Update: '99 OBS CC SWB Brake Issue
 

Thought I would update this.....
http://67-72chevytrucks.com/vboard/s...d.php?t=829456

The pulsating pedal is no-more but the spongy brake thing has still been a concern after a few miles/weeks of in city driving. More than once if I was aggressive on the brakes, the pedal went down farther than desired & the in-dash brake warning light came on. It would go back off after the next 1-2 pedal strokes. Beyond that, the pedal feel was not consistent.

We had crap weather so I dealt w/it as is. When we had better weather & I could align help schedules, I did another round of bleeding. I was happy w/the pedal feel after so again I went w/the 'drive it & see' approach. While the brake warning light hasn't come back on, the pedal still is not consistent. Sometimes the 'pressure' @ the pedal can be felt earlier in the stroke vs. others.

So my next step will be the 'automated' bleed sequence as suggested in the closed thread. I'll follow-up after to share the results.

Re: Update: '99 OBS CC SWB Brake Issue
 

"Autobleed", or whatever you want to call it, works. There's a Tech Service bulletin from Kelsey Hayes about this service process.
Driving on dirt roads and activating the ABS doesn't do the same thing as the diag tool initiated sequential ABS motor actuation.

If there was air through the brake system it may take two or three or even four bleed-ABS actuation-bleed sequences to work it all out of the lines and firm up the pedal. Voice of experience here. I've gotten air out from three cycles with the fourth cycle no longer producing air. The important thing is to get it all out of the system.
I would highly recommend using a pressure pot bleeder like the Motive Products or homemade weed sprayer tools. The GM service manuals call for using a $500 Kent Moore branded version of the Brannick pressure pot bleeder tool. No need to buy one of those. The weed sprayer tools work quite well.

You'll need a Tech2 with the GM 32mb linear flash card or an equally capable high end Autel or Snap On Virus:lol: diag tool. The less expensive aftermarket tools don't work and play well with the 1996-2001 GM T400 trucks nor do they work well with the ST trucks & blazers and many other vehicles of that vintage. Even the high end aftermarket tools have severe limitations on vehicles that old. Most mechanics do not like working on vehicles from the 1990's for that reason... and the super brittle plastic connectors & other plastic bits and pieces.

My Tech2 clone was $250 a decade ago. They've gone up to around $300 now and it's still a bargain. It's only useful on 1991/1992 up to 2012/2013 GM vehicles. It'll give you access to everything that the GM techs could do with the ECM/PCM, TCM, ABS, TCCM, & BCM on said vehicles.
The Autel Maxsys and Snap On Verus tools don't work on 1995 or prior and have limitations on the 1996-2000 vehicles but are very useful on current vehicles so they cost several thousand dollars.

Re: Update: '99 OBS CC SWB Brake Issue
 

Yes, there is practically no support for 96-99. The Tech2 is the golden tool for them.

Re: Update: '99 OBS CC SWB Brake Issue
 

I'm guessing this is one of the reasons many opt to bypass/remove the ABS on these (lack of continued support).

Re: Update: '99 OBS CC SWB Brake Issue
 

Scot if it was mine I would find a pressure bleeder and flush that dude good and maybe find, borrow a scanner to cycle the ABS.... No, with the size of that truck I would remove that pia system and be done with it. If it was mine. ;)

Re: Update: '99 OBS CC SWB Brake Issue
 

I'm trying to decide just that.

Not sure I want to keep a set-up around that will be more difficult to service because of a lack of support on an ABS set-up that likely doesn't do squat for a truck like mine. I'm not sure how much of an impact different size front/rear tires have on how effective the ABS functions. Add in the bleed/purge needs if the system is opened. Seems removing the headache is looking very probable.

Trucks stopped fine for decades w/o the aids. It won't be 'as good' but will still work fine.

Re: Update: '99 OBS CC SWB Brake Issue
 

88-95 are said to benefit from removal of the ABS. 96-99 have a different "better" system. I've never felt the ABS work on my 99, but I have felt it work wrong on my 93.

