March 12, 2010

My speedometer and my RPM gauge are off. Can someone tell me what needs fixing please. I`m new to this and would like to do this my self.

Tim

March 13, 2010

There`s a small gear that is held into the driver`s side of the transmission with a single small bolt. It`s located right where the speedometer cable enters the transmission. It`s plastic and it`s easy to swap out.

If the previous owner changed the rear gears, but didn`t change the little gear in the tranny, the speedo will be off. You will need to figure out how far off it is, and what gear you have now in order to figure out what new gear to buy. Should cost under $20 and take less than 10 minutes to swap out.

The tach should NOT be off. Are you sure it`s off? A stock `88 5.0 runs out of steam right around 5k RPM. It might spin faster than that but it`s not pulling very hard. It might make funny noises above 4K or so if the valve springs are dead (not unusual). The only way the tach could be `off` is if it was from a car with a different number of cylinders. Is this an engine swap car?

SoCal94

March 13, 2010

The RPM gauhe probably is not off but how should i check on the rear end gear?

Tim

March 16, 2010

Stock rear gear ratio is either 2.73:1 or 3.08:1 for `88.

So, you could jack up the back end, put it in neutral, and turn the driveshaft (by hand) to see how many times it goes around before the rear tires go around 1 time. It`ll either be about a quarter turn less than 3 turns total, or just a hair over 3, if it has the stock gears.

More likely it`ll be closer to 3 and a quarter (3.27:1), 3 and a half turns (3.55:1), or 4 turns (4.10:1), since your speedo seems off.

OR, go out and drive side by side next to a friend who has a stock car with stock sized tires (which means that their speedo should be no more than 5% off). Have them drive at a fixed speed, and look at what your speedo says. We can calculate how far off your speedo is from that. Be safe.

SoCal94

March 27, 2010

ounow what RPMs i should be running at certain speeds. I can tell you what my RPM reading is at 55 or whatever and maybe calculate it from that. Just an idea.

Tim

April 13, 2010

Well, I don`t have my `88 with 2.73 rear gears anymore, so I can`t give you a perfect reference.

If you post your RPM at a specific speed, AND post your tire and wheel size, maybe somebody can tell what you have right now.

SoCal94

April 15, 2010

Alright, I will give it a shot. Thanks for the help!!

Tim

August 22, 2012

I have a 96 Mustang with the OEM computer removed. I have a VSS in the trans. Does the OEM speedometer take the pulses directly from the VSS? Or, do the VSS pulses go through the ECM before making it to the speedometer? I would love to have a functioning speedometer and hoping I can simple run a couple wires and get it working.

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