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Old 03-04-2005, 19:40   #1 (permalink)
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C4 shifting very early

It's done it as long as I've had the vehicle, but it's never really bothered me, I just do it manually with the B&M Mega shifter. I'd like to sort it out though, as I may be selling the vehicle soon. It shifts up at around 1500 rpm, unless you really plant it, when it shifts at about 2000rpm.

I don't know if the vacuum gear was hooked up properly when the C4 was installed so lets start with the basics.....

Cheers,

Muff.
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Old 03-04-2005, 22:01   #2 (permalink)
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Re: C4 shifting very early

Could be that you don't have enough vaccuum and the box is "stacking" the gears. Does it do it in 1st only or all the gears.
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Old 03-05-2005, 01:18   #3 (permalink)
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Re: C4 shifting very early

It shifts early in all gears. I was underneath the car most of today (@$%#%$^$# handbrake cable) and I think I can see a vacuum line coming out of the mid section just behind where the oil pan finishes. I guess I should trace that sucker and see where it goes.

Thanks,
Muff.
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Old 03-05-2005, 13:53   #4 (permalink)
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Re: C4 shifting very early

Sometimes the rubber connecting hose is cracked
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Old 03-06-2005, 00:59   #5 (permalink)
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Re: C4 shifting very early

A cracked hose or not enough vacuum will give late shifts.See if you have an adj modulator with the little brass screw inside the vac tube and screw it in a turn at a time which will make the shifts later.
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Old 03-06-2005, 05:31   #6 (permalink)
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Re: C4 shifting very early

Quote:
Originally Posted by gregaust
A cracked hose or not enough vacuum will give late shifts.
Sorry but I'm confused now..... A leaking vac hose will give LATE shifts?? Or did you mean early? This is at odds to what I have heard so far.

Cheers,
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Old 03-06-2005, 17:26   #7 (permalink)
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Re: C4 shifting very early

No vacuum or a very leaking hose will give late shifts, not early shifts.

So maybe the problem lays elsewhere...
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Old 03-06-2005, 17:31   #8 (permalink)
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Re: C4 shifting very early

Early shifts usually happen if the engine has a non-stock camshaft. My old C4 used to change @ 3500rpm with full throttle application due to vac. It used to change ealier when cruising. No amount of adjustment would improve it.

I eventually manualised a C4.

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Old 03-06-2005, 18:46   #9 (permalink)
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Re: C4 shifting very early

Yep,

A crushed /split vaccuum line or buggered modulator which is not drawing enough vaccuum will cause late shifts.
Too much vaccuum due to pinched rubber line or sticking modulator valve may cause early shifts.

As with all these things, it can take a while to pinpoint the issue and you may find it is a combination of 2 or more issues !!!!!!!!

My car has issues with 2 -3 shift ever since I installed the High stall. 1 - 2 change is OK but it wants to change from 2 -3 way too early......it's almost like it skips 2nd gear sometimes as the change is so quick.

I too need to look at my vaccuum lines and mybe even the governor etc to make sure its all clean and in good working order.
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Old 03-09-2005, 22:32   #10 (permalink)
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Re: C4 shifting very early

Quote:
Originally Posted by ESP
I too need to look at my vaccuum lines and mybe even the governor etc to make sure its all clean and in good working order.
I think I'll do the same, thanks guys.

Muff.
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