Re: Update: '99 OBS CC SWB Brake Issue
 

I knew the 1st go @ it was less than ideal (in general as well as especially for the GMT400 series).

I recall the 2nd go was F&R ABS vs just fronts. Not sure if one series (1500 vs 2500/3500) got a different set-up vs the others on the 2nd round. I know the 'brain box' is much different in my '99 vs my previous '90.

Re: Update: '99 OBS CC SWB Brake Issue
 

The 88-95 Bosch RWAL benefits greatly from removal. This system still has a proportioning/metering valve like older vehicles with the ABS motor in the rear brake line.

The 95-2001 GM T400 Kelsey Hayes system handles the proportioning/metering inside the ABS block so deleting it is a bit more involved than just moving the plumbing around.

Personally I'd just get a Tech2. The access this tool gives you to the whole truck is well worth the price of admission. When you sell the truck you can likely get the whole investment back on evilbay.
Your other option is to find someone local to the Dallas Ft Worth area that has one and is willing to help you out.
If you were in Northern NH or along the NH border in ME or VT I'd be willing to setup a time to help you out. I've driven into the Northeast Kingdom and over to Freyburg ME to help some folks from my church out. Dallas is a bit of a hike from here.:lol:

Re: Update: '99 OBS CC SWB Brake Issue
 

I'm already looking for the Tech2 but through KNOWN sources. Concerned w/getting something off ebay that's crap & then I get stuck w/the buy-in + repair tab. I reached out to some friends in the business to see if anyone has a lead on one.

I knew (well, assumed ;) ) the later style did both the anti-lock as well as proportioning based on the plumbing. My thought was to get something like this Wilwood prop valve & plumb it in place. This has a pressure switch & adjustable proportioning. I know this would allow dialing in the pressure for even/consistent F/R braking w/the mis-matched tire sizes. Since I've always ran taller tires on my stuff, the balance bias was a given. Some you noticed it on; others not so much.

I've seen www threads with how-to's for bypassing the set-up but never really studied up so that might play into the decision tree as well.

Re: Update: '99 OBS CC SWB Brake Issue
 

You would need the proportioning valve from an 88-95 and plumb it in. Plus the tee for the front lines. I think that's it.

Re: Update: '99 OBS CC SWB Brake Issue
 

I was going to go look @ my old '90 to see how it was set-up. Since I haven't looked under the hood of an earlier model OBS lately I can't remember. My buddy owns my old truck so I have access to it for a look-see....

Also gives me an opportunity to see how the 5.3/4l60e swap is going.

Re: Update: '99 OBS CC SWB Brake Issue
 

The SAAB guys are heavily into the Tech2 clones. You can likely find a good source for one through them.
That's how I found the seller OBDII365 in 广东 that I bought mine through.

I just checked the package with the blowmolded case that I bought. It's $368 and shipping has gone through the roof. It was $25 shipping from Guangdong just under a decade ago. Shipping is just shy of $120 now.
The same tool in a cardboard box without the case is $268 + $75 shipping. The blowmolded case sure looks sweet but it ain't sealed and it ain't worth $200. I'd put all the jiggly bits in ziploc freezer bags and drop em all in a $20 canvas tool bag to save $200. A Pelican 1550 is $154, if you want a hard sided case... The Pelican is sealed up tight so humidity wouldn't be an issue. You could drop a Pelican in a lake or flood your garage without getting the tool wet.

Re: Update: '99 OBS CC SWB Brake Issue
 

Nobody @ the F@#d dealership had one.

My buddy reached out to his old boss @ the independent shop & he said he has one. We're going by there Sat AM to see if we can get things sorted.

Re: Update: '99 OBS CC SWB Brake Issue
 

I got stood-up on the Tech2 session. Maybe next week.

I did swing by my buddys place & checked out my old '90 underhood for a peek @ the LS sawp progress which provided the opportunity to also look @ the brake line routing. I'm on the hunt for the early OBS underhood brake lines. Just in case....

