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vacuum leak and transmission shift problem

1220 Views 8 Replies 5 Participants Last post by  erblo
I am in the process of cleaning out my engine bay. I have already removed the vacuum canisters for the flip up headlights and the hoses were in loops. I decided to get rid of the extra hoses, so I cut them off where they come out of the firewall, and connected them there, thus making a smaller loop, right? Well now my transmission won't shift into second gear. It will drive in first and shift to 2nd, then downshift to first, then kick hard into 3rd. Any suggestions?
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you cut the hoses flush with the firewall?!?! one idea comes to mind....

sell that car and go buy a are a certifiable hazard to classic cars.
Well, I'm guessing you cut the vaccum hose that connects to the adjuster on the transmission. Reconnect it and it'l be fine.

J. Boggs
Sharkmouth, you might want to fill out your profile so we know something about you.
Ok, the vacuum hoses go from the light switch to the headlight doors, and nowhere else. They weren't connected to anything before, they just went in loops where the headlight vacuum canisters were. I just figured that it would make no difference if it was a big loop or a small one.

Since your problem is with the transmission, could you verify that the vacuum modulator, which is located at the rear of the transmission, is receiving full engine vacuum? You can locate it and remove the short rubber hose from it and hook a vacuum guage to the hose and operate the engine, noting vacuum readings. Post those.

Did you do anything else to the car while changing the vacuum hose routing for the headlights?

Get back to us..
Ok, I took my car to my mechanic, and he verified that the modulator is working. The hoses were leaking and were replaced but the problem remains. I figured out that the hoses I am getting rid of are part of the headlight system and nothing more. He told me to drop the car off later and he would drop the pan and stuff. The shift pattern has become 1-2-1-3. This sounds like it is getting expensive...

I hope he'll read the manual and do the recommended diagnostics before dropping the pan...there might be a simple solution here and we're missing it.

After all, the car worked fine immediately before you did some work on it...

You're sure you didn't do anything else to the car, even if not related to the trans, yes?

C4's are pretty reliable and predictible, IME.....the hard part is folks like myself need to be there sometimes to really get a feel for's hard to diagnose over the internet..*G*

Keep us posted!

**Edited to add an example of a typical diagnostic sheet...this one's for a C6 but is very similar to a C4.
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Yeah, he really knows what he is doing, so I'm sure he'll go through it (he already checked half of it) but I think that the problem might be just a coincidence with what I did. Now that I think of it the problem did not turn up immediately after working on it, it took 30-60 mins. later to show up. I was driving on the freeway that day and it was actually quite hot outside, could this have anything to do with it? The vacuum lines were the only thing I did that day, and they should have nothing to do with the transmission, only the lights... thanks for the help so far!

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