Brake advice needed

[farnelle]

I am replacing rotors, hoses, and calipers on my 90 coupe. Don't ask why. This all started with replacing front and rear struts, front pads and changing the fluid. Once into it, decided to go all the way and not have to do it for another 10 years. Anyway the question is about gravity bleeding. I have already done the front calipers and hoses and replaced the fluid in the resevoir with clean fluid. I am getting ready to put on the rear calipers and hoses and then got to thinking about how to properly bleed the system. Read the FAQ's and the frist step seems to be pump the pedal numerous times to release the pressure. I did not do that before changing the front calipers. Did I screw up? Can I go ahead and change out the stuff on the rear without doing anything about the pressure and still get the system to gravity bleed? A mechanic told me he always lets gravity do the work and that bleeding with the pedal can create problems. I guess my question basically is if the Teves antilock system is designed in such a way that it will not gravity bleed.

Thanks for any advice you guys can provide.

[Guest wally888]

Don't think you'll get any fluid from the back calipers unless you push the pedal down! And w/o system pressure think you'll get little, probably none. (you can determine by ,key off, depress pedal 25 or more times, open rear bleed valve and observe)

Options: After rear caliper replacement, key on, bleed/flush rears using pedal(as described at reatta.net)(sequence=RR,LR-RF,LF) then re do fronts manually. Keep reservoir full!

or

Have pressure or vac flushed.

[farnelle]

Thanks Wally. Do I understand that I leave the key on during the entire bleeding operation? Also I understand, unlike the old time bleeding process, it is just one slow pump not all the way to the floor, hold, bleed and release. Is that correct. Also since I have already replaced the front calipers and hoses, there has got to be air in the system, so does pumping to depressurize with the key off do any harm at this point. One last question. I recently purchased a mighty vac tool that I used on my MG. What is your thoughts about how it will work on the Reatta? Thanks. Ed

[Barney Eaton]

The Teves system is not a conventional vacumn boosted power brake system.

The power assist comes from a hydraulic booster. The booster uses the brake fluid.... without flushing the "boost" side of the system you will put dirty fluid back into the resevoir.

First I am not sure how you removed the old fluid from the resevoir, You start by pumping the pedal until it gets hard. That tells you that you have discharged all the pressure in the accumulator and all the fluid from it has been push back into the resevoir.

I disconnect the gravity feed hose and let it drain out.... then add about 6-8 oz of clean fluid as a chaser. Reattach hose, add at least 9 oz of fluid to the resevoir, turn on the ignition....this turns on the hydraulic pump, sucking clean fluid into the booster section, filling the accumulator.

Repeat the step above......

Now you have the boost section reasonably clean.

One additional step I started taking is to remove the pressure switch (caution..this must be done when the system is discharged...hard pedal)

There is a small orfice between the pump section and the pressure switch. and it needs to be free of contamination.

With the pressure switch out (this is not the simplest thing to do without a 36 mm deep socket) examine the end of the switch and clean any junk from it.

With the pressure switch OUT... clean the cavity with an old clean rag.

Then cram the rag into the hole the switch screws into.

Wrap a second rag over the unit to catch any excess brake fluid in the event you force too much fluid out.

Attach the connector to the pressure switch (the pump will not turn on unless they are connected)

Make certain you have clean fluid in resevoir.

Turn the ignition switch on for ONE second...this blows fluid through the orfice and cleans out any contaminants.

If everything goes as planned, you do not have brake fluid all over the engine.

Remove the rags carefully and use caution not to get brake fluid on the paint.

Screw in the pressure switch and proceed with flushing the brakes.

[Guest wally888]

Key ON bleeding the rears and your assistant will just push on pedal a little, increase push as needed (no pumping of pedal!)

Key OFF, then pump pedal 25+ times to relieve pressure for fronts. Leave key OFF, is Manual Bleeding, takes a lot of pumps and time.(pedal to floor w/ bleeder open, tighten bleeder, pedal up........repeat......repeat...

Barney's suggestions are all good, more efficient.

I just sucked all the fluid from reservoir w/ a syringe before beginning and kept it full of new fluid till just before the end. Remember after you finish the fronts, key ON will pressurize the system (some fluid goes to reservoir) and reservoir level drops below fill line. At that time I would turn key off, pump pedal 25+ times then fill reservoir to fill line (little black triangle). If you kept the reservoir too full while bleeding, you may have to remove some fluid!?

[Jim]

Ed,

Barney and Wally's ideas and suggestions are excellent. The only thing I can add from experience is sort of monitor the amount of fluid coming out when you are bleeding the rears. After about a cup or less comes out stop and refill the resevoir as you can deplete the fluid quite fast when the rear bleeders are open and stand the chance of running low and maybe getting air into the system. If you get too much in the resevoir you can always siphon it out as a last step.