Re: Update: '99 OBS CC SWB Brake Issue
 

It's good to have a plan. A backup plan. ;)

I remember way back when I had my 88 GMC with rwal. It had the soft pedal that would occasionally go to the floor while at a stop light. I replaced the master cylinder, no help. I looked into replacing the anti lock control mess but I didn't like the price of that so I just dealt with it while I owned it. Was sure glad to move on to a 97 with a different system. I had no problems with it.

Re: Update: '99 OBS CC SWB Brake Issue
 

Well, I'm here to stay both are suseptible to issues. I read mutiple stories of pump issues on the later AWAL set-ups & the RWAL set-ups just weren't that good to begin with. We knew of that once you start changing tire sizes. I don't & have no plan for same size F/R tire OD's so that's another wrench in the ABS skunkworks.

No ABS & ability to adjust rear psi seems to be the best strategy.

Re: Update: '99 OBS CC SWB Brake Issue
 

There's also two different RWAL systems, but I don't remember what year it changed. My mother's 89 has the earlier system and my 93 has the later. Her brakes never really felt right.

Re: Update: '99 OBS CC SWB Brake Issue
 

I've been watching this quietly since my current truck is a 97 model.

I've about decided to go to PicknPull and grab the plumbing off of an earlier truck and go full non-ABS. I'm about to go into the brake system for some maintenance anyway. Now would be the time.

Re: Update: '99 OBS CC SWB Brake Issue
 

I found 3 pre-94 possible donors @ my local go-to yard/s (proximity to work/shop). Hopefully, they'll still be there on Sat & the weather cooperates so that things are open.

Re: Update: '99 OBS CC SWB Brake Issue
 

SCOTI is there any advantage for you to switch to the GMT800 (99-07) master cylinder?
I’ve seen posts where obs owners are using the kit from LittleShops Mfg.
I assume that would keep the abs system.
https://www.littleshopmfg.com/gm-ck1...hoCFRwQAvD_BwE
This kit does say 1500 trucks and NON-hydro boost applications.

Re: Update: '99 OBS CC SWB Brake Issue
 

IDK. It's a good question & one I have been asking myself as well.

The GMT800 master cylinder swap was the No.1 recommendation in the www threads I've recently read concerning GMT400 ABS issues. But, in a lot of those same threads, the guys made no reference to having done the spec'd 'Auto Bleed' sequence when they were having issues. I'm curious if they had actually purged the ABS system the way it was designed to be, how much of a difference would they have noticed? More than one mentioned that logic in their threads but were happy w/the overall outcome after changing things.

My logic is I don't see how just going to a GMT800 master cylinder is a magic fix but I haven't compared the 400 vs 800 specs. it's a hydraulic system @ it's core. If the bore size is different (smaller) I can see the swap making a difference w/no other changes. But I don't see how that would be any different vs. using a GMT400 master cylinder w/a smaller bore size. Again, I have not compared or researched possible/available bore sizes.

For 'Spot'? We're thinking the pump unit is done. Apparently GM/KH wants the ABS unit purged/flushed as part of the systems service schedule because the internals are sensitive to moisture & crap within the fluid. So it's replace the dead part & hope that makes a difference or try replacing it all since it is >20yrs old & doesn't appear to have made many regular service appointments. At the prices I read about where guys did replace the whole shebang as well as now knowing/understanding the bleed procedure required for future maint, it has me considering alternative solutions.

I've read/studied about ABS while researching stuff. It requires definitive input data/specs to work as programmed just like the factory ECU. Start making changes to the original parts (parameters) & it no longer works as intended or expected. Changes like tire diameter impact things. I think of the ~30 vehicles I've owned over my driving years, only 2 had the same size F/R tires & they were temp rides for one reason or another. My 'keepers/reachers' always have taller rear tires. So it seems a separate/manually adjustable prop valve (w/the proper residual check valve for the rears if needed) is my best bang for the buck.

*EDIT*
If the KH ABS set-ups 'brain' did self tune/learn/compensate for changes (different tire sizes), I would definitely prefer to keep the best/latest technology available.

