Chinook RV

I thought I'd write up an experience I had with the rear axle in my Concourse this past year in case it might help others. My Concourse came stock with a Dana 70 Limited Slip axle with 4.10 gear ratio. Ford axle code E2.

The Concourse had 49k when I bought it. Before purchase I took it to a Ford dealer (agreement with seller, plus I was away from any mechanics I knew, or else I usually prefer smaller shops). Amongst other things, they said it needed a pinion seal (this is just forward of the pumpkin, IIRC). So they did that, along with a few other non-rear-axle related things.

I drove merrily along until last winter (~75k by then), when I first noticed an issue (when I say merrily along, I have done other maintenance but just speaking of the rear axle). The symptom was that when I was doing slow speed turns there was a juddering feeling (not a sound as much as a feel) coming from somewhere in the back. I first noticed it at a small camp spot where I was doing a bunch of backing and filling with the wheel hard over to get settled in my spot. It wasn't about the ground surface as that was smooth, but seemed more related to the turning.

The juddering was not apparent when I pulled out of that spot in forward. But I did notice it a few miles later when I pulled away from a wall as I did a slow short-turning maneuver to get myself clear of it - this was on smooth pavement.

So I started Googling. I wasn't driving anywhere anytime soon in the Chinook so I had some time to figure it out. I didn't suspect wheel bearings as there was no sound and I have already had those serviced. After reading a bit I started to suspect the Limited Slip clutches in the rear end. Either they were wearing out/damaged, or the rear end was low on Limited Slip additive (Ford makes this, a specified number of ounces should be in the rear pumpkin along with the regular gear oil).

Interestingly, you want just the right amount of that additive. Too little and the clutches can shudder; too much and they are quiet but you no longer have any Limited Slip function - it's then just a regular open diff for all practical purposes (not what you want). So if the axle starts out new/empty, you can just put in the number of ounces of additive Ford specifies; but if it might be low you of course don't have a specified amount to put in -- so you put in the least amount possible to make the clutches quiet down, and no more than that. i.e. add a little, drive, add a little more, drive until the clutches JUST quiet down (which they will do presuming nothing is damaged in there).

As a side note, I started to wonder if the Ford dealer that had replaced the rear pinion seal had replaced any additive. I called them and the mechanic did remember my Chinook (guess they don't get many RV's), but said "well no of course I didn't top up the additive, RV's are never limited slip." Guess it was too much trouble to check, because of course *this* RV does have it. Still, people I talked to said that probably not much gear oil was lost/replaced during that change, so that may not have been a cause. And also it didn't make any shuddering for nearly four years and 25k after that service. Interesting anyway, as something to double check when having any service done.

I then contacted two differential specialist shops and spoke with both of them about it. They said it is possible for the additive to dissipate somewhat over a long period of time, plus maybe a little was missing from that pinion seal change. So they both agreed with my plan to simply add a little bit of the Ford additive and see if that cured the problem. However, I was helping a friend with a job, and thus staying at an RV park, and they frown on mechanical work. Also, I felt it was time for a complete fluid change anyway, and I decided I'd really just like a professional's eyes on the whole business. They said that unless it was already something that needed serious repair (in which case making it worse probably wouldn't matter), driving to their shop would likely not hurt anything (plus it didn't shudder on the highway anyway). I wasn't driving it at all during the research time period leading up to my trip to the diff shop.

I also did some research and decided that if possible, I'd add a Mag Hytech pumpkin cover. This uses an O-ring seal (vs. gasket or sealant), has a bit more room for fluid, fins for heat dissipation; and even better, has a dipstick to check or add fluid. But there was some question whether it would fit or not. There could be interference with the anti-sway bar or with something else about the RV parts under there.

Come July I was released from my "job" and away I went to the differential shop. No shuddering on the way there, and in fact it didn't even do it when they took it for tight spins in the parking lot. But I knew it had been doing it, and time for service at any rate. So up she went on the lift, and after a while they called me in to view the patient mid-operation and explain what they had found. Happily, they said everything looked just great, and showed me the area where you would see wear if the clutches were ailing. It looked just fine (the metal of the gears where bad clutches would cause wear). Whew! So they did a complete fluid change, added the correct amount of Ford limited slip additive, and for under $200 I was on my way. (Could have been $2500 or more if there had been something damaged or broken in there - of course I would have had it fixed but how nice that there wasn't any problem.)

BTW, I don't know for sure whether I would have been able to fit the Mag Hytech cover. They did have it in stock, but they felt it might contact …. gah, I forget now… I think it was something above? Some part of the RV floor/works? (I don't think it was the anti-sway bar, which *was* something mentioned in the Mag Hytech literature.) Anyway, they simply recommended I have the fluid completely changed every 40,000 miles or so. I might have pushed a bit more to try the Mag Hytech cover but I don't see having the fluid changed at 40k* to be a problem - good to have someone take a look (vs. with the Mag Hytech cover I would have done the changes myself, but without being able to see the guts).

