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  #1  
Old 06-25-2017, 04:00 PM
83_380SL
 
Join Date: May 2016
Location: Minnesota
Posts: 14
Angry Braking = Engine "chugging" / "pulsing"

1983 380SL (R107)
With the engine running and in gear (e.g. D, N, P) and the brake pedal is NOT depressed, there is no issue. However, when breaking (e.g. at a stop, light, etc.), the engine will "chug" or "pulse"...it is (slightly) more noticeable when cold and less "severe" when warmer. I've read on posts that this may be due to a break in the line from the master cylinder to the intake manifold...but am hopeful to get a bit more concrete direction from some of the experts on this forum. Thank you in advance.
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Old 06-25-2017, 05:04 PM
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Pay attention to your "economy" pointer when you hit the brakes. Does it move off the stop on the far left? If it does, you may have a failing/failed brake booster. If the diaphragm tears or develops cracks you can have a big vacuum leak through it, which of course will throw off your fuel mixture badly.
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Old 06-25-2017, 09:23 PM
83_380SL
 
Join Date: May 2016
Location: Minnesota
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Hello Diseasel300...Yes, your insight was spot on...braking moved the "economy" needle to the right (less) whereas when in P, N, D (without the brake engaged), the "economy" needle remained as expected, to the left (e.g. more). See pics attached.

Your guidance suggests a "failing/failed brake booster"...so what do you suggest nest? Thank you in advance for all your assistance. Truly appreciated.


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Old 06-25-2017, 09:57 PM
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I kinda figured that would be the case based on your description of the problem. Pressing the brake pedal doesn't do anything to the engine other than change the level of vacuum in the brake booster. If the diaphragm cracks or tears, it's time for a new one. Not only does it cause a vacuum leak which affects running, but it also reduces your braking power due to lack of assist.

Time for a brake booster.
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'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
'86 300SDL - "The Diseasel" 189K (Totaled 1/31/19)
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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Old 06-25-2017, 09:59 PM
83_380SL
 
Join Date: May 2016
Location: Minnesota
Posts: 14
Thank you again Diseasel300...I hope I'm not looking a gift horse in the mouth but could you say whether (or not) this would be a suitable replacement part?

https://www.summitracing.com/parts/aaz-53-5936/overview/year/1983/make/mercedes-benz/model/380sl

Again, thank you in advance.
Christopher
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  #6  
Old 06-25-2017, 10:28 PM
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I'm personally not a huge fan of Cardone parts, but you use what you have to. To be absolutely sure what you have, it could be a good idea to pull the part number from your existing brake booster and search by part number for a replacement. 1983 had a VIN split for the booster and master cylinder based on chassis number. I went through that recently in my SL when redoing the master cylinder. Mine was even more difficult since it was a grey-market Euro model. The forum sponsor (Pelican Parts) has a decent amount of info on their site and can help verify which part you need if you call them. Could be worth your time based on the VIN split confusion.
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'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
'86 300SDL - "The Diseasel" 189K (Totaled 1/31/19)
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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  #7  
Old 06-28-2017, 09:07 PM
83_380SL
 
Join Date: May 2016
Location: Minnesota
Posts: 14
Hey Diseasel300...just wanted again to say Thank You...I've not (yet) tackled the issue...in part as I've a few pressing distractions but also as I'm a bit stalled based upon the $600+ Brake Booster price tag...6X the Cardone part. I did, however buy a Brake Booster Line (Part #107-430-19-29-M22) in the very lucky event it's just the line that is cracked/failed and not the Booster. Again, many thanks!
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Old 06-28-2017, 09:53 PM
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It is doubtful that the line will cause that behavior since if it were cracked, you'd have problems all the time, not just when braking. Replacing the line is probably not a bad idea anyway since it has a check valve made of plastic in it. The one in my SL broke (crumbled) for no apparent reason and left the car with both a high loping idle AND reduced braking power. Fun combination!

If you don't mind a used part, you might post a "want to buy" ad in the "For Sale" section of this forum.
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'11 Honda Accord EX - "The Daily" 64K
'83 500SL Euro - "The Money Pit" 116K
'91 350SD - "The Diseasel Jr." 168K
'86 300SDL - "The Diseasel" 189K (Totaled 1/31/19)
The Diseasel Thread - Everything You Didn't Know You Wanted To Know
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  #9  
Old 06-29-2017, 06:51 AM
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You could always have the original booster rebuilt - there are any number of competent shops ready to assume this task. Do a search for recommendations.
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  #10  
Old 07-08-2017, 01:34 PM
83_380SL
 
Join Date: May 2016
Location: Minnesota
Posts: 14
Thanks for the additional recommendations Diseasel300 and ejboyd5.
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