Whats going on with my c4? - Ford Mustang Forums : Corral.net Mustang Forum
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post #1 of 8 Old 02-28-2016, 09:05 PM Thread Starter
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Whats going on with my c4?

Ive had this car together now since the beginning of the year, and have been to the track with it nearly every weekend...I have never noticed this issue before, because i have never shifted into drive (3rd) at less than WOT

100% track only car.

Had to drive down to the other end of the track at part throttle yesterday, and noticed while 1 and 2nd gear hold at 2500 or so, as soon as a shift to 3rd, it goes to 3000. Almost acts like the converter got much looser, only in 3rd, is really the only way i can describe it

Keep in mind this is a rather right 3500 tci converter that only flashes to 3300 on motor

Otherwise it seems to pull fine in 3rd, although it flashes higher in drive, then in 1st. So, at the risk of sounding like an idiot, what the heck is going on here? Normal? Increased load in 3rd gear at part throttle to blame?

Ive attached two videos to show what i mean...One full out pass at the track, to hear how it does at WOT, and the other at part throttle...

In the part throttle video, you can hear the 1-2 shift barely changes rpm at around 2500, then 3rd gear goes straight to 3000

What say you guys?

https://www.youtube.com/watch?v=X7mTrv9WtdU

https://www.youtube.com/watch?v=Re7eQ5khxpI

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post #2 of 8 Old 02-28-2016, 10:16 PM
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Your videos are marked private and will not play.


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post #3 of 8 Old 02-28-2016, 10:37 PM Thread Starter
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videos set to public now. thanks!
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post #4 of 8 Old 03-01-2016, 10:24 AM
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I had a bte full manual c4 that direct from bte had a 2-3 flare. I ran it for some time with this issue and then finally had a local guy tear into it. He said it was a mix of fluid flow and band adjustment. Claimed he had to drill out a couple holes larger in valve body, but he informed me that in a manual c4 it was difficult to get all the flare out and that I still may have a little. When I called bte complaining about it they told me every full manual c4 they sell does this, I was like well my 8 year old pa I just pulled out never done it.
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post #5 of 8 Old 03-01-2016, 05:50 PM Thread Starter
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Originally Posted by d_dogg07c View Post
I had a bte full manual c4 that direct from bte had a 2-3 flare. I ran it for some time with this issue and then finally had a local guy tear into it. He said it was a mix of fluid flow and band adjustment. Claimed he had to drill out a couple holes larger in valve body, but he informed me that in a manual c4 it was difficult to get all the flare out and that I still may have a little. When I called bte complaining about it they told me every full manual c4 they sell does this, I was like well my 8 year old pa I just pulled out never done it.
I appreciate the info. Funky issue for sure. Ill keep running it until it becomes noticeable at WOT or until my mph drops off i suppose...i agree it doesnt seem right...I have an Art Carr c4 setup in another fox and it does nothing of the sort like this one is doing. Crazy
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post #6 of 8 Old 03-06-2016, 11:20 PM
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Can't tell from the videos, but the engine sounds really good! Had one that sounded (and ran) real similar, though not for very long with a C4.

Could be flare but I've never seen one flare and not drop back almost immediately after the shift is completed.

C4 is known for the flare and it happens for a lot of reasons. The way the trans is designed, it has a lot going on at the 2-3 shift; and the design of the servo doesn't help either. I have a few ideas kicking around that I might attempt to play with as far as helping the hydraulic system, which may help with flaring. May try some stuff on the other car which I haven't messed with in ages. "Normally" 2-3 flare is due to either (1) worn high clutch, (2) worn case bore at the servo and (3) leaky servo, or sometimes (4) wrong servo. Occasionally a valve body issue, though I've always built my own valve bodies and never had it happen with them but have heard other builders open up a hole which can aggravate the flare when the high clutch gets a little worn.

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post #7 of 8 Old 03-06-2016, 11:31 PM
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Something else worth looking into is the servo mod. Meaning grind flats on the smaller portion of the servo piston, remove the seal on that part, then plug the hole in teh case with an allen screw (with loc-###). BUT the problem with this is that it puts fluid against the larger part of the piston when engaging the band; and a flex band ain't up to the task. I've seen a few of them break the lugs off. Rigid band I have not seen this. No firsthand experience doing mod, as mentioned earlier, never saw a need for it with my home built valve body as they always shifted pretty good until the high clutch got worn (dust in the pan). Usually had to re-pack them about once a year.

'92GT, 427" and '93 "LXVO" coupe
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post #8 of 8 Old 03-11-2016, 08:41 AM
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Stall will "increase" at low rpm as you shift up because you're loading the converter more (I noticed that effect when I switched from 3.73 gears to 3.08s this winter); but it's really hard to tell what's going on in the video. Try to keep the throttle steady. It sounds like you're giving it more throttle on the upshift, but then you almost immediately goose it for some reason. Try going down a flat road at a rock steady throttle position, and it would be helpful to know when you shift - better camera placement, perhaps. That doesn't sound like a flare.

Either way, my experience is primarily with AODs and powerglides.

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'84 LTD LX - 9.83 at 140.09. Whippled 365 SBF with a glide and 3.08 gears. Driven to and from the track 60 miles without even changing tire pressure.
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