1966 f-100 rear end issues

[tammyphxaz]

hi,i am new here,i bought a 1966 f-100 long bed with no engine,i was very excited about getting it up and going.i got a 351 windsor from a friend and a c-6 automatic, it went in pretty easy after modifying the motor mounts. i got it up and running and was very dissapointed to realize that my top speed is about 40 mph in 3rd gear and the engine is wound out to the max and sounds like i am running in 1st gear,so i immeadiatly thought "rearend gears" and began to investigate,,this truck has a dana 60 rear end i had to pull the cover and count splines to find out it has 3:54 gears,,,i have a number of different people telling me a number of different things,1 says that 3:54s are just fine and that i need taller tires,another is telling me that i need to put a ford 9" 10 bolt rear end in it,with 3:08s ???another told me that it is my transmission ,,at this point i am lost,this truck also has an overheating problem and i am told it is because the rear end gears are too low causing my engine to rev too fast ,making my water pump push water through the radiator too fast not letting it cool the water,,,can anyone please help,,i out of ideas.

[spartman]

Are you sure it is shifted into 3rd?

My 240 six banger with 3.70 gears only runs about 2700 rpm at 65.

That little bugger isn't wound out at that speed yet.

[390Nut]

It's not your gearing. Sounds like your tranny is slipping, or the 351 you bolted in is toast, and you have no compression.

[tammyphxaz]

i know it is shifting i manualy shift starting out in 1st shifting to 2nd then to 3rd.

[tammyphxaz]

no im startin to think about the trannt thing,,,,,hmmmm could it be slipping? it seems to be strong and shifts really solid

[ToughOldFord]

It shouldn't be a Dana 60 unless someone put a 3/4 ton rear end under it. Which can be done, I've done it, no problems 'cept you have to carry two spares.

3:5's are just fine, like the others posted above you have other problems, you should cruise @ 70 with no problems.

[layedout72]

not that it will help at all, but what do the RPM's do once you are in the next gear. Do they drop like they should? Only a little? None at all? Like I said, I have no clue if that would tell anything but seems like if it IS in fact shifting, the RPM's would drop quite a bit into the next gear.

[tammyphxaz]

the drop in rpm is quite noticible.but mabey not enough.

[tammyphxaz]

i got this truck with no motor,the tranny that was in it wouldnt fot my windsor,so itraded it (the tranny) to the guy i got the truck from for a c-6 that fit my windsor,i put front/rear seals,new filter and fluid,new torque converter and flywheel,everything bolted together smoothly,the truck the c-6 came out of was a 1975 give or take a year,,,2 wheel drive that had a lift kit and some pretty huge tires,,i was kinda worried ,not knowing the history of the tranny but everything seemed to go together good,,,

[AlleyCat]

As far as I know all C6 transmissions are 1 to 1 ratio ( direct drive) in 3rd gear. With 3.54's it should do better than 40 mph on bare wheels ( please don't try it) let alone taller tires. From your explaination it sounds as if you may have a torque converter problem.If you happen to have a friend who is a trans rebuilder ask them to have a look.If not I'd suggest finding a good trans shop and having them diagnose it.Hope this helps.

[FORDification]

It shouldn't be a Dana 60 unless someone put a 3/4 ton rear end under it. Which can be done, I've done it, no problems 'cept you have to carry two spares....

You could special-order a 5-lug Dana 60. Heck, I've got one under my '67! Seems like all the ones I've seen all had 3.54 gears.