Right Front Brake Dragging - Proportioning valve??

[kartracer03]

This started a few weeks ago. I first noticed the pedal being soft occasionally. I flushed the brakes and bled them. This made it worse so I figured that I flushed the crud out of the master cylinder that was making it occasionally work. I replaced the master cylinder. The brakes felt great.

After master cylinder replacement, I noticed that it took more acceleration and my mpg went down. I figured that a brake was dragging and I was correct. The right front pads were toasted white and half the thickness of the left front. I figured the caliper was frozen. I replaced both front calipers and all front brake pads. I went out for a test drive last night and still dragging.

I unbolted the master cylinder from the brake booster to see if the booster push rod was too long. The booster push rod must be ok because when I got the master cylinder away from the booster, the RF brake was still dragging.

I unbolted the RF brake line from the proportioning valve and the brake free'd up. The RF wheel spins freely like the LF wheel.

Does this mean that the proportioning valve is no good? I took the proportioning valve out of the car and flushed it thru the parts cleaner then brake cleaner spray down. I don't have pressure gauges so I cannot test the proportioning valve like the Camry service manual states.

Where can I buy a proportioning valve besides the dealership? Anybody know cost?

What else could be causing the RF brake to drag?

Thanks for the help.

[kartracer03]

I guess it might help to give vehicle information. It is 1992 Camry LE with 2.2 4cyl, auto tranny, front discs, and rear drums.

[Mike Gerber]

I'm going to take a wild guess and say the rubber brake line leading to that front brake may be collapsing internally and not allowing the brake fluid to flow back. This would seize only that brake caliper.

Mike

[fenixus]

was about to say the same thing.

easiest to check is to make the caliper stuck and remove wheel, then open the bleeder valve on that caliper, if caliper stops binding to the rotor after opening it then the brake line (rubber) is internally collapsed. you would need a new rubber hose for that caliper.

I have to check the same things on my car, though I have no drag anymore with new MC, pads are simply gently rubbing the rotors, they do not get worn out because of that though.

[tweak1029]

Remove and grease the slide pins on the caliper mounting bracket. If they're siezed you'll want to replace that bracket. If you have a mechanic do your brake work or if you do your own brake work and let the caliper dangle from the brake line that's a likely culprit. If the brake line is bad and you use a mechanic, go watch him do a brake job and see if he lets the caliper dangle.

[JohnGD]

It's always good to double check the pushrod length before MC install. But the fact the RF caliper released when you loosen the line at the proportioning valve, I'd say some debris might have gotten lodged in there and it's probably the source of the problem.

I couldn't find an aftermarket proportioning valve, and the dealer probably will charge you an arm and a leg. Maybe check with the ToyotaPartsMan here and see what deal he can offer or pull one from the junk yard.

I wouldn't clean the valve with a petroleum cleaner. Petro solvents damage rubber parts. So soak it thoroughly in alcohol before you even consider reinstalling it. I'd just replace it instead of risking getting petro solvent into the system.

Like others said rubber brake hoses could use a replacement too. After 100K miles I would. I'd also rebuild the calipers too.

Use Valvoline synthetic brake fluid or Castrol GT LMA (both are Low Moisture Activity fluids).

Originally Posted by kartracer03

After master cylinder replacement, I noticed that it took more acceleration and my mpg went down. I figured that a brake was dragging and I was correct. The right front pads were toasted white and half the thickness of the left front. I figured the caliper was frozen. I replaced both front calipers and all front brake pads. I went out for a test drive last night and still dragging.

I unbolted the master cylinder from the brake booster to see if the booster push rod was too long. The booster push rod must be ok because when I got the master cylinder away from the booster, the RF brake was still dragging.

I unbolted the RF brake line from the proportioning valve and the brake free'd up. The RF wheel spins freely like the LF wheel.

Does this mean that the proportioning valve is no good? I took the proportioning valve out of the car and flushed it thru the parts cleaner then brake cleaner spray down. I don't have pressure gauges so I cannot test the proportioning valve like the Camry service manual states.

Where can I buy a proportioning valve besides the dealership? Anybody know cost?

What else could be causing the RF brake to drag?

Thanks for the help.

[tweak1029]

Originally Posted by kartracer03

I unbolted the RF brake line from the proportioning valve and the brake free'd up. The RF wheel spins freely like the LF wheel.

