hey! been a long time ford owner but new to the site. i have a real quick question. i just came into a 1998 ford ranger 4.0 and the tranny has started to make a clunk or thud upon downshifting around 20-25 mph. i have been pulling my hair out trying to figure it out. i have been told it can be the sensor on the rear end but i have no check engine light. is it something mechanical like the shifter or torque converter? i dont even know where to start with this. oh and one more thing, it seems to still shift purfectly fine going up through the gears, just that last "coming to a stop" clunk and if i am applying the brakes semi hard it seems to activated the abs. thanks for your time guys and look foward to brousing this site!

 

Downshifting at 20-25... may be 2-3... I suggest 2nd gear band...

 

and that would cause the abs to activate?

 

If yours is a supercab, then you might be experiencing the infamous "driveline thunk". CLICK HERE.

 

A faulty rear differential ABS speed sensor could cause the ABS & the tranny shifting to act out, as the computer also uses the rear speed sensors output to help determine tranny shifts.

A bad speed sensor on my Taurus at the same speed range as yours, caused rough down shifts, such that the tranny would "grab" first gear when coming to a stop, which destroyed the front fluid filled engine mount & it would sometimes down shift to 2nd as high as 50 mph & that was exciting!!!!! lol

The computer also uses the speed sensors output to operate the in dash speed-o, so if it's acting out & jumping around, is unstesdy, or the cruise control dropps out, or otherwise acts out, those things are also more clues to suspect a faulty speed sensor.

It's located atop the front center portion of the rear differential & is held in by one 9mm bolt & has one electrical connector.

Should you find it needs replacing, it has a rubber "O" ring seal, so it may be snug to remove. Lubethe new one before installation.

Not very costly, easy to replace & is a common cause on the problems/items listed above.

If you have a two piece drive shaft, it may be the source of the clunk sound, on the rough down shift as Rockledge suggested.

Let us know what you find.

 

thanks for the quick replys guys. i doubt its the drive shaft cluck because i have that similar problem in my f250 sd and know what that feels like. i would like to think its the sensor cause it does have some of that problems characteristics. i got on it hard yesterday getting on the freeway and it was shifting all over the place before it inevitable settled in OD. but i was told by the dealer if it was the sensor it would throw on the check engine light? and i have ran the dtc on it and no codes.....

 

It could set a trouble code in the Tranny or ABS computer & unless you have a special scantool, you wouldn't be able to read their codes.

There is a proceedure for pulling the ABS system codes in the Tech Info thread atop this forums thread listing page.

A tranny shop should be able to scan the tranny computer.

My Taurus never did turn the CEL on, I found the problem while monitoring the speed sensors PID output, on my scantool, while the wife drove it at speeds where it would act out.

With your rear wheels activating the ABS when stopping & the tranny shifting acting up, it sure makes me want to put the speed sensor high on a suspect list!!!!

 

Whether or not it sets the CEL depends on its behavior. IF the sensor is inaccurate, but within operating parameters, no code will be set. But if you can observe it doing strange things, you are smarter and know it is bad. The sensor is fairly cheap and easy to replace.

 

alright update time...so i got the new sensor at the dealer today, and the upshift seems to be better, but after about 5 min of driving the thud came right back in the exact same spot. do you guys think it might be one of the other 2 speed sensors up front? if not then i may just get it diagnosed at a tranny place. hopefully its nothing big.

 

Did you pull the B- battery cable while you were installing the new speed sensor, to reset the computer. so it could relearn it's shift inputs with the new speed sensor?????

 

i un hooked the battery for about 20 minutes total. before i even started the work. finished putting the sensor in and hooked the battery back up. thats long enough time right?

 

While that should have been enough, I'm of the old school and disconnect mine overnight. Dealing with what is apparently a bad MAF sensor I let the truck sit dead overnight several times just to be sure that all codes were gone when I cleaned and re-cleaned that dang sensor.

 

20 minutes should have been long enough to clear the computers memory.

After a battery disconnect, I usually start mine cold witout any electrical lodes on & after it idles down some I shift into ALL gears including R, long enough to feel each gear engage.

Then let it fully warm up in "N" or "P", without touching the throttle, or applying any electrical loads, then sfift into all gears again as prviously done.

This will help the computer quickly relearn it's cold & warm idle.

 

i spoke to the guy that i got the truck from and he said he had it diagnosed at aamco and they said it was a speed sensor on the outside of the transmission. is there another one besides the speedometer sensor?

 

ok so the thud never really went away, and now after about 2 weeknd of driving it the trans is slipping and taking a few seconds to engauge reverse. so my ? is does it sounds like "valve body" problem or a bum tranny? thanks!