too.

For me, that's just enough miles since repair to think it is okay but not enough to keep my newbie brain from wondering "what if". Must say, the belt and U270 did perform well on our return drive from CA in December. Had to boogie back for work, went 75-78 for a bunch of the open straight areas. Hate to go that fast. Next trip, starting in August is a slow one one, 3 month loop thru Canada to New York and back to Oregon... A big reason I want to be as sure as possible this HYD pump is on track and the bracket is sound. I can't imagine how my wife would manage steering a rig this heavy if the power steering suddenly went out. (I wouldn't be much help from my wheelchair, except to say uh ohhhh, Love ya sweetie!.)

2002 U270, 36' WTNS, Build # 6030, Cummins 400 ISL.
Wheelchair accessible modifications by ForeTravel, Braun UVL lift.

2001 Dodge IMS RampVan, M&G tow brakes, Sterling tow bar.

Re: Shredding HYD belt, Bad Pump/Bracket??

Reply #11 –
Quote from: John44 –
Looking at your picture,at the harmonic balance,are you missing the rubber insert part or does it just look that way?

3 months later and I have a sort of answer. Nothing unusual for this harmonic balance except the outward appearance of no insert for vibration dampening. Asked mechanic at Oregon Motor Coach while we were in having a few items checked out. Also asked a Cummins shop I was at two weeks about it and they saw nothing unusual either. I would have asked them more about the configuration but it was after closing.


2002 U270, 36' WTNS, Build # 6030, Cummins 400 ISL.
Wheelchair accessible modifications by ForeTravel, Braun UVL lift.

2001 Dodge IMS RampVan, M&G tow brakes, Sterling tow bar.