newbie, need electric brake booster advice, I think I'm 1/2-way there...

[fury fan]

Please read thru all this and give me some advice! I'm a decent mechanic but need a little help. I wish I had a FSM in front of me, that will have to go on the must-get list.

I'm new here, had an LSC about 2 years ago, sold it (at the suggestion of others) and immediately regretted it. Bought a replacement Mark 2 months ago. It's been a great car up until now; I've been doing a few upgrades but now unfortunately have to do my first un-anticipated repair.

Car is an 88 LSC with 'electroboost'. Drove it the other day and lost the brake assist. Stopped at the parts store and ordered another booster but it won't be in for a week. Ironically, the brakes worked again on the way home but then quit again.

I've been reading some posts on here trying to learn more about this system. On a vacuum booster I'd be pretty confident the booster was at fault, but based on what I'm reading I need to verify further, this system has a few more components.

The red brake light in the dash did not have a bulbsocket in it. I swapped the seat belt light in and the red light is now on. Mastercyl fluid level is OK and park brake pedal is fully up.

I have not seen the yellow overhead light come on and based on the other bulb being missing I'm suspicious that it's been removed. In addition, when I bought the car it came with an 'extra' overhead console - the one in the car has a sunroof switch but I have no sunroof. Methinks somebody swapped the console and/or removed the bulbs and stuck me with a known intermittent brake problem!!!

How do I remove the 'pod' in that overhead console? So far it is resisting my gentle prying with a puttyknife. :( Based on what I've read, I don't think I can fully diagnose my problem unless I know if the yellow light is coming on.

I do NOT hear any electric motor at ignition-on. I hear a few relays click in succession but that's it. The air susp has been converted to coilsprings and that motor isn't there to mask anything.

I found the 4-pin connector for the brake motor. On the car side of the harness I have +12v on 2 pins (when the ignition is on), the other 2 pins have continuity to ground. I checked continuity back to the ABS relay near the mast cyl and wiring is good (which makes sense).

Questions:
1. How to remove teh overhead console display? Need to see if that yellow bulb might be trying to tell me some additional info.
2. If I am seeing ign-switched 12v to the motor, but I have a hard brake pedal, can I assume that teh 'booster' assembly is bad? If the pressure switch wasn't operating, the relay wouldn't be triggered, then no power at the 4-pin connector, right?
3. If the accumulator was bad I would still have brakes but the elec motor would run at every braking event, right?

Here's the part I ordered, it is listed to fit 82-89 Cont and 84-89 Mark. The guy did ask if I had ABS (and I told him yes).
http://www.partsamerica.com/productdetail.aspx?MfrCode=A1C&MfrPartNumber=529391

Based on the pic there are some physical appearance differences and it looks like it does not include an accumulator or a pressure switch. Is this a hydroboost valve for a non-ABS car?

Here's what looks like what is on my car:
http://www.partsamerica.com/ProductDetail.aspx?MfrCode=RAY&MfrPartNumber=ABS540054

The more I read and the more I type I am guessing I am looking at a $900+ repair?

I guess it could be worse, at least the car is movable around the driveway...

Help!

[marked4life]

hi, welcome to the board.. if i remember correctly you need to remove the lamp lenses/trim part and there are screws behind them to remove the console. also there is a screw on each corner of the unit underneath the inside door trim...i remember it also being stuck on with that black shit in the front closest to the windsheild...

the brakes are useally the pressure switch...there is a real good thread about converting them to regular brakes with an SVO master and an 87 - 93 booster and some plumbing..use the search for " brake conversion"

hope i was able to help

attached is a diagram of converting the brakes

[fury fan]

I think I'm gonna like this board, got a quick reply already! If anyone can help with my other specific questions I'd sure appreciate it!

marked4life:
Thanks for the thoughts on converting it to 'regular' brakes! I had read some posts on that already though and decided against it for Mopar-related reasons. In spite of the cost of repairing the original stuff, converting to the SVO stuff is beyond the scope of what I want to do with this car right now. I have a 68 Fury (that's where my name came from) sitting in the garage like a beached whale 1/2-way thru a disc brake conversion (and 4 other old Mopars crying for attention, too). I bought this Linc for an enjoyable daily driver and I can't afford to have another car sitting for brake modifications - I'll have to bite the bullet and keep the ABS. It will sting putting $900 into a car I paid $1250 for, though.:(

This whole situation sucks for another reason: I have new O2 sensors, an X-pipe and some other goodies on-hand that I was planning to put on this week while I'm on vacation - based on my experience (with other cars and with a prior LSC) I was figuring to make 20 more HP, some more MPG -- and a much better sound.:) This brake thing ruined my 3-weeks-in-the-making plans!:mad:

I was able to peel the overhead console label back and see that there is no light in there for the ABS. I'll get the console apart, put a bulb in, and see what it says.

