Important: ABS Accumulator Notes, replies welcome

90SCinKC

Registered User
I am in the process of replacing my ABS accumulator with the entire pump assembly removed from the 90SC. I have seen posts that mention that Priorreman.com has consolidated both the long and short nippled accumulators down to only offering the short accumulator. I see a serious problem with this. In my case, i have the long nipple version, and here is where the problem is: If you look in the bottom of the hole in the pump body where the accumulator threads into, you will notice an O-ring at the very bottom of the threads in addition to the one on the accumulator itself. The O-ring in the bottom of the pump body lays around a conical seating surface that is designed for the accumulator, when installed, to bottom out onto the bottom O-ring and the conical Seating surface in the pump body. If you put a short nippled accumulator into the place of a long nippled accumulator, you will have the O-ring on the accumulator sealing to the pump body, but the accumulator will have NO contact to the second O-ring or the conical seating surface at the bottom of the threads in the pump body. I know people are saying that using a short nippled accumulator in place of the long nippled one is working, and maybe so, but it is not seating like it is supposed to. If you have any thoughts on this, please feel free to post. Good Day to all.
 
I'd like to know too since I replaced one earlier with a prior unit. My original had the long nipple too. I can say that it doesn't leak and it hasn't blown up yet. I think my pump is still coming on after 2-3 pumps still.

A side note to testing accumulator too; I changed mine because pump came on after 1-2 pumps, but I was also having other brake problems. The old accumulator was not logged with brake fluid and probably okay still. The prior unit acted the same way after install. I ended up replacing the whole mastercylinder/pump accumulator with one from a junkyard because my seals were bad in the mastercylinder or something. I think that and the air that kept getting in the system had something to do with the pump cycling on after so few pumps.
After install and bleed of new/used unit found accumulator bad that was on it (1 pump motor starts). Different than last unit I removed though, it would cycle the pump for a very short time just like a water logged well tank due to lack of compressable area in acc. I pulled that acc. and it was full of brake fluid trapped in behind diaphram, you could hear it swashing around when shook. I put the prior unit on this brake system and it cycles for a lot longer time like it should.
So anyway, it might be a good idea to pull your accumulator if you suspect it as bad. See if it is actually logged with fluid first. It may be okay but that was my situation.
 
Interesting point you made there

Another observation I have noticed that may be affecting your situation is that on the accumulators, you will notice a hole in the conical seat of the accumulator in the center of the bottom, but there is also another hole machined into the side of the bottom of the threads on the acc. also. If a short nippled acc. is used in place of the long nippled acc. and those conical seats of the pump body and the acc. don't touch each other, than there is no isolation between the two holes of the accumulator. Therefore, what ever function the 2 holes have, they appear to be isolated by factory design due to the lower O-ring and the conical seating surface. If fluid or pressure is not isolated according to the factory design, it could well be your problem. It just doesn't seem right to use a short nippled acc. in a long nippled version, it definitely alters the fluid flow design. I am tempted to cut my old acc. open to see how much of the total capacity of it is on both sides of the diaphragm, for example, is it 75% volume behind the diaphragm, and 25% brake fluid capacity.... Also, once cut open i could investiagate and try to figure out what the hole machined into the side of the threads near the bottom of the accumulator actually do. I feel this is a very important point, and I hope the two of us can start a serious discussion of this matter and bring other people in on it. I will be watching the post closely... Later...
 
I think those that are concerned should contact Prior directly. I'm sure they would be more than willing to talk with you. And it could be that all that is necessary is that you should remove the deeper o-ring to prevent it from just floating around in there.
 
ummm wont cutting it open blow it up, or is there no pressure behind the diaphragm when removed(some sort of gas?)
 
I wouldn't cut a new one open, but an old one wouldn't be bad. It's nitrogen gas, and it's pressure is limited in an older unit. And it's highest pressure is when the diaphram is compressed.
 
contacting Prior is probably the best route

I will call Prior Friday and see what the tech guys say. True you can remove the lower O-ring so it's not just sitting in there, but there is still the concern of the conical seals of the accumulator and the pump housing not seating when using a short nippled accumulator in a long nippled pump housing. I will get technical with them and see what they say and post it here.

