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Discussion Starter · #1 ·
Last time I was at the track, I let my buddy drive my car and for whatever reason he side-stepped the clutch and it came out of 1st. Next pass, the car jumped all over the place.




The car was way out of shape partially because he was out of the groove..too far to the right.


Initially, I thought the tranny mount was busted because it looked pretty tweaked. Put a new one in and same thing..bad vibration around 45 mph or 3rd gear @3500.

I jacked the rear end up and let the clutch out in 1st to see if anything was bent. The driveshaft looked like it had a little bit of runout in it so I pulled it, took it to the driveline shop, and they said it was tweaked. They had to add some weight to the front and rear of it. Put it in and still got the nasty vibration.

I was thinking maybe a bent output shaft? When its in gear and cruising, you can put your hand on the shifter and it shakes at that same high frequency the vibration. Even if I push the clutch in or shut the engine off at speed.

Any ideas? Thanks guys.
 

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Discussion Starter · #2 ·
Update: 99% sure its a bent output shaft. These are two videos of the yoke coming out of the transmission. The rear axle is up on jack stands and the car is idling in 2nd gear.



 

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Something isn't right for sure. Usually you will bust a u-joint first. You can pull the yoke, straight edge it and also check the splines to make sure that it isn't the yoke. Looks like it might be the output shaft to me too but it could be a spline issue inside the yoke or the yoke could be cracked up inside there.
 

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Discussion Starter · #4 ·
I looked at the splines on the yoke and I didn't see anything out of the ordinary.

The U-joints felt nice and tight and the guys at the driveshaft shop didn't mention anything about them. Normally they charge me 20 bucks a piece for new ones whether the old ones are worn out or not.


I spoke with the guys from G-Force and they were saying that you usually see a tooth break or another link in the drivetrain before the main shaft bends...

..And..along with the vibration, you can hear a clunking noise. You can kind of tell if you listen close in the videos of the yoke.

On a side note, I have a 28 spline 9 inch with stock axles. I watched the wheels when they were spinning in the air and they didn't look crazy enough to cause concern. And plus, I don't think a bent axle would cause a high frequency vibration seeing how the axles spin once for every 4.3 turns of the output shaft/driveshaft.


Either way, I'm ordering a bearing and synchro kit from Southern Gear out of Atlanta and my buddy has a spare main shaft I can throw in it just as a temp. fix. Fingers crossed and I hope that's it. I'm kinda looking forward to tearing it down and getting a full manual tranny rebuild under my belt.
 

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I'm not sure if it's the way you have your suspension sitting or what but it looks like you have way too much yoke sticking out of the trans(driveshaft too short)...You should only have about 1 inch max for drag racing..The stock type yoke is only about 4 inches long so you want as much of it in the trans as possible to prevent twisted splines and breakage....
 

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I could hear the clunk noise too. Almost sounded like rear end I thought but I've never had to bug out a manual tranny problem like yours. You will find it sooner or later. Weird ass noises like that are hard without tearing into stuff.
 

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Discussion Starter · #7 ·
I'm not sure if it's the way you have your suspension sitting or what but it looks like you have way too much yoke sticking out of the trans(driveshaft too short)...You should only have about 1 inch max for drag racing..The stock type yoke is only about 4 inches long so you want as much of it in the trans as possible to prevent twisted splines and breakage....
frdnut, I actually cut a half inch out of the driveshaft a year or so ago because I could not get it out without jacking the frame up, and prying down on the rear axle. I thought it was a little too much sticking out also but its just barely comes out now as it is.
 

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Does your clutch fell the same when you push it in as before the sidestep? He could of took a small hunk of the clutch making it vibrate. I had one once that vibrated bad after I snatched into second. I looked at everything, no luck. So I pulled it into the highway at around 5000 and poped the clutch. What was left came apart . I went then to local speed shop and got a zoom clutch and we put it in, Clutch was harder to push in but that was the problem. I know you say that will tear up alot more but I am just like that. You should of seen the crowd around my mustang once looking at the engine pulled half way on trailer. I knew it was hurt , so I laid it on the bottom and the crowd went running. In a bit she went BOOM. Found out what that was as well.
 

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Discussion Starter · #9 ·
Thanks for the insight Rcode but I don't believe it is related to the clutch because I can push the clutch in, and shut the engine off at highway speed and with the motor/clutch/input shaft stationary, it still vibrates.

I've pretty much isolated it to being somewhere between the mainshaft/output shaft and the pinion gear of the rearend. I have 4.30 gears and at hwy speed, all of that spins very fast and causes the high frequency vibration.

So for now, I'm sticking with pulling the tranny and going thru it for now.
 