Re: Update: '99 OBS CC SWB Brake Issue
 

I am following closely as I have a 91 1500 with all stock brake components. While they are working great it does have 82,000 miles and at some point in the future I expect the ABS to go bad and thinking about what I might do with it. My initial thought is to deactivate and or remove the ABS system altogether. Much easier on the wallet firstly and vehicles performed very well without ABS for many years and can still do so today. The 91 model is 30 years old now so replacement ABS parts may become hard to find, if not already. My thoughts on it.

Re: Update: '99 OBS CC SWB Brake Issue
 

It all comes back to that Tech2. I would like to have one for mine but since I can't buy one at a store I fumble around without it. So far I've managed fine without it, but it seems things would be easier with one. One of the reasons I prefer OBDI. My special code reading tool is a paperclip. Buying the Tech2 or buying the lines, valve, and master cylinder and the labor of gathering and installing. Sounds like it wouldn't be money wasted since it even holds its value if you wanted to sell it.

Re: Update: '99 OBS CC SWB Brake Issue
 

Well sure. I'd like to have a tech 2 as well but mainly for the engine performance diagnostics. That's why I've been asking around about a laptop cable and diag program such as Winaldl or Tunerpro or something like that. There are some hand held scanners out there that the listers say they read OBD1 but I've not found one available that I would chance the money on. I've found some OBD1 to OBD2 adapter cables and for cheap but some reviews show they are junk, do not work so I am left still wanting something useable for less than the price of a Tech 2 type.

Re: Update: '99 OBS CC SWB Brake Issue
 

If the Tech2 was $250 its close enough I'd call it a draw. $350 or more, what then?

A new aftermarket prop valve is $125 or under. A donor 88-92 prop valve is <$10. Brake lines? Re-use what you can or snag some parts off wrecking yard donors. After that? You're done. Ever have an issue w/the master cylinder failing in the future? Replace it & bleed the brakes like any non-ABS hydraulic system. No need for the computer access.

*EDIT*
I've only had 3 vehicles new enough to utilize a scanner (my old '93 x-DPS Mustang, my old '90 model OBS, & it's replacement Spot).
All my stuff has been older carb'd rides.

Re: Update: '99 OBS CC SWB Brake Issue
 

OBDI doesn't need a scanner. The "scanners" available for them don't do anything but show you the codes, which you can read off the check engine light with a paperclip and not waste your money. GM and Ford, paperclip. Dodge is even easier, turn ignition on, off, on, off, on. Codes start flashing.

I'm not trying to change your mind on how you want to fix your truck, just that it probably won't be the last time you need to fix it and the Tech2 may come in handy later. Of course, I still haven't gotten one either though.

I thought the air would eventually work its way out on its own anyways. Like how a pressure tank with a ruptured bladder gets waterlogged. Fluid displaces the air. When I would bleed the clutch on my F150 I couldn't get all the air out, I had to drive it to work out the rest of the air.

Re: Update: '99 OBS CC SWB Brake Issue
 

Your 1991 is the old GM ALDL 8192 baud serial communication protocol with a completely autonomous Rear Wheel ABS system that communicated on a different terminal in the 12 position ALDL jack. There were ABS brake cartridges for the Tech1 but good luck finding one of those in working condition for a price that you can afford. Even the Bosch Mastertech 3100 (basically a Tech1A with a larger screen) isn't cheap anymore... and GM cartridges for your truck will cost you dearly as well. I repaired a Tech1A about a year ago for a Corvette guy and sold it with no cables, no adapters, and no cartridges for a fair chunk of money. They guy that bought it sent me his non working Tech1 for the postage but it was beyond repair... obsolete proprietary part failure.

A Tech2 only begins to be useful on 1993 and newer vehicles. The earlier ECUs are fairly embryonic tech. Not much in the way of bi-directional controls if anything. The Tech2 will not give you much more than WinALDL or TunerPro on a 1992 and will not give you anything on a 1991 or earlier rig whereas the WinALDL and TunerPro will let you view you any data that's available on the serial comm port back to the 1985ish TPI systems.
If you eventually intend to get a 1995-2007 truck I'd keep your eyes open for a Tech2. You can still buy them new from China right now and it'll be something you can sell if you need to.

