Cruise control vacuum

[kenwa]

My cruise control has been acting up lately, not maintaining speed all the time, so I looked at the vacuum lines and found that the big one is shot. No actual splits that I could see, but it's crumbly, cracked, and dry. It comes out from under the power brake booster, and I couldn't replace the whole hose without a lot of work, so I replaced as much as I could. I also replaced the small hose, since I could see all of that one.

However, there's no improvement. I then put a vacuum gage on the two hoses (duh) and found no vacuum at idle on the big hose, and 1.5" on the small one. Now, this doesn't seem like enough to do anything, but the cruise control does in fact work on a level road. Engine vacuum is 17.5" at idle. So, I gotta start digging.

Can someone tell me what the vacuum should be on the two cruise control hoses, so I know when I've fixed it?

Thanks,
Ken

 

[MBDiagMan]

Whatever amount of vacuum you have at idle is what should be seen at all points of the cruise control system with very little loss. Don't forget that there is a release port that if leaking would bleed off your vacuum.

I would recommend that you dig in however far is necessary and replace ALL of the soft lines.

Good luck,

 

[kenwa]

Thanks, Doc. I bought a variety of different size hoses the other day, and will replace all I can get to. Where is that release port you mentioned?
Ken

 

[gmjunkie]

I would recommend that you dig in however far is necessary and replace ALL of the soft lines.

Good luck,

Agreed!! junk!!

 

[MBDiagMan]

The release port or brake switch on earlier C4's is at the top of the brake pedal bracket. I would expect the same arrangement on your late C4.

Good luck,

 

[KOPBET]

Carefully check the condition of this piece underneath the right side fuel rail cover. If it is old it may be brittle and could break or already be cracked or broken.

 

[kenwa]

Carefully check the condition of this piece underneath the right side fuel rail cover. If it is old it may be brittle and could break or already be cracked or broken.

That check valve broke last year and the dash vents and cruise control both stopped working. I replaced it and all was good again. This time the dash vents are fine.

I'm start hunting this afternoon.

Thanks,
Ken

 

[kenwa]

Got it.

The hard plastic line that runs by the battery had a hole in it where it rubs on the positive battery terminal. I had a battery leak at the positive terminal not too long ago. I didn't see the damage when I changed the battery.

The vacuum tank also has a crack on the fitting where the hose plugs into it, and the hose doesn't fit right, so I will replace the tank. For now, I plugged that line.

Thanks everyone,
Ken

 

[MBDiagMan]

Atta boy! That's being thorough.

Good job,

 

[Moonunit 451]

Carefully check the condition of this piece underneath the right side fuel rail cover. If it is old it may be brittle and could break or already be cracked or broken.

I like your new avitar KOPBET, so, I STOLE IT, for use at another time and place of course

 

[gmjunkie]

I like your new avitar KOPBET, so, I STOLE IT, for use at another time and place of course

Stop Theif!!otfl junk!!

 

[KOPBET]

I like your new avitar KOPBET, so, I STOLE IT, for use at another time and place of course

Red Rocks!!!

 

[MBDiagMan]

I love that avatar as well, but I'm no thief.

Have a great day,