Axle Ratio on U320

Topic: Axle Ratio on U320 (Read 1051 times) previous topic - next topic

Axle Ratio on U320

September 05, 2018, 11:03:18 pm

Where can I find the axle ratio on the differential for our 2003 U320? I might be getting the ring and pinion gears changed next week because of the noise our coach is making.

I thought I remember seeing it somewhere but cannot find it.

Thank you

Ed

Re: Axle Ratio on U320

Reply #1 – September 05, 2018, 11:22:49 pm

I found a couple old posts saying the U320 has a 3.91 rear axle ratio. I DO NOT know if this correct, so do your own due diligence.

Replaced P-3 Carrier and Bearings

Replaced P-3 Carrier and Bearings

Re: Axle Ratio on U320

Reply #2 – September 05, 2018, 11:28:16 pm

The odds of the gears being bad are very low. Wheel bearing? Drive shaft? Trans output bearing? Motor mount?

Re: Axle Ratio on U320

Reply #3 – September 05, 2018, 11:31:15 pm

no matter what you believe the ratio to be, if you do remove old differential, count the teeth to be sure the replacements are the same if you want the same performance.

Any chance the sound is from the bearings on the differential or transmission? It is hard to diagnose gear noise. Also I assume there is an adjustment in how pinion meshes with ring gear.

Re: Axle Ratio on U320

Reply #4 – September 05, 2018, 11:52:24 pm

Once the ring and pinion have been run in any adjustments to them will only create more problems. Carrier bearings or pinion bearing can make noise. If the bearings are bad and the coach gets too much mileage afterwards the ring and pinion will go bad..

Re: Axle Ratio on U320

Reply #5 – September 05, 2018, 11:53:30 pm

3.91

Re: Axle Ratio on U320

Reply #6 – September 06, 2018, 02:33:18 am

If you think the differential gears/bearings are bad,change the oil to a good synthetic and see if that helps with the noise,you'll
know you have the correct weight and new oil,would be the least expensive thing to do and if later you get new gears just save the
new oil.

Re: Axle Ratio on U320

Reply #7 – September 06, 2018, 03:35:55 am

There should be a tag on the rearc end and it will have ratio stamped into it

Re: Axle Ratio on U320

Reply #8 – September 06, 2018, 09:40:45 am

Thank you for the responses. I will look for the tag on the axle. The differential fluid was changed 20K miles ago. Looked at it again yesterday, still light in color and no particles floating around.

Re: Axle Ratio on U320

Reply #9 – September 06, 2018, 10:13:31 am

Once the ring and pinion are run for a while and establish their mesh pattern any noise from then (other than normal noise) usually happens at a specific speed. If the noise is all the time at any speed then maybe look at bearings.

These things are big heavy duty contraptions. They make a lot of noise in anycase. I had Keith Risch at MOT go for a ride with me to listen for abnormal sounds and see how it handled. He drove. He said it drove well and sounded like it should. Ours is the only one I have driven for any time so my sense for what is right by noise or feel is very limited.

Re: Axle Ratio on U320

Reply #10 – September 06, 2018, 10:22:01 am

Allisons had a problem with the output shaft bearing and a nut that came loose. Can't remember it now but it might have been on the retarder equipped transmissions. I would check before replacing the ring and pinion. Quite a bit of labor setting up a new ring and pinion. It's not just R&R. Bit of an art to it so it's not noisy after installation. There is also a crush sleeve, bearings, preload and correct torque to consider.

If a rear end whines, the ring gear as well as the pinion can be adjusted until the contact patch is perfect. This will get rid of any whine if the gears and bearings are good. No particles or on magnetic plug are a good sign.

Pierce

Re: Axle Ratio on U320

Reply #11 – September 06, 2018, 10:37:27 am

I swapped in a whole new (used) differential to change the gear ration in my u270. The used one was from a truck and did not have polished gears. It made a slightly higher gear whine going down the highway, but it's not noticeable over the wind noise of me going faster, lol.

Quote from: Pierce & Gaylie Stewart – September 06, 2018, 10:22:01 am

Allisons had a problem with the output shaft bearing and a nut that came loose. Can't remember it now but it might have been on the retarder equipped transmissions. I would check before replacing the ring and pinion.

I believe the Allisons that had that problem were the MD3060 on the 8.3 engines, not on the m11 with hd4060

Re: Axle Ratio on U320

Reply #12 – September 06, 2018, 12:22:07 pm

Foretravel decades ago, was rumored they bought some farm/truck rear axles that were quite loud, some were replaced after delivery. Looks like RV axles are put together differently so they are quieter.

