Hi, active duty military, 33 yrs, 14 deployments, cleaning up a stock 84 for my son as he joins the service as well. car seems completely stock.

1984 speedometer calibration. consistantly 9 MPH below actual speed as verified on GPS. (54=63) cheapest way to calibrate/fix this? from what i read its gears. where cable enters trans? just the gear on the cable, or is there an internal gear that would have to be replaced "as a set" before I pull it out, want an idea of what I'm getting into. not into splitting a trans for any reason. assume I just need to look at current gear and guess size up/down to compensate for 9mph.

car shifts well. though it has a whine in the rear end. unsure if I want to pay to fix that - tight budget. drive it until it fails I suppose. not the first car I've had with a whiny read end. fluid level is good.

thanks for any advice Frank

 

What size tires are on the rear?
IIRC they should be 255/50/16's or 26" dia. or 800 revs/mile

 

We can get pretty close with some basic information and give you some things to check. What's needed and the easiest with out tearing things apart more than twice is the axle ratio, the tire size and transmission type. Is the SPO label still in the storage compartment behind the drivers seat?

Speedometer error should be a consistant percentage and not a MPH figure Drive it 40, 45, 50, 55, 60, 65 MPH by GPS and record the speedometer readings. There's the percentage. Axle ratio we could approximate by rotating a rear wheel one complete rotation and see how many times the pinion turns in relationship.

From SPO label axle ratio should be a three digit code GXX, original tire size was a single tire so no worries there. So we'll just use what's presently on the car and what was originally available to check the car. With an error as you report it would seem the axle ratio has changed or just the wrong parts have been installed either by a used transmission replacement or just screwed up.

The unfortunate part here is if I'm correct we would need to add driven gear teeth to slow it down and our choices are limited. If it was originally a 3.07 rear axle and an A4 we're good I believe. If it was originally a 3.31 ratio it is already maxed at 45 tooth. The drive and driven would need replaced. Worry about that later, let's check first.

1. If SPO label present GXX information, A4 or M4 transmission, rotate rear wheel and count number of pinion rotations. I'm guessing a number less than three probably closer to two and one half.

Your speedometer is electronic not cable driven.

Questions?

 

There are a few different speed sensor gears that fit the transmission, they are made for the various diff ratio options. (easy to change the small plastic speed sensor with trans in car) but check link they will be able to help you

Scroll down they even have electronic converters !!!!!!!!!!!!!!! re some gears need a larger diameter hole in your extension housing to fit the larger speed sensors. So simplest way to go is splice the electronic converter in your speed sensor loom and just adjust dip switches to get the exact speed sent to your ECM via the converter.

http://www.transmissionsone.com/speedometer_gear.htm

My 85 with the 3.07 rear shows almost spot on to my GPS around 1kmh higher than actual GPS speed. Not sure what it would show with 255 50 16 as i run 275 40 17 on all 4 wheels, but should not be 9mph difference as the tire outer diameter should be close.

At 100kmh (62/63mph) my T700R4 with 3.07 revs at 1,900 rpm in overdrive i think from memory.

 

Thank you sirs!

Will investigate and provide data this weekend. Pretty sure eng/trans is stock. Rear ratio could have been changed.

This Dana is loud/whiny. Not obnoxious, but definetly needs something, mainly under power. really don't want to pay to fix this. hoping it lasts the boy a year or so before it need rebuild/dies.


thanks again, will get info!!

 

My 85 still has the original D36, i cannot hear any noises from it and the car has 170,000 miles on it. Check the fluid level first