does inaccurate speedo confuses the ABS?

[swak6287]

i got the truck to the shop for repack bearings and he said the brake pads aer worn (1 year old) and the rotor is warped beyon repaair. he said the speed on the meter and what the computer is sensing is different that it thinks the car is going to stop, causing the ABS to kick in. i had not felt the truck stopped without me stepping on the brakes....but last few days before going to the shop, the brakes are hard to punch..like stepping on blocks of wood trying to push down....happens occationally.
now i drive with no ABS until the speedo is readjusted. the tire size was from standard 235's tp 33s with 4.10 gears.
anyone had this happen before?

 

[KPT]

Sounds like BS to me. ABS has its own sensors to tell when a wheel is locked. Doesn't even use the speedo as a factor AFAIK.

The shop might have screwed up an ABS sensor.

 

[swak6287]

well, should i try to get the speedo adjusted to see if that is the case or just plug the fuse back in for the ABS and see if the brake pads fry itself?

 

[ld50]

my speedo jumps around like crazy, it does nothing to the ABS. I am pretty sure the only sensors are at the rotor (at least with my 93). Make sure that the hubs have been tightened properly, because a loose hub can mess with your ABS sensors.

Seems silly to tie in a braking system with a speedo cable, actually it seems dangerous (?)

 

[JDraper]

The speedometer has absolutely nothing to do with the ABS. ABS looks at differences in rotation from wheel to wheel via the abs sensors on each axle. The vehicle speed is taken from either a gear or a sensor in the rear of the xfer case.

I'd find another mechanic because he does not know what he is talking about. The speedometer is a meter, nothing more. It just shows a speed. You could remove it from the truck, and it wouldn't make a difference in how your truck runs.

The two items that are tied together are the ABS sensors and the Control Trac. If I remember correctly, the Control Trac uses the abs sensors to detect wheelspin, and applies power accordingly.

 

[AdamsGuitar]

Also, I am 99% sure that you cannot just have it adjusted. AFAIK, there is no built in calibration method. If you have to adjust it for tire size/axle gear change, you'll need to get a TruSpeed speed sensor calibrator, which is an external device that sits in between the speed sensor at the rear of the tranny and the rest of the wire loom.

For the record, SuperLift (the makers of TruSpeed) claims that the speed sensor and ABS systems are linked.

 

[JDraper]

You can adjust the speedometer. If you have a mechanically controlled speedometer, you can change the gear on the end of the cable to alter the readings. If you have an electronically controlled speedometer, you can have it re-programmed.


The link between the ABS and the speed sensor is there, but does not cause the abs to kick in when it shouldn't. There is no link between the ABS and the Speedometer. The ABS computer monitors the speed sensor to determine if the vehicle is going fast enough to warrant the ABS turning on. If the vehicle is going slowly, the ABS does not engage. Therefore, with larger tires, your speed sensor would be reading a speed slower than you are actually going, which would cause the ABS not to activate until you were going slightly faster than the computer thinks. This info is coming from my Ford Service CD.

For example, let's say that the ABS computer is programmed so that your ABS won't activate below what it perceives to be 20 mph (don't know if this is the real speed it kicks in, but it will do for an example). With your larger tires, you may actually be doing 30 mph when the computer thinks you are doing 20 mph, so the ABS wouldn't engage until a true speed of 30 mph.

 

[AdamsGuitar]

My mistake, I thought he was posting that the mechanic was claiming his SPEED SENSOR was giving inaccurate readings, not just the speedo.

 

[JDraper]

His speed sensor will be giving inaccurate readings because of the larger tire sizes, but those readings should match the speedo, unless something in the system has been altered.
My point is that the mechanic is full of BS if he is saying that the speedometer reading inaccurately is causing the ABS to kick in. The only thing that causes the ABS to kick in are the ABS sensors when they sense a variation in relative wheel speed.

 

[boominXplorer]

Originally posted by swak6287
i got the truck to the shop for repack bearings

Isn't the ABS module in there? Its probibly somehting they messed up. I know on my 4x4 its all 1 assm but i dont know abou 2wd.

