Rear End and RABS...

[Fortunateson]

I have a "87 F250. When putting it into gear there is a "clunk" sound. I presumed u-joint(s) but upon inspection the tech?mechanic said rear end. The pinion is a little loose but he said it shouldn't be a problem. It sounds like it is a problem to me! So what do you guys think? He also said if has posi it could be something to do with that... I don't think it has posi.

And does anyone have a simple way to by-pass the RABS? When I drive the warning light comes on. After I park it goes out and doesn't always come backon for a few days. I'm thinking time to by-pass...

[KULTULZ]

No. 1, you need a qualified tech to look at the truck. It may be the pinion brgs pre-load if clunking. Any pinion seal leakage?

If you defeat the RABS, you are risking loosing the truck on wet road braking. Fix it.

[55blacktie]

Excuse my ignorance, but is RABS" an acronym for "Reverse Automatic Braking System"? Although these new vehicles have an abundance of safety features, there are hell-of-a-lot of vehicle collisions these days. Maybe distracted drivers are using their cell phones to figure out how to operate their vehicles. Could it be that the ambulance chasers, not the insurance companies, have been lobbying for these " safety features."

[miker98038]

No, it’s the early versions, rear antilock only. I remember complaints from my fleet guys when it first came out. Stopping going over railroad tracks right down the street would activate it and drove them crazy.

But I like your level of cynicism. Reminds me of ……me.

[KULTULZ]

Just like PREGO, it's in there - https://www.thedieselstop.com/thread...od-idea.48519/

[Flathead Fever]

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I was a mechanic for the phone company for 30-years. One thing you can check in the rearend is the spider gears for excessive wear. It's pretty common for them to wear out. Lots of worn spider gears in rearends to look at on the YouTube channel.

[KULTULZ]

And does anyone have a simple way to by-pass the RABS? When I drive the warning light comes on. After I park it goes out and doesn't always come backon for a few days. I'm thinking time to by-pass...

As bad as I hate to get involved again, let me address this ...

You cannot defeat this system. If you attempt without understanding how and why it is designed, most likely it is going to bite you at some point.

RABS replaces the previous mechanical PROPORTIONING VALVE in the hydraulic system. If you unplug it, you will have no correctional rear/front brake bias control.

The only PROPER WAY to modify the system is to retro-fit with a pre-RABS system, i.e. a PPV and any associated plumbing.

Now before the FOOD FIGHTS start, let me say I entered my first FORD DEALERSHIP in 1965. I fully understand braking systems and how certain modification(s) can go wrong (and usually do).

These so called KIT MAKERS are the worst offenders. How they haven't been sued is beyond me.

- TO WIT -

BJR POSTED – 24 JUL 2024

The pads do not retract, they are knocked back a few thousands by the rotor run-out. Nothing in the brake system retracts the pads, no springs nothing.

You need to go to another forum where people will believe your misinformation. I'm done here. Have fun.

[55blacktie]

Originally Posted by miker98038

No, it’s the early versions, rear antilock only. I remember complaints from my fleet guys when it first came out. Stopping going over railroad tracks right down the street would activate it and drove them crazy.

But I like your level of cynicism. Reminds me of ……me.

I should have paid closer attention to the year of the truck. There was nothing as sophisticated as I suggested in 1987.

I would like to see a braking system that automatically activates while I'm attempting to cross an intersection in a crosswalk. Drivers either don't know that pedestrians have the right-of-way, or they don't care. In the meantime, I'm making every effort to not be dead right.

[Flathead Fever]

The mechanic said the pinion is a little loose. That means it either has excessive play when you rotate it back and forth. Two different problems, the fist is probably worn spider gears, the second is worn pinion bearings. Very few mechanics have experience rebuilding rearends. Thanks to the gorillas driving the phone company trucks I have 30-years of experience with blown-up rearends. I stocked all the bearings, seals and spider gears to rebuild them. Crawl under the truck and see which way the play is. If it is spider gears, you should be able to do that yourself.

[55blacktie]

When I had a gear swap and Auburn limited-slip differential installed in my 55 Tbird Dana 44, "Miles" of Valley Differential" said that if the bearings looked good, he would reuse them because the quality was better than what's available today.

[Flathead Fever]

Originally Posted by 55blacktie

When I had a gear swap and Auburn limited-slip differential installed in my 55 Tbird Dana 44, "Miles" of Valley Differential" said that if the bearings looked good, he would reuse them because the quality was better than what's available today.

We tried to use Timken or BCA bearings at work, they seemed to last as long as the originals did. By the time you press off a bearing it might destroy it, so I never chanced it. I stuck new bearings and races back on. We bought that stuff so cheap through our national parts account. You cannot believe how much markup there is on automotive parts.

