Master Cylinder Rebuild - DIY (1 Viewer)

[Roosevelt T]

Without me going back and reading your post. Why do you think fluid is leaking if you've not found a wet spot.

Two things to keep in mind:

1. Look for leaks with key on and someone pressing brakes pedal down hard, or just after hard braking drive.
2. Too check level in reservoir; turn IG (key) off, pump pedal 40 times. (Just opening hood and looking level will vary each time)

I'm going through brake fluid over time and having to refill. After replacing everything in March/April I figured everything was good, and the level seemed steady. In August or so it was low (light came on) so I filled it up (using the procedure you mentioned). Earlier this month, it was low on fluid again and the light came on.

 

[2001LC]

Sounds like a leak. If so the booster pump will run longer than 40 seconds during test. Have you time it?

Procedure: IG OFF, pump pedal 40 times. Now turn IG ON timing how longer booster pump runs. Spec is 30 to 40 seconds.

I regularly will find a bleeder weeping just a drop after work on them. Ever time I know to look, because I fail this test hitting ~45 seconds before pump motor stops.

 

[ClassyJalopy]

This is a great thread - I have learned so much here.
Here's what I am dealing with 242k mile 98 LX470:

I have owned my truck for about 6 months now and I have always had the '2nd pump' brake issue. I finally took it into a reputable indy shop and they diagnosed it as a failing accumulator. They suggest replacing the part number 47050-60010: Brake Booster Assy, W/Master Cylinder and everything buttoned up, it would cost $2800 or so

I have checked the following so far to see if I can diagnose it myself:
1) Turned the key off and pumped pedal 40+ times. Turn the key on and pump runs (very quietly) for about 40 seconds - SO PUMP IS FINE
2) Looked around the assembly and pedals area (inside) no leaks - SO NOT SURE MC EVEN NEEDS REBUILDING?
3) Brake fluid is kinda dirty

I suggested to the shop to rebuild the MC (04493-60330: Cylinder Kit, Brake Master - $56) and see if that improves and their mechanic told me that in his experience the original MC (@242K miles) is too old to rebuild (chances of it being enlarged inside or gouged are too high)

Here are the best prices I could find on the parts, but I am afraid I might have to bite the bullet and replace the whole assembly:
04493-60330: Cylinder Kit, Brake Master - $56
47070-60010: Pump Assy, Brake Booster W/Accumulator - $810
47025-60010: Cylinder Sub-Assy, Brake Master - $1320
47050-60010: Brake Booster Assy, W/Master Cylinder - $2350

I am just not very thrilled about dropping $3000 on a truck that probably worth only $7000 or so

 

[Qtonic]

Has anyone with a double pump symptom also experienced their booster pump running too frequently? I'm about to do this rebuild and am wondering if those things are related. It comes on briefly every 5-10 times I apply brakes.

 

[ClassyJalopy]

I am now convinced that every one dealing with double pump issue should try adjusting the clavicle length where it connects to the brake pedal. I had the double pump issue and even though my pump and booster were working like a champ at 240k miles, I replaced the pump and booster assembly (47070-60010: Pump Assy, Brake Booster W/Accumulator) and rebuilt my master cylinder (04493-60330: Cylinder Kit, Brake Master) and still had the flipping double pump issue

After paying to the local Lexus stealership to bleed my brakes I still have that issue , Finally I ended up tweaking the length by may be 1/3 of a turn and voila! The difference was instant and very gratifying
Now my 3 ton truck's brake response puts our much newer and lighter Sienna to shame. And gives my 530xi a run for its money

Moral of the story: adjust your clavicle length before your spend on anything else.

Oh by the way my still working brake booster and pump assembly will be posted for sale soon.

 

[Qtonic]

I tried the push rod adjustment. It really doesn't take much to notice a big difference. Unfortunately I found that I was dragging brakes, and when I loosened it even enough to minimize the drag to only lightly perceptible, then the firm brake pedal was largely gone. It was better, but like I said, I know I need to back off it even more. Plus, my booster pump is still running too much, so I want to try all my options before going there. So on to MC rebuild...

 

[PabloCruise]

Assembly is reverse order.

I bled the brakes in this order.
With key off, Right front, then Left Front. This is to get fluid into MC.
With key on, Right rear, then Left rear.
With key on Right front, then Left front.
Don't be shy about bleeding, long run to rear.

Two options at this point.
1. Carefully drive it to dealer for full system bleed.
2. Do some braking that activates ABS, gravel road, etc, then bleed again, rears then fronts.

I did option 2 and it seemed to be working fine, but then chickened out and did option 1.

You can use TechStream to do this as well, yes?

 

[uHu]

Has anyone with a double pump symptom also experienced their booster pump running too frequently? I'm about to do this rebuild and am wondering if those things are related. It comes on briefly every 5-10 times I apply brakes.

Running after 5 times is not too often. It will start after braking 1 or 2 times if you press hard enough, and I believe that is normal. The booster has to replenish the used brake fluid/pressure in the accumulator right away.

 

[hickuptruck]

So mine I just had a rebuilt one off eBay. It turns on every 2-3 pedals down and is audible in the cabin. Checked tis and no codes. Seems good right and not to worry ? It's the 2-3 pedal strokes where it turns on again and audible noise that worries me.

 

[Qtonic]

My 07 LX, which is my only other point of reference, does not cycle the pump so often. I understand that the parts are a bit different and probably improved, but this often seems unusual based on what I'm used to. Maybe others can continue to chime in and we can get a baseline expectation. The fact that my pump is more audible doesn't help with my expectations. I will be sure to listen more closely when I drive the newer LX.

