Brakes work better when it's cold and humid

[White Stripe]

My thought is perhaps some of the brake fluid seals are stretching or letting some fluid slip by once the seals warm up a little. If fluid is slipping by seals then this would be seen as a leak in the calipers or wheel cylinders. If fluid is slipping by in the master cylinder this may be not seen as a external leak. In addition brake pads have a cold and hot friction rating. Different brand pads have different ratings.

 

[jonheld]

Although you come across as a cantankerous old fart,

I resemble that remark...
In all seriousness I'm very anal about brakes. It's way more important to stop than it is to go. Calipers/pads/rotors get inspected yearly, brake fluid flushed through the system yearly. I keep a spare set of rebuilt, painted, and loaded calipers in the garage and swap 4 corners when I feel it's time. Then I rebuild the spare set at my leisure.
Since the LX450 was an unknown to me when I bought it, the master was replaced, the valve in the booster, the vacuum hoses, etc. were all replaced.
I only use OEM 80 Series parts and I can lock up my 35s and activate ABS on dry blacktop.

The drum brake rear of the 91/92 is critical to pedal feel. I always ran the adjuster in 1 or 2 more clicks than the FSM states. That gives you s shorter pull on the handbrake, and a firmer pedal.

You also stated that you can lock your fronts before the rears. That is opposite of what you would want to happen. You always want to be able to steer.
However the fact that you can lock up your wheels indicates that the brakes can't be all that bad.

 

[jonheld]

Including transmission fluid??

I do a passive drain/refill of ATF every year.
All fluids get contaminated over time, even if you don't drive that often.

 

[Izeloz]

I think I have figured out at least part of the problem. I believe the aftermarket master cylinder I put in is very possibly for a model with 4 wheel disc brakes. As such, it lacks an internal residual valve for the rear drums. That would cause a low pedal and potentially a little bit of a squishy feel. Since it wasn't that much money, I ordered a Wilwood residual valve (10 lbs.) to plumb inline with the rear brakes. Hopefully that will help alleviate at least part of the issue. As to the cold/humid thing, I'm still a little baffled. It's been quite dry in Utah lately (although chilly at times) so I haven't had a chance to see if it still behaves the same as it it did before. I am 100% certain this time around that there is no air in the system and ALL the fluid is nice and clear and clean. As to the brake bias, a factory system is designed so the front brakes provide ~70% of the braking and you would notice on a gravel road that the fronts actuate slightly before the rears. This is just as it was designed. That doesn't mean I magically lose the ability to steer. I will post up again after I get my residual valve and fittings and get it installed. Thanks for everyone's input!

 

[Dave 2000]

Fluids in general should be changed annually.

I am not a follower of that idea. I do change of engine oil and filter around twice per year, depending on usage but a minimum of at least once.

The EP 90 oil in the gear/trans and axles could be left as long as four years or more. Antifreeze every three years and the brake fluid at the same time. I use DOT 4 and find that this is fine for three years or more. My usage and environment dictate my all my decisions on mine and my clients cars, although I am obliged to follow minimum manufacturers guidelines for customers.

regards

Dave