Speaking of which, have any of you looked up the axle fluid/maintenance recommendations in the Ford manual? Could they be ANY more confusing? And the part about "if you tow or run heavy and have the conventional fluid, change it every 3,000 miles" almost sounds like a typo. I mean, come on, who changes their axle fluid more often than their engine oil? And that's not the only confusing verbiage (there's more… much more). Anyway, the upshot I got (from calling Dana Spicer plus the differential shop) was that for this axle the standard (non-synthetic) fluid was recommended (this is mentioned in the Ford manual as well, albeit confusingly), and changing it every 40k or so is fine (*I'll likely do 30k since I don't put on that many miles over time).

There was also some confusion on Ford's part wherein I saw our axle mentioned as the Dana 70HD in a few places. Also the parts counter fellow at a Ford dealer (when I went to buy additive, which I didn't end up using since I took it to the diff shop) swore it would be something completely different like the Dana 80 (which I think was the one they put in F-series). On the HD designation I was suspicious because the "70HD" has an axle weight rating of 9xxx #, and the regular (non HD) Dana 70 has rating of 7,500#, which exactly matches the Chinook's rear axle weight rating. I specifically asked the diff shop about this when I was there - so I could definitively clear it up - and they said it is the Dana 70 (non HD), which makes sense and matches some of Ford's literature. Geesh, why is this hard? (BTW Dana puts a "BOM" number on the axle tube but I couldn't readily see mine - if you have it you can get more specific info from them on the phone. I could easily see my axle tag, but that's not the same as the BOM [bill of materials] number on the tube.) Nevertheless, I'm happy now as I know just what I have.

Figured I'd put this out there in case anyone else has similar symptoms (noiseless juddering in rear while making slow/sharp turns). I did find mention of this in a few places online (more generically for limited slip type axles in many types of vehicles), but thought it would be good to have it here as well.

BG

Funny, I had nearly the same thing a couple months after I bought my Concourse. Only the juddering, as you call it, came and went. Sometimes pretty bad, as in it even hopped a bit when turning slowly, though it actually felt to me like it was in the front. Finally found a truck place, Donco Truck, in Austin, TX, and the guys there took me immediately (since I was in an RV driving through) and figured out in 5 minutes that the differential was binding. When they took it apart they said it looked fine, except it looked/felt to them like someone had put in the incorrect fluid type!

Mine had not been driven for most of a couple of years before I bought it, and after they replaced the fluid and additive, it still was a bit stiff. The guy said if it was him, he'd drive it around a few days or weeks, and see if it worked itself out. That it might be partly an issue of residue that was still in there. A few hours later I drove away, and over a period of a few weeks it totally went away, just like he guessed.

Bob

Mine did come and go a bit too, although it was never very bad (but noticeable to me). It started last winter and I experienced it a few times over a month or so (was only moving every 14 days so not much driving). It was not "grindy" or really bad seeming, but was most definitely there.

Then I parked up at an RV park for a couple of months (during which I had plenty of time to worry about it ), and then drove straight from there to the differential place. It didn't do it on the way there or in their parking lot prior to going into their service bay.

Since it has happened to both of us, maybe this will also help others. I would have sweated a lot less (in the months parked while I waited to go to the diff shop) had I known it was fairly likely to only be fluid related. Oh well, on the bright side I was fully prepared to be there for days, see lots of buggered up metal, and pay $2500 or more -- so three hours, nice smooth gears, and ~$200 had me giddy with joy!

Speaking of the wrong fluid, I did come across a post, when I was researching last spring, from a fellow with an E-Series camper van who suddenly had this problem on a long trip. Turns out that the preventive maintenance he'd had just before leaving on the trip had included a differential fluid change. And -- as you can probably guess -- the mechanic had put in regular gear oil with no additive (the fellow was able to contact the mechanic, who had apparently missed seeing the LS on the axle tag and simply treated it as an open differential). He had that adjusted (can't remember if he went for all new fluid or just added LS additive) and all was well.

I knew that wasn't my specific problem as it started up nowhere near the time of a fluid change, but your post reminded me of it.

BTW I did ask about why not just use synthetic gear oil (as I'm generally pro synthetic oil), and apparently it's because it's "too slippery" so it negates the Limited Slip friction that you need to make it Limited Slip. Or maybe it's just that you can't really control how slippery it is (vs. using regular gear oil and adding a precise amount of the Limited Slip additive). Basically both are the same concept though: Either too slippery or just not measurable slipperiness.

I first learned about limited slip fluid forty years ago while driving a Dodge Monaco station wagon between Army bases, from California to Texas via Colorado.

I couldn't figure out why my wheels were binding on turns through the mountains. I'd stop, jack up the car, check the bearings and brakes, but couldn't find anything. It was quite nerve wracking.

