vibration on the freeway

ok, i have a 66 mustang with a 302 (its not perfectly balanced, but good enough, not a race car), it has a T5 and 4.11's. When im on the freeway at about 80 the vibration starts, and at 90 its unbarable, the car shaks, but the shifter is shakeing uncontrolably. Its gets WAY worse if i put the clutch in (so the engine and tranny are disengaged). So that gives me the idea that its not the engine. But before i swaped in this engine, it went to 115mph without shakeing like this. What gives?

Did you put a new clutch kit in with the engine swap? If so what kind? Cheapy possible not balanced right. Or another possible problem could be the driveshaft. More likely the U-joints. Check the rotating parts after the tranny. Could be something simple which it sounds. Even a tire balanced problem. Good Luck

No, i used the same clutch stuff, there was plenty of meat on it, and im not useing it as a race car. Ill try the wheels, and then the ujoints, how hard is it to replace those, and how do i know if those are the problem?

I had that problem on mine after putting a 9" rear in and found out that the driveshaft was improper length and a little out of round. You should have about 3/4-1" clearance before the yoke bottoms out in the tailshaft. It can be too short or too long My shaft was 1/2" too long. I just took it to a driveline shop and they shortened, trued, installed heavy duty u-joints, and balanced it for $95. Rides smooth as new now.

You can rule out anything in front of the tranny by raising the rearend and dropping the drive shaft and running it to 6000 rpms in high gear.

You can rule out tires by raising the rear up and pulling the tires and running it up to 6000 in high gear.

_________________
1966 Mustang, Custom glass hood, 331 stroker, 5.4 H-beams, Probe pistons, ported TrickFlow heads, ported Stealth 8020, XER solid roller, Holley 750 HP, Hedmans, 4spd, 9"/3.50, BFG DR

"Too much for the street, not enough for Pro Stock"

<font size=-1>[ This Message was edited by: bluestreek on 2/6/03 6:02am ]</font>

I would have the driveshaft checked as the vibration occurs at freeway speeds. I had a vibration at 60-70 MPH. I checked everything w/o pulling the differential: wheel balance, alignment etc. I thought the axles were bent but an unbalanced driveshaft was the cause of the vibration.
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I had the exact same symptoms in my '65 mustang and it turned out to be that the transmission mount rubber had seperated from the mount itself. Very hard to tell without taking it off the car as it sit's solid and looks fine until you torque it up via the engine.
A friend had a similar problem which turned out to be a really loose engine mount.
Check both of these first before you go playing with the drivetrain (especially if they haven't changed from before the rebuild).

Cheers,
Trav.
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I had the same problem with my '67 Mustang. The T-5 rebuild kit from Ford included everything but the tailshaft bushing. I read in Mustang Monthly that when it craps out it leads one to believe the driveshaft is out of balance. I've met a few high mileage late model guys with this problem in their T-5's. The article also said the bushing is supposed to wear in with the yoke, so they are both supposed to be replaced together.

I pulled the tranny back out, replaced the bushing, had the driveshaft rebalanced with new Spicer u-joints only since the yoke was new, wasn't scored or under-sized, and had the tires balances within half a gram for good measure. The vibration which shook the coins out of the ashtray at 70 mph is gone, but I still have another driveline vibration at higher speeds. It's annoying more than anything, but I still don't like it.

I'm thinking the 9" I got from a Granada is warped or twisted, the swap meet Trac-Loc saw too many launches on slicks, or the cheapo Summit gear set I put in got damaged from all the bad vibration. A buddy of mine slipped in an aluminum shaft, which really helped due to the softer material not transferring as much vibration, but I know the root cause will still be in there somewhere.

Any body with some fresh ideas? Thanks.

Mrgray,

Bent axles? Only a guess.[img]/phpBB/images/smiles/icon_confused.gif[/img]
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When you took the drive shaft out did you mark it so you could put it back on the rear end the same way. It could be 180* out of phase. This would cause your vibration. Also Transmission mount and motor mount as previously mentioned
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I have a 1965 mustang with a T5 and had the exact same problem and its now fixed. The real problem was that the swap article that I used as a reference when putting in the T5 claimed that the cross member mount must be dropped by one inch because of the tranny mount height difference on the T5. The article was wrong about the tranny mount(from what I can tell from measurments against the original top loader its actually at the same height, the real problem is that the T5 itself is taller and to avoid interference with the transmision tunnel their solution was to drop the back of the T5. Dropping the back of the tranny creates the vibration problem because the tail shaft of the tranny is no longer parallel with the yoke on the differential. Originally I thought the driveshaft was not properly balanced. The drive shaft place told me it was not bad but was not perfect, they took my money and re-balanced it did not help. I surfed a bit and found a web site with a good article on driveshaft vibration. In the end I modified my cross member to get the back of the T5 as high as possible without interference. (it's about 0.2" lower than original toploader now). This solved the problem. Next time the T5 is out I might dimple the transmision tunnel to get it up to the exact original location. I hope it works for you.