Rear Driveshaft Question

[hatleyjm]

Hello all, my 70 Bronco has a 2.5" suspension lift but no body lift. I was doing some maintenance on my rear driveshaft today and noticed that with the lift, the driveshaft is now too short for proper service (no big surprise there). The driveshaft I currently have appears to be aftermarket and does not have the CV joint/Double Cardan assembly at the transfer case. My question is, could or should I get the current driveshaft lengthened by a driveshaft shop or should I order a new one from one of our vendors with the CV joint/double Cardan assembly on it? The front driveshaft has the CV joint so I assume it originally came with them on both the front and rear driveshafts...

Since we're on the topic, how exactly does the CV joint benefit the drivetrain? Is it necessary for proper articulation?

 

[okie4570]

Hello all, my 70 Bronco has a 2.5" suspension lift but no body lift. I was doing some maintenance on my rear driveshaft today and noticed that with the lift, the driveshaft is now too short for proper service (no big surprise there). The driveshaft I currently have appears to be aftermarket and does not have the CV joint/Double Cardan assembly at the transfer case. My question is, could or should I get the current driveshaft lengthened by a driveshaft shop or should I order a new one from one of our vendors with the CV joint/double Cardan assembly on it? The front driveshaft has the CV joint so I assume it originally came with them on both the front and rear driveshafts...

Since we're on the topic, how exactly does the CV joint benefit the drivetrain? Is it necessary for proper articulation?

Yes definitely get a new one with the double Cardan.

 

[DirtDonk]

But if your current setup is driving and not vibrating, then your rear pinion angle may have been set up for that type. Can we see some pictures of your setup now?
If you convert you will need to replace your transfer case output yoke to the proper type. Unless the existing one is correct and the coupling was rigged in the first place.

The rear pinion angle tends to go downward too when lifted. If that's what happened in your case that might be why the shaft appears to be too short now. Normally a 2.5" lift is not nearly enough to require a new driveshaft.
If you can take a pic of your rear pinion yoke and driveshaft from the side, just in front of the rear tire, that would give us a pretty accurate representation of the angle. It's always a little hard to tell from pics, but that location gives a half-way decent view.

Paul

 

[hatleyjm]

Wellllll... a little back history--I finally got the Bronco back on the road after about a 6 year stent as a garage catch-all. I noticed that when I am coming to a stop I hear a rattling sound that is coming from the vicinity of the transfer case (in gear, out of gear, clutch in, clutch out makes no difference). I figured the U-joints were a good place to start so I was checking the rear driveshaft's front and rear u-joints when I noticed the rear slip yoke issue I wrote about in my first post. This led to a look on Wildhorses regarding driveshafts and is where I found the info about the double cardan/CV joint that is stock. After my inspection, I now believe the u-joints are in good shape, but now i'm worried about the rear output shaft yoke on the T-case. While I had the front u-joint loose I checked it and it has a small amount of movement fore and aft--but not side to side. By small I mean probably way less than 1/64". I re-torqued the yoke nut but still have some movement. All that to say, I think the screw-on dust cover on the rear slip yoke may have not allowed the driveshaft to extend as needed during driving/stopping and may have pulled on the output shaft. The difference between where the driveshaft's length when connected to the diff and when extended to its maximum length (splines hitting the dust cap) was only ~1/4". That's what got me wondering about a new driveshaft with CV joint vs modification of what I currently have.

Just FYI. Per measurement technique spec'd by WH, my rear driveshaft length (when loaded as usual) is 35.5"

1st photo: Rear pinion angle (sorry it's upside down--is there a way to fix this?)
2nd photo: Rear slip yoke with screw-on dust cap removed
3rd photo: Front of rear driveshaft u-joint and T-case rear output shaft yoke
4th photo: side view of the entire rear driveline
5th photo: close up side and bottom of T-case rear output shaft yoke
6th photo: close up bottom of T-case rear output shaft yoke
7th photo: close up side of T-case rear output shaft yoke

 

[hatleyjm]

Fixed the photos

Photo 1: Rear pinion angle
Photo 2: Rear slip yoke with screw-on dust cap removed
Photo 3: side view of the entire rear driveline

 

[hatleyjm]

Yes definitely get a new one with the double Cardan.

Thanks Okie. That's an interesting article/photo you uploaded. Where is that from?

 

[DirtDonk]

Yep, wrong angle on the driveshaft and WAY too short.
Someone swapped in an existing shaft for something else perhaps. Possibly even a front driveshaft off of one of the oddball '66 models that came from the factory with single-cardan shafts.
Otherwise I don't see anyone measuring that far off since they don't change that much with modest suspension changes. Then again, your measurement indicates the need for a shaft that's a full 2" longer than stock, which is odd in itself.
Maybe you have more lift than you think? Or maybe there is a change in the location of the engine, or transmission from a swap? Or just the difference in the two types of yoke.

The yoke at the transfer case looks like it's been changed to accommodate the type of shaft. The slinger is the wrong size and the gap too wide.

Your rear pinion angle is set up perfectly for a double-cardan shaft. It's improper for a single-cardan shaft like you have, and is potentially why you get the rattling sound. It's a harmonic being transferred from the shaft into the area with the most slop, the gears in the transfer case.
Depending on how long it's been like that too, it could be why you have some slop in your output shaft. It's not like they don't wear out all on their own, but a driveline vibration will certainly accelerate the normal wear and tear.

So, it sounds like you measured correctly, but it's extremely odd to need a longer shaft. I would check the yoke and change it out to the proper style if needed, and then re-measure to make sure. Means more downtime while you experiment, but saves you the trouble of ordering the wrong shaft.

