I just purchased a 1968 F100 Ranger. The original engine was swapped for a 429/460. The truck has a few problems and I need some informed opinions on whether or not they are related to the swap. First off, it seems that the truck is very high (numerically low) geared. It cruises on 31 inch tires at highway speeds well under 3000 RPM, and has very little power "off the line." What was the stock gear ratio for a 68 Ranger (or did they vary widely)?

Secondly, the truck vibrates when pulling out, but smoothes out after you get up a little speed. I'm wondering if this could be due to bad pinion angles (changed in the swap) or some other driveline / rear end issue? I've already replaced the center support bearing, as I was told that was the problem, but it still vibrates.

Also related to the driveline/swap, how much clearance should there be between the tail shaft of the transmission (c6) and the driveline? Should the driveline splines (for lack of a better vocabulary) fit all the way into the tranny, or should some of the shaft be visible outside of the rear tranny seal (I realize that isn't worded very well, but I hope someone will know what I mean). The reason I ask is once I replaced the center support bearing, you can still "wobble" the driveline side to side, with the loose area being where the shaft fits into the tail housing of the transmission. Does this mean my transmission is worn out?

And last but not least, the 9 inch rear is leaking like a seive. Could increased friction or excessive wear in the rearend be causing my shaky launches?

Thanks a lot, and I hope to learn a lot from this board.

 

Everything seems to point to problems with the lift of the truck due to the tire size. You should have a shop check your driveshaft for balance, possibly the old stock driveshaft was reused without properbalance, or possibly some weights have come off.. The angle problem sounds like it is wearing out alot of connected parts. If the rear end was lowered for clearance, were shock extenders used?? Had a friend with a monster type truck, he had a custom 2 piece driveshaft made to get the correct function from his truck. Seems to work very well..

 

I have the same vibration problem and will hopefully be putting in a new slip yoke this weekend. The spline engagement feels worn.

 

My 69 F100 has a semi floating Dana 3.50 gear in it. I was running 31 inch tires without suffering symptoms from the two inches of lift. It sounds like if for no other reason than it's leaking so badly, to pull the third member to inspect, and either replace, or at least reseal it. I'd talk to a driveline shop about the other wobbles, that doesn't sound too good. If you pull the slip yoke out the back of the C6 it'll leak out it's tranny fluid. Do you have a knuckle on the back of your C6 or a slip yoke? As far as your RPM's, the math is this: At 60 mph w/ a 1:1 high gear (standard non overdrive in high) engine RPM=20168 X gear ratio/tire diameter. With my 31 inch tires, and my 3.5 gears this was around 2300 rpm... well under 3000 but not especially high geared. Currently I have a 3.25 gear nine inch w/ a T18 and 390, this runs about 2100 rpm @ 60. I'm looking at a matrix and seeing that 4.11's and 32 inch tires yield 2590rpm, 2763 w/ 30" tires.

BBT

 

Thanks all for the input. My c6 has a slip yoke that doesn't seem to seat firmly inside the tailshaft (wobbles around a lot). Also, to my knowledge the truck has not been lifted. The 31's fit okay, but I'm not sure they wouldn't rub with a bit of bouncing around. I think probably a good place to start is getting that drive shaft assembly tested for both fit and balance. Since the engine was swapped, I'm not real comfortable that the driveline fits properly. There are two sets of holes where the center support bearing bolts up. One set of holes is obviously home-drilled, and puts the bearing an inch or two closer to the front of the truck, and allows the slip yoke to insert fully into the tailshaft of the tranny. On the other end, it takes away an inch or two of the splined area where the two driveline sections fit together. If I use the other set of holes, I get a more solid connection between the two shaft sections, but it leaves an inch or more of the slip yoke outside of the tailshaft. Which is worse? Again, thanks for the help

 

A shaky or wobly lauch also could be worn tranny/motor mounts.
+ the tranny won't leak out all it's oil if the rear is elevated enough. -just another angle at the situation.

 

Bud, it sounds like your engine was installed by some "good old boy" in his back yard. That is not always bad though, as long as it runs good. You have to implemment two courses of action:
1. Enlist the expertise of a drive-shaft shop.
2. Replace your motor and tranny mounts.
If it is not making a grinding or clanging sound in the rear, then your rear-end is fine.
Nastruck
69 f100 ranger
360 w/flow tech headers
w/3spd in floor out of tree