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PostPosted: Mon Oct 07, 2013 5:03 am 
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Location: IL
Doubling the HP and 600 ft-lbs of torque, it was bound to happen. 55 mph speed limit, 2 lane road, and stuck behind someone drifting between 45 to 48 mph, it was just too much to stand. This is what this baby is built for. Hit the performance shift mode on the trans, and waited for the opportunity. Finally had a good open spot and nailed it. Trans shifted from 4th to 2nd, the engine revved to 3200 and the coach jumped to life. Yes, we were going around this guy, even towing my Grand Cherokee. Engine wound out to 5200 rpm, coach hit a little over 80 mph, and we were around him, and pulling back in, life was good...or so I thought. A few miles later, I coming up on some cross roads, I let off the throttle to stop and that is when I began to hear a funny noise. The farther I drove, the louder the noise got, but only off throttle. No noise accelerating or cruising. Only was about 30 miles, from home, so I babied it the rest of the way, thinking it was probably a U-joint. I've had U-joints go bad before, but this seemed different. U-joints usually vibrate off throttle, but this only made noise, no real vibration. Fortunately, I made it home OK. Time to get out and see what we can learn. Lifted one wheel off the ground, crawled underneath and started looking. U-joints all looked good, but I could hear a noise as I rocked the tire back and forth. Also seemed like a lot of slop in the differential. Time to drop the cover. Pulled the cover and Oh boy, do we have a problem. There were chunks missing from the ring gear. Not only that, but the bearing race which is supposed to be a pressed fit on the carrier, slid on and off easily.
Image
So that is where it all started. Knowing that a full throttle downshift was going to break my differential, I set out on a quest to find a solution. The internet took me in a couple of different directions. The first was cryogenics. Much of what is posted on the internet about cryo is black magic. Racers do not want their competition to know what they are doing. Wild claims by those who sell the service, and a lot of insanity. Finally came across a real lab report of testing that seemed to demonstrate the truth about cryo treatments. What I found was that it does not increase strength, or hardness but that is where the black magic comes in. What the tests did show is that it dramatically improved the uniformity of the hardness. Apparently when metal is hardened, there are still microscopic areas on the surface, that are not hardened. This results in tear out. Once the tear out begins, the pits become larger and larger, till eventually the surface becomes rough, which causes wear at an ever increasing rate. Since cryo treatment makes the hardness uniform, these soft areas are not present, so the tear out does not begin. This dramatically decreases the wear. The second observation is that cryogenics increases rigidity, without making it more brittle. In other words, the tensile strength stays roughly the same, but the elongation is significantly less. OK, so hold those thoughts, we'll get back to them later.
The second place the internet took my was to a guy out west who had done some interesting modifications to differentials. Had a educational conversation with Jantz Engineering. One of the things he does is build up differentials for guys who compete in off road racing. He has found that when pulling apart Dana differentials, there will be 2 wear lines on the bearing races, one for on throttle, and the for off. The conclusion is that there must a significant flexing as torque is applied to the diff. If anyone knows anything about rebuilding a Dana, they know that the housing must be spread to get the carrier out. The device that does this is rated for 10,000 lbs. If the case can be spread with only 10,000 lbs, then it is no surprise that it flexes under torque. As a result, he created a way to reinforce the case, as well as stabilizing the bearing caps with girdles. Our conclusion was that if we could prevent the case from flexing, that would maintain proper gear mesh, so the teeth would not be as prone to breaking. Secondly, the reduced flex should also prevent the race from walking on the carrier, so that will not wear as well. All good.
So what did we end up with. Now understanding the problem, it became obvious to me that both the reinforced case, bearing girdles, and cryogenics all are a step in the right direction. Cryogenics helping by making the case and carrier more rigid, as well as reduced bearing wear, and teeth wear. Here is the bearing girdles:
Image
And the Revcon differential with the Jantz cover
Image

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Dave

The Flying Fortress
'83 Revcon Prince 31' FWD
502 w/Howell/GM 16197427 ECM/Edelbrock MPFI,Thorley's & Magnaflows,
4L85E 4 speed, KoniFSD,
Yes it is SOLD

FMCA F298817


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PostPosted: Mon Oct 07, 2013 2:32 pm 
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Joined: Wed Sep 18, 2013 12:51 am
Posts: 25
It's kind of odd that they put a differential that spreads with 10000 pounds of force in a 14000 pound vehicle. I'm surprised it lasts as long as it does . Do you think there is anything that we could put in the differential to help extend the life of it ?(Synthetic gear oil, an additive or some kind of friction modifier?)
I like what you had done with your differential .Did it take them long to modify your differential ? It would be neat if they could also put in an eaton true-track differential for driving in bad weather. I still have to get under mine and check it out and see if my clunk is the differential or not.
Thanks for the info on the modification .If I have it reworked I would only like to have to do it once and it looks like that's the answer.

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87 Slantnose 31'


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PostPosted: Sat Oct 12, 2013 4:08 am 
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Joined: Sat Sep 14, 2013 12:36 am
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Location: IL
One could never apply the full weight of the coach of the differential. Otherwise you would be climbing a 100% grade. Still the rating is based on engine torque, not necessarily vehicle weight. Technically the biggest problem the differential has is the fact that the torque is pulling against the ring gear, rather than pushing. It makes a difference in how the stress is dissipated. Differentials that are specifically designed for front application have a high pinion, which changes the stress. There is a high pinion Dana 70, but it is based on the heavy duty 70 case, which is bigger than the standard case. As it turns out, the Dana 70 HD case is almost the same size as the Dana 80 case. We actually looked at if we could put 80 gears in the standard 70 case, but it would require removing too much metal in critical areas, so there would not be any real advantage. Jantz Engineering puts 70 gears in a 60 case, which does work, as the places where clearance is required does not affect the case integrity. I also looked at putting an 80 case in. Dodge made a hybrid 80 case with 70 tubes. The case is just a little wider, so I was too worried it would not fit.

