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Hi Folks,
I have a 95 2500 4x4, but the front axle does not engage. I have read some troubleshooting advice Diagnosing 4WD Engagement Problems on Dodge Ram pickups My problem is a little different than what is described there. When I shift into 4H, the dash indicator light DOES come on. The transfer case does engage (can't turn the front driveshaft by hand), but with the passenger side wheel jacked off the ground, I can turn it by hand.
Does this suggest anything? It seems to me that the vacuum motor must be getting vacuum, and moving, at least somewhat, or the dash light would not come on. Maybe it's just not moving far enough? I will do more checking when I get a chance, but just wondered if these symptoms are familiar to anyone.
Very likely you have a problem with the sliding collar not engaging properly or being worn out.
If the wheel turns a bit more "notchy" with 4WD engaged, I assume that the splines of the CAD are gone-.
My first move would be to remove the vacuum actuator and take a look inside- I hope you have a factory service manual.
Thanks, Alpine. As the truck is down on another repair and awaiting parts, I pulled the CAD vacuum motor and housing tonight. The vacuum motor is quite rusty, and one of the port tubes broke off as I was removing the vacuum lines. The shift fork, collar, and splines all looked good. The right wheel U-joint showed a tremendous amount of slop, but that is a different problem. I bench tested the shift motor with a vacuum pump, and it would move the fork, but wouldn't hold a vacuum. I would pump, and it would move a little, then stop, and would require several repeats to move all the way over. I guess it moved enough to turn on the indicator light, but not enough to engage the collar. Also a fair amount of rust came out of the broken port; clearly time to replace that, with something. I may go with the Posi-Lok.
Comments & opinions welcome.
There is a bushing in the right front driveshaft that centers the inner to the outer half of the shaft.
With a bad U-Joint you can ruin that bushing, and since the shafts don't align properly anymore, and the outer shaft can wander outwards you can get an indication for 4WD but the collar does not reach the outer shaft anymore.
I do like the stock vacuum CAD, if it does not rust through it works really good IMO, and you can easily convert the truck to 2 low with a small solenoid valve.
I don't have experience with the other systems on the market, but on other 4WD vehicles with cable operated lockers the cable can be a path for water ingestion into the axle.
As for the vacuum motor- these trucks require a good bit of care for the vacuum system, since any leak anywhere changes it to a vacuum cleaner that deposits all the stuff it ingests into your crankcase. This is especially nice when submerging the front axle, (regardless of 2WD or 4WD selected) the pump will try to get the whole river into your crankcase... DAMHIK...
So if you go Posi-Lok, you need to address the whole vacuum stuff for the transfer case and front axle.
(You can simply remove the vacuum supply to the transfer case, and plug it in the engine compartment.)
Thanks -- I am having trouble finding a diagram (in the FSM or elsewhere) that shows where the plastic bushing is, and what else is in the right axle tube between the CAD and the wheel U-joint. When I look down the tube from the CAD towards the wheel, I can just see what looks like a red seal a little ways into the outer tube. I don't see the bushing (maybe it's missing?). Or is it on the differential side? Or on the outside end of the tube, inboard of the U-joint? (I have found the bushing for sale online, I just don't see anything inside the CAD opening that looks like it.)
I'm thinking that since I have to replace that U-joint, I may as well replace whatever else is in that tube. I am a little worried that the loose U-joint may have worn the outer end of the tube out of round.
There is an oil seal on the outboard side of the CAD.This rides on the polished surface in the second picture.
This is the part that sticks in the differential, the little nub is on the ouboard side.
This shaft rides in a bushing with it's polished surface. (So the shaft doesn't slap around)
This nub sticks in a hole on the outer part of the shaft opposite to where the u-joint goes
And in that hole there is that bushing:
This keeps the outer half from slapping around.
And then there is the collar that connects the inner and the outer halves of the shaft if you engage 4x4
So, if your U-joint is gone, the outer half can go outboard far enough so that you get the light (Activated by the fork that slides the collar) but the collar is only grasping air instead of splines.
I am not affiliated with quad4x4, just got the pictures from their site.