[Flathead Fever]

I went to all the factory classes for ABS brake systems when they first came out when I was working at the phone company. What they taught us was that if an ABS sensor failed the vehicles brake system just returned to a normal brake system until the ABS system was repaired. It should work just like a system without ABS brakes until the ABS is repaired. You should be able to pull codes on the ABS system that will send you in a direction to find the problem. A lot of the time the speed sensor magnet in the rearend resting over the top of small toothed rotation gear located behind the ring gear will have a bunch of metal filings stuck to it. That magnet is supposed to see the teeth moving on the gear which tells the computer thes wheels are rolling or there stopped. When it gets a bunch of metal filings stuck to the magnet it can interrupt the signal making the computer think the rear wheels are locked up when they are not. It compares the speedo reading to the ABS sensors. When it sees the car moving and the rear ABS not, it figures out something not right and it turns on the light. When you get a rearend that has worn spider gears that metal gets stuck to the rear ABS magnet and can set the light. The fact that you have clunk in the rearend and the rear ABS sensor light is coming on makes sense. I'd still look for worn spider gears being the culprit. It's really common for them to wear out and that worn metal in the gear oil would eventually build up on the sensor magnet until it could no longer read the teeth going by it and it turn the light on. This is a really-really common cheap fix to clean the sensor. It could also be the pinion bearings are worn so bad that it has play in them. Same thing, the metal filings end up stuck to that magnet and the ABS light comes on. Tou can easily pull the sensor and clean the magnet, and it might fix the ABS sensor light, but you still need to fix the rearend.

[miker98038]

A lesson I learned long ago. Listen to the fleet mechanic. Nobody can screw them up like the fleet drivers. LOL

[KULTULZ]

If the RABS VALVE (or any part of the system) fails and gives a MIL, the system is defective. There is no mechanical PPV in the system, as it is replaced by the hydro-mechanical valve in the RABS SYSTEM. You may have hydraulic pressure to the rear brakes and you may not. You decide to bypass the RABS VALVE, there may be enough hydraulic pressure to operate the brakes or there may not be.

If it fails, there is no mechanical pressure valve(s) to control rear braking bias.

If you are diagnosing the system, pull the sensor and it is covered in metallic shavings, you have a rear failure and that needs to be addressed and the housing fully flushed/cleaned before going any further.

On a 4W BRAKE SYSTEM, if the ABS fails, you will still have hydraulic pressure but no valving. Try your luck.

[Flathead Fever]

Originally Posted by miker98038

A lesson I learned long ago. Listen to the fleet mechanic. Nobody can screw them up like the fleet drivers. LOL

You are so right. The drivers don't have to have to fix it, let the garage mechanic do it. The older guys were really good with their vehicles. The young guys beat the crap out of them and thought it was funny. I put a clutch in a C-50 truck, machined flywheel, factory GM clutch, and they had it down to the clutch rivets in a week. I heard they had swung the boom around back and extended it out and were popping wheelies with the truck. It would do it; it was a really short-based truck. I could have had that truck back in service that night, we kept spare fly wheels already machined and new clutches in stock. Instead, I didn't get around to fixing that truck for about a month. Let the guy drive the worst van we had and climb poles with a 28' ladder. I was in the San Bernardino garage for 28 years and transferred into the Hemet garage. Me another mechanic had it all figured out, we'd both transfer there. I got there first and ended up the only person there with 150 vehicles doing "everything" on them. There were supposed to be two mechanics there, well they never filled the second spot. I was the only person in the yard at night; I didn't even have time to take a break. That was my last two-years out of 30 I worked for them. I let my smog license expire, all my ASE licenses, my commercial truck license and I swore I would never work on vehicles again. except for my old Fords.

[miker98038]

I hear you. I would have hid the ladders, and let them go up with a belt and hooks. A real bitch on steel poles LOL. Not much better on wood.

[Gene F]

Originally Posted by KULTULZ

As bad as I hate to get involved again, let me address this ...

You cannot defeat this system. If you attempt without understanding how and why it is designed, most likely it is going to bite you at some point.

RABS replaces the previous mechanical PROPORTIONING VALVE in the hydraulic system. If you unplug it, you will have no correctional rear/front brake bias control.

The only PROPER WAY to modify the system is to retro-fit with a pre-RABS system, i.e. a PPV and any associated plumbing.

Now before the FOOD FIGHTS start, let me say I entered my first FORD DEALERSHIP in 1965. I fully understand braking systems and how certain modification(s) can go wrong (and usually do).

These so called KIT MAKERS are the worst offenders. How they haven't been sued is beyond me.

- TO WIT -

I agree with your remarks on this topic. If nothing else, take it to the dealer and ask that a NIASE certified technician drive it, and inspect it.

However, buying a kit from some vendors is acceptable. These are not kits by some guy in a garage. I bot a brake conversion kit once from Performance Suspension Technologies (Back cover of Hemmings for years), and it was as promised, and works prefectly. Wilwood, LEED Brakes, people like that are ok.