As far as cutting the accumulator open, DON'T unless you are 110% sure it has a colapsed diaphragm, or yes, you could hurt yourself if you cut into the back side of a charged diaphragm. And once again, as posted soooo many times, NEVER remove the accumulator until you have the key out of the ignition, and you pump the pedal a minumum of 20 times.
 
This is interesting.
I have a '90 SC and also ordered a new accumulator from Prior last year because I was only getting 2 or three pumps before it cycled. I installed the new one, and I am still only getting 2 or three pumps before the pump cycles.
Up til this post, I was wondering if perhaps I had gotten a defective one.
 
I also noticed my pedal was stiffer (I replaced mine for fun:D) and there was littlle warning before the ABS kicked in, instead of 2 pumps I get 3-4 now:confused: . I went from one short style to another, I think Im kind of used to the pedal feel now
 
I never looked in the hole on mine when I changed accumulators, I hope the o-ring isn't floating around in the system now I think I will put my old accumulator with the long nipple that seemed fine on in place of the new prior unit to see if they act similar. Right now the pump comes on during the 3rd pump.
I noticed the other hole in the side of the nipple too and questioned it, others have seemed to have no problems. Some said that the # of pumps will increase with time before pump comes on after installing a new unit.
 
PICTURES NOW, and I talked to Prior today.

I called Rick at Prior today and had a nice long talk with him. He said that originally when they started rebuilding the Teves ABS system back in 96, that they had the same accumulator supplier that made Ford's OEM accumulator. A couple of years ago, another company who made accumulators came to Prior and showed them one that they could make (im assuming cheaper than the Ford OEM!), and that one size fit all. Rick then said they tested it, and that the unit worked just fine. What he couldn't tell me was how was it tested, or what it was tested in, for example, was it really tested in both a long nippled hole and a short nippled hole? I then went on to ask him about the number of pumps of the pedal a good, new system should give before the motor clicks on (cycles), he said ALL ABS systems consisting of a pump and accumulator averages 2 pumps, which is strange, My red SC I bought new in 1990, and was always noticing the pump when it would cycle because it was my first car with ABS, and i wasn't used to hearing it. It seemed like the pump did NOT come on every 2 pumps of the pedal, but i could be wrong, engine noise and supercharger wind noise i guess could mask it, but anyways, Rick seemed sure of his answer nonetheless. Rick went on to say that the pressure switch on our ABS pump assembly shuts the pump off at 2,500lbs pressure, and turns the pump back on at 2,2000lbs pressure. He could not tell me what the holes in the threads of the accumulator do, he had NO answer about that... ??? Here are some nice detailed close up pics showing you guys the holes in question, when looking at these, remember that the hole in the very end of the nipple, is O-ringed and conical metal to metal sealed from the holes on the sides of the threads. So, to sum things up, when a short accumulator is used in an application where a long accumulator (referring to the thread lengths) came out of, the lower O-ring and conical metal to metal seal do not touch, and do not isolate these holes.... Im still not convinced by what Rick said that this is a good idea.
Let's hear some more from you guys..... Jump in, don't be shy... Later All...
 

Attachments

  • dsc00310.jpg
    dsc00310.jpg
    61.8 KB · Views: 362
Has anyone investigated whether one of the following manufacturers carry a compatible accumulator.
Of course there may be some subtle differences between systems so you would actually have to compare them side by side.
It would be interesting to see if there is an exact match for our SC's.

"The TEVES Mark II ABS System was equipped on many different cars of the 80’s. Included in the list is the Pontiac 6000 STE and 88-90 Riviera and Reatta. The system also appeared on some SAAB, Mercedes-Benz, Jaguar, Alfa-Romero, and Lincoln Town Cars."

Thanks to Duffy Floyd for the above info.
 
Keep in mind that when dealing with this ABS system, we are dealing with simple hydraulics. The Accumulator consits of a simple dual chamber design, where one chamber is filled with pressurized nitrogen gas, and the other fills with brake fluid.

So... the real question here is, does the valve body have some special ports that utilize those openings that a short nipple will screw up?

Well, I'll say NO. Why No? Because Accumulators are simple two chamber hydraulic pressure storage devices. No moving parts. No complex valving. Fluid goes in, and fluid goes out.

Perhaps the long nipple system was used in some applications to help direct the output of the fluid a little tighter. But in a closed hydraulic system, pressure at any point should be the same. So as long as the threads from the short nipple don't block these possible ports, the ports will still get their pressure.