Re: Axle Ratio on U320

Reply #13 – September 06, 2018, 01:05:21 pm

Oshkosh built Foretravels chassis long ago and to save $43 wholesale cost they used non "whisper quiet" rear axle housing gears. In Oshkosh's defense they had not built rv chassis before and the tiny howl was not noticeable in any other use

I changed the rear axle lube to B & M drag racing rear axle 85/140 oil and added a few pints of gm positraction rear axle additive to the housing on every 300 cat ORED I sold and the tiny howl under a load went away.

In 50k miles or so the gears polished themselves from use and the ring and pinion could be reset on a bench and were noise free afterwards.

Re: Axle Ratio on U320

Reply #14 – September 06, 2018, 06:21:57 pm

Quote from: Pierce & Gaylie Stewart – September 06, 2018, 01:24:42 pm

It takes a sharp mechanic to reset the ring and pinion correctly. I watched an ex-GM assembly line worker do it at a shop I apprenticed at. Used crush sleeve, bearings, etc vs new required different torque settings for long and quiet life. He used a lead paint on the gears to get just the right contact area in just the right spot. He was like watching a excellent artist as work moving either the ring gear or pinion and getting just the right pattern and lash..

Yes, gears will polish themselves after after 50K. We would pickup new Mercedes from the factory at Sindlefingen in Germany and drive them north for shipping. Mercedes always said top speed was cruising speed as the engine/transmission package had several hours of high output on the dyno before installing. They did say to watch sustained top speed on the Autobahn because of the heat generated in a new rear end gears.

Never let a shop install new gears when just an adjustment will quiet things down.

Pierce

This is the pattern I set up on my 9" in the Camaro Have over a hundred runs on it now.

Re: Axle Ratio on U320

Reply #15 – September 06, 2018, 06:36:42 pm

Quote from: craneman – September 06, 2018, 06:21:57 pm

This is the pattern I set up on my 9" in the Camaro Have over a hundred runs on it now.

Needs caulk (yes, a boat thing)!

And I SUSPECT that rear end noise is NOT the dominant noise (or concern)!

Re: Axle Ratio on U320

Reply #16 – September 06, 2018, 06:38:49 pm

Nice job with the gears. White gear setup grease?

A guy with a Rambler I knew told me he got a real deal on a rear end for the one that went out in his car. He just installed the used R&P himself. A couple of days later, he was not so happy. My wolf can howl but not as much as his car did.

Good to see someone that can do more than change a lightbulb.

Miller time means wire feed to me not beer.

P

Re: Axle Ratio on U320

Reply #17 – September 06, 2018, 06:46:10 pm

Yes white gear set up grease. Still have the white lead from years past. Dana 60's and Olds

Re: Axle Ratio on U320

Reply #18 – September 06, 2018, 08:20:43 pm

Quote from: craneman – September 06, 2018, 06:46:10 pm

Yes white gear set up grease. Still have the white lead from years past. Dana 60's and Olds

I like the white, I use Prussian blue on the valve seat faces when I do cylinder heads on the bikes. The white might be way easier to see.....

Re: Axle Ratio on U320

Reply #19 – September 06, 2018, 11:50:59 pm

Crane man did you ever use a "spool" rear end? Henry's machine shop part?

Re: Axle Ratio on U320

Reply #20 – September 07, 2018, 12:28:08 am

That is a spool Mark Williams I believe.

Re: Axle Ratio on U320

Reply #21 – September 07, 2018, 01:26:02 am

My buddies and I had Henry's build a spool for us with ten spline axles to fit the olds. 1.5" axles.

He asked if we minded that he built a few more. No problem.

Found out he built 10,000 of them.

Same as the tow hubs we made up.

Re: Axle Ratio on U320

Reply #22 – September 07, 2018, 09:56:21 am

Chuck and Bob, are you talking about Henry's Machine Shop in L.A.

Re: Axle Ratio on U320

Reply #23 – September 07, 2018, 09:59:03 am

I'm sure Bob is. I didn't use him, Had Cooks machine make up some axles in the early 70's

Re: Axle Ratio on U320

Reply #24 – September 07, 2018, 10:21:38 am

Cook? "Mumbles?". Old buddy from Qualifiers ll drag race car club. 50 years ago. Scary. Mert Littlefield and don cook did the motormounts and dropped in my 427 engine into my 58 corvette in cooks driveway. In Trade for a small block intake manifold and $40.

We drew the spool setup in the orbit coffee shop in Long Beach then took it to Henry's to machine it.

Same as the tow hubs. Had to be careful as with the tow hubs on the rear the car rolled if unhooked from the tow bar.

Sorry for the hijack. Went to a 3.08 ratio rear with the big block.

30moh per 1,000 rpm in fourth. Over 200 wound out.

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