Might as well measure the suspension height while you're under there too. Take a reading between the top of the axle tube and the bottom of the frame rail in all four corners. Anything over 7" in front and 6" in the back is the amount of lift you have. Approximation only though, as it can easily vary by 1/2" or so.
And can you take a couple of shots of the rear springs and if there are tapered shims under them?
Thanks

Good luck. Might be curing multiple ills with one fell swoop.
Oh, did you say what kind of shaft is on the front?

Paul

 

[hatleyjm]

I was looking at the rear driveshaft tonight and found a sticker on the side that says "American Clutch and Driveshaft Co." so now we know it is aftermarket.

I was pretty sure that I ordered a 2.5" suspension lift from TBP but that was way back in 2012. I measured as you recommended, Paul, and found that it is around 3.5" higher than stock. While I put the lift on in 2012, i've probably put less than 100 miles on it since then. I would imagine the lifts settle with time and driving but probably not over an inch, right? If not, then I must have ordered a 3.5" lift--does that make more sense with my driveshaft length measurements? When I put the rear springs on I also installed the provided tapered shims to accommodate the new height. I've included pics of the shims (photo 1).

I'm not sure if the drivetrain is original but I believe both the motor and trans are the stock style (302 and 3-speed column shift). They also appear to be in the original location with a stock appearing transmission crossmember and motor mounts.

The front driveshaft appears to be stock but i've included pictures of that to let those who know better than I confirm that. It has a double cardan/CV joint at the T-case. I checked the front driveshaft length from its normal driving position and also to its maximum length (hitting the dust cover) and it's about 3/4". Is that enough length for the front driveshaft? It measures 25" from front output shaft yoke to differential yoke (center to center as spec'd by WH). (photos 2 & 3)

 

[DirtDonk]

They can and do settle, but how much can vary. Of course they settle even more over time as things get old and tired, but the initial settling should take place within a few hundred miles, or a few trail rides, or a little bit of time with some heavy loads placed on the truck to compress the springs.
Some springs take more to settle than others as well.

But the bottom line is that at least right now you have a 3.5" lift and the shims are exactly why your rear pinion angle is correct and proper for the expected stock double-cardan shaft.
See the difference between the front transfer case output yoke and the rear output yoke? A slinger/shield that fully encompasses the seal area, and a different way of attaching the u-joint. Bolts vs the u-bolts that the rear one currently has.

You can buy a new rear output yoke to go with the soon-to-be new rear driveshaft. You can take some measurements of the front one and compare it to the rear one, and add, or subtract the difference to get the desired length for your new shaft.

The front and rear shafts really don't use as much of the slip yoke aspect as you might think. I bet during the entire suspension movement process they move less than an inch overall. I keep forgetting to test that theory, but I believe someone here did a few years ago so the information is probably around somewhere.
It looks like your front shaft has plenty of "shaft" in both directions to slip, but I do see what looks like a mark where it was compressed to at some point? That mark looks more like the normal spot to me, so even your front is extended slightly more than I would expect to see. But it does not look like it's far enough out to worry about.
Maybe someone's second and third opinions would be good though.

For the rear, probably 90% of the lifted Broncos out there did NOT need a new longer shaft for 3.5" of lift. So why yours needs one that's potentially two inches longer is an unknown for my part.
But measure the two yokes first, and you might find that at least some of that two inches is in the yoke.

Paul

 

[hatleyjm]

Will do. Thanks for the help. I'll be ordering a new output shaft yoke and driveshaft (after I measure it again, of course). I loosened the dust cover on the rear and front slip yokes to buy me a little more room in the meantime, if I need to drive it, but it will likely remain parked in the garage until I can get the parts in.

 

[hatleyjm]

Just for my edification, can I just buy the double cardan parts and use my old driveshaft front yoke? Or should I just bite the bullet and get a new shaft?

 

[DirtDonk]

Well, it's probably less expensive to buy an entire new shaft than it is to have someone locally reconfigure yours. The CV stuff is available, and will fit as long as your existing driveshaft is the correct diameter tubing.
But would that make it the correct length? You can check using the dimensions of your other shaft, but I still think that the cost of a new yoke and an entirely new shaft will beat out reworking the old one.

Been a long time since we've talked about those prices though, so I could be wrong.

Paul

 

[DirtDonk]

I just realized you were asking (I think?) if you could use the old yoke. To that the answer is no, you can't.
The front diff yoke stays the same naturally, but the one on the transfer case is a completely different style when used with the double-cardan style driveshaft.

Paul

 

[sprdv1]

Definitely wouldn't hurt to go new..

Yes definitely get a new one with the double Cardan.

 

[sprdv1]

I just realized you were asking (I think?) if you could use the old yoke. To that the answer is no, you can't.
The front diff yoke stays the same naturally, but the one on the transfer case is a completely different style when used with the double-cardan style driveshaft.

Definitely.....

 

[hatleyjm]

I just realized you were asking (I think?) if you could use the old yoke. To that the answer is no, you can't.
The front diff yoke stays the same naturally, but the one on the transfer case is a completely different style when used with the double-cardan style driveshaft.

Paul

Definitely.....

I see what you're saying Paul--the rear output shaft yoke needs to be changed to accept the double cardan driveshaft. What I was meaning was to buy a new output shaft yoke and new CV joint and then somehow attach my current drive shaft to the new CV joint. After I thought about it a bit I realized that even if it could work I would still have an old driveshaft that's been through who knows what with the PO and that I should quit being cheap and just buy the new driveshaft!! ;D I can't tell you how many times I thought that piecing something together would save me money. In almost all of those situations I didn't actually save any money--I just lost time and gained aggravation. At least in this case you both had the good sense to steer me in the right direction. Thanks for your help--I ordered a new driveshaft and output yoke.

 

[DirtDonk]

Well, for once ordering the new part may even have saved you money!
Certainly less frustration and hassle, but some money is a nice bonus too.

Paul