Ford Muscle Cars Tech Forum banner
1 - 20 of 22 Posts

·
Premium Member
Joined
·
1,704 Posts
Discussion Starter · #1 ·
So I took the old 2:79-1 gearing out of my Mustang yesterday and replaced it with a 3:55-1. The third member was a good deal at $200 with new bearings etc and was set up. After a whole afternoon it was in. Not realizing that a gear change could do so much to the response of the 66 mustang. This thing is off the line when I let the clutch out and gets it up in the power range where the cam is designed to operate. Wish I did this a long time ago. Just letting the clutch out is nice with out revving the engine. Thanks for all the prior info on the benefits of this work. The engine and gearing should be a match when building a car.



Thanks

Greg
 

·
Premium Member
Joined
·
1,704 Posts
Discussion Starter · #4 ·
Happy around town , but seems t be a bit of a vibration issue at the 2800-3000 rpm range . That is about 78 mph. Might be the drive shaft needs balancing. Had this car since 1981 and never checked the balance on the drive shaft. U joints had been lots of time....Any suggestions. Hope it isn't the gear set up. Then you go past that speed 80 and above it is fine.


Greg
 

·
Registered
Joined
·
5,082 Posts
The money that you spent going from a 2.79 to the 3.55 gives much better bang for the buck than adding HP to accomplish the same thing.

A simple thing to try for your vibration is to remove the driveshaft from the pinion yoke and rotate it 180 degrees and then reinstall. Sometimes that's all you need to do.
 

·
Registered
Joined
·
10,461 Posts
Flipping is a good trick. If that doesn't work, vibes in a particular range is usually the trans output bushing and once in a while the rear axle pinion bearings. When you go under to flip the driveshaft, get under the front U-joint and shove straight up with 20-30 pounds of force. If you get any perceptible up/down play in the yoke - it's the bushing. Check the rear joint the same way.

David
 

·
Premium Member
Joined
·
1,704 Posts
Discussion Starter · #10 ·
Since you mentioned the movement of the yoke. My car went from a automatic to a manual swap. I was told that the automatic drive shaft on the 1966 Mustang would work. One thing I did was notice that the yoke went in deeper into the automatic than the manual by looking at the visible wear on it. My Toploader is rebuilt and has only a couple of months on it of use. Maybe I need to look at the drive shaft not being in deep enough into the transmission. I will do both the inspection and the rotating of the drive shaft.
If I need a longer drive shaft that may do as well. Or maybe the yoke on the standard is longer to catch the splines on the transmission.



Thanks

Greg
 

·
Registered
Joined
·
5,082 Posts
It is also possible that you have had the vibration all along, but with the old rear gear it was at a much higher MPH that matches the same RPM. That could point back to driveshaft balance.
 

·
Premium Member
Joined
·
1,704 Posts
Discussion Starter · #12 ·
Can't seem t find anything that would indicate the drive shaft on a 1966 mustang with an automatic would be longer or shorter than one than has a manual transmission. (Toploader) How much should the yoke be exposed from the tail shaft of the transmission.




Greg
 

·
Registered
Joined
·
5,082 Posts
Driveshaft length is the same as an auto so that is not the problem. (It measures 51 1/2" U joint center to center, IIRC.) There can be a little manufacturing difference. The yoke is interchangeable too. The type of rear seal can change appearances as some have an extended dust shield.

You should have about 3/4"-1" max exposed when level setting on the ground. Unless you are bottoming it out in the tranny, the length shouldn't be the problem.

One other thing, do not over tighten the U bolt clamps. That is one of the leading causes of U joint deterioration.
 

·
Banned
Joined
·
6,355 Posts
Can't seem t find anything that would indicate the drive shaft on a 1966 mustang with an automatic would be longer or shorter than one than has a manual transmission. (Toploader) How much should the yoke be exposed from the tail shaft of the transmission.




Greg
there is rear seal , one plian , other with a dust boot.
one with the boot you see less slip yoke .
 

·
Premium Member
Joined
·
1,704 Posts
Discussion Starter · #15 ·
After thinking about it , there may have been that vibration , but because I never had that rpm when driving it it was never an issue. The dust boot on the tranny is flush like the automatic..C-4 . I will rotate and test drive. If that is not the cure , I have a company here that I can take my drive shaft to to get checked. This car has been used by me in some not so grand conditions when I was younger. Might need balancing ...lol


Thanks

Greg
 

·
Banned
Joined
·
6,355 Posts
After thinking about it , there may have been that vibration , but because I never had that rpm when driving it it was never an issue. The dust boot on the tranny is flush like the automatic..C-4 . I will rotate and test drive. If that is not the cure , I have a company here that I can take my drive shaft to to get checked. This car has been used by me in some not so grand conditions when I was younger. Might need balancing ...lol


Thanks

Greg
flush ... would mean there is'nt a dust boot type seal
 

·
Registered
Joined
·
2,111 Posts
In the early 60's, I went from a 3:36 to 4:11 on my 57 BelAir. In 68, I went from 3:00 to a 3:50 on my Cyclone GT.

Felt like I put a new motor in the cars, but that 4:11 on the Chevy was rough on the NJ Turnpike. (Stock wheels/tires.)
 

·
Registered
Joined
·
734 Posts
Since you mentioned the movement of the yoke. My car went from a automatic to a manual swap. I was told that the automatic drive shaft on the 1966 Mustang would work. One thing I did was notice that the yoke went in deeper into the automatic than the manual by looking at the visible wear on it. My Toploader is rebuilt and has only a couple of months on it of use. Maybe I need to look at the drive shaft not being in deep enough into the transmission. I will do both the inspection and the rotating of the drive shaft.
If I need a longer drive shaft that may do as well. Or maybe the yoke on the standard is longer to catch the splines on the transmission.



Thanks

Greg

Thats what she said.... :D
 

·
Registered
Joined
·
734 Posts
Driveshaft length is the same as an auto so that is not the problem. (It measures 51 1/2" U joint center to center, IIRC.) There can be a little manufacturing difference. The yoke is interchangeable too. The type of rear seal can change appearances as some have an extended dust shield.

You should have about 3/4"-1" max exposed when level setting on the ground. Unless you are bottoming it out in the tranny, the length shouldn't be the problem.

One other thing, do not over tighten the U bolt clamps. That is one of the leading causes of U joint deterioration.

so if i find a 3 or 4speed toploader, say of the same year as my 67(for tail shaft length). my drive shaft off my c4 should fit? im looking in the near future to do a auto to manual swop. thanks
 

·
Registered
Joined
·
5,082 Posts
so if i find a 3 or 4speed toploader, say of the same year as my 67(for tail shaft length). my drive shaft off my c4 should fit? im looking in the near future to do a auto to manual swop. thanks
Yes--see your other post for more info.
 
1 - 20 of 22 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top