C4 shifting late and downshifting early with new motor

Hey Fellas,

The new motor is running about 9-10 in. of vacuum pressure (old stock motor ran 22in.) and when using the full automatic feature on the street/strip Dynamic C4 it shifts late and when slowing down to a stop, it downshifts to 1st at about 15-20mph (a little too high IMO, since you can feel the car revving up). My first thought is to back out the vacuum modulator about 3 turns on the C4 since it's screwed in about 4 turns. Am I on the right track for diagnosing this problem?

Thanks in advance.

Erik

p.s. Could someone post a link or instructions on how to change the U-joints on a driveshaft (front and rear).


[addsig]

It is very simple for the most part to change u-joints. The key is having something to press the cups out of the yokes. Either a vice, press, C-clamp or if you feel lucky, hammer them out without beating up the yoke.

With the driveshaft out of the car, remove the clips that holds the cups in the yoke. They can be on the outside or inside of the yoke.

Since I normally use a vise, I am going to say vise when you could be usning a C-clamp or press.

With the clips removed, find two sockets. One larger than the cup (not by much). Regular depth sockets are okay, deep sockets aren't required. Then find a socket slightly smaller than the outside diameter of the cup. Place the larger socket on one side of the yoke and the smaller on the other side. Tighten the vise and press out the cup into the big socket. Once removed, lay it to the side. If you are going to re-use it, make sure all the needle bearings are in the cup.

next, place the big socket on the other side of the yoke, make sure the smaller socket has the ratchet end against the trunion of the u-joint and press the u-joint to the other side of the yoke removing the other cup. With both cups removed, you can now remove the u-joint from that yoke. Repeat as many times as needed.

To install, place the u-joint without cups in to the yoke. Start both cups into the yoke and gradually press them into the yoke while watch the u-joint to insure it is aligned with the cups. (You can do one cup at a time and might be the best way at first.) Once both cups are in, place your small socket against one cup and press it in untill you can install the clip for that side. Once installed, place the socket on the other side and press it in to installe the clip.

Repeat for the other cups. Grease u-joint if it has fittings and install driveshaft.

If one cup will not go in deep enough and the other one does when you are installing the clips, then most likely you have a needle bearing that has fallen over. You will have to find the cup and place the needle bearing back into position.

Hope this helps
[addsig]

Vacuum is the issue here. It makes your modulator work for shift points. Adjust it and go for a drive. Drive it the same way after you adjust it each time. You might have to shorten the linkage rod. But only .030" at a time.

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2002-10-22 01:36, dacofa wrote:
Vacuum is the issue here. It makes your modulator work for shift points. Adjust it and go for a drive. Drive it the same way after you adjust it each time. You might have to shorten the linkage rod. But only .030" at a time.
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

I backed the vacuum modulator out about 3.5 turns (almost sticking out) and it still seems to downshift too early (~15mph) when coming to a stop. It never used to do this with the old engine, but then again the old engine made 23 inches of vacuum. Current motor is 9-10 in. Does the transmission downshifting early have anything to do with the vacuum?
I'm not sure what else to look at at this point. Anything else you guys think I should check? The vacuum modulator tubing is connected directly to the intake manifold fitting.

Thanks in advance.

Erik

p.s. dacofa, what do you mean by adjust the linkage rod?


[addsig]

Dacofa is refering to the modulator pin..which is located in behind the modulator..

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2002-10-23 06:04, gregaust wrote:
Dacofa is refering to the modulator pin..which is located in behind the modulator..
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Gregaust and Dacofa,

I called Dynamic Racing yesterday (the maker of my C4) and they said I need at least 15in.hg of vacuum or it would shift late and downshift early. Explains everything. They also said that I could shorten the linkage rod by 1/16" and maybe change to a bigger vacuum modulator. He said it would help, but not by much.

Is there anyway to increase vacuum pressure?

Thanks in advance.

Erik


[addsig]

Oh great...I think that I'll be in the same boat as you, when I put in my c4. With the cam I'm running, I'm down around 5 in of vacuum at idle...Maybe it's time for that manual valve body now.[img]/phpBB/images/smiles/icon_smile.gif[/img]

66GT350,

I may switch as well when $$$ permits. I don't think manual valve bodies are that bad. I was never really good with a 4 or 5 speed though. I have a tendency of shifting too fast w/o the clutch being in all the way, therefore, screwing up my synchros.

Anyway to increase vacuum pressure guys?

Thanks in advance.

Erik


[addsig]

To increase the idle vacuum you need to do some fine tuning of the engine.You need to have your idle circuits in the carb just right and check out your ignition timing also..You may gain a little here...
You definitely do have a good vac source?I say this as i recently had a similar prob and found where the guy had the vac hose connected to the carb actually had no vacuum.
Also i dont know if it will really help but maybe if you take the vacuum from right under the carb,just in case you might currently have the vac point on a single manifold runner as some manifolds do..It's just a thought..

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2002-10-24 06:51, gregaust wrote:
To increase the idle vacuum you need to do some fine tuning of the engine.You need to have your idle circuits in the carb just right and check out your ignition timing also..You may gain a little here...
You definitely do have a good vac source?I say this as i recently had a similar prob and found where the guy had the vac hose connected to the carb actually had no vacuum.
Also i dont know if it will really help but maybe if you take the vacuum from right under the carb,just in case you might currently have the vac point on a single manifold runner as some manifolds do..It's just a thought..
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>

Hey Gregaust,

When you say "idle circuits" are you referring to idle air/fuel mixture screws? If so, they were turned in until the car started to stumble, then turned back out .25 to .50 turns. The timing has been set to 34 total, no vacuum adv. The vacuum modulator tube is connected straight to the intake manifold. The manifold is a torker. The carb spacer vacuum port is connected to my PVC tube. All the open ports on the carb have been plugged. There is a base gasket on the intake to spacer and no gasket between the spacer and carb. Should there be one there?

Thanks in advance.

Erik


[addsig]