Finally I stopped at a Dodge dealership, expecting an enormous repair estimate. They took one spin around the parking lot, and instantly knew what it was.

As a young Private, I was so thrilled that it was a cheap fix of replacing the fluid.

Kev

Timely post as I need to drain and fill my rear diff. at some point. My 1998 E350 ambo had single rear wheels and the 70HD. I had the LS clutch packs rebuilt and serviced by Six States Distributors here in Portland, OR. I think it was $4-600 total? They’re the shop all the other shops order parts from or outsource to... It was good to know it was setup right, and the noise while turning went away.

I looked up that axle off of the metal tag on it, I’ll try and do that for the Chinook and see what it’s got. I believe all factory cutaways had the LS?

Lots of info here:
https://en.wikipedia.org/wiki/Dana_70#Dana_70HD

Doorjamb Axle code/ratio (I've got E2)
http://www.drivetrain.com/parts_catalog ... _posi.html

I don't know if all cutaways had LS. My buddy's E-450 RV cutaway (not a Chinook) did not seem to by the axle code when we researched it. But you do have the same axle code as I do, E2. So I would suspect the Dana 70 (non HD) Limited slip same as I have. Mine shows this on the tag:


Just so it's searchable, the tag says 4.10 VF8UA ABB V606158 - 2 LS

Is yours the same?

When I took it in to the differential specialist, I was totally willing/expecting them to take it apart and do things with the clutches. But they recommended not doing that. They did take the pumpkin cover off (of course), and they showed me the place where the clutches would make marks if there was a problem. That place (also metal) looked perfectly fine. So they recommended a fluid change, the Ford additive (I think they mentioned they used the "racing" additive instead of the regular - I would expect it holds up to heat better?), and then see how it felt. So that's what I did. Has been fine between then and now (I've traveled around 6,000 miles since the service).

I knew I could get back to the area and that shop if necessary, and they could always go in again and do more, so their recommendation seemed like a good approach. So far all is well. But also mine was just "barely" making the judder. I had to really pay attention (which I just tend to do by nature - also a curse as I hear every rattle or squeak) to hear it, and even then it had stopped doing it by the time I got to the shop. Other cases may turn out differently.

Good thread. Great information. No, not all cutaways came with LSD. Mine is definitely open (confirmed when I took the cover off to change the oil). I think the VIN also says so.
Edited to add: 52 on the door tag axle code = non LSD. E2 is LSD

*Ah, sorry I was thinking about factory cutaways for ambulances that had the LS. It was part of the "Ambulance Prep" package, with HUGE 215 amp alternator, added connections for rear heat and AC, 4.10 gearing, etc.

E350 cutaway fleet box trucks probably don't need the LS as much...

Ok, here's your tag: 4.10 VF8UA ABB V606158 - 2 LS

4.10=Axle ratio

606158-2=Axle BOM ="1998.5-99 E-350 Cutaway SRW or DRW Option - ABS" Powr Lok Diff,

Odd that it isn't specifically labelled as 70U or HD in the catalogs. Looks like it uses all the same parts as the 70U. Dana parts site lists the 2017530 bearings as 70U.

You can put the 6 digit BOM "606158-2" into this table here:
http://www2.dana.com/expertforms/deabill.aspx

And then by looking around on there it seems they went to a 70HD in 1999? Those use the 2017529 70HD bearings.

I think easiest tell is that the 70HD has 4" axle tubes instead of 3.5" tubes?

Interesting info, thanks. I didn't know it was officially called Powr Lok.

Funny, but I called Dana Spicer's tech dept. (after reading about how if you called them with the BOM they'd give you info) and the fellow told me that, no, none of the BOM info was on that tag I posted a photo of (and gave him the numbers from), but instead it was engraved into the axle tube somewhere. Darned if I could find that. But maybe it IS on the tag after all.

The one thing that made me think no, not HD is that the "HD" specs I found said they had the 9,xxx# rear axle weight rating, whereas the non-HD had the 7,500# rear axle weight rating, which, of course, exactly matches up to what we have on our door jamb weight tags. The 9,xxx# seems to align closely with the typical E-450 rear axle weight ratings, FWIW.

Oh well, I know a lot more now than I did when I was researching this over the winter, and I'm happy to have a full floating, LS, 4.10 Dana 70 in good order. It was kind of demoralizing sitting in an RV park for two months thinking I was semi-immobile (or facing a big $$ job). Now I know that if I had put a bit of LS fluid in the pumpkin it would have been fine, but.... I was ready for a full fluid change anyway, and I'm very happy to have had a good look-over on the guts. I had visions of doing the fluid adding at midnight (to avoid the campground authorities) and then having something go awry and become totally obvious that I was under there wrenching away. Just wouldn't have minded not waiting/dreading it for months (but I was kinda tied in place doing a job).