redmach

Ok I took everyone's advice and still come up with 3 1/4 turns per tire revolution. Jacked it up, both tires off the ground. Both rear tires turn in the same direction, at the same time. Positraction, or Traction Lock as Ford calls it. Tranny in neutral, no clutch slippage.
The number tag on the diff. matches what the book says WFB-C, 3L25. I'm stumped.
Do I just change the Ring and Pinion to the lowest I can find or try to find another tranny? Thanks to all so far for your inputs.

ttoney

Well, either your cam is really lame or you have an odd tranny gearing setup. Perhaps you need to jump under the car and get the Tranny tag info to decode. It sounds as if you have some old truck tranny with really low gearing. With 3.25 gears and 26.5 inch tires, @ 4000 rpm's, you should be at approx 97 MPH.




It might be worth starting to plan a 5 speed upgrade. What does your motor look like for Horsepower, modifications etc?

highhilleer

Your test and tag say you have a 3.25 rear end. The math says you should be at ~ 3000 rpm at 70 mph, in top gear with a 3 or 4 speed. Something is wrong. You would burn out your clutch if it was slipping that much. How about hooking up a tack and getting some actual measurements?

redmach

Hooked up a tach today and ran it down the highway. 3600 RPM at 60 MPH and 4000 RPM at 65 MPH. Startin' to **** me off. Tag on the tranny is RUG E 3. What the book says it should be. I talked to one mechanic today and the first thing he asked was what kind of fan is on it. It happens to be one of those 6 bladed lightweight Flex fans. I can see that making it louder but not raising the RPM's. I think the engine is stock. 351W 4BBL 4 Speed manual, headers and dual exhaust. Any other thoughts?

ttoney

Head Shake. Decode the Tranny. Other than that, hit it with a hammer.

Oh, and post some pics of your car. We like Mach's around here.

redmach

How's this for stupid, I just noticed the tach I borrowed was set for 6 cyl. It sure sounded like 4K though, I'm still hoping it's the fan, probably wont test again till sunday.
What happens to the reading when it's set at 6 cyl.?

Scott H.

Actually that is a pretty astute observation. Stupid would have been not diagnosing the problem before replacing components.

IMO... GREAT JOB!!!!!

Set on 6 cylinder will be a 25% difference.

So 4000 rpm divided by 1.25= actual RPM at 65mph, or 3200rpm at 65, which sounds much closer.

Scott

redmach

Thanks for the info .....

redmach

OK, I am gettng closer to solving this. I hooked up the tach again, and hit the highway. It was 2500 RPM at 55 MPH and 2900 at 65 MPH. Right where it belongs . Now I'm focusing on the fan. It's too big to fit inside the shroud so someone shortened the spacer when they installed it. What type of fan should I be running?

Thanks to everyone for your input into this matter, redmach

67t5ponycoupe

Dang I'm glad you figured that out because it was driving me crazy! For the fan, If it was me, I would figure out how much to cut off of the fan blades you have now and get a fatter spacer to get the fan in the shroud.