: Anyone ever used dealer tech2 scan tool to bleed ABS ? Having spongy brake problem.

05-02-13, 09:46 AM
'96 FWB. Upgraded HD12 limo calipers, Harper (kore3 hubs) etc, Harper rear disc conversion. So most rubber is pretty new and apparently undamaged. (Except rear intermediate hoses) Also, car is 99% rust free TX unit. Hard lines are great.

Recently did a major brake and suspension overhaul. In the past had occasional abs light. No codes pulled. Now, firm pedal at rest, but going down 3/4 and sponge while running.

Rebuilt bench bled master ( a few times), all calipers r&r'ed, all hoses check for bulges by hand while assistant presses brake while running. Hoses look/feel fine. New copper crush washers, yada yada.

been all over ISSF (impy forum) to solve this nagging soft brake pedal. At least one circuit was run dry during attempts. But did bleed many times and yielded great no-bubble stream of fluid.

Wondering if anyone in the past needed the GM tech scan tool to activate ABS for proper bleed ? Ours seems to be different because of 4-channel setup. Impalas and rest of B-body tribe are 3-channel abs.

Thx in advance

link below should have a soothing image:

The Ape Man
05-02-13, 12:32 PM
Are the bores of old and new calipers similar? IIRC the scan tool backed out some DC motors on ABS. There's a way to do that with clip leads IIRC.

05-02-13, 01:39 PM
Are the bores of old and new calipers similar? IIRC the scan tool backed out some DC motors on ABS. There's a way to do that with clip leads IIRC.

Nothing to suspect with the limo calipers. I have been running them for a few years till I did suspension and brake refresh. And whamo, spongebob brakes. That being said, I did run at least one circuit dry, front or rear. And have since bench bled with great fluid flow to each corner.

And so I am now believing I may have air in the ABS.

I have heard that the Mercedes of this vintage needed the scantool to backoff the DC motors as you said. Which is why I believe the Fleetwood is a similar beast, it also has the 4-wheel ABS vs 3-circuit for Impala/caprice/roadmaster.

wish I knew that trick with clip leads....

Anyone ?

05-03-13, 01:32 PM
I have run the ABS dry on FWD 4 channel ABS and just bled them normally and got lucky. The service manual says you are supposed to use the Tech 1 or 2 (?) and I was worried about it but got lucky a couple times now. If I didn't have a Tech 2 (which I don't) then I would try bleeding and more bleeding until I was convinced that it really isn't going to work. I wish you luck.

05-03-13, 07:07 PM
Heres one you can try.... Get both rear wheels off the ground.. start car , put in gear... now open bleeder and lightly touch the brake to activate antilock system pump... This is where the air is trapped... You might want to put your finger over the bleeder to act as a check valve to help keep air from going back in...Good luck and if you try it let us know if it works.. Dave

The Ape Man
05-03-13, 08:37 PM
Another trick is back-bleeding. Use a brake fluid pump. Crack a bleeder screw, pop the master cyl top and apply hose from pump to bleeder. Pump away. It works on tough jobs including trucks.

Always try a panic stop to actuate anti-lock in a safe place before driving on the road.

05-03-13, 09:03 PM
I have just let gravity bleed a system in the past that gave me fits, no pumping or pressure bleeding. I was having issues with pressure regulator though when bleeding.

05-06-13, 08:10 AM
Thx for input fellas. From my research this particular Bosch V cannot be actuated without the tech1/2 or equivalent. However, I went down to a sandy road and was able to activate the ABS. Bled again. Did this twice. My pedal is now quite firm at 3/4 throw, very responsive at panic brake, and I can lock-em-up on dry pavement.

Given that I have Bill Harper's HD12 Limo caliper upgrade up front (large bore pistons ?), and fairly old hoses (not ancient), this amount of pedal travel may be about right.

I did talk with a very experienced older Volvo mech who has run his own shop for aeons. His experience with these ABS units is that a standard bleed should be fine.