Another cracked vacuum distribution block - Mercedes-Benz Forum
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post #1 of 32 (permalink) Old 06-16-2016, 10:21 AM Thread Starter
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Another cracked vacuum distribution block

Having a classic vacuum fuel pump issue (it cycles on every 15-17 seconds), I pulled the vacuum distribution block aka vacuum manifold located behind the false firewall on the RHS. Sure enough, a small crack next to the metal ball socket.

Reading several posts on the subject, this must be one of the most usual wear items on these cars, at least when they approach 25+ years!

So if you experience a vacuum leak, either the pump cycles or some vents are not functioning on the climate system, check this valve first! Very easy R/R DIY job! Part number 129-800-14-78. Cheapest find on Pelican parts for $25,50.
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post #2 of 32 (permalink) Old 06-16-2016, 10:48 AM
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The pump has nothing to do with that block

Pump controls C/L
Engine Vacuum controls climate control flaps.
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post #3 of 32 (permalink) Old 06-16-2016, 11:54 AM Thread Starter
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I respectfully disagree. The pump delivers vacuum to the block in a separate line, in case the engine manifold does not produce enough vacuum for the climate controls to operate properly. They are linked together by a clear hose. So if the pump detects a small leak, either from the central locking OR the manifold connections, it will cycle on 2-3 seconds every 15-17 seconds. It will do so 31 times before it stops (built in protection).

The clear line has the marking PU (vacuum for aux consumers for supporting the intake manifold vacuum). It's all there in section 80-010 - Function description of central locking in the repair manual.

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post #4 of 32 (permalink) Old 06-17-2016, 01:14 AM
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You're right, I'm wrong.

Everyday is a school day, sorry for jumping in like that.
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post #5 of 32 (permalink) Old 06-17-2016, 05:01 AM
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The sad truth is your block didn't just split, it's been split for a very long time and a new block will split shortly.

Your best course of action is to merely repair the split (unless the ball has actually fallen out) with gasket sealer.

A new valve block will split within a year and you will be back to square one.
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post #6 of 32 (permalink) Old 06-17-2016, 12:01 PM Thread Starter
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Really?! I'll keep a close look.

If this is the case, the vacuum pump issue is unrelated to a cracked manifold. Have to investigate further, I guess.


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post #7 of 32 (permalink) Old 06-17-2016, 01:09 PM
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Quote:
Originally Posted by mahunt View Post
The sad truth is your block didn't just split, it's been split for a very long time and a new block will split shortly.

Your best course of action is to merely repair the split (unless the ball has actually fallen out) with gasket sealer.

A new valve block will split within a year and you will be back to square one.
Surely they have JBWeld in the Nordic countries?

JB Weld | World's Strongest Bond

Maybe we need to send a care package?

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post #8 of 32 (permalink) Old 11-10-2016, 03:09 AM
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Wow, just replaced mine and....HOLY F!

I've been steadily replacing most of the soft parts in the engine bay that could cause a vacuum leak, and with every old, cracked, and leaky hose I've replaced the engine has gotten better, but since replacing the vacuum block, the car is on another level in power and responsiveness. Kinda amazing actually. Before, I'd have to leave the car in 4th gear to feel like I could get satisfying response and power around town. Now, I leave it in 5th and it feels more powerful and responsive than how it felt before in 4th. The exhaust is clearly rortier, the brake pedal is firmer and has better overall feel, and the transmission shifts faster and more smoothly. A-freaking-mazing.
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post #9 of 32 (permalink) Old 11-10-2016, 11:22 AM Thread Starter
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Glad you got improvement, but you've must had a very significant vacuum leak in the manifold to get these effects. Mine was cracked (barely visible), but no effect on either pump or running conditions.

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post #10 of 32 (permalink) Old 11-10-2016, 12:27 PM
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Thanks man! However, my cracked dist block looked exactly like yours. So, maybe it's a difference in engines with mine being a 99 with the m113 engine? Or perhaps you have some more unidentified vacuum leaks? Hopefully the former, and not the latter. As far as I can tell, I've now replaced every hose, seal, or gasket in or somehow connected to the intake tract and it's running better than I thought the portly beast ever could.
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