strange master cylinder problem ...

WhiteThunder

WhiteThunder

Registered User
'90 automatic SC. Master cylinder pump quit. Purchased a good working pump. Pulled the master cylinder, switched the motor and put it back in. Now the motor runs and runs and runs, but there's nothing at the rear bleeders - no air and no brake fluid - and I had them both open at the same time. (Did the conventional bleeding on the front calipers - got plenty of air out.)

Finally disconnected the rear brake line from the master cylinder. Turned the key on. The MC motor runs fine, but nothing is coming out of the master cylinder to that line.

Started the car and the front brakes grab fine. Doesn't have the rock hard pedal as when the accumulator goes bad. But I'm not going to drive it like that.

The world's largest air bubble in the master cylinder? Master cylinder is shot?

Anyone else have this happen?

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
Had a thought ...

When I searched this forum yesterday I read about a member who found out his master cylinder motor was running in reverse.

When I got the motor, I ran it over to a local auto electrical shop where it was tested. It was running fine and it's humming along in the car.

Is it possible that when the guy at the shop tested the motor he somehow ended up making it run in reverse? And if it is, how can it be changed to run correctly? (According to the Ford shop manual, there's two positive and two negative posts on the plug for the master cylinder motor.)

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
I ran across this same issue when I swapped out the pump motor on my 92.....

Pump would not pump fluid, but when directly wired to the battery, it would push fluid through the lines....

FYI: the pump motor should spin CW when viewed from the pump end of the motor....

Check the wiring on the pump motor and see if the same wires are in the same position on the main wiring harness (grey matches up to grey and grey / red matches up to grey / red)....

If not, you can disassemble the connector on the main harness and install the wires in their correct orientation.....
 
WhiteThunder said:
When I searched this forum yesterday I read about a member who found out his master cylinder motor was running in reverse.

When I got the motor, I ran it over to a local auto electrical shop where it was tested. It was running fine and it's humming along in the car.

Is it possible that when the guy at the shop tested the motor he somehow ended up making it run in reverse? And if it is, how can it be changed to run correctly? (According to the Ford shop manual, there's two positive and two negative posts on the plug for the master cylinder motor.)

Eddie
'90 5-speed SC modified
'90 automatic SC stock
Click to expand...

The only way to reverse it would be to switch the position of the wires. But as the-big-e said, it appears that some years had the wire positions reversed at the factory. So I would try wiring it directly and in both configurations.

Just to be clear - the motor is from the donor assembly and the pump is original to your car? Or what is new to your car?
 
It's a used master cylinder ...

S_Mazza said:
The only way to reverse it would be to switch the position of the wires. But as the-big-e said, it appears that some years had the wire positions reversed at the factory. So I would try wiring it directly and in both configurations.

Just to be clear - the motor is from the donor assembly and the pump is original to your car? Or what is new to your car?
Click to expand...

The pump is not original to the car. The master cylinder in the car was purchased (used) from a SCCOA member about a year ago. I took the new pressure switch, installed by the previous owner, from the original master cylinder and put it on the used one installed in the car.

Last night I jumped the master cylinder motor from the battery to one set of positive and negative pins going to the motor. (The other positive and negative set are from the relay.) The motor sounds like it's spinning like a top. I disconnected the brake line for the rear brakes from the master cylinder and ran the pump - nothing. No fluid coming out.

I did take the master cylinder out the other day to double check that the slotted tab with two ears between the motor shaft and pump was in the correct place. It is. The motor will not bolt up correctly if the slotted tab is not positioned correctly. (The motor will bolt up to the pump if one forgets to install the slotted tab.)

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
Hmm, interesting.

So, if you jump the pump motor to run and then press on the brake pedal - do you get any fluid at the rear port then?

(The MC does not pressurize the fluid to the rear brakes conventionally via a piston. Rather, all the pressure for the rear brakes is generated by the pump motor and fed from the accumulator. However, pressing on the brake pedal opens a control valve that allows the pressurized fluid to flow through the MC and to the rear brakes. If the brake pedal is not pressed, the pressurized fluid will be stopped by the control valve and will not travel to the rear brakes. Assuming there is any pressurized fluid. ;) )

A way to isolate the problem to the pump assembly is to remove the accumulator and then jumper the motor. If no fluid is forced out of the accumulator's hole, then there is a problem between the reservoir and the accumulator. You could also remove one end of the hard line between the pump and the MC, as they are fed from the same cavity.

There could be a blockage in the feed line to the pump motor.
 
Still checking ...

I have the car at a friend's shop - someone who has experience working with the Teves system. He's checking out the various circuits for the master cylinder to determine what's going on. I'll let everyone know the outcome.

I did drive the car to the shop. It's only one mile away. Disconnected the connection to the master cylinder motor. Drove slow and used both feet on the pedal to stop the car - the front brakes are working.

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
"pump don't work ... "

The shop put a 3,000 lb. pressure gauge between the pump and the accumulator. Zero pressure from the pump when the master cylinder motor is running. We ran the master cylinder motor in reverse just to see if that was the problem. Still zero pressure. Looks like the pump isn't doing it's job.

I have a used working master cylinder with pump on the way. Will update after we install that puppy.

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
It's working now ...

The pump on the master cylinder in the car was bad.

Purchased a used working master cylinder from an SCCOA member. My mechanic was able to take the pump off the "new" used unit and put it on the master cylinder that's in the car, along with the working motor, without removing the master cylinder. Turned the key on and got pressure right away.

Put the car on the lift. Pulled the wheels to bleed the rears and was good to go.

Eddie
'90 5-speed SC modified
'90 automatic SC stock
 
I think the pump could be rebuilt, though it's far from bolt-on (as I am sure you know).

Best pics I know of:
http://thelincolnmarkviiclub.org/phpBB3/viewtopic.php?f=12&t=5723&start=25

I suppose that it could be done, if the impeller drive coupling could be pulled off without damage (haven't tried). And if the pump cover plate (with port) can be removed and saved, or a similar substitute can be easily supplied and staked into place as the original was.
 
KMT said:
Aren't some Jaguar pumps the same?

http://www.ebay.com/itm/1988-1994-Jaguar-XJ6-VDP-XJ12-ABS-Anti-Lock-Brake-Pump-Motor-/221306500255
Click to expand...

Adaptable, anyway. Different pump motor plug.

http://www.ebay.com/itm/93-94-JAGUA...:Jaguar|Model:XJ6&hash=item27d6065ce3&vxp=mtr

The GM Reatta pump is adaptable, and was available new last I checked. It even comes with a new pressure switch, at a great price! But it also requires wiring adaptations for the motor and the pressure switch, and one of the pump hangers is in a different spot. I tried to find a wiring adapter for the pressure switch, and I think I found the right pigtail ... and it costs like $40. So the price starts to get less attractive once you factor in scrounging the wiring parts and soldering, or replacing the pressure switch with the Thunderbird one. (Thought I suppose you could resell the Buick switch to a Reatta owner ... if you can find one! ;) )

http://www.amazon.com/gp/product/B000C9KNGA/ref=oh_details_o06_s00_i00?ie=UTF8&psc=1

http://www.ebay.com/itm/1989-BUICK-...fits=Model:Reatta&hash=item3cd45978e8&vxp=mtr
 
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Yes, I suspect the connector is different.

And as Big E has noted, some Saabs use a similar system, so it looks like we have three other makes to at least source adaptable used parts from.

You'd think with all those applications someone would be selling reman'd pumps - maybe these guys [ http://www.bba-reman.com/catalogue/index.aspx ] - they list several Fords, but no 'birds. I'll send them an email and see what they say.
 
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