Hey all,

Just got this truck down south for a trade on my rust bucket bronco.

Its a lowered truck (Not my fancy) but needed a pick up.

Truck has a 6.9 Diesel with the factory 4 speed with a new clutch (Under 10k miles) The rear is not a f150 rear.. Its an 8.8 rear with I believe seems to be 3.55 gears in the back. Long story short truck tops out at 55MPH but engine still sounds like it wants to go. I know these trucks arent the fastest but I was wondering what I can do to atleast make this thing do 70 so i can atleast move alittle bit. ALSO truck was a 4x4. but now its RWD still has transfer case if I ever want to put the damn thing back together.

 

welcome to FTE.
you have a home made truck there.
F150 never came with diesel.
88 used the 7.3, not the 6,9.
88 also used a 5 speed, not the 4 speed.
the F150 for 88 came with the 8.8 rear, and 3.55's was a factory gear option, so it most likely is the original axle in it.
my bet is that the speedometer gear in the trans is for a different gear ratio and the speedometer is not reading correctly.
3.55 gears with a non overdrive trans should give you around 65-70 mph at 3200 rpm.
i would try using a gps to see how accurate your speedometer is.

 

It is a 6.9 and 4 speed from an 86.

I was told from the guy the axel was replaced from a mustang. It is only 55. I have a speed on my phone 55. Is max and the engine wants to keep going but wont.

 

The Mustang 8.8 is about 5" narrower than an F-150 8.8, I can't imagine that would work right at all without some huge wheel spacers. You might want to actually verify what gears you have in your truck.

Also, what size tires do you have?

 

Post a pic

 

Ill get some pics tom.

But it is a regular 8.8 for an f150.. (New to the f150 truck). The owner said it has 3.20 or 3.28 rear. Which is not so reassuring.

 

Do you have a tachometer?

 

Not one that works. Seems like he tried to attach an aftermarket tach for a regular gas truck. But it dont work i rewired it as well and no luck

 

All i have working is the oil pressure and engine temp

 

What size tires does it have? 3.55 gears with 29" tires should do 70 @ 3000 RPM or 63 with 4.10 gears.

You need to figure out exactlh what gears you have, and then get a working tach to verify engine governor speed.

 

<disregard>

 

Here's a wheel pic.
235/75/15

 

Yup, those are 29" tires.

You should verify that the injection pump's throttle control is actually traveling to full throttle. 29" tires @ 55 MPH with 3.55 gears in 4th gear should be ~2200 RPM. The IDI's governor is around 3000 RPM.

 

They are 3.20 -3.28 rears. Not 3.55 sorry. He said either or. I need to verify

 

In that case the RPM should be even lowe and furthwr away from the max engine speed.