 

[GJarrett]

The whole thing doesn't make sense to me; you've got a '99. The front bearings are a sealed unit and cannot be repacked. The rear axle bearings are a mother bear to replace and are lubed by your diffy fluid and are inside of the axle seals and only accessible when you R&R the axle seals. What "bearings" are you paying this guy to "repack"?

In addition, JDraper is right-on concerning how the ABS works, I've gone to 35" tires without any of this happening. The only thing that is affected by my speed sensor thinking it is the wrong speed is (1) speedo reading is off; and (2) the tranny shift points aren't quite right. ABS is totally unaffected.

Just what exactly are you paying this yahoo to do to your truck? I'd find someone else.

 

[swak6287]

hhmm..that is what i thought...that abs hasnothgin to do with the speedo. inthat case, does anyone know why the brake pad and the rotor is worned so early (other then that bigger size tire)? does the worn out rotor affects the braking function, ie feels like hard to step down on the brake... and feels like the abs kicks in... pulsing. make sense?

 

[swak6287]

oh really? i dont really know. they just said they repack the 2 front bearings, maybe they meant replacing them? this is the 2nd time the front bearings been replace this year. i guess i need to learn how to do it.

 

[AdamsGuitar]

Methinks they're trying to take you for what they can. I would ask them "Have you already repacked the bearings? If they say they've done it already, call them on it.

 

[GJarrett]

Originally posted by swak6287
... does anyone know why the brake pad and the rotor is worned so early (other then that bigger size tire)? does the worn out rotor affects the braking function, ie feels like hard to step down on the brake... and feels like the abs kicks in... pulsing. make sense?

New rotors need to be "broken in" to new pads as the new pads wear into and mate with the rotors. If you use your brakes hard for the first hundred miles or so and heat up the rotors, they will eventually warp and the pads will wear unevenly. If you've replaced them before and then gone out and hammered them hard when they are new, you've already sealed their fate later on. You must drive and brake conservatively when they are new. I may be wrong on the specifics, but you can PM mrboyle to ask him, he's ASC certified tech mechanic specializing in brake work.

In addition, if you really have a printed receipt from this yahoo that states that you paid for him to repack your front bearings, you've got proof of fraud on his part, unless he can prove how he repacks a sealed unit.

Oops, EDIT: I am thinking front 4wd hub/bearing assembly and forgot you have 2wd. I don't know about the front 2wd, so until you hear from mrboyle or someone who knows what he is talking about, hold on that thought.......
Sorry for posting something I may not know anything about

 

[swak6287]

seal unit, eh. guess i learn soething everyday. they said new rotor and pads... and they took out my ABS fuse. ok,... i will be conservative with the braking for the next month or so. should i put back the ABS fuse to let the ABS work again?

 

[GJarrett]

I just reposted and edited my previous post; did you re-read it? You may not have a sealed unit. I suggest you PM mrboyle and ask him about all of this.

 

[swak6287]

thanks gjarret. will do that too.

 

[swak6287]

btw, they also said the spindle will need rep[lacing in a year due to wear???????

 

[Jefe]

incorrect info

On the 99+ Ex, the ABS sensors ARE the speedo sensors. The PCM gets the VSS (Vehicle speed sensor) info from the ABS module, as the ABS module averages the speed between the three sensors. There IS NO speedo sensor on the tranny/t-case.

On the 2nd Gen 4x4, yes the hub is a sealed assembly, but on the 2wd it is like any other 2wd front end, so the bearings do need repacking.

However, larger tires should not be throwing off the ABS module. I've run 35's with no problems with the ABS, except that it doesn't kick in as often. It will greatly affect tranny shifting though and you should either try to get the PCM or ABS module reprogrammed to correct the speed or put in a Superlift TruSpeed. I have the TruSpeed and it works great, and is probably near the same price as you're going to pay your dealer to try to reprogram your PCM.