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Discussion Starter #1
Hey Folks,

So here we go . . . I have a 1965 Mustang Coupe. It came with a 351 which was mated to a toploader that needed a rebuild. A couple of years ago, I purchased a used 1993 Cobra T5 to put in it. So finally this summer, I got it to one of my mechanics and he put the T5 in. I supplied a new Flywheel (28oz, 157 teeth) and clutch. The Driveshaft was cut accordingly. The cross-member I used, I bought from a guy down in New Hampshire through Ebay. The crossmember was built by this guy, and reviews were positive.

When I picked up the car, I pulled out of the mechanics driveway, and something was NOT right. as the RPMs went up, it would shake and get worse. The first thing that popped into my head was the flywheel is wrong. And, it was. So I ordered a 50oz flywheel, and that was put in. The shaking was better, but still present. I got on this forum and saw somebody recommended new dowel pins, so we did that, because the old dowel pins were pad. That also helped a little bit, but still shaking. One of the Engine mounts was also bad so replaced that.

This Thursday my mechanic is putting the car on the lift to carefully watch the drivetrain under acceleration to watch the drivetrain, and see if he can see what externally might be unbalanced (Like the Drive shaft).

This all being said, I am also concerned the crank got messed up from driving (Although not far) with the 28oz flywheel as I know this can happen (God help me if that is the case). The other thing could be that since the T5 was used (I bought from prestige Mustang in Georgia) perhaps that was damaged previously and this is something internal with the T5. The car did not shake like this with the top loader.

So here are some questions:

1. It looks to me like it's fine to mate a T5 to a 351 (No I don;t know if the 351 is modified. There was no Information on it.) Please confirm if that is correct, and advise of any caveats.

2. I have heard that if rear gears are even the slightest chipped, that can cause shaking.

Not sure what other things to check, and my mechanic is not sure what else to do here.

If anyone has some sort of check list, or suggestions, I am desperate and would gladly welcome the help.

Thanks for the assistance on this.
 

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Does it shake when it’s out of gear and not moving but Rpm’s are brought up?
Or only when the wheels are spinning.

That answer would help you isolate to motor or driveline.




Sent from my iPhone using Tapatalk
 

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68 Mustang Coupe
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The first thing that sticks out to me is the 351w never used a 50oz flywheel, they were all 28oz. It is fine to mate the to the 351w. Does it shake only when moving? Does it get worse or better with speed? How long was your car sitting? Flat spots on the tires? I'm assuming it drove smoothly with the top loader?
 
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^^^^^ This

Did you check the harmonic balancer to ensure it was matched to the flywheel (28oz)?

Also, is there a correct pilot bearing installed?
 

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67 coupe, 69 Sportsroof, 86 hatchback
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As already stated above, a 50 ounce imbalance flywheel is completely incorrect. And I think we need more info.

If it were me, I would have bought the $100 adapter plate to mate a T5 to the existing bellhousing. That way you could reuse all the clutch linkage, clutch, and flywheel. In fact you wouldn't even disturb the clutch unless you felt it needed replacing, much less the flywheel. So I suspect you and your mechanic decided to approach the swap from a more difficult path . Like I did. My reason was because I wanted to see if I could put together a DIY hydraulic clutch setup on my 351W/T5 setup. (I did) Plus I didn't have one single piece of the stock clutch linkage to start with.

I don't see chipped gear teeth being a vibration issue. They will make a whine though.

So what clutch setup did you use? Which bellhousing? Stock linkage, hydraulic, or cable?
 

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Discussion Starter #6
Thanks for your response: No it doesn't shake when it's just sitting, ONLY when the RPM's get higher, with speed. The car was being used prior to this with no shaking, so it's not flat spots.

I checked with some Mustang shop's and they told me the same thing. Should be a 28oz. But I went down to Butler McMaster and spoke to one of their guys, who is a ford racer. He showed be the difference between the 28oz and the 50oz harmonic balancer weights. So when I got home, and put my hand behind the harmonic balancer, the weight took up about half of the Harmonic Balancers' circumference Vs. the third a 28 oz would. So it had to be a 50oz.

Not sure on the pilot bearing, I will find out and get back to you.
 

