I recently posted this message on the transmission thread but got no response so I hope it will do better here...

I'm new to this site and I think it is fantastic.

I own a 1994 Aerostar 3.0 Automatic w/OD, cruise,rear ABS - 115,000 miles.

1. 6 months ago had the trans rebuilt at a trans shop (When the trans was rebuilt they replaced the rear main seal and differential seal).
My kids drove the van to school and noticed noise in the rear.
I checked the fluid in the rear differential and it was low. Took it to Ford they said there was enough fluid to protect gears and that they felt it was the pinion bearings. I thought it might be related to replacing the differential seal and not having the fluid topped off. Ford said no; I probably had it going bad the whole time.

2. So 2ooo miles after having the transmission rebuilt I had the pinion bearings replaced at the same transmission shop. The differential cover gasket was replaced.

3. Now my speedometer fluctuates wildly. I also noticed that when I apply my brakes they click like the ABS is engaging. (Trans shop says the speedometer might be cold. This never happened before.)

4. I began studying up on the speedometer. I couldn't find the speed sensor per my Haynes book (shows it on the transmission) Hallelujah! I'm glad I found this site. Now I know the sensor is on the rear differential and related to the ABS.


Anyway, could the fluctuation be related to the work that was done on the pinion bearings? (BTW: where are the pinion bearings located? In the differential?)

How do I check to see if it is just the sensor?

I'm hoping its not the speedo or the excitor ring.


Thanks...

 

the speed sensor is located on the top of the differential and is held in place by I believe 1 10mm bolt. Pull it out and clean it off.
I think its a little magnetic. Put it back in and make sure the wire connector is in securely. The trans shop might have damaged it so look for crackes, chips, or scratches. Any flaws on it will cause problems with your ABS and speedo. If you need to replace it it's in your haynes book under the ABS section and I believe is also mentioned in the section on the differntial, I'm not sure what they call it. Hope this helps fix your problem.

 

Well I did replace the sensor and no change. It seems odd that this did not happen until after the pinion bearings were repaired. I'm wondering if there was some kind of calibration he should have performed when he did it. The ABS still "clicks" when the brakes are applied but the ABS light is not on to indicate a malfunction. Speedometer still fluctuates...

 

There's no calibration for the ABS sensor in the rear end, but the tone ring has to be installed correctly and the sensor has to be fairly clean and installed all the way down. It sounds like your rebuilder may have bumped the tone ring - you might be able to see it thru the fill hole on the front of the axle, but pulling the rear cover may be inevitable.

 

Steve ,
I think you may be right that he bumped it . I know he didn't replace it when he did the pinion bearings. Is there a possibilty that the tone ring can be adjusted while on the vehicle or am I looking at the rear having to be dropped and opened up to replace the tone (excitor?) ring?

 

There's no adjustment on the tone ring, either - it's just pressed onto the lip of the carrier right behind the ring gear. If he hit it, it might be bent or cocked enough that it misses the sensor at some point in each rotation. If you can see it thru the fill hole, you might be able to work it back into place by prying on it thru the hole with a flat screwdriver, but I expect you'll have to open the cover and tap it back on with a small hammer. It's certainly not necessary to drop the axle.

Go to my sig link and look in the truck parts album (I just changed the main pic to the diff carrier). Almost the last pic shows the carrier with the ring gear behind it and the tone ring lying on top.

 

Steve,
I'm not having any luck accessing your pics.
When I looked in the VSS sensor hole I saw a large verticle ring with teeth. I dont know if I am confusing this with the ring gear or if this is in fact the tone ring. I have read in other posts what leads me to believe that the tone ring is something smaller and in a different location. I accessed a link in an earlier post (yours maybe?) www.cybrrpartspro.com that shows a diagram of the rear diff. but it does not explicitly identify the tone ring. Anyway, I tried to access the link last night and evidently it has changed and I can no longer use it.
I called Ford and they tell me the VSS sensor only relates to the RABS yet my speedo and RABS are both being affected...

