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Discussion Starter #1
My cars PO installed a shift kit and it shifts too hard for my taste. I don’t know what brand he used. Is it possible to remove the kit or just soften the shifts? I don’t really know how these kits work. My transmission is the original C4.

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If your PO installed a adjustable modulator, you could try to turn the inside screw "out" for softer (and earlier) shifts.
My C4 transmission had a very soft 1-2 shift. I bought a shiftkit to solve this problem but the night before I wanted to install the kit, I discovered that this problem had everything to do with the adjustment of the modulator.
The transmission shifts so nice now, that I decided to keep my hands clean and not install the shift kit.
 
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I think that in installing most shift kits, you end up drilling a couple of holes in the valve body, so reversing it may not be possible.

The though of adjusting the modulator has merit though.

Worst case, get a stock valve body from the salvage yard and a rebuild kit. You don't have to drop the tranny, just pull the pan and the valve body.

Working on the valve body isn't too hard, but you do need to be mechanically inclined.
 

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Remove vacuum hose from modulator; install vacuum guage; start engine....note vacuum reading at idle and at 2000 rpm. Post those back here...

While vacuum hose is off modulator, look for screw slot inside nipple where hose attaches...if present, unscrew (CCW) 1/2 turn. Re-attach hose and test drive vehicle.

Personally, I'd leave the shift kit in the trans...it will markedly increase trans life, especially if you increase engine performance in the future...

Good luck...!
 

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Pat's right. The firmer shifts are actually saving the clutch pack surfaces in your transmission. To achieve "smooth" shifts the factory sets the tranny up to slip. That wears the clutch packs out sooner but provides a more saleable shift to the non-enthusiast. Even backing down the modulator will result in increased slippage (and heat) in the transmission.
 

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Discussion Starter #6
I'll check if the modulator is adjustable. I'll take the vacuum measurements too. What does that tell me?

I understand the clutch packs will wear faster as slip increases but I'm not really concerned about that. The car is a weekend driver so I don't put too many miles on it. The transmission really slams into gear under the lighest acceleration. I would just like it to be a bit smoother.

I'll think I will research the exact changes that were made when the shift kit was installed. If orifices were drilled out I may just replace the valve body and install a milder shift kit.

Thanks for the advise.
 

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I'll take the vacuum measurements too. What does that tell me?

Measuring the vacuum at the hose outlet will tell you the condition of the vacuum line from the engine as well as the state of engine tune, if you compare it with readings taken with the same parameters off the engine intake manifold itself.

A blocked/restricted line or poor engine tune can result in lower vacuum readings at the modulator, which makes the transmission think the engine is at a higher power/load setting than it really is. This causes the shifts to come later and firmer.
Simply put, high vacuum means earlier and softer shift, low vacuum means later and firmer shift, all else being equal.

I've found the installation of a shift kit markedly improves trans performance and life, even in stock applications like my D-coder. I've been installing them in C4's since the mid 70's (in my high school/college daily driver/street racer) through present, both in street cars and vehicles like my race car.

I firmly believe this is one reason (of several) I've never seen any reliability problems with my trannies and those I've done for friends. I do understand your desire for a more comfortable shift and respect that...if some compromise can't be achieved by adjusting, then putting a stock valve body in will likely achieve the results you desire. With maintenance and a reasonable driving style, you should still experience long service.

Good luck!
 

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Imagine a icy, twisty road and banging shift while taking on a bad corner. Sometimes gives you a handful. That's why we call them XXXX kicks.
Oops, I noticed that there is a four letter word screening. But you know, the word shift without f.
 

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Discussion Starter #9
I can imagine. North Carolina has plenty of twisty roads and a fair amount of black ice on winter mornings. My open rear end helps a little.
 

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Discussion Starter #10
I did a quick check of my vacuum. 19" in park at idle and 20" in park at 2000 rpm. Does that sound normal?
 

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19" in park at idle and 20" in park at 2000 rpm. Does that sound normal?

Yes, Perry, that's actually quite good....so we know your modulator is seeing good engine vacuum. Perhaps you could test drive the car in Drive range and share your perceptions of the shifts at part throttle from a stop and then at WOT from a stop(if you're comfortable doing this), noting the MPH when the trans shifts under both parameters, along with your impressions of any changes between the two (part and full throttle)...

This is all part of diagnosing...also, did you note an adjustable modulator when removing the hose to check vacuum?

Get back to us...
 

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Discussion Starter #12
Well, I finally got a chance to test drive the stang. I ended up spending the whole weekend cleaning the garage. I thought it would take just a few hours by my estimate was seriously off.

Anyhow, accelerating moderately, the 1-2 shift happened at 15 mph and the 2-3 shift at 30. The shift was hard enough to make the steering wheel vibrate. I think that why I find it irritating. At WOT, it shifts from 1-2 at 50 mph. I got to 80 without the 2-3 shift and decided to slow down. The speed limit was 55 and the road was not suitable to high speed. I'll try it again later on the highway.

I may have time next weekend to check the modulator and try adjusting it.
 

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Wow...80 in 2nd, Drive range at WOT with no shift...?

Definitely a scheduling problem, IMO...hope it's as simple as a modulator adjustment...

Moderate throttle (I'm assuming typical acceleration during driving) numbers sound a bit high too...do you have 2.80's in the rear? (can't remember)....I've got those numbers adjusted down by 5-7 mph lower with the shift kit and adjustable modulator in the D-coder...it's got 3.0's

Is the 1-2 the one that rattles the steering wheel? Usually, that's the hardest one (band)

Update us when you have some time to test further...
 
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