Again - if anyone can answer my other specific questions I'd appreciate it.:)

[LSRX101]

Welcome to LOL fury fan! Pull up a chair, grab a cold beverage, and hang out a while.

Wow! It looks like somebody pulled the bulbs to mask an ABS problem just so they could sell the car. That's just wrong!! I've known people who have done things like that and it wiped out my respect for them. I've been in situations where the thought crossed my mind and was tempting, but I could never bring myself down to that level.

Cancel that parts order! The part in the link is a Hydro-boost unit. Those were used on 84-85 (maybe later?) Marks without ABS. It used pressure from the power steering system for brake assist. It's a great system, I prefer it over the later ABS and vacuum assist.
To buy the entire ABS unit on your 88, you can almost add another zero to the price tag. :eek: Ouch!!
Advance\Murrays\Autozone don't seem to list it anymore. It's funny, I know I was looking at those ABS parts on one of their sites just a week or so ago. Rock auto is showing the HCU and the pump/motor asy. separately for about $2250 for both. I can't tell if the pump actually comes with the HCU assembly from the listing.

The "good" news is that you probably don't need the HCU, for $1380. The "bad" news is that IF the pump is actually bad, it's $865! Now you know why the PO removed the bulbs.

Obviously, you will need to do some testing before you start replacing parts. There is a great article in the Tech section on diag and testing of the ABS system. The usual culprits are the pressure switch, pump relay and accumulator, but if the switch or the relay doesn't fail open and the accumulator is bad, it can wear out the motor pretty quickly. It does happen, but one of the "usual culprits" normally gives up first. Get the indicators working right and go through the tech article.

In this situation, if there is actually a failure in the HCU or Pump, there is no shame in used parts. I wouldn't normally use "pre-loved" parts in a brake system, but for this system I would make an exception. ;)


As for converting to vacuum boost, weeelll, we're talking brakes here. It's the only thing between me and that Tractor-Trailer.
I'm not an engineer, so do I really want to redesign my brake system? I was a Ford Master Tech before I left the business, I'm pretty confident that I know what I'm doing on a motor vehicle. I've also been known to overlook a small, but important detail when modifying a system on a vehicle. It's usually just an "aww crap, I gotta redo it" situation. With brakes, I might not get a "do over".:eek:

There's a couple of guys here that are very familiar with the Teves ABS system. Wait a bit, one of them is bound to show up.
In the mean time, work on finding that Shop Manual. It gives complete testing procedures. It's also useful for every other part of our Mark VIIs.

Edit: After typing this reply I saw the second link to the ABS unit. That's the complete HCU asy with the pump for your 88. That is the listing that I came across a few days ago. I wasn't able to get to that page from the Advance Home Page tonight. I played around with model years, etc. and couldn't land there. If it comes down to that, you might want to verify availability

Edit again:
Where are my manners? Good Luck!
Let us know what you find, and ask questions if you have any.

[fury fan]

OK, got the overhead console apart, put a bulb in the ABS light and it is now on constantly (as I anticipated).

I've read the 3 ABS files in the tech tips section. However, according to what I've read, I could still have 2 problems - bad motor in the HCU and also an unrelated ABS problem (which could be as simple as a bad wheel sensor signal).

I'm off to the local junkyard tomorrow to see if they have any 7s or if there is a different year of Linc that could be suitable donor. I'm hoping to find a car that's hit in the rear or been T-boned, not sure I want to get parts from one that's hit in the front.:rolleyes:

[Bluegrass]

Welcome to the board.

The brake and suspension system are to two most difficult systems for the owner to deal with. It first takes understanding of how they work, then logic troubleshooting with a few tools. Many owners get frustrated or even sell the car due to the failures.

Your car is an example with the suspension already changed to coil spring. Brake system is an electric pump driven pressure system. No pressure no work. The red lamp is a total failure of power or pump except those times the fluid level is low or the emg lever is off normal.

The pump must run at ignition turn-on and is sensed by the pressure switch that operates a power-up relay to run the pump. At this point, the pressure switch , the relay or the ignition switch could all prevent the pump from running plus any wiring or connector issues.

Getting deeper, the yellow is a more of a pre-warning that an issue is at hand and must be addressed such as the accumulator is nearing end of life. The system fault detection is a combination of why and when these lamps light that gives the clues to what might be an issue.

First the pump must run to pressure the system and run to shut-off on high limit pressure. Next, the brake action and yellow lamp give an indication of system storage ability before the pump runs again. Get your warning lamp issues cleared first so you can see what conditions are present then proceed to find what issue is preventing the pump from operating.

The pump control circuit is a two level arrangement. The pressure switch operates a low current relay circuit that in turn closes a high current path to the pump. If voltage is not present at any point, check the source at the starter relay terminal and thru the fuse link. Be sure the pressure switch circuit is bringing up the relay then the relay is providing power to the connector at the pump motor and the connector is not open circuited from corrosion etc.

After pump is operating, then evaluate to brake operation and what the yellow lamp does, to determine what else needs attention.