Thanks, now that I know where to look, I can see the bushing. Although my U-joint is very loose and sloppy, there's not a whole lot of axial play in and out along the shaft.
For anyone new to this who may be following along, the terms "inner" and "outer" can be a little confusing when talking about the CAD. There are three shafts on the right side of the differential. From the diff to the CAD is the "intermediate", AKA "differential output shaft". From CAD to U-joint is the "inner" shaft, and from U-joint to wheel is the "outer" shaft.
I don't see much play in the bushing between the intermediate and "inner" shafts, but it certainly makes sense to replace the bushing when I have this apart.
Is there anything like a bearing at the outer end of the axle tube, i.e., the outer end of the "inner" shaft? In the picture of the above, it doesn't look like there would be because there's no polished area there. But if there's no support there, the design must rely on the U-joint to keep the outer end from slopping around. And when the U-joint fails, what's going to happen to the "inner" shaft and end of the axle tube?
The outer shaft is centered by the wheel hub.
The inner shaft is held by the u-joint and centered by the bushing in the intermediate shaft.
The intermediate shaft is centered by it's bushing in the axle tube.
So, a worn u-joint will lead to the inner shaft wobbling in the bushing, but the intermediate shaft will still be centered by it's bushing.
If you get too much wobble, say from a bad u-joint plus a worn bushing, this can lead to the oil seal being damaged.
If you wait very long (u-joint grenades) you can damage everything, including the axle tube.
Excellent info! I've been working on a fuel system issue, but when I get the truck running again, I'll attempt to get the the hub off and see what damage has been done. I will plan on replacing the inner shaft bushing and oil seal, but hopefully the inner shaft itself will be ok.
Regarding the CAD, I haven't decided yet between the Posi-Lok and the original type vacuum actuator. I'll try to do a vacuum test on the rest of the tubing / piping, and see if there are other parts that would need to be replaced. I kind of like the simplicity of the cable lock system vs. the original from a mechanical point of view, but the vacuum system is easier for the driver to use.
With the CAD removed, try to wiggle the intermediate shaft. If it has only minimal play (less than 0.5mm) you should be good.
The plastic bushing is highly suspect, wiggle the inner shaft and check for movement relative to the intermediate shaft.
To remove the unit bearings-
Remove front axle nut cotter pin, front axle nut, wheel, brake caliper.
Losen all 4 bolts about 4-5 turns, take a slightly bigger socket (Needs to be able to wiggle on the bolt head, but still push on the lip of the bolt head) and a short extension. Use the power steering to wedge the socket plus extension against the little boss on the axle tube, jerk the steering wheel and the unit bearing will be pressed outwards without any stress on the brake rotor, the bearing etc.
The method in the manual using a puller on the brake disk is plain wrong IMO.
After the first few mms of movement, push the driveshaft inwards. (Maybe with a rubber mallet)
Press until all 4 bolt heads are back to flush on the knuckle, losen bolts again 4-5 turns, rinse and repeat until the unit bearing wants to fall off.
Ok, so here's the inner end of the "inner" right front axle, which runs from the CAD out to the U-joint. I am trying to understand this wear pattern and determine what to do about it. Maybe there have been two seals already over the life of the truck, with one located at the very end of the journal. But the area in between the two bright rings is very rough. Should I (a) install a new seal more to the left (towards the CAD) this time, (b) get a repair sleeve, or (c) replace the whole shaft?
Side question: I got a cheap Miller 9039 tool set, which claimed to be a seal installer for the Dana 248 FBI, but the seal drivers are much too big for the axle shaft seal. Maybe they're for pinion seals or something, or a later model of this axle (1995 Dana 60 aka 248). Anybody know what it's for?
This looks like you have some corrosion damage going on here.
If you still have the seal and the intermediate shaft installed you can try to find the positioning by putting some grease onto the shaft and pushing it in- ypu will see where the seal pushed the grease.
Nevertheless I would polish the surface, since it is only used for the seal a little bit of out of round is not that critical.
Can't help you with the tools.
09-28-2016, 02:35 AM
