2nd Gen Non-Engine/Transmission Changing brake fluid, something is not right!

[rweis]

2002 ETC DRW 45k decided to change the brake fluid in the brake system.



I used a MityVac 4050 with the rubber brake bleeder attachments.



First I sucked out all the brake fluid from the master brake fluid reservoir, at least as much as I could get to (about 400 ml, 13. 3 oz). Refilled it with fresh Valvoline Syn (DOT 3,4) fluid.



Next went to left rear caliper. Took rubber bleeder screw cap off, used 3/8, 6 point socket to loosen bleeder screw 1/4 turn. Put rubber boot from MityVac on it and did the suction thing. I understand that you will draw in air from around the rubber boot contact to the bleeder screw. I had good fluid flow (plus the air of course) and kept a good vacuum going to get the line flushed out. Took out about 300 ml / 10. 14 oz (until the fluid went from a dark brown to a slightly brown color). I could not get a pure clean color fluid. I kept the suction up so air would not get into the brake system, closed the bleeder, replaced the rubber OEM cap. So far so good.



Next the right rear caliper. Same proceedure until I started with the suction to draw the fluid out the bleeder. Barely any flow at all. Finally I got 75 ml / 2. 54 oz and the fluid at a light brown color and closed the caliper bleeder, rubber OEM boot back on etc.



WHY could I not get a decent flow through the right rear caliper brake bleeder screw?



Ok, decided to do the fronts.



Next was right front, a little better flow than the right rear, but not much flow. Finally got 75 ml / 2. 54 oz and a reasonably light brown color. Closed the caliper bleeder etc.



Last was the left front, very low flow here as well. Since I could see the catch bottle (and all the while I made sure the master clyinder reservoir was full during the entire process) I decided to pump the brake and see what the fluid flow was like. I only had the bleeder screw open about 1/4 turn, but was able to push fluid with the master cylinder into the catch bottle. Not fast, but was considerably more fluid than I was able to move with the suction method. I got about 100 ml / 3. 38 oz of fluid and the color was a light brown. I did notice there was some very fine suspended particulate in the fluid going into the catch bottle. Not a LOT but enough to be noticable. I went back to the suction approach to insure no air in the brake system, closed the bleeder screw.



Why was I not able to move much fluid except on the left rear caliper?



I had recently installed a BrakeSmart (which tells you the master cylinder brake psi of the sensor) and before I did the fluid change I had taken psi readings on different types of stops (slow stop, medium stop, hard stop) and the psi readings after the fluid change were about the same.



What was the deal about hard to get clean reservoir fluid through the respective caliper?



As a side note: The dam* anoying brake squeal I have had for 2 years (45k) magically disappeared after the fluid change.



Thanks, sorry it is long



Bob Weis

 

[Straight6Jeff]

I believe it has someting ot do with the ABS module. I know when manually bleeding an ABS system, it is advised to wait 15-20 seconds between bleeds so that the ABS Module can completely "recover" with fluid.



I might be way off base though

 

[Rman]

Well, I have a pressure bleeder. I just bled my brake system about a month ago. I pressurized the system with 15 psi, and opened each bleeder one at a time. I bled a quart through each bleeder. I had no flow problems at all and everything went smoothly. I noticed no change in pedal feel, but did have cleaner brake fluid. I was at about 40k at the time.

 

[rweis]

RMan,



What year truck?



That is what I thought would happen with the vacuum bleeding. Lots of fluid flow, flush out all the old, run several quarts through it to get it really clean. Is NOT what happened.



Bob Weis

 

[rweis]

Could be the ABS idea. RMan did you hold open the HCU control valve? what year is your truck? Might be unique to 02 - xx with ABS disc?



SM 5-36 Standard Procedure - Bleeding ABS



(out of context) ... bleeding requires conventional bleeding methods PLUS use of a DRB scan tool. The procedure involves ... base bleeding, followed by use of the scan tool to cycle and bleed the HCU (Hydraulic Control Unit) pump and solenoids. A second base brake bleeding procedure is then required to remove any air remaining in the system.

(1) Perform the base brake bleeding ...

(2) Connect scan tool to the Data Link Connector

(3) Select ... ABS Brakes. Follow instructions. ... Test complete.

(4) Perform base brake bleeding a second time.

(5) Top off master cylinder ...



NONE of the above is mentioned in the

SM 5-7 Standard Procedure - Manual Bleeding.



Ok, what about the scan tool? Where can you get one?, rent one?, borrow one? It sounds like an expensive tool.



I did the bleed yesterday. Drove the truck some (about 30 miles). I am going back out and re-bleed the right rear that had minimal fluid flow to see if there is any difference.



Maybe you have to manually bleed one HCU system at a time? (HCU systems are left front, right front, both rears are on the same HCU system)



Any ideas?



Bob Weis

 

[Rman]

I have a 2002. I have the service manual and recall reading something about the HCU. I thought that if I did it the old fashioned way I just wouldn't get the fluid from the HCU out, but everything else would flush. It appears this is what happened, but I truly don't know. I'd try it again, perhaps have your wife come out and try the tried and true pedal pump method one time and see if you get more flow. I have a mity vac, but really like the pressure system I purchased. The mighty vac comes in handy for testing vacuum switches though.

 

[rweis]

I was discussing the problem with a friend of mine that had a collapseing brake flex line. Said the collapseing line acted the same way, would pass a small amount of fluid.



I did the left front again today all by itself to see if there was a difference. Basically the same scenario. The fluid was cleaner, but the flow was the same.



I think I am going to get one flex line (probably left front since I can see it and do the pedal if need be) and change that out and see if there is a difference.



Depending on that result, I will have the fluid change done by the pressure method. At least brake fluid is fairly inexpensive.



Something is up, just don't know what.



ATBGO (And The Beat Goes On)



Thanks for the suggestions though.



Bob Weis