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Discussion Starter #7
This is the clutch and flywheel we originally put in (But we then replaced with a 50oz):


Order Information Click here to track your Order Status
Order Date: 3/30/2019
Order Number: 2227912 Tracking Number: Will be sent in Shipping Confirmation Email
Customer Number: 16085140

Bill To: HUGHES WALSH

Items Purchased on This Order:

Item Status* Price Qty. Total

Ford Performance Parts M-6375-A302B - Ford Performance Parts Flywheels FMS-M-6375-A302B
Flywheel, Billet Steel, 157-Tooth, 28.2 oz. External Balance, 25 lbs., Ford, 302, 351W, Each
(Mfr. #: M-6375-A302B)
Ready to Ship
Ground

SPEC Clutch SF481 - SPEC Stage 1 Clutch Kits SXC-SF481
Clutch Kit, Stage 1, Organic, Full Face/Sprung Hub, Ford, Mercury, Kit
(Mfr. #: SF481)
 

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Discussion Starter #8
The Toploader needed to be rebuilt, and the clutch was on it's last legs.
 

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68 Mustang Coupe
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Thanks for your response: No it doesn't shake when it's just sitting, ONLY when the RPM's get higher, with speed. The car was being used prior to this with no shaking, so it's not flat spots.

I checked with some Mustang shop's and they told me the same thing. Should be a 28oz. But I went down to Butler McMaster and spoke to one of their guys, who is a ford racer. He showed be the difference between the 28oz and the 50oz harmonic balancer weights. So when I got home, and put my hand behind the harmonic balancer, the weight took up about half of the Harmonic Balancers' circumference Vs. the third a 28 oz would. So it had to be a 50oz.

Not sure on the pilot bearing, I will find out and get back to you.
If you have a 351w it will be 28oz balance unless some serious mods have been done to the rotating assembly. No idea why anyone would...
 

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68 Mustang Coupe
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I would think if it doesn't shake at idle or when the engine is revved, trans in neutral then you have a driveshaft/drive train issue.
 

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At this point I think I'd put all your stock stuff back on (bellhousing, flywheel, new clutch) and buy the adapter plate.

If you know the car never vibrated before, you're eliminating everything but the trans with all stock stuff.

Also, check your driveshaft angle and for giggles, make sure something didn't go in the rear end. As suggested get it up to driving speed and push the clutch in.

I know this can suck. I had a similar issue with my T5, mine ended up being 2 items. I pulled my trans in and out 3 times. Very frustrating.


1 - I bought a cheap ebay flywheel and clutch. Spent A LOT of $ on a matched RAM set up.

2 - Because I used the "longer" 1997 V6 T-5 and bellhousing, it was hard to see, but the back of my trans was just barely touching the metal part of the aftermarket trans mount. I clearanced it.

It's now vibration free through 90.
 

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Do you have the old flywheel that was on the car when you bought it? That will show you what flywheel (28 oz. or 50 oz.) is needed.

I was a bit unclear on your earlier answer about whether it vibrated out of gear. If the car is kept in neutral (brakes on not moving) and you rev the engine up to say 4,000 rpm is the vibration evident?

Also who cut, welded, and *balanced* the driveshaft? Was that work guaranteed?

What driveshaft slip joint/yoke did you use?
 

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Discussion Starter #13
Ok, I think I might have figured this out. When the 28oz was in, the dowel pins were bad, that would've caused the vibration. But we had already taken out the 28oz and the 50 was installed with the NEW dowel pins. So it would make sense to remove the 50oz, and put the 28oz back in with the new Dowel pins. So we'll try it tomorrow, and I will report back. Let me start with that . . .
 

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If you keep the 50 oz on your 351, it's going to wreck all the bearings, and probably loosen all your engine's screws while it's at it, possibly break the crank. So, you decide if it makes sense. =)


The balance for a flywheel (and damper!) not only has to do with the size of the weight, but also how far in or out it is, because rotational mass has more effect at a distance. Much like a weight on a lever.


All 351 engines *must* have a 28 oz setup, or they shake themselves apart. It's pretty important!
 

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68 Mustang Coupe
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Any news?
 
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