A T800 Master cylinder is not biased for Disc/Drum brake systems because the T800 brake bias is controlled by the ABS system. It'll work but it won't be quite right.

On a 1994 and earlier truck I'd bypass the ABS pulse motor between the master cylinder and the metering/proportioning valve with a longer piece of brake line and bleed out the system. It'll work surprisingly well after you get all the air out and properly manually adjust the drum brake shoe clearances.

Re: Update: '99 OBS CC SWB Brake Issue
 

If you're careful, you shouldn't have to buy anything. The line doesn't have to move far and it should be coiled under the fitting.

Re: Update: '99 OBS CC SWB Brake Issue
 

Thanks for the refresher.
IIRC you have to change the ferrule on the end of the coiled brake line because the ABS pulser has a different diameter and thread pitch from the Combination valve.

Still pretty darn easy and non intrusive.

Re: Update: '99 OBS CC SWB Brake Issue
 

I was thinking the same thing after I posted. Might need an adapter, union the two lines together, or cut swap fittings and reflare.

Re: Update: '99 OBS CC SWB Brake Issue
 

So.... I don't have an official plan but I secured parts for Plan-B today. This was removed from a set-up similar to what @Just call me Sean attached in post #29.

Re: Update: '99 OBS CC SWB Brake Issue
 

Is that like what's on a 91 model? So, at most, you may possibly need an adapter for the rear tube?

Re: Update: '99 OBS CC SWB Brake Issue
 

It's like what @Just call me Sean posted in #29. I pulled the parts I posted from a '92.

My '99 has the big Kelsey-Hayes ABS set-up. But if you remove all of the KH stuff until the master cylinder, the earlier stuff can be integrated by simply splicing a 'T' in for the fronts & connecting to a diff location for the rear line vs. where mine is.

I got as much as I could to have the xtra fittings. Will prob have to make some new lines so things can be spliced where it will be easiest under the hood.

Re: Update: '99 OBS CC SWB Brake Issue
 

I tried to get a decent picture of my 99 so everyone can see what you're dealing with.

Re: Update: '99 OBS CC SWB Brake Issue
 

Bingo!

You were successful w/your attempt so TY for sharing the image. I took pics of mine as well but it was cold, dark, & raining outside when I did so the JY parts images were decent but the under-hood shots were less than usable.

Re: Update: '99 OBS CC SWB Brake Issue
 

Old thread, but how did this turn out Scoti? I have a 93 that I just did a L86/8L90 conversion on and I would like to remove the RWALS. Can I unplug just the module or do I have to delete the solenoids? The current master cylinder is leaking at the seals between the reservoir and the base. Can these be replaced or do I need to buy a whole new setup? Thanks for the help.

Rob

Re: Update: '99 OBS CC SWB Brake Issue
 

I got the earlier model lines & that's where it ended. I kept digging for info but was not gaining any real insight.

On NYE, I went over to my buddy's place to see the LS swap updates on my old '90 & to help w/some exhaust routing solutions. Conveniently, he still had the core support out which made it easy to again see/visualize the line routing up front (under the motor + where it connects each side @ the flex lines) as well as the placement of the factory unions for a '90.

This thing is scary when braking on irregular surfaces (railroad track crossings & ginormous asphalt road patches) when anything beyond an easy/soft pedal effort braking is used.

We discussed my lingering issue & about the latest 'upgrade' guys are doing for the OBS brake systems (GMT800 series & later master cylinder swaps). So that's going to be my plan moving forward. I'll replace the original OBS master cylinder w/a fresh GMT800 (or newer) unit, plumb the lines to a bias adjustable prop valve, make new connecting lines up front, & dial in rear bias once everything is in place & purged/bled. We'll simply delete the ABS alarm in the gauges as a start.