Uh-oh, I think my C-4 is going bad...UPDATE 3/21

Mark · Mar 6, 2006

Crap, starting this morning, when I got into town when accelerating from a stop, the engine will rev up to 2500 - 3000 rpms, I'll let off the accelerator, then reapply my foot, and the automatic will then shift into 2nd and my RPM's will drop to the normal range.
Seems to shift fine the rest of range up to 50 mph (the fastest I'll risk in town).
I think my C-4 automatic is beginning to fail.

I guess changing the fluid and filter won't change anything, huh...

Can someone guess what is going wrong with it?

iwlbcnu · Mar 6, 2006

iS IT JUMPING IN AND OUT OF 1ST? Mine did that and the modulator had sprung a leak. Pull the vacumn line off and see it fluid is in it.

bannind · Mar 6, 2006

Mine was doing some bad 'flaring' in between the gears and replacing the modulator made a ton of difference. It still slips occasionally, but it is much better. Try a new modulator, fluid and filter(make sure you don't loose the spring and pin with the filter change). See if that helps before you start worrying about the big ticket rebuild options.

Just my 2 copper pieces.
dan

BroncoMark · Mar 6, 2006

Yeah, sounds like a vacuum modulator.

Mark · Mar 6, 2006

Thanks men,
Napa will (should) have my new modulator tomorrow.
I have the red striped one - the most expensive of course - $45.
I hope that takes care of it. Can't imagine I could be that lucky.

Naildriver111 · Mar 6, 2006

If the modulator doesn't help, add some Lucas transmission treatment to it. It kept mine going until I could afford a rebuild (around 4 months)

Mark · Mar 7, 2006

Well, it helped - a little. Now it revs to maybe 2100 rpms and will then shift, but it's still not right. There was a pin in the end of the old modulator about 1 1/2" long that I put into the new one - I'm guessing that was proper.
The vacuum line seemed old and cracked, I guess this weekend I'll replace that.
I'm hoping the damn thing fixes itself!

BroncoMark · Mar 7, 2006

I was sure that would have been it. It's possible that the governer(?) is sticking a little maybe. It's shown uder the guys hand in the picture. Of course, it usualy sticks when the fluid is contaminated with brass from a thrust washer that is wearing into a drum or something equally hideous.

SaddleUp · Mar 8, 2006

When mine started doing this (I.E. It would slip when I floored it to pass someone) it lasted about 8 months before it completely failed. When it failed and was taken apart the front pump was shot. Of course when it did fail it was in about 3 ft. of some of the ugliest mud around.

Mark · Mar 21, 2006

Well, on the 12th I replaced the modulator, ran a new vacuum line from the intake manifold to the modulator, replaced the stock pan with a 2 quart extra capacity B&M pan with cooling fins ( http://broncograveyard.com/bronco/i-11102_c-4_transmission_pan.htm ) replaced the fluid with B&M trick shift fluid, and readjusted the adjuster bolt/locknut near the neutral safety switch.

At first, the improvement was marginal, but I did not have to let off on the accelerator for the C4 to shift into 3rd (after further evaluation it was shifting from 1st to 2nd fine, but not 2nd to 3rd). As I've been driving it the last week and a half (my daily driver), I have noticed significant improvement to the point of slight hesitation now (better when it's warmed up). Before I didn't even notice when the C4 shifted, now it seems to have a slight hesitation from 2nd to 3rd, but then again I am now "hyper-aware" of the tranny's shifting behavior since this problem has cropped up.

I have Coby Hughey's old C4 that has blown clutch packs that I intend now to repair, since there are some nice upgrades over the stock C4 parts (custom 3000 stall converter with 2.4:1 torque multiplication, kevlar clutches, steel hub, arc welded vanes, torrington bearings). Once it's ready, I'll push my current C4 and if I don't "kill" it, then I'll swap it out one nice long rainy weekend and be done with it.

Yellow75 · Mar 21, 2006

You have Coby's old bronco right? What ever happened to Coby? Still in bronco land I hope!?? Didin't he have a 408 in there? I'd bet with a stock C4 it puts the hurt on the little auto if so.

Mark · Mar 22, 2006

Yellow75 said:
You have Coby's old bronco right? What ever happened to Coby? Still in bronco land I hope!?? Didin't he have a 408 in there? I'd bet with a stock C4 it puts the hurt on the little auto if so.

*droool* A 423ci multiport sequentially fuel injected Windsor with forged rods and pistons, and ported Trick Flow racing heads good for 450HP/550ft-Ibs *droool*
Coby ate up a few C4's before having this one built. It lasted the longest. I'm sure it can handle my puny stock 302 in my daily driver.
Coby is around, he'll post up on the Bfix or EBML email list from time to time. I'm sure he'll return more actively to the Bronco world.
I still consider the Black Cloud his, he built it, I'm just a care taker.

BwoncoHowie · Mar 22, 2006

Mark Troy said:
Well, it helped - a little. Now it revs to maybe 2100 rpms and will then shift, but it's still not right. There was a pin in the end of the old modulator about 1 1/2" long that I put into the new one - I'm guessing that was proper.
The vacuum line seemed old and cracked, I guess this weekend I'll replace that.
I'm hoping the damn thing fixes itself!

I noticed you said you had the Red stripe modulator. Is yours the dual port version?
One thing you might try if yours is the Dual port modulator...

Try disconnecting and plugging the source feeding the small vaccuum line then take it for a road test. see if that makes a difference.

Report back what happens and I'll explain later.

Mark · Mar 22, 2006

BwoncoHowie said:
I noticed you said you had the Red stripe modulator. Is yours the dual port version?
One thing you might try if yours is the Dual port modulator...
Try disconnecting and plugging the source feeding the small vaccuum line then take it for a road test. see if that makes a difference.
Report back what happens and I'll explain later.

Well, one of the ports (the thin black one, see arrow) is plugged.
So was the unit that I pulled, so I plugged this one.
Maybe run this one somewhere?

BwoncoHowie · Mar 26, 2006

Mark Troy said:
Well, one of the ports (the thin black one, see arrow) is plugged.
So was the unit that I pulled, so I plugged this one.
Maybe run this one somewhere?

Re-install the new one the way it came off, if it has an adjuster screw, turn it in 2 full turns, then drive it.

BwoncoHowie · Apr 3, 2006

Did you get it fixed yet?

Mark · Apr 16, 2006

BwoncoHowie said:
Did you get it fixed yet?

It's gotten gradually better almost to the point that it shifts as smooth as it did before (keep in mind that before I wasn't as tuned into the shifting behavior as I am now). Does better when it's warm.
If it was my module, then the new one required a "break-in" period.
I still plan on rebuilding the spare C-4 I have just for kicks and giggles.
I plan on doing that next winter and hopefully this tranny (if it is going bad) will last until next spring (fingers crossed).

Uh-oh, I think my C-4 is going bad...UPDATE 3/21

Mark

Bronco Klutz

iwlbcnu

Bronco Guru

bannind

Sr. Member

BroncoMark

Bronco Guru

Mark

Bronco Klutz

Naildriver111

Full Member

Mark

Bronco Klutz

BroncoMark

Bronco Guru

Attachments

SaddleUp

Bronco Guru

Mark

Bronco Klutz

Yellow75

Bronco Guru

Mark

Bronco Klutz

BwoncoHowie

C-4 Wizard

Mark

Bronco Klutz

Attachments

BwoncoHowie

C-4 Wizard

BwoncoHowie

C-4 Wizard

Mark

Bronco Klutz

Similar threads