Odd R129 brake issue ?

Odd R129 brake issue ?

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Old Merc

Original Poster:

3,538 posts

172 months

Wednesday 7th July 2021
quotequote all
I`ve had my 1997 SL320 for over 15 years and always serviced it myself. ( I`m a retired old school mechanic ) As its been on SORN for the best part of 18 months due to Covid, I thought I would give it a good service and change the brake fluid.
I always use a rubber tube on the nipple to a bottle, open the nipple and pump away on the pedal, do this on each corner and give it a good flush through. I`ve done this many times on this car ( and countless others in my working life ) without problems. This time though I immediately realised somethings not right when I went for a road test. The brake pedal was right at the top with no travel. Just touch the pedal and it stopped. Sure enough after a few miles I could feel the brakes binding up. Got home and all four wheels were hot and I could not push the car. Slackened a bleed nipple, slight pressure on the pedal, tighten the nipple, brakes back to normal?? Normal travel on the pedal, good brakes.
Any of you R129 experts got any comments.

How u doing

27,344 posts

188 months

Wednesday 7th July 2021
quotequote all
Old Merc said:
I`ve had my 1997 SL320 for over 15 years and always serviced it myself. ( I`m a retired old school mechanic ) As its been on SORN for the best part of 18 months due to Covid, I thought I would give it a good service and change the brake fluid.
I always use a rubber tube on the nipple to a bottle, open the nipple and pump away on the pedal, do this on each corner and give it a good flush through. I`ve done this many times on this car ( and countless others in my working life ) without problems. This time though I immediately realised somethings not right when I went for a road test. The brake pedal was right at the top with no travel. Just touch the pedal and it stopped. Sure enough after a few miles I could feel the brakes binding up. Got home and all four wheels were hot and I could not push the car. Slackened a bleed nipple, slight pressure on the pedal, tighten the nipple, brakes back to normal?? Normal travel on the pedal, good brakes.
Any of you R129 experts got any comments.
I'm not an expert but sounds like a master cylinder or servo problem.