I missed this part. I looked in the factory service manual and in my car and discovered that the proportioning valve only operates from pressure given to the RF brake. The LF brake pressure comes from the 3-way union which separates the front pressure line from the master cylinder into the left and right wheels. The RF pressure goes through the proportioning valve on its way to the caliper.

Got any pictures of your disassembled proportioning valve? I'm curious to see how it could be acting like a check valve on the RF brake.

[kartracer03]

I pulled the RF rubber brake hose. I flushed it in the parts cleaner and had good flow both ways. I did the same with brake cleaner and had equal flow both ways. I don't think it is collapsed.

I guess I'll be pricing a proportioning valve tomorrow. The MC & caliper is new and brake hose checks out so that only leaves the proportioning valve.

Any thoughts.

Thanks.

[fenixus]

if you submerged the rubber hose in brake parts cleaner than you can go ahead and replace it.

[kartracer03]

Thanks for all the ideas and tips on my problem.

The calipers are sliding good. When I replaced the calipers, they came with new slide bolts. I greased them well with brake grease.

Tonight I put the whole system back together with original RF brake hose and proportioning valve. I bled all four brakes and still had the problem with the right front brake dragging.

Since I knew the brake line from RF caliper to proportioning valve was free flowing, I backed up to the MC. I cracked the front top brake line on the MC and the RF caliper freed up. From my understanding of the brake system, the front top port of the MC controls the right side brakes and rear side port of the MC controls the left side brakes, correct? If this is true, maybe the remanufactured MC I installed is the root of my problem. I makes sense since the problem didn't start until I replaced the MC.

Let me know you thoughts. Thanks.

[JohnGD]

That's why double checking and maybe adjusting the booster push rod length is so important. This is done while pulling a 20" vacuum on the booster so it flattens a little. A digital caliper helps make this easier without having to buy a special tool to use with feeler gauges.

As mentioned, if you used brake cleaner on rubber parts then you really should replace them. When the brake hydraulic system is contaminated with oil or petroleum products, the rubber will swell up and fail. Alcohol is used to flush the system clean and all rubber components replaced. That's why always keep petroleum cleaners and products away from the brake hydraulic system.

[kartracer03]

That's why double checking and maybe adjusting the booster push rod length is so important. This is done while pulling a 20" vacuum on the booster so it flattens a little. A digital caliper helps make this easier without having to buy a special tool to use with feeler gauges.

I didn't measure the booster push rod length but I did remove the three bolts that hold the MC to the booster. There was no contact between the push rod and MC but the RF caliper was still dragging. I'm thinking I might have got a defective remanufactured MC.

Is it possible to damage the MC during bench bleeding? Can you go too deep on the strokes during bench bleeding and damage the MC?

Thanks for the reminders about brake cleaner and rubber parts. I'm addressing the components that I've exposed to brake cleaner.

[fenixus]

I think it's possible for a remanufactured MC to be faulty. chances that you broke it while bench bleeding are slim, and if actually that is what happened then this MC unit is garbage anyways... just my 2 cents.

I would get new OEM MC assembly at around $150 from dealer online (e.g. PM member Toyopartsman), that's what I did to avoid problems with remanuf units... more expensive, but it works right...

[tweak1029]

Originally Posted by kartracer03

Since I knew the brake line from RF caliper to proportioning valve was free flowing, I backed up to the MC. I cracked the front top brake line on the MC and the RF caliper freed up. From my understanding of the brake system, the front top port of the MC controls the right side brakes and rear side port of the MC controls the left side brakes, correct?

That line goes to the two front brakes. They should both drag if that's where the problem occurs.

[kartracer03]

Update: The car is back on the road and out of the garage.

I picked up another reman MC to try out. (I know, if I thought the first reman'd MC was the problem why did I go with another reman'd MC.)

I verified pushrod length this time. I actually had to lengthen it.

I could tell when I started bleeding the brakes that it was different. The fluid actually started to gravity bleed itself. I vacuum bled each location.

I started the car while on the jack stands (I know somebody will probably blast me for that). Previously when I did this, only the LF wheel would spin when in drive. Last night both wheels were spinning freely.

I learned not to assume that "new" parts cannot be the problem.

I still believe that the front of the MC controls right side brakes and rear of MC controls left side brakes. You can see this while bleeding. The front resevoir drains with RF caliper and vice versa.