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If the yoke will slide all the way in and out without resistance (meaning splines are straight even deeper), and the yoke is not cracked, I'll be it's just a bad tailshaft housing bushing. If you can wiggle the yoke around at all when it's at it's 'normal' position, the bushing is toast and will cause cruise vibration. The yoke should have zero perceptible radial play.

David

EDIT: Okay, I got your vids to work (they only came-up as stills the first time). Yeah, it may look bent, but unless the output has no play, it's the bushing. Get under the car and push up on it with 20-30 pounds of force near the front U-joint. Any perceptible play in the yoke is your sign.
 

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Discussion Starter · #11 ·
Every time I slid the yoke in, it was very smooth so I reckon the splines are straight and undamaged.

I'll try and get some time this weekend to work on it and give the yoke a good shakin'!
 

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Discussion Starter · #12 ·
UPDATE:
Went to pull the tranny this afternoon and started off with the driveshaft. Couldn't hardly get the damn thing out. When I finally did, I made sure to look inside the yoke and here's what I found




Went to Summit and grabbed a new one



The new one is a Ford Racing and its a bit longer so it should hold up a little better.

Just took it for a test drive and the vibration is nearly GONE! Just gotta bring the driveshaft back to the shop and have them balance it with a good/straight yoke on it and I should be track ready!

Thanks again everyone for all the feedback and ideas!
 

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I hope your output shaft on your trans is ok. I have bent and broke those before. Makes me wonder when you said the vibration is " Nearly" gone. I guess you'll know for sure when the driveshaft is balanced. Keep us posted.
 

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So the splines were not straight and it wouldn't slide in and out easily. ;) Well, if your bushing was OK before, it's probably wallowed-out now. Be sure to check it again. Not only can you get vibes by a worn bushing, you can split the yoke easier on launch. Somebody has as video of that on here somewhere...

David
 

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If they balanced it before with the twisted yoke that would put it out of balance with the good one now. I'm not sure if the shop did mine with the u-joints and yokes in place or if that is typically how they do them. Could be.
 

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Discussion Starter · #16 ·
Alright so I got the new yoke on the driveshaft, took it back to the driveline shop, and they did have to put some more weight on it to balance it. I slid everything back in and the vibration didn't get any better..:mad:!

I got it up on the lift and took another video of the driveshaft, front and rear yokes, and the rearend.

Don't know if that video helps or not...

It was making a clunking noise but I believe that might be caused by the erratic idle loading and unloading the driveline with zero resistance caused by the suspension being being fully extended and wheels off the ground.


I've got the tranny out and just have to tear into it now. I'm very curious as to what the output shaft looks like. I'll keep yall posted and keep the feedback coming! Thanks again!
 

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The new longer yoke should help but I really don't understand why you need so much yoke sticking out of the trans?..The driveshaft should be easily removeable with only around 1 inch sticking out.Mine comes right out with only 3/4 of an inch clearance at the trans...The further the yoke sticks out the less spline you have inside the trans and the more leverage it has on the output shaft to cause problems.....Also are your spring perches ok on the rear end?..Might be just the way its hanging but the pinion looks tipped up pretty far to me?
 

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I think the noise is still a problem that you have. It may or may not be causing the vibration. It would have been really nice if the yoke was the only thing that got hit but hey, you are finding your weak spots. It doesn't sound consistent with rotation to me which is strange. If you are under there listening does it sound like it is coming from the rear end or the tranny? Hate to say this but it sounds like rear end to me but still hard to tell.

Ok, LOL, had another thought. Before you take it apart I would disconnect the drive shaft from the tranny and spin it up with just the tranny. See if it still vibrates and makes that noise. You can also rotate the rear end with the drive shaft disconnected and see if you can hear the noise from just the rear end. It might help isolate it before you have to tear into it.

Well ok nevermind on part of that. I just saw where you have dropped the tranny.
 

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Discussion Starter · #20 ·
The new longer yoke should help but I really don't understand why you need so much yoke sticking out of the trans?..The driveshaft should be easily removeable with only around 1 inch sticking out.Mine comes right out with only 3/4 of an inch clearance at the trans...The further the yoke sticks out the less spline you have inside the trans and the more leverage it has on the output shaft to cause problems.....Also are your spring perches ok on the rear end?..Might be just the way its hanging but the pinion looks tipped up pretty far to me?
The reason I couldnt get the driveshaft out originally was because the splines were tweaked on the yoke and it would not allow the driveshaft to slide into the tranny enough to get it out of the rear yoke. After jacking and prying and cussing, I got it out and had a 1/2" taken out and thought that solved the problem. I did not know the splines were damaged at the time.

I totally see what you're saying about it hanging out too far and having more leverage to do damage. Unfortunately, it's a little late now..lol
 
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