[steve sturgin]

Thanks in advance for any assistance you can provide,

My 66 is a c code with a crate 345HP + C4 (old) + good balanced drive shaft (I am told, and it looks the part) + 8” (2.75:1 I am told) and seems to have a lot of thumping up and down the gears. It has a vibration that I am having trouble diagnosing:

Vibration is becoming apparent at around 50-60 MPH, I have repeated this while up on axle stands, my question is where could this be coming from.

Steve

[RagHead]

Sounds like the drive shaft since it will do it on jack stands. Have a shop that specialize in drive shafts (balancing, shorting, etc.) to check it or try another shift if possible.

[silver69]

Make sure the u-joints are in properly, and centered in the pinion saddle EVENLY, tighten ubolts EVELY,
remove wheels- run test, remove drums, run test, remove driveshaft and tape up trans output, run test. this will will eliminate things one at at time till you find the culprit. Make sure you support the car by the rear end at shock plates. what about harmonic balancer?good luck keep us posted

[steve sturgin]

Hi Folks,

We spent yesterday going through the motions:

Took the wheels off; same issue not as pronounced
Took the driveshaft off and stuck it in park, lifted the revs to where the vibration seemed to come in and; same issue not as pronounced.

The vibration seems to "phase", almost like running over cats eye strips on the motorway but not nearly as “loud”. The vibration seems to disappear in lower revs (under 1500rpm approx and over 2500rpm approx) but this is not for sure as the cam is “lumpy” and at lower revs it doesn’t rev smoothly so might just be difficult to detect.

So we went round to the front, the balancer we pulled out is the type where the weight is in the centre and is the removable, i believe it is the correct weight (50 oz) although i am not 100% sure it is in exactly the correct place in relation to the keyway. The centre of it (looking from the rear) with the keyway at 12 o’clock points to seven o’clock, does this sound correct? I have looked around to find a picture on the net but haven’t found anything as yet to confirm this.

After confirming the counterweight location and replacing the balancer I will try running it without the fan / alternator / power steer to eliminate these.

I installed the flex-plate (50oz) myself when we put the motor in, so I am almost positive that it is correct.

Any assistance would be appreciated.

[silver69]

It sounds like you have eliminated the drivetrain so you are down to engine. that vibration you are describing is a " harmonic resonant" type of vibe and can be balance related. is your engine tuned properly with no miss? you are right to keep eliminating mechanically driven components. I cant answer about the location of the balance weight. 50 oz means your engine is 82 or newer.

[mwillis]

Just a suggestion... I had the same problem (cyclical vibration) earlier this year and had several people tell me to replace the trans mount. Sounds like a waste of time, but that was it. Try it. It's about a $10 part, and about 30 mins.
Mike

[steve sturgin]

Thanks for the replys folks,

The motor was tuned by a pro a few weeks back and runs sweet.

I went to the shop that sold me the ballancer to check on the weight location of the ballancer and out of the box these are in the same place so i assume that this is ok and stuck it back on. And yes; the motor is a new ford racing crate 302/345HP with GT40 Heads etc...

Yesterday we put the front back together and disconnected the fan / alt and power steer pump, vibration still there.

I have also been told to have a look for something rubbing on the body so we will have a look at this also.

mwillis: once you pulled the gearbox mount did you see any problems with it ? I havn't taken a look at this yet but will over the next couple of days.

Regards
Steve

[bubbamace]

After you check all the above, don't rule out the rear end. My 1966 was making noises and vibration and it turned out to be a rear end problem. It had the original rear end and needed to be replaced ( or rebuilt ). I replaced it.

[silver69]

do you have performance engine mounts like uratahane?? Trans mount suggestion good too.
if you have disconnected every driven part and the vibration persists I would call Ford Racing for support. Solid mounts will send various vibrations into the frame of the car and you would definately feel them, keep looking and dont give up.

[steve sturgin]

Thanks once again for the feedback,

Last night i decided to get a little more clearance between the cross member and the sump by packing the engine mounts with washers between the mounts and the block.

While doing this i discovered what i think may be the problem, the steering looks like it has been rubbing on the sump for some time



I have tried to insert a picture so you can see what i mean.

I will report back once I have had a go at fixing this.

Steve

[silver69]

Great to hear it I think you are on track now, keep us posted

[steve sturgin]

Well that certainly made a big difference;

The cross member was defiantly touching the sump as was the steering. As said before, I used some washers to lift the engine up and set the mounts (with the cross bolts) a little higher.

Now I have plenty of clearance and the car is a different machine to drive and ride in, I didn’t realize that it was transferring so much vibration.

Unfortunately bubbamace might be right also as I can now feel other issues that weren’t as noticeable as before, there is defiantly some issues with the rear end, far too much back lash and the wheels seem to have a “wobble” when up on axel stands and rotating at around 60MPH. I guess I need to find a Diff thread now.

Thank you all the people who persisted and helped me with this problem.

Best Regards

Steve