I don't know if i like the idea of the o-ring laying around inside the port, possibly blocking it eventually. But otherwise I don't see a problem with it... In theory. I'd think we would need to dig into valve body for a long nipple device and see what it really looks like. But in general, it's probably fine.

Also keep in mind that the problem with most cars that require a new accumulator is not that the pump runs after 2 presses of the pedal. It's that the ABS light comes on after a couple presses of the pedal, or if you do a sudden stop. That's how you really find you need a new Accumulator because it hasn't stored sufficient pressure to operate the ABS system since the pump is unable to supply sudden spikes in fluid pressures needed by certain braking situations.

Another sign is ABS and Brake light on for extended periods when you start your car after overnight. This shows the pump is having to run for quite some time to build enough pressure.
 
i hear ya Mike

Good points that i have already thought alot about. The theory of operation is very basic as you stated. And for the most part, i agree. BUT, it is NOT in Fords nature at all to use a part that is more expensive to manufacture if they don't have to. The machining on the OEM accumulator is much more complex then what Prior sells, so I have to question still why the OEM accumulator had so many ports on the threads. If you look in the pump body where the accumulator screws in, there is a hole at the bottom of it obviously, but there is also a hole going off to the side of the threads inside the pump body. We need to understand why Ford's design attempted to isolate the ports in the pump body. Like I said, i agree with what you say about the accumulator is simply fluid in, and fluid out, but we still need to question what Ford's idea is behind the design to be safe. I would rather know and feel better, then to guess, and theorize the design. Ford is not going to do the extra work unless there was a reason....
 
What bites is that getting access to Ford engineering is a bastard. And it really wasn't their brake system, it was Teves, so they may have just used what they got.

I feel the only way to know for sure is to take a unit a part and inspect it. The only thing i can think of is concern that the port the accumulator screwed into wouldn't be able to handle the pressure itself, thus by sealing things out except at the ports, ensured the threaded part of the valve body did not experience the pressure of the fluid. Just the nipple and the ports.

With the shorter nipple, that threaded area of the valve body also experiences the fluid pressure. Again, just theories. Can't give up on that Garage Logic.
 
Well..looking at the technical info I have from both GM and VW on their version of the Teves Mark System I don't see a reason or function for a second port in the area of the Accumulator. In the valve body there is a check valve between the Hydraulic pump and the accumulator to prevent backflow and then the "out" port is connected to the rest of the system. The "in" line is actually a tee so the pump can supply pressure to the system if needed as well as to recharge the accumulator if there is no demand.

Also bad idea to saw on an accumulatore unless the diaphrapm is known to be punctured. It can have between 600 to around 1300 PSI of N2 behind it being contained by the accumulator "bottle".

Not sure why Prior indicates that 2 presses of thre brake pedal should trigger the ABS Pump to run. My experience is a fresh accumulator should get you 6 at least. I guess the definition of "press" should be explored. The longer and harder the press of the pedal the more fluid pressure drop you will get for each occurance. This is because the porting valve to the rear brakes is opened further and there would be less pressure drop across the porting valve. It should be also noted that when you are driving around the pressure in the brake lines is basically atmospheric. So the higher the pressure goes to on the brakes when you press the brake pedal the more fluid/pressure is bleed off the pressurized portion of the system. For the rear brakes that means the accumulator.
 
Duffy,

Do you have a hydraulic diagram for the TEVES II setup?
I'm sort of curious as to why the rear brakes are so different from the front other than the proportioning.

Also as far as the second set of port(s) there are the 2 cresent moon-circles and the hole in the thread side. Is it possible that these are relief ports? If you shut your car off and listen closely by the HCU, you can hear the fluid as it depressurizes. I am using the longer threaded accumulator. Tried to take pics, but the focus was no good.
 
I do have schmatic hydrulic diagrams but given I have never torn down a unit it is hard to tell how complete they are or what context they are in (detailed accurate representations of the actual routing or just simplified drawings to explain the theory of operation). I can tell you the front brake channels (both of them) employ an actual master cylinder piston while the rear brakes get ALL of their pressure via a ported valve that supplies pressurized fluid from the accumulator.

There is overpressure protection for the accumulator given if pressure get too high pressure is relived back to the reservior. I had a sticking ABS Relay and intermittently would hear this valve opening as my pump stayed running too long.
 
Back
Top