DOT 4 ? Oops never noticed.

[doclees]

Funny thing happened on the way to the store today. After a somewhat firm use of the brakes I lost some pedal pressure as if there was low fluid or air in the system. If I pumped the bakes 3 or 4 times it felt solid. This continued for 10 miles until I got home.
So naturally i checked the fluid. Level wise it was fine. A lovely shade of dark brown. Figured maybe the fact it has never been changed could possibly cause the fade. Didn't have time for a proper bleed so I used my vacuum bleed to empty the reservoir.
After filling with fresh DOT 3 I cleaned the reservoir I see it should have DOT 4. At least the DOT 3 helped clean the sludge. Refilled with 4 and drove around the block. Good enough for now until a proper bleed is done.
So the take away might be that you can go 180k miles on mostly the wrong fluid if you don't ask too much from your brakes. I read that this could be a cause of an ABS light.

[FiberFast]

I think the reason for the Dot 4 fluid is the fact that your clutch system and brake system are one in the same and share a reservoir.

[Eric93se]

Anyone try DOT 5.1 in their e36?

[doclees]

GM automatic.

[XnWarden]

Dot 3 and 4 are very very similar. Dot 4 has a higher boiling point and can absorb more moisture. A dot 3 vehicle can upgrade to dot 4 with no adverse side effects. Going from dot 4 to dot 3 is a down grade.

Sent from my VS987 using Tapatalk

[craigjimc]

Been using Motul DOT 5.1 for over 10 years with no issues whatsoever.

[Eric93se]

Looks like Bosch has next generation brake fluid, exceeds 5.1 specs.

https://www.amazon.com/Bosch-ESI6-32N-Brake-Direct-Replacement/dp/B07338GQM8

[doclees]

So now with about 350 miles on the reservoir refill the ABS light stays off for a couple of miles in the morning. Who knows maybe a full flush will clear it up completely.

[doclees]

Just an update. Haven't had the time for a proper bleed flush. No hard pedal and the ABS still off for a few miles on first start. Been doing 650 miles each weekend. Had a few firm brake usage over the holiday highway traffic. Pedal went soft again. Back to normal after about 200 miles with minimal use. I check the reservoir and the fluid was not as black as before but a good grade B maple syrup. Sucked it out and refilled.
This just reminded me that some are convinced and some are not that the fluid "circulates".

[FiberFast]

Just an update. Haven't had the time for a proper bleed flush. No hard pedal and the ABS still off for a few miles on first start. Been doing 650 miles each weekend. Had a few firm brake usage over the holiday highway traffic. Pedal went soft again. Back to normal after about 200 miles with minimal use. I check the reservoir and the fluid was not as black as before but a good grade B maple syrup. Sucked it out and refilled.
This just reminded me that some are convinced and some are not that the fluid "circulates".

Maybe the tinyest little bit on the circulation, but doubtful. The resivouir feeds the clutch and brake master cylinders, the fluids are exchanged from the master cylinders to the slave/calipers but not the reservoir. If I where to exchange out all the Ate Dot4 with dot 5.1 or better, I would buy several quarts and run a full one into the res, followed by about a half quart more for each caliper. Don't ever drain the reservoir completely, I wouldn't mess with the slave cylinder unless its broken.

[doclees]

Still no slave cylinder in my automatic. One would think there isn't an exchange and I'm not saying there is or at least much of one but don't forget the ABS pump. That aside I just put another 325 miles on it and the pedal went soft again. Dirty fluid again. Now more like a grade A amber maple syrup. Will vacuum out the reservoir tomorrow and refill. I will be interesting to see what color comes out when I do flush the lines.
I suspect any exchange that maybe happening here is due to the crappy fluid boiling over. The reservoir appeared rather clean the last time but the crap has got to be coming from somewhere.

[doclees]

Finally flushed the lines. Also had rust pitted front rotors so changed them and the pads to new. Cleaned the front ABS sensors but the backs seem rather stuck and didn't want to force them. No change in the ABS light. Pedal feels a nice comfy amount of give now. Might just do it again in a few thousand miles to see if any more crud will come out. In the event you don't torque the caliper bracket bolts down enough just know when you lose it on the crappy PA highway and the caliper starts clunking around you can fit a lug bolt for a temp fix. Guess how I know this.