Bronco project, 351W, C4, D20, different driveshafts?

Hi Guys,
I'm building my project and need a little info. Do I need custom length driveshafts?
I'm going with a 351Windsor, have WH 3.5" SL, 1" BL, using original C4 and Dana 20. Since the 351W mates up to the C4, do I have to change the C4 tranny mount, or can I leave it in the stock position? I read here that there's plenty of room in the engine bay for the 351W, and I will be going with a Sniper EFI kit, hopefully with my original hood. I know the suspension will increase the need for longer driveshafts, but I was unaware that I would need to move the transmission mount rearward as a buddy mentioned today. Is this common? I do plan to reinforce the body a bit, so, ther will be added weight of larger engine, more steel on tub, larger rear gas tank, full family roll cage, etc., which will load the suspension. I plan on about 20% off road, 70% around town and 10% hwy. Anyone with a similar setup using 35" tires and such please chime in. Thanks, F

No, you don't need to modify tranny mounts for a 351W swap.
I would plan on new driveshafts.

The body doesn't have any thing to do with the weight of the new engine..351 and 302 are the same length so trans and transfer case stay in the same spot.
only reason for longer drives shafts is the 3.5 inch lift you are going to add. I have 35 bfg s with a 3.5 inch SL and 1 inch BL and it s a nice set up you might have to change gear ratios not an abolsute but would help with performance

The only thing that will change the driveshafts is the suspension lift. The front is typically fine as the radius arms arc nearly the same as the driveshaft so the length stays good. The rear is questionable. I would not buy a driveshaft until the lift is done, but I would keep the money in the budget in case you do need it.

Thanks guys, this makes sense, especially about the radius arms. So now I can finish the rebuilding and assembly of the front driveshaft. To clarify, I have 4.56 gears front and rear, trac locs, and I'm putting in a wrap trap from WH as well. I have some new HD perches from Ruff Stuff to install for the rear axle once I get it all back together. I'm hoping the slight rotation of the rear axle along with the wrap trap will allow me to keep the standard length drive shaft in the rear even though I have gone to the 3.5" lift. I can only think that I might have to check the extension of the suspension system by jacking the frame way up and seeing if either drive line falls out or is too "sloppy". Anyone know what the minimum engagement of the driveshaft should be when fully extended? Especially under power?

You can't really go by overall travel for sizing a (standard) shaft. You set it up at the proper length for static ride height and if for some reason you have more travel than the shaft's slip joint can handle, you need a longer travel shaft.
But not many EB's ever need anything like that. And most EB's with 3.5" lifts don't need longer shafts either, as long as the rear pinion is correct.
Since you're going with new perches and a WrapTrap, it's up to you to set it up right and then you'll likely never have an issue.

But the final tally is taken at the time your rig is put together and back on the ground, so you can either see if your old one fits, or measure for the new shaft.
If your old one is not in good shape anymore, now's the time to get the new one. If it is, then wait and see.

You can do it sooner than getting it back on the ground if you want, but to do that you have to compress the suspension to expected ride height (approx. 9.5" give or take a 1/2" between the top of the axle tube and the bottom of the frame rail in the back) by either weighing down the body while the axle is on the jackstands, or by using ratchet straps to compress the springs until your measurements are as stated above.
At this same time, you need to set up your perches so that your pinion angle is correct. Once you do, your driveshaft length can be determined.

And just in case you didn't know, our double-cardan style driveshafts are properly set up when the rear diff pinion angle is pointed just below the imaginary centerline of the driveshaft by 1-2 degrees. You can get away with zero degrees because you're using the Wrap Trap, but I would not. I would still set it up at least to the 1° down angle setting.
That should keep your rear u-joint happy for years and miles, and keep your ride vibration free for the duration.

Obviously then, you need to just tack-weld the perches in place until you're 100% certain they're holding the axle housing at the proper angle.

Good luck.

Paul

So, I compressed the front axle to 10.5" and the rear to 9.5", and started lining up my TRO as well as my driveshafts. It was weird, the rear axle was shifted to the left by3/4" and the front was shifted right by an 1". So, I ratcheted the axle to be equal distance by measuring the frame to the inside tire dimensions till they were equidistant.
The front axle still fits, just fine. The rear is still short by several inches. And my TRO is really tight because the TR, TB, & DL are all level and parallel. I'm mounting the TB riser and the TB drop bracket tomorrow. I may wait for the rear Dave shaft since I have not body on it yet not the engine for weight. Can I put the wrap trap in at this compressed position, or should I wait till it is assembled?;D

I don't see why you could not assemble the Wrap Trap with the body off, as long as you've compressed the suspension to near where it's going to sit normally.
Just make sure that the rear pinion is pointed correctly too. It might not be as big a deal for mounting the Trap, but will definitely skew your driveshaft needs.
Won't hurt with the Wrap Trap either of course, to have the pinion angle set properly. That way there is no extra, or at least very minimal adjustment needed once everything is assembled.

Paul

TRO fabrication

So, I now have the 3.5" WH SL installed, the axles compressed to the frame in front at 10.5" and rear at 9.5". The rebuilt front drive shaft fits, the rear is short by several inches. My main cause for concern is the tight tolerances I am having for the clearance of the TB, the TR, the DL, and the proposed future ram. The TB and DL are at about the same length of 28.5" The TR is about 50". How much more compression will I see when I'm out wheeling from this "Normal position" that I have approximated by ratcheting down to?? Should I expect another 5" of compression of the suspension from where I have it ratcheted down???

My TR, TB, and DL are all parallel at this compressed position. It will be interesting to see how close I come to this position once the build out is done. Remember, this is with a F-100 steering box that sits inside the frame and really low. I had to reinforce my Pittman arm after I drilled it out to make the TRE for thge drive link fit on top of it. Any pictures of other person's builds, especially with a custom made track bar, would be appreciated. The 1st pic is uncompressed, the others are compressed. The last picture shows the Grade 8 nut I welded into the drop bracket and the clearancing of the pitman arm by grinding it down. The Pittman arm was significantly strengthened by adding 5/8" of metal circumferentially around the end that the TRE for the drive link fits into.
Thanks;D

74 Bronco Billy said:

...The rebuilt front drive shaft fits, the rear is short by several inches.

Click to expand...

Are you sure your pinion angle is correct yet? This is generally the reason someone's driveshaft is too short in the rear.
While it's not the only reason, and yours could certainly be short, it's only 1 out of 10 (or less) that needs a longer one even when the pinion is correct.
Just double-checkin' ya there.

Lot of work you've been to! Looks like great stuff, but hard to make it all fit in the available real-estate.
I'm still not comfortable with the ram pushing on the pitman arm. Can't tell you why, or whether or not it's an acceptable design from an engineering standpoint.
It's just that I don't feel it's correct to do it that way.

Hopefully others will know.

Keep the progress pics coming.

Paul