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72 RS 351 
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 Posted: 25-June-2025 at 6:51AM |
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There have been changes to the output shaft size over the years. If the new trans and driveshaft were from similar years of the 70's, they should be compatible. But you need to check when mixing parts just in case someone used something that was different enough(but close), and seemed to fit initially. This is a common thing to do with Fords in general, they have changed countless parts over the years, you gotta be wary.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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Inkara1
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Posted: 25-June-2025 at 5:36PM |
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Is there an acceptable amount of play? I could move it side to side or up and down a little. It wasn't much, but it was a tiny bit. Not sure how to quantify the amount. If a little play is acceptable, it's probably OK. If no play is acceptable, this might be the issue. If that's the case, how pressing is the issue to get fixed besides how it affects my own enjoyment? If it's the wrong yoke, would it have that tiny bit of play but still seal well against the rear seal? (Like, is there a way I can know I just need a yoke instead of to change the bushing?)
I have this much engagement of the yoke on the tailshaft. Apologies if the photo appears upside-down. It shows correctly on my phone but appears 180 degrees out when posted here, and there doesn't seem to be a way to rotate it.  |
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Booyah45828
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Posted: 26-June-2025 at 2:12AM |
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I'd inspect or replace my u-joints before I'd look at anything on the trans output. If there is brinelling on the coast side of the cap or cross that could be where your noise is coming from on decel.
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Inkara1
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Posted: 26-June-2025 at 5:14AM |
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Both U-joints have been replaced already.
In fact, they've been replaced twice. A few years back, I put in high-end genuine Spicer non-greasable U-joints as preventative maintenance around the same time as I rebuilt the front and rear suspensions. They never really loosened up, so I thought that might be the source of the noise. Now I have store brand greasable U-joints at both ends. That didn't fix the noise, but the joints do move much more easily, so I'm sure there's some horsepower or fuel efficiency benefit.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Inkara1
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Posted: 27-June-2025 at 10:43PM |
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So I have a new theory. According to a forum post here: https://www.vintage-mustang.com/threads/how-far-should-the-slip-yoke-slide-into-a-c6.472393/, when I have the rear U-bolts on the back U-joint removed, if I push the slip yoke all the way into the transmission, the back U-joint should be 1.5 inches away from the rear yoke. Mine's only half an inch away when I do that. I think I just figured out what caused the damage to the thrust bearing in my engine -- as the suspension moves around, it causes the yoke to bottom out and push the entire transmission and engine rotating assembly forward.
So I guess this means I need to find a driveshaft that's shorter by one inch, or see if I can find time to drive 90 minutes to get to what Google says is the closest driveshaft shop to have mine shortened. I don’t know if the shaft is the original one to the car, just with the slip yoke changed from the C4 one to the C6 one, or if it's from something else entirely since the C6 is more than an inch longer than the C4. I think I do need to replace the yoke, too, since the barrel measures at 1.681 to 1.685 OD depending on where I measure it (even though it seals up OK and doesn't leak fluid). Other than that, I didn't see any obvious damage or wear on the splines. The trans output shaft moves around the same as the whole yoke did when I checked that. I can't really measure or see the tailshaft bushing with the oil seal installed, but I don't want to pull it just to take a look. Could the driveshaft being a bit too long also cause the deceleration rumble?
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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aquartlow
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Posted: 28-June-2025 at 2:10AM |
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There is normally about 1/16-3/16" clearance between a C6 torque converter and flex plate, I do not believe the driveshaft is causing the thrust bearing issues, for if the driveshaft was to take up all the endplay within the transmission(should be around .035-.040") and overcome the 1/16-3/16" clearance for the torque converter, the trans itself would have probably grenaded internally or at least taken out some of the transmissions thrust bearings and/or snap ring lands. Now if the TC to flex-plate clearance isn't correct, then yes, you may have found your thrust bearing damage culprit if EVERYTHING else inside the engine is correct. If there is/was no TC-flex-plate clearance and if the driveshaft indeed pushes the transmission internals forward through suspension travel taking up any trans. endplay, these conditions could result in the thrust bearing wear and causes vibrations, but those are some pretty big "if's". FWIW, the clearances for the rear u-joint on my Ranchero is roughly 5/8-3/4" and has been that way for 20+ years with no issues, but it has been lowered about 5". Now with having FULL suspension travel such as your ride, it may indeed make a difference. Another "ah ha" going by what you have told us, is that you have full trans output shaft to driveshaft yoke spline engagement
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www.supermotors.net/22468
Yeah, It's a Hybrid...It burns gas and tires. No matter how good she looks, somebody, somewhere, is tired of her sh*t. Beauty is skin deep, ugliness goes clear to the bone. |
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Rockatansky
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Posted: 29-June-2025 at 1:15AM |
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IMO 1.5" of pull-out on the slip yoke is slightly excessive and potentially a cause of tail bushing wear & unwanted vibration. also there are thrusts and clearances in the transmission, they would be on the front lines of a driveline interference issue. then the converter / pump gap. converter ballooning gets blamed for engine thrust damage, IDK but i have to wonder what the converter gap was at the time of install? FWIW i'd have the shaft spun up to check balance and straight, if it passes those hurdles replace the yoke and the tail housing bushing. i wouldn't pull it down just to take a look either, just change it. i used a cam bearing install tool
 Edited by Rockatansky - 29-June-2025 at 1:21AM |
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72 GT Ute
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Rockatansky
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Posted: 29-June-2025 at 1:44AM |
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to check to see if your slip yoke pull out is sufficient or lacking, raise the rear and put the frame on jack stands with the rear tires off the ground. measure slip yoke pull-out. now disconnect the rear shocks, remove the springs, jack the axle the axle to full compression and measure slip yoke pull-out note the slip yoke position at both limits
Edited by Rockatansky - 29-June-2025 at 5:44AM |
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72 GT Ute
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Inkara1
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Posted: 29-June-2025 at 12:18PM |
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I'm definitely going to try that, since it'll tell me if I really need to go to the effort and cost of either driving 90 minutes to get my driveshaft shortened or buy a new one.
