Hey everyone Ive got a 75F250 4x4 with a 93 Cummins and a Diesel ZF5 Trans, I recently installed 3.54 gears because I was at max RPM at about 60. After installing the gears I haven't seen much difference in max speed just lower RPM through the first 4 gears. I don't understand why I cant go at least 75MPH? Help please!

 

well, not sure if it will help tremendously but you might try changing the governor spring to the 366 spring.

 

Thanks but I already installed the 366 Governor Spring...

 

You might want to look at the throttle linkage. There's a pair of screws on either side that limit throttle travel. Mine had the one turned in so I was limited to 140 km/h. After turning it to get full travel I could do 150 something. Now with the spring I've pegged my speedometer a couple of times (180 km/h)

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Either side of the pump that is

 

What are your RPM's at top speed? If you have 33" tires 3:54 rear gear and and overdrive ratio of .72 like most ZF5 trans your top speed at 2500 RPM's is only going to be 96.33 MPH

 

Thanks guys, the screw on my pump is unscrewed for max travel, This truck is running 35's with 3.54 gears and a ZF5 out of a 96 Powerstroke. I can rev to 3000RPM but still only max speed of maybe 65MPH. I thought my speedo was probably off so I used a GPS Speedo and the speedometer is dead on. Its really getting frustrating...

 

Bad Clutch?

 

Its got about 200 Miles on it...

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The slave cylinder seems a little weak so I might change that and see what happens?

 

Are you turning 3000RPM down the road under load or just holding WOT in the driveway. I may have said wrong about the 5th gear ratio it could be a 0.76 If so your top speed should be 116.15 MPH at 3000RPM. With the 3:54 rear gear and your tire size. If your clutch was slipping that bad you would have burnt it up by now.

 

Cruising down the road hitting about 65 MAX running close to 3k. Like I said the clutch is brand new. I don't understand it.