Driveline. Let's pretend for a minute that my race tune easily gives the same dyno numbers as a 6.7L off the dealership lot. What kind of driveline does the 6.7L have? Which U-joints?

Why am I asking? The little run I made pictured below introduced an all-too familiar vibration in Stinky, but worse than before. The last time I had this vibration, I had a driveline that was bent 20 thousandths out of true.



I have a Neapco dealer/driveline guy in town that's very reasonable on price and we're talking options. Stock driveline is 3 1/2" .083 with 1410 U-joints. We looked at making a beefier 3 1/2" .095 with 1480 U-joints, or going a single shaft 4" .083 with 1480 U-joints.

I like the single-shaft idea because it really simplifies things. However... the dampener will be gone. Does anybody know what happens if I cut the weight of the driveline by about 20 - 30 pounds and lose the dampener? Is there a cookie-cutter approach to dealing with this? If so, what are the pros and cons?

Here we go, guys... we're diving into what happens when you blast too much bacon under the bonnet.

 

Guys have more power and don't
have a problem. That said, the driveline guy should know whats best. Did you or him take it out and look close at it. Could just be something simple Rich.

 

Just saw a F550 6.7 with the bed off today. Lifted enough that I would need at least a four foot step ladder to get into to it. Was not looking at it in your terms but everything was BIG. Sorry not much help but I would think everything needs to be modified, U-joints,
shaft, slip spline ( if used ) ETC just to avoid a weak link.

 

IIRC Andy (Fatdesl) is happy with his single aluminum jobbie.

 

I spoke with shop that has a dyno machine and they said a stock 6.7 liter Ford pickup puts down about 335-340 hp at the wheels. My guess is that your truck exceeds that figure by about 80hp at the wheels. Have you had your truck on a dyno yet?

I would imagine a sticking slip joint could be a bit harsh on the driveline components. I think you need quite a bit of traction as well as torque to bend/break the OEM stuff.

 

Rich,

I would recommend a 1 piece if it keeps the angles at both ends (u joints) in the right place. Remember you do not want them to be straight on, but you dont want them to be too much. I just installed a custom built one piece on my truck and noticed a MUCH smoother transfer of power, as well as zero vibration. As we all know, I'm at a little bit more HP than you, and its lifted. I went with the one piece after literally cracking every U joint between the rear axle and transmission, and the rear yoke actually breaking causing my driveline to come unattached while driving at 30 MPH. Cost less than a stock replacement, and I'd say its MUCH beefier.

IMO the carrier bearing at this age is just problems. A one piece driveshaft like you said simplifies everything. only 2 u joints, no carrier bearing, and when I was checking prices, it is MUCH cheaper usually than replacing a driveshaft with stock. As far as U joints go, I wouldnt go TOO beefy, because you want them to be the weak link, not the driveline. Much cheaper, and easier to replace a u joint than a driveline.

 

It's possible that since the shaft was already bent and straightened, it was compromised. I told the driveline guy I was sneaking up on 800 ft/lbs of torque (theoretical, based on dynos with similarly equipped/tuned trucks). He said he sees it all the time - guys jack up their diesels, then bring in bent and broke drive shafts.

My driveline guy described something like this [LINK] on the 6.7L, but it's still a two-segment shaft.

No Dyno yet. I heard about last years dyno debacle in Spokane - Woodnthings's truck with stock injectors throwing down 400 HP... plus many other trucks with absurd numbers? I had enough torque to break the rear end loose when I hit TCLU... I'd estimate that's pretty "torquie".

The driveline guy and I agree the single piece is ideal. My hesitation was not knowing how the loss of the dampener would effect shifts and accel/decel.

You bring up a good point about keeping the U-joints as a weak link, how did you address this when you already broke all your U-joints? Was your driveline made for you, or is it off the shelf? Where did you get yours?

 

interesting thread..I am putting 532hp on the dyno and have had no drive train issues. stock carrier bearing with 285000 on the clock..wondering if axle wrap has anything to do with this? are eather of you running traction/ladder bars? I have looked at the 1 piece dr shaft and after a lot of research,I believe the 2 piece is stronger. It is easier to bend or twist a long tube vs 2 short ones. IDK though, its just my take on the matter

 

I'm on this exact same journey, Tug. Found this

https://www.ford-trucks.com/forums/1...ive-shaft.html

 

If axle wrap is a problem I highly recommend slapping a set of ladder bars on the truck. Joey are you running ladder bars?
With my setup my axle wrap was unbelievable. If I stomped on it and let off you could hear the axle drop back in place. Since I made my ladder bars from scratch and put them on the truck there is a night and day difference. The back end plants to the ground and were off in the blink of an eye with no funny feeling or strange noises.

EDIT: I beat the snot out of my truck with no ladder bars and I was chewing up rear universals about 3 in 6 months and when I changed one of them it looked like it was chewed on. Some how I stripped the splines in my ds. I had everything rebuilt and balanced threw my ladder bars on there and we've been good for about two years now.

 

Yes, have been for a couple of years

 

Yes it it. Although, from the photo you posted....it looks like the rear end was already broke loose before the TC locked up. TC lockup is the firmest 'shift' on both of my modified trucks. On my 450, the lockup is very harsh when using select calibrations at WOT so I avoid doing that when possible. Getting the rear end to break free on a dually with 6300 lbs on the rear axle is kinda hard to do, but it does happen from time to time. The other times, (when traction is sufficient) the TC lockup at WOT for some calibrations feels like the truck was rear ended by a small car. I am very surprised that my u-joints have survived up to this point. I suspect the pump on that truck has been converted from PWM to On/Off so that may be the reason for the excessively harsh TC lockup under some conditions... I won't know until I tear down that transmission someday and see what modifications have been done by ATS.

I think John is on the right track. Axle wrap has been a problem on all these trucks from the beginning. It's a severe problem on the newer trucks since their springs are very flexible and they sag a lot when under load. Ford has a TSB out that addresses this issue to a degree....I think it involves shimming the center carrier bearing. I am sure your drive line shop will have some good suggestions. A true 4 link system (with floating spring pads) should improve traction quite a bit. Then you'll break stuff quite easily.

 

As is the usual for one of Rich's threads, this is a very good discussion!

In one of the links above in this thread that I followed, I came to a photo of a replacement, one-piece driveshaft that had a double-cardan (in essence a CV) joint, but only at the transfer-case end.

I was under the impression that if a CV is used at one end, it should also be used at the other to avoid the introduction of rotational-velocity changes.

A single at both ends results in a smooth pinion rotation (while the driveshaft is not, in itself, constant, the changes are cancelled in the end product).

A double-in and double-out results in smooth rotation throughout.

Can anybody with some real mechanical propulsion knowledge explain and justify the use of a double-cardan (CV) at only one end.?

Pop

 

Bryan at Alligator Diesel in Spokane had it made locally, yes it is completely custom. Traction bars are next on my list, probably towards the end of the month.

 

Naw... I was hooked up (I rolled into it). The initial black marks were from Stinky taking some chip seal off the road... then the dark stuff was a combination of rubber and more tar. That's when things got all squirrely... as evidenced by the "wow" in the track.

Axle wrap. I've been looking for symptoms of this. Ladder bars would completely blow away the "sleeper" appearance of the truck.