Sounds like I should still plan on replacing the bushing and slip yoke, though? I found a bushing removal/install tool on Amazon for $85. I'd rather spend that than spend the time (and gasket cost) to remove the tail shaft. I don't have a cam bearing tool I can use.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Inkara1
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Posted: 01-July-2025 at 9:07PM |
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The yoke didn't move very much farther in with the suspension fully down or fully up.
Slip yoke with car on wheels on the ground (again, these look right when I view them on my phone but appear upside down when I post them here):  Slip yoke with axle at bottom of travel:  Slip yoke with axle all the way up against the center bump stop:  Looking at these pictures, it sure does look like the yoke comes out at an angle, but I'm trying to determine how much of that is camera angle.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Inkara1
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Posted: 08-July-2025 at 11:09PM |
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Got a new slip yoke and a new bushing. That little bit of play is now completely gone. No difference in the noise.
If the noise goes away at 3500 RPM (with the 3.00:1 axle, that's getting close to 90 MPH), that would be indicative of a driveshaft vibration and not an axle bearing, right? The noise went away at that RPM with the 3.50:1 rear also, which was about 78 MPH, so the driveshaft was spinning that same speed but the wheels were turning slower. Seems like if it were an axle bearing, it would have done it at the same MPH instead of the same RPM. If I put the car on jackstands and run it to an indicated 70 mph, then shine the flashlight on the driveshaft, will I be able to see anything? Like, will the vibrating be visible?
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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pyntre
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Posted: 09-July-2025 at 8:05AM |
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That’s not really a very safe plan in my book !
You might see what’s on the backside of your garage wall too . Take it to a business that does that work , balancing driveshafts . Please don’t be under a car on jackstands , running , at 70 mph ! |
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Booyah45828
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Posted: 09-July-2025 at 8:29AM |
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If the noise still occurs at 3500 rpm in final gear after the rear ratio change, then yes, your noise concern would be between the pinion and rear of the transmission. I'd have a pro go through your other gear before I'd condemn the driveshaft, that is if returning to and using that other gear is your eventual plan.
Or you can send the shaft out to be inspected and balanced. Wouldn't hurt to do either one first.
I wouldn't run anything on stands, too much movement to chance the thing shaking off and falling. I get leery running them up to speed on a hoist. I really doubt the vibration would be visible. |
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72 RS 351
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Posted: 09-July-2025 at 11:30AM |
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Yeah, I'd bet on the driveshaft balance and have it checked. I know that any driveshaft work is much higher than it used to be, but you have to do it if it's needed.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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72FordGTS
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Posted: 09-July-2025 at 3:15PM |
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I agree with the others, I wouldn't run a car up to 70 on jack stands. I wouldn't got beyond idle speed on stands. I did run a car at speed years ago on a commercial grade hoist in a shop, but even then it seemed kind of risky and we had put some safety measures in place. If you don't want to send the driveshaft to get checked, you could always see if you can get another used shaft from a wrecking yard if there are any with old cars around your area. Any 1972-79 intermediate Ford with the 118" wheelbase should work - 4-doors, wagons, and Rancheros.
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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Inkara1
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Posted: 15-July-2025 at 12:04AM |
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So finally some success: I put in a new aluminum driveshaft from Southwest Speed, and now the noise is gone. Deceleration rumble is completely gone too. I'm excited to finally get it hunted down.
