Replaced the master clylinder on my 90 350. Have bleed brakes in the traditional manner several times but the balance light still comes on. Is there some trick to bleeding the brakes I am not aware of? They seem to be working fine and the pedal is firm.

Balance light? The 126 has an ABS light, and if you have ASR that has a light, my '91 didn't have a "balance light" that I recall.

Can you give more information on this light please?

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Gone to the dark side

- Jeff

If you are bleeding with the old school pedal method please consider using a power bleeder.

Motive bleeder kit is about $60 on the sponsor site. If that is too much $ you can make your own with a garden sprayer, a replacement GM brake booster cap (readily available at your local auto parts store) and some tubing and fittings from the home center.

Bleeding brakes the old school way is frustrating and can damage the seals in the master cylinder - because you will be pushing the pedal into a region of its travel that it normally does not go. The piston has worn over the normal travel region, and when you push into the un-worn region, the ridge formed between the worn and un-worn area blows out the seal.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Ya there is no balance light, just a low fluid level switch.

Are you sure the parking brake switch is working properly?

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.

The reservoir on most Mercs has two sections, one for the front and one for the rear, with a low partition in between. In order to fill the rear section, you have to fill the front until it overflows into the rear. When bleeding, you can easily end up with an empty compartment, yet the reservoir will look full because the other compartment isn't empty. Sooooo...you don't need a pressure bleeder. What I do is to fill the reservoir to the very top in order to make sure that both parts of the reservoir are filled. Once the system is bled, then bleed a little bit more to bring the fluid down to the correct level.