 

George

Whoever you talked to at Ford didn't know what he was talking about - theABS sensor is used for a variety of functions from '92-up. You ARE seeingthe tone ring thru that hole; that's why the hole lines up with it so well.
As you rotate a wheel &/or the driveshaft, does the tone ring seem to moveside-to-side? Are any teeth bent over or otherwise NOT exactly like all theothers? Does the tone ring seem to be fully pressed against the back of thering gear (to the L as you look in the hole)? I'm attaching a photo of the carrier, ring gear, & tone ring disassembled, and another of them installed.
The tone ring is the thin one.

Steve83

 

Steve,

Thanks for spending the time to send the attached photos.

Unfortunately, I don't have the van in the air right now as the kids need transportation. When I changed the sensor I did rotate the tires but saw no rotation of the ring. Therefore; I didn't notice if there was any play or runout in the tone ring. Maybe I should have tried harder to rotate the axle. I guess I just gave up too easily.

I am scheduled to take the van back to the trans shop tomorrow morning. At least I can act like I know what I'm talking about when I try to convince him that the rear does affect the speedo. When I picked the van up after he did the pinion bearings I noted to him that the speedo wasn't fluctuating before I brought it in. He kinda blew it off saying his speedo does it when its cold. I asked if there was some adjustment in the rear that might need to be made and he told me that working on the rear would not affect the speedo because the sensor was in the trans and he was no where near the trans. Funny; he is the same guy who rebuilt the trans in July. Either the location of the sensor slipped his mind or he's hoping I'm a total idiot. I'm going to try to convince him to open the rear and check for runout or damage to the ring and get him to fix it. I don't know what else it could be unless by coincidence the speedo decided to go on the fritz at the moment I picked it up. I don't know how hard it will be to get him to accept responsiblity if it is something he did or didn't do but hopefully he's a stand up guy. Is there anything else you can suggest I say or do short of watching him open the rear (if he lets me)?

I'm glad I found this site and the wealth of info offered. If all else fails I will at least be more educated. I will take it in tomorrow and see what happens. I will keep you posted.

thanks...george

By The Way: I will copy and paste our e-mails to the thread I have going so it might help some one else.

 

George

If you have a Haynes manual, you can show him in print that the PSOM is fed by the ABS sensor signal, and so is the E4OD - NOT the other way around.
The same signal is used by the PSOM, RABS, E4OD, and cruise servo.

If the rear axle is opened, it takes some time for the oil to stop draining enough to clean the sealing surface & replace the cover with silicone, so he may charge you for the time. Otherwise, he really has no excuse NOT to open it up & prove to you there's nothing wrong.

Steve

 

Steve ,

Unless I am not looking in the right chapters or am totally clueless my Haynes doesn't address these issues. I was going nuts trying to find the sensor while looking at my Haynes. I found it when I joined this site and read all the posts pertaining to the issue. The Haynes only discusses speedometer cables and gears on the trans. When it comes to discussing RABS it says the system is complicated and to seek pro advice. There is no mention of the PSOM only how to replace the cluster. Now my books last printing was in 1996 maybe thats the problem. Maybe I should have gotten a Chilton or Ford manual.

george

 

No, just look in the wiring diagrams in the back and follow the circuit from the rear axle sensor all over the rest of the diagrams.

 

Steve,

I told you I would keep you posted.
It turns out that he accepted responsibility for chipping a tooth on the tone ring. He replaced it at no charge. Speedometer fluctuation, cruise over compensating and RABS clicking all are back to normal.
By the way I did look at the electrical schematics before posting here ( which is really not my forte') and it only seemed to cover the speed/cruise control. I didn't see where it led to the rear differential. Kind of a moot point now. But I'm either not reading it right or they don't show it which would seem to me to be consistent with not discussing it in the Haynes anyway.
Well, thanks for all your input it was a big help...
george

 

Wow! An honest mechanic! Put his number on your speed-dial and alert the press!

Seriously, you might send a short note to the BBB mentioning his cooperation.

 

the speed sensor on my ford aerostar is giving me major problems with my speedometer and shifting just want to find info on repairing the problem and other related repairs i might need now that there is a problem.