Brake & Clutch master cyl. woes (1 Viewer)

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Jul 27, 2006
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Location
Cloverdale, B.C.
In my '84 BJ60 I replaced the brake master cylinder a couple of weeks ago with a new part sold under the Beck Arnley brand. Post install inspection reveals that it's already leaking out the back, and down the front of the brake booster. I used a generic auto parts store brand of brake fluid, DOT 3 spec in the system. I have used this or a similar brand of fluid since I've had the truck. The clutch master cylinder (EBI carried part / non Toyota) also leaks out the back too. This wasn't leaking as quickly, but didn't stay leak free for more than 2 - 1/2 yrs. after install. It was the replacement for a new Toyota OEM clutch master cyl. that started leaking within a year of installation.

I swapped out the brake master cylinder to trouble shoot a brake fade issue that I thought could be attributed to brake master cyl. bypass. It did not solve the problem. I might end up putting the original brake master back in as it wasn't leaking at the rear.

Just wanted an opinion on what I could do to not have leaks as mentioned above. Are the non-Toyota parts garbage? Has anyone else had the same issues? Should I use DOT 5 fluid instead? Should I look for a better quality brake fluid? My thoughts were to use Toyota parts only but after the new clutch master leaked, I figured they might be just as bad.

When I push the pedal, the brakes grab OK. If I apply them hard enough (emerg. stop) the pedal seems to sink further with no increase in brake effectiveness detected. I thought I remember being able to lock the front tires on dry pavement (BFG ATs 33 x 12.5 R 15) but maybe I am being optimistic for the stock system.

I can push the pedal to the point where it stops the truck, and then continue to push the pedal further without any resistance besides the pedal return spring. I drove another 60 series once and when brakes were applied, the pedal firmed up and couldn't be moved further towards the firewall. That's what lead me to believe my original brake master was bypassing and why I replaced it. But I don't drive many other cruisers besides mine so I don't have much to compare to in terms of first hand experience.

Many thanks if you can help.
 
Are you sure your rear wheel cylinders and front calipers are not leaking at all? DOT 3 and 4 are compatible, Do not use DOT 5.
I bought an aftermarket clutch master once and it leaked in no time, always try to buy Aisin (what Toyota uses).
 
On my 42, I can stand on the brake pedal and cannot get it to go to the floor.
 
Jzilla, pretty sure the calipers/rear cyl. aren't leaking, but I'll inspect them to confirm. I was thinking the DOT 3 I'm using might be eating the rubber (or whatever material, neoprene?) seals as I notice a black contamination in the clean fluid after cycling the brakes a few times. but the seals should be compatible with it. I hope the aftermarket parts are made to work with the original spec. (to the vehicle) fluid. I thought it might just be existing crud in the old master getting stirred up when I replaced the fluid. Regarding the brake master - kind of what I thought too, spend the money on Aisin parts to avoid problems. After the Aisin clutch master leaked within a short period, I became wary.

Rob, thanks for your insight. That's what I figured I should be able to do. I'll do some more investigating.

Has anyone had issues with the proportioning valve? Not the type close to the rear axle that's adjusted by the arm connected to the rear axle (LoadSensingPV) I'm referring to the one that's close to the master cylinder. Doesn't seem like it has any moving parts to fail, but I guess some contaminants could cause issues.

Might have to set up pressure gauges like the factory manual shows to see what I'm getting front and rear.

A friend's theory regarding the brake fade was that my rotors are warped, and as I push the pedal further they are pushing the caliper pistons back into the caliper housing and reducing brake effectiveness. I can feel some feed back through the pedal during heavy application.
 
Some general thoughts:

DOT 3 or 4 as Jzilla said.

old brake parts don't like to be cycled outside their normal range. Often corrosion or crud that can damage or get caught in the seals and cause a leak. So I'd be careful about bleeding the old MC if you decide to reinstall. proportioning valves can get stuck

Are you sure the brakes are bled properly with the new MC? Does the pedal travel change by pumping brakes (air), how about if you pull the e.brake (brake shoes not properly adjusted)?

Look for a leak somewhere in the system if no air remaining in the system.

You should be able to lock up under heavy braking.
 
Rear cylinders are dry, no leaks there. I bench cycled the new master cylinder into a jar and continuously topped up the reservoir until no bubbles were coming out of the lines. After install I bled the brakes with another person pumping the pedal and holding press. Then starting at furthest bleed point and working to the closest, bled each point until fluid was solid (no bubbles). I may not have been thorough enough in this step. I usually use a mighty-vac brake bleeder, but it currently needs a rebuild. Using this tool might not be effective enough to get all the air out of the lines.

Will check pedal travel while pumping and with pressure held on pedal.

Another thought is that the brake booster might not be operating properly. There is a noise associated with the pedal travel going past the point of the brakes initially grabbing. There is still vacuum released when I take the vacuum line off the booster, even if the truck has sat overnight.

Thanks for your help Martin.
 
Hmm, sounds like the cylinder was bled fine. Have you lost any fluid since putting it together? Pinhole in a line maybe? Have seen on other cars where a master cylinder leak fills the booster with brake fluid, but the booster shouldn't let the pedal drop with steady pressure, that points to a hydraulic issue. An internal leak in the master cylinder can let one circuit lose pressure and the pedal drops until it is just on the one circuit, shouldn't hit the floor and you still have brakes either front or back. Damaged hose the swells when brakes applied. Just throwing ideas out there. Good luck with it Mike.
 
Last time I bought a Beck Arnley Master cylinder, it was an Aisin. Was yours not? Mines been working fine for 100,000 km. I have been buying the whatever Lordco has for brake components (Raybestos etc) and they have been working well.
Having said that, anything can also be bad right off the shelf...
 
Hey mike, both you and Martin have pretty much covered the bases......two other thoughts that aren't all that common but can cause issues are the rod length that comes in contact with the master cylinder piston being either too long or too short, in your case possibly too short not allowing the piston to travel far enough and give the pressure needed and another issue that I'm sure you have ruled out but I thought I would throw it out there anyway......the one way valve off the vacuum pump can malfunction and pull engine oil into the booster but I'm pretty sure you have determined that what you see is brake fluid and not engine oil. The point that Martin brought up regarding any of the four brake hoses being old and loosing there integrity and then expanding upon application is something to ruel out as well.

Good luck!
 

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