BTW: Here is the contact info for Jantz:
Jantz Engineering
20555 Pugh Rd NE Poulsbo, WA 98370
(360) 598-2773

You can visit his website here: http://www.jantz4x4.com/jantz.php?p=home
So if you need your differential rebuilt, I would just ship it to Carl and let him do the whole thing.

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Dave

The Flying Fortress
'83 Revcon Prince 31' FWD
502 w/Howell/GM 16197427 ECM/Edelbrock MPFI,Thorley's & Magnaflows,
4L85E 4 speed, KoniFSD,
Yes it is SOLD

FMCA F298817


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PostPosted: Tue Oct 22, 2013 8:26 pm 
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Joined: Tue Sep 17, 2013 3:49 pm
Posts: 11
That's just stunning.

Even without the Cryo, just the girdle would help put quite a bit. I might consider the girdle for my slightly build 455, since it got a bit less HP and Torque.


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PostPosted: Sat Mar 05, 2016 6:20 pm 
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Joined: Sat Feb 13, 2016 6:16 am
Posts: 20
Location: Charlotte, NC
After reading Dave's earlier post, sent Mr Jantz an email, as I am less than educated when it comes to diffs. He was nice enough to send me the following response along with an estimate.

"I have done two now. The one on the forum got half the bells and whistles. The second one got it all.

Cryo’d ring and pinion, Detroit tru track, and load bolt. The Trutrack is made of much higher quality steel than the cast stock spider gear case. Bearing are much less likely to “walk” or spin, maintaining rigidity and alignment for many more years. (virtually every stock carrier I pull apart with 100,000 mile on it shows signs of bearing slippage. Also the main thing to remember is that ring and pinion is designed for the rear of a vehicle, so you are running it in reverse. Under high loads this is what causes the ring gear deflection. The load bolt on the back side of the ring gear will keep the gear from being pushed away under high loads.

I designed my system similar to the early GM 1 ton rear ends that came stock with load bolts. Here is a vid showing the .030” defection you get with even mild torque loads on a gear set run in reverse vs forward.https://search.yahoo.com/yhs/search?p=y ... mp=yhs-001

Here if you go through the instructions you will see just how its done, and the last few pics should make it all clear. You can’t actually see the ring gear as it would have been in the way for the picture however you can see where the load bolt will ride on the back of he gear to prevent defection. It is not rubbing all the time, we set it with a few thousands clearance, so it only comes into play in extreme torque situations. http://www.jantz4x4.com/jantz.php?p=man ... &mid=jlbig

...both of these also got the Cover Girdle set up to prevent housing spread. Think of a Tupperware box without a lid, it will move all over when you flex it, but put the lid on it and its instantly far more rigid."


Attachments:
Jantz Eng Invoice Diff Upgrade.jpg
Jantz Eng Invoice Diff Upgrade.jpg [ 123.23 KiB | Viewed 6086 times ]

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Mfg Date 0679
30' Revcon Mid-coach bath/Double Bed LR
VIN RFS279000143 Ser # 9310
454 Quadrajet Dexter Rear Axles Stock Drivetrain
16.5 950x16 x 6
Soon to be 225-75R16 on GMC 8 Lug Wheels
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PostPosted: Thu Jan 11, 2018 11:20 am 
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Joined: Sat Nov 11, 2017 3:22 am
Posts: 5
so when I install my Chevy performance 454 i should probably have this done?, what about u-joints and other drivetrain items, as you mentioned, one doesnt plan on stomping her down 2 gears, but one never knows when the occasion rises


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PostPosted: Fri Jan 12, 2018 1:27 am 
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Joined: Sat Sep 14, 2013 12:36 am
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At least girdles and the reinforced cover. If your diff is still in good shape, it would be a ton of work to pull it and ship it out. If you unbolt the hangers - 3 bolts on either side, and the U-bolt, you can flip the input shaft straight up. This will give you access to the cover. You can remove the cover and pull the bearing cap bolts and replace them with the long studs that go through the cover. This should stabilize the bearings, so they can't spread under load. You can do this cheaply and easily. Even if you blow the differential down the road, you can rebuild it and still use the studs and cover, so you haven't thrown money away.

You know, even with my 502, and towing the 4600 lbs Cherokee, all the rest of the drivetrain seems to survive, so I suspect the diff was the only weakness. Make sure the U-joint grease fittings are installed so they are under compression when torque is applied to go forward. If the area where the fitting is, is on the expansion side, rotate it 90 degrees, or otherwise it will break.

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Dave

The Flying Fortress
'83 Revcon Prince 31' FWD
502 w/Howell/GM 16197427 ECM/Edelbrock MPFI,Thorley's & Magnaflows,
4L85E 4 speed, KoniFSD,
Yes it is SOLD

FMCA F298817


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PostPosted: Sat Jan 13, 2018 5:58 am 
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Joined: Sat Nov 11, 2017 3:22 am
Posts: 5
thanks for the info, sounds like a must when the bigger engine is installed


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