‘86 300SDL…Brake Bleed Problem
 

Just replaced caliper on passenger side rear and can’t get either rear brake to bleed? Can’t seem to get brake fluid (just a very little) to either caliper, even using a vac unit attached to my compressor? Cap is off reservoir as I bleed and plenty of fluid in reservoir. Haven’t tried to bleed the front wheels until I do the rear. Brakes were fine before I replaced caliper that locked up. Do I first need to bleed at ABS unit and if so, which connections?

Appreciate your thoughts.

Bill

Go out to the vehicle.

Look at the reservoir from the passenger side. Or, if you're tall, lean over into the engine compartment and look in reverse toward the right side of the reservoir (passenger side).

See if the rear chamber is empty.

If so, fill the front chamber until it's just about overflowing and it will spillover into the rear chamber.

The design is a PITA until you understand it.

Thanks so much Brian. I will give that a shot and let you know the result

Bill

If you plan to have an MB or just about any European car in your stable, get a pressure brake bleeder like Motive sells - http://www.motiveproducts.com/

Sixto
87 300D

The motive works great on domestics too. My Sister's grand prix has an ATE master cylinder with Bosch ABS :o

-J

Oh, yes. The basic fitting fits most European cars. There are adapters for US and Japanese car reservoir caps at extra cost.

Sixto
87 300D

ditto for the Motiv bleeder, except I wish they installed a swivel on the line so you dont have to rotate the whole bottle to screw it on :(

Do these cars have a proportioning valve on the rear axle lines somewhere? Ive had to jack my VW track car rear axle up to simulate load, or else it wont allow break fluid to rear axle.

Looks like Brian called my problem correctly, the master rear brake reservoir being empty. Question now is, once I fill that, can I get away by just bleeding at the two rear wheels or do I need to first bleed the line/fitting at master that goes to the rear? Then, after that, do I need to also bleed at the ABS unit and if so, where? Lastly, since the rear brake reservoir is separate from the front reservoir, will I need to also bleed at the front wheels?

Also, Paul brings up a good question as to whether there is a proportioning valve in that rear line and if so, what is its effect on the bleeding operation?

Thanks
Bill

I've run the '86 out of fluid several times in the rear when I had a leak. I have not bled the master to get it going again..........but..........the '86 has the softest pedal of all of them. So, I'm a bit undecided if the master still has a touch of air within it. It's not worth the effort to chase it for me. If you do decide to bleed the m/c, you'll be bleeding the forward hard line. Yes, I realize that it makes no sense.

You do not need to bleed the ABS.

You do not need to bleed the front wheels unless you did work up there.

The proportioning valve will not affect your work.

You do need to be very careful that you don't run the rear chamber dry. You'll never get both wheels done with the small amount of fluid in that chamber...........and it's very easy to mistake how much you have.........as you know.

Brian, thanks for that very complete answer. I'm sure it will be very helpful as I hope to get back to it today. I'll let you know how I do.

Bill

Brian, your diagnosos of my problem and subsequent recommendation for solving it were right on! Thankyou.

I got the pedal back by following your suggestion of just bleeding the rear wheels. I too, have had that uneasy feeling at times with the ’86 that the pedal is a little soft.

Bill

Excellent.

Help is what we do here!