The driveshaft was $350, and since Southwest Speed's driveshafts come with 1310-series U-joints, I got their 1310/1330 combo joints so I could still use my nice, new, made-in-USA slip yoke I just got. So shaft, joints, and shipping came out to just over $450. Not too bad compared to the cost of driving 90 minutes out of town to get the old shaft balanced considering it also means an upgrade to aluminum.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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72 RS 351
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Posted: 15-July-2025 at 12:51AM |
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Very good, and relief to you in finding it. Now go drive it like you want to all the time.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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72FordGTS
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Posted: 17-July-2025 at 1:14PM |
Nice upgrade and glad you solved it. How much was it going to cost to get it balanced? At some point I'd like to have mine balanced or upgrade it like you did. Any pics after the install?
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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Inkara1
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Posted: 17-July-2025 at 8:48PM |
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I never took the old one to be balanced because the nearest shop I can find that can do it is a 90-minute drive away, so like $40 in gas plus half a day total. If it costs, say, $150 plus tax, then that plus gas and I'd be at a bit over $200, so that makes the cost of the upgrade feel a little better. That, and I saw a story from a guy with a '65 Mustang fastback that had a noise at 70 from new, and balancing the shaft didn’t fix it, and a new steel shaft didn't fix it, but an aluminum shaft from a 2001 4-door V6 automatic 4x2 Explorer fits and did solve the problem.
I'll have to remember to get some pictures when it's light out. It's 3-inch diameter, so no issues with the exhaust or the transmission counterweight I put on in an earlier attempt to quiet things. One interesting thing... I measured the old one at 58 inches between the centers of the U-joints, so I got the new one at 57 1/2 inches, figuring I could spare half an inch of yoke-tailshaft engagement and wanting a little more wiggle room as discussed earlier in this thread. But it's just as tight of a fit, so either I measured long by half an inch or they measured short. It did go in, so at least I don't have to exchange it. But the new tailshaft seal on the transmission has that rubber extension cone, so I can't push it in as far as before, so I have to take the caps off the U-joint to get it into the pinion yoke, then put the caps back on before tightening the U-bolts to hold them to the yoke. I'm considering cutting off that rubber extension, since it also has the lip seal that does the actual sealing.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Inkara1
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Posted: 18-July-2025 at 9:59AM |
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Install pics:
  Found a neighborhood kitty hanging out under the car:  |
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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72FordGTS
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Posted: 18-July-2025 at 10:52AM |
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Looks great! Nice upgrade for sure.
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Vince
1972 Ford GTS Sportsroof - Survivor, One Family car GTS.org Admin |
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72 RS 351
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Posted: 18-July-2025 at 12:19PM |
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Very nice upgrade. Good work at hunting for the issue diligently.
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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Inkara1
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Posted: 18-August-2025 at 8:55PM |
So on the crosswind thing... turns out it would do it in calm conditions too. The back end felt loose and fishtail-y enough that it was a bit scary. So tonight, I tightened up the Del-Sphere ends on the bottom control arm. The tool that I bought from Spohn would require me to unbolt the arms from the car, and I didn't feel like doing that. So I used a skinny-tipped punch at the right angle to push on the adjustment holes and a hammer, and I was able to tap on them to tighten them 3/8 turn on the front joints (both sides of the car) and 1/8 turn on the rear joints. Drove it afterward and it was a lot more stable. I'd like to get a wrench with the two little prongs to turn them a little more, and to be able to do the rear joints on the top arms, but for now, it's a lot better.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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72 RS 351
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Posted: 19-August-2025 at 5:49AM |
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How much space is there for a tool? Can you use a pair of pliers with snap ring tips, the 90* type? I have a small set of those for working on trans snap rings. How big are the holes to adjust those arms?
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Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker 73 Ranchero GT 351C-4V &4R70W for sale later. 92 Lincoln Mark VII SE GTC, OBDII 347/4R70W |
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Inkara1
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Posted: 19-August-2025 at 8:56AM |
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Quarter-inch maybe? Maybe a little more. I pried on the bottom of the joint to tilt it as much as it would tilt for better access. I have snap ring pliers, but they don't open wide enough, which is why I used the hammer and punch, since it was like 10 at night and Harbor Freight was closed. The holes are probably 1/8 inch round. I could get them tighter with the wrench, I think -- the 3/8 turn and 1/8 turn were just taking up slop, I think, and I'd need a wrench to actually make it tighter to affect handling. This was more that I assumed when they said it was set up to match stock, it meant I wouldn't need to adjust anything, when I really should've snugged them up with the tool I bought from them when they weren't in the car yet.
I was thinking this might work. It's meant for changing the wheel on an angle grinder.
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1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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Inkara1 wrote: