PMIII or ABS brake updates.

[jiggity76]

I know it's been beaten to death but now that I'm considering buying an STE, what do I have to worry about on the PMIII or ABS brake booster setup?  I've read some threads but just wanted to get the most up to date information on these systems since some or most STE's will have it right?  I know parts are rare.  Is doing a swap from ABS to a NON ABS system still feasible?  Should I not even consider buying a car with ABS if I do find one?  I'm nervous about this subject and just wanted to be prepared if I come across a car that has it and need some advice or whether to walk away or have the confidence in knowing they can be repaired or swapped.

[Addicted To Boost]

1990-1991 STE models could have the PMIII as an option.  It was not standard equipment on those cars.  If you happen to run across a 1990 STE Turbo, the system did come standard on those. 

If the PMIII has been maintained, they are a lot easier to deal with.  (Regular brake fluid flushes and accumulator replacements as needed.)  That said, most people neglect them and there are a few things to look for on a PMIII car. 

First off, when you turn the key on, you should hear the pump motor running to pressurize the system.  It should run immediately after turning the key on and continue running for up to 60 seconds.  If it runs longer than that, doesn't shut off, or doesn't run at all, there are bigger problems. 

Next, check how many presses of the brake pedal it takes before the pump has to run to pressurize the system again.  If the accumulator is in good shape, it should take 3 presses before the pump has to cycle again.  If the motor cycles every time the pedal is pressed, the accumulator is likely bad.

Look at the dash- are there ANTILOCK or BRAKE lights on?  The system will set codes for low accumulator charge, long pump run time, bad wheel speed sensors, etc.

Take a look at the fluid level and condition in the reservoir, also for fluid leaks on the rear pump housing of the PMIII.  They can develop cracks over time and leak here.  Also look at the rear proportioning valve near the fuel filter, these will leak sometimes as well.

I think I've pretty well covered the common bases.  More often than not, a full system flush and a new accumulator will make the PMIII work properly again.  The downside of the system is that there isn't a failsafe for it, if it does fail.  They are 100% electronic.  Others have vacuum brake-swapped their PMIII cars, but it is a very tedious and time consuming task.

[jiggity76]

Great info, thank you very much.  I came across a 1990 STE non turbo car and the brakes felt good but forgot to check to see if it had the PMIII.  My biggest concern is if I decide to swap to a vacuum system or if parts aren't available to repair the PMIII one, I don't want to be stuck with a car I can't drive.  The 1990 STE I looked at yesterday, I've decided to not purchase for major rust issues.  I have come across another STE that is most likely rust free but not running at the moment.  It's a 1993 car and most likely does have the PMIII system.  It has the windshield washer fluid reservoir mounted above the battery so I'm assuming it's an ABS PMIII car correct?

[55trucker]

91 was the last year for the *dreaded* PMIII system. If the vehicle you were looking at is a 93 & it has ABS that will be the Delco-Moraine ABS VI.

 

 

*excuse my misprint*..ABS VI not IV

[jiggity76]

91 was the last year for the *dreaded* PMIII system. If the vehicle you were looking at is a 93 & it has ABS that will be the Delco-Moraine ABS IV.

Alright, thank you.  That's a big relief.  Is that also an electric system or vacuum?  How is the reliability of this system?

[55trucker]

ABS VI is electronic over hydraulic w/ vacuum assist, it's an improvement over what PMIII was, but VI has drawbacks as well, most common is the need for a scan tool to service the master cylinders piston solenoids, they have to be *cycled* with the scanner before any service work can be done to the modulator assembly.

 

See the attached PDF link file on servicing that system (you can dl it or just view it)

 

PDF SERVICING DELCO ABS VI - MOTOR | Automotive Data

[jiggity76]

Wow,  both of you guys are the right people to talk to about this!  I feel more confident now in pursuing this new STE lead.  I will post what happens, planning on calling the seller today. 

 

So these units are serviceable and maybe even replaceable and hopefully at a reasonable cost and parts availability.

[jman093]

Wow,  both of you guys are the right people to talk to about this!  I feel more confident now in pursuing this new STE lead.  I will post what happens, planning on calling the seller today. 

 

So these units are serviceable and maybe even replaceable and hopefully at a reasonable cost and parts availability.

 

Yeah, Delco VI is god awful at being an ABS system, but is mostly reliable, and when it isn't, there's a bajillion of them in salvage yards. PM3.....good luck. Failure rate is 100%. I have 3 and none currently work. One cracked its housing. When that happens, they blow fluid everywhere when the pump runs. Also very common on PM3s. All 3 have a bad accumulator, and at least one has a bad relay. When it's warm out, it usually works. Relays were also problematic on them. None of these parts mentioned are available.

 

As mentioned, swapping is doable, but a huge job. That being said, braking with the system inoperative is not terrible. Brake pedal is hard, but the car stops. If you've ever driven an old muscle car with manual drums, its pretty close to that. I essentially haven't owned a car with properly working brakes for 3 years now.

[Imp558]

Wouldn't it make more sense to just convert it to the early non-ABS master cylinder? I'm assuming this won't be winter driven by a 16yo girl so why bother retrofitting a different ABS?

[55trucker]

Where the PMIII system is concerned that process would in my mind make the most sense *if one wanted to keep the car*,

 

but the changeover is not a 5min job. A non ABS master is required along with the booster, the firewall plate has to be replaced with a non ABS plate, (unless one has fabricating/welding skills to alter the existing plate), the rear brake lines have to be replaced as the PMIII ABS system is a three brake line design (not 4), the PMIII splitter (with the proporting valve) is at the rear of the car. One will need the plastic clips from a donor car to support the new brake lines.

 

Doable as mentioned but it is a large task.  

[jiggity76]

After reading your guy's post, I'm really glad it doesn't have the PMIII!  That sounds like a nightmare.  I appreciate the advice guys.

[White93z34]

I'm of the opinion that ANY PMIII working or not is dangerous and should be binned in favor of anything else. 

 

It was a bad idea when new and now 30 years later, its aged even worse and all the common failure part are NLA

[jiggity76]

It might be a good idea for me to start collecting all the components now to swap it over later then.