[fury fan]

Thanks Bluegrass! I had seen good info from you in a bunch of other posts on this subject, I was hoping you'd visit this thread!

I ran jumper wires to the 4-pin motor connector and it did not run at all. I used only 1 positive and 1 negative wire. I understand that Ford used 4 wires to get amp capacity, but for testing purposes only 2 would be needed, right?

Next question:
Because both red and yellow lights are on, and if my motor is totally dead, I don't really know the extent of my problem, right? If I replace the $900 hydraulic control unit, I could possibly find that I still have an ABS problem and that I really needed to replace the whole $1300 ABS/HCU thing -- and the ABS section doesn't seem to be available separately.

And on the $900 HCU I haven't found any websites with a picture, so I don't know if the accumulator is included.

At that point at least I would have brakes again but being that this car will be my wintertime car also if I drop that much coin I'll wish I had the ABS. But $1300 is more than I paid for the car!!! :mad: At that point I'd have been better off to go the SVO MC / GT Stang booster route.

This is one of those situations where you can't know what the right thing to do is until after you do it!

[Bluegrass]

Testing the pump requires that the leads need to handle at least 30 amps hence the reason for 4 leads at the connector for long term reliability. 2 each.
The shorten the power circuit testing, if the power relay pulls up when the ignition switch is to run, the pressure switch contacts are closed and circuit is complete but does not prove the pressure switch will open on high limit.
Next do an ohm meter check for an open pump motor.
In rare instances the motor is good but the pump has a problem.
The rest is module control and alarm indication per the conditions the module is signaled. (the pressure switch has mutiple contacts that provide the module with alarm information.) (the rest of the circuit looks at the ABS, seperately.)
The rest of the alarm info can concern the electrical circuit conditions for the ABS involving the modulating valve assembly and the wheel speed sensors.
This is about all there is to the basic system.
Good luck.
KM3F

[fury fan]

I got lucky and scored a complete unit from an 88 T-Bird turbo coupe in a junkyard today. Its appearances are exactly the same from what I can see except it has a proportioning valve plumbed below it. Rockauto shows the same Cardone 124410 part# for both the T-Bird and my 88 Mark. Something that was quite strange, though - on the T-bird one line went from the ABS valveblock to the driver-front wheel, while the pass front line went thru the prop valve first. Strange...

Checked the motor on the JY part and got about 1.5 ohms across power and ground leads. Checked the one in my car and it shows to be open. My suspicions were correct that the motor in my car died.

For more good news:
Prior Reman has really good prices on these things, they are about 1/2 the price of everybody else and they have a 1-year warranty.
They rebuild the motor, replace all the ABS valving, install a new accumulator, and test the pressure switch and install a good used one if needed (they said the pressure switches are no longer available). It's about $700, more than I wanted to spend, but way better than $1300 of everybody else Also better than the $800 hydraulic control units that parts stores sell, those don't have any of the ABS stuff with them..

I figure converting to the SVO MC / GT booster would cost around $200, so for $500 more I have my ABS, too, and that might be truly cheap if it saves me from an accident.

Now I just have to decide whether to install the JY part, or drop the $$ to Prior and keep the JY part as a spare. I suspect this might not be the last Mark I ever own and a spare would be good to have.:)

[marked4life]

this place has alot of stuff for us,,door panels, inserts, fenders hoods abs parts , susp. prts etc even the pressure switch.. theyre pricey though..almost 600.00 for a brand new door panel...but sometimes ya just need the part..

useally someone on the board or fordvschevy will have anypart ya need, just ask

http://www.trademotion.com/partlocator/index.cfm?siteid=214270&referrerid=1500343

[fury fan]

That pressure switch is $135!!! I hope I never need one of them!

Thanks for the link, I just bookmarked it. This car will be more of a performance and MPG toy for me, so I probably won't be wanting any restoration-type parts for it. Certainly not any $600 doorpanels, anyway!:(

[fury fan]

Final result:
I got a booster setup from a JY and swapped the elec motor from it onto my existing unit. Brakes now work as normal but the ABS light is still on. I can live with that, I drive like an old man in the wintertime anyway. This particular Mark isn't worth the $$ to fix the ABS.

[joeythefixer]

While I'm not happy with it my ABS light has been on for a couple of years. Driving the L.A. freeways I have had to panic brake more than a few times and everything worked fine except no anti-lock activation. The ABS system is separate form the brake system. My 86 does not have the connection for a code reader, but I think the 88 does. might make it a bit easier to diagnose. the connection is in the trunk at the ABS brain.
a few things that i have discovered when checking the ABS:
1. check the gap between the tone ring and the wheel sensor.
2. check the wheel sensor wiring in the wheel well and the engine compartment for damage.
simple checks that might help.
good luck!

[bryang423]

i am having a similar problem with my brake boster could someone tell me where the pressure switch is and or where i could get a diagram or schmatic on the booster wiring and which is the booster relay?