 

[Rizon25]

So I just replaced the master cylinder in hopes of solving the soft pedal on first pump/second pump firmer brake issue. I have driven the car 600 miles so far and have not experienced the same issue. Brakes feel great. However, I’m getting these codes on Techstream: Abs malfunction and accumulator pump low pressure code. I’ve done the 40 pump and accumulator pump timing which was about 33 seconds. Does anyone think I need a new assembly? No dash codes show up on the car display, only in tech stream. Thanks for the help guys.

 

[Roosevelt T]

Sounds like a leak. If so the booster pump will run longer than 40 seconds during test. Have you time it?

Procedure: IG OFF, pump pedal 40 times. Now turn IG ON timing how longer booster pump runs. Spec is 30 to 40 seconds.

I regularly will find a bleeder weeping just a drop after work on them. Ever time I know to look, because I fail this test hitting ~45 seconds before pump motor stops.

Just to bump this... It runs 35 seconds, every time. I can't figure out why it seems to lose fluid over time, I checked just about everything. I'm sure at some point I'll bump this thread again haha... But at this point I have no conclusions.

Thanks again for your help.

 

[abuck99]

Did you clear the DTC’s in techstream and how quickly do they reappear? Might try some further bleeding using techstream to actuate the abs unit.

 

[Rizon25]

Did you clear the DTC’s in techstream and how quickly do they reappear? Might try some further bleeding using techstream to actuate the abs unit.

Haven’t cleared the dtc. I thought it automatically resets every time I log in. I’ll try that out! Thank you.

 

[abuck99]

Haven’t cleared the dtc. I thought it automatically resets every time I log in. I’ll try that out! Thank you.

I think they remain until you manually clear them through techstream. If you can pull the freeze frame data you can review the date time and conditions that triggered the DTC’s and compare against any subsequent ones that come up.

 

[2001LC]

Just to bump this... It runs 35 seconds, every time. I can't figure out why it seems to lose fluid over time, I checked just about everything. I'm sure at some point I'll bump this thread again haha... But at this point I have no conclusions.

Thanks again for your help.

Repeatedly adding fluid, using correct topping procedure, indicates a leak.
Passing the booster timing test (35 sec) indicates no leak in pressurized components.

So I'm thinking leak could be at reservoir or primary camber of master cylinder.

Reservoir leak would show itself with fluid on bottom halve of master assembly. Feel under it on bottom of master. Do this after fluid topped and shortly after actively activating braking (pressing hard on brake peddle with key on). If wet at all you've a leak, which is likely at reservoir. Possibly the seal(s) in the bottom of reservoir.

Leak in primary camber of master cylinder "may" show in foot well. Look where rod from peddle goes into brake master for wetness (oil). This area I'm really kinda of uncertain. I'm thinking only one camber get pressurized by booster, until peddle is depressed. This back or primary camber may be separately sealed until peddle depressed.

 

[Roosevelt T]

Repeatedly adding fluid, using correct topping procedure, indicates a leak.
Passing the booster timing test (35 sec) indicates no leak in pressurized components.

So I'm thinking leak could be at reservoir or primary camber of master cylinder.

Reservoir leak would show itself with fluid on bottom halve of master assembly. Feel under it on bottom of master. Do this after fluid topped and shortly after actively activating braking (pressing hard on brake peddle with key on). If wet at all you've a leak, which is likely at reservoir. Possibly the seal(s) in the bottom of reservoir.

If this is your opinion, than I am going to say with 99.9% certainty that this is the issue. I have previously noticed a very small amount of fluid under the master assembly, and that's why I pulled it again. I couldn't figure out how to diagnose where the leak was from or what seal to replace... admittedly I got sidetracked and didnt pull the assembly apart or anything. At this point I want to drive the truck again, but I am going to have to replace whatever seals are in there at some point in the future.

Thank you again for your help. Sincerely... your experience is awesome to have around here.

 

[2001LC]

Yes, you have and issue without a doubt. Series 100 do not use any fluids. Especially not brake fluid. Note: new brake pads as they wear, the level will drop a little bit as caliper pistons extend further. But not much, and certainly not below low line.

As stated above, based on you finding fluid on bottom of master without pressure loss. Assuming you are topping correctly (not over filling). My guess is reservoir leak. Most likely the grommets at bottom of reservoir are not seated or are damaged/bad

Leaks of coolant, engine oil, gear lube, ATF can be hazardous to it's component(s) if level gets to low.

Brake fluid leak can be hazardous to life.

 

[Rizon25]

Did you clear the DTC’s in techstream and how quickly do they reappear? Might try some further bleeding using techstream to actuate the abs unit.

Update: Thank you @abuck99 ! I appreciate your help. I cleared the DTC's in techstream and prior I used techstream to bleed the brakes about 2 times on each brake line. Haven't had the trouble codes come back since and the brakes work great, no soft pedal issues any longer. I think the key is to change out the master cylinder piston asap once you get the soft pedal issue to prevent overworking the accumulator motor and hence causing it to wear down faster. Am I thinking that correctly?

 

[YardPig]

Can we make a confirmed list of items for a full piston/seal kit, then let's request a sticky. @2001LC would you be willing to circle?
This is strictly for piston/seal rebuild, but including problem area's like new screws for the motor electrical connectors, common disintegrated boots, etc.