Ford Mustang Forum banner

1 - 6 of 6 Posts

·
Registered
Joined
·
56 Posts
Discussion Starter #1
I bought a 65 mustang with a 289 and a c4 transmission. It would always shift rather hard from 1st to second and later gears were less and less hard. I recently brought the trans in and had it rebuilt. Now that I got it back, (quite a while later) I still feel that hard shift from first to second and I am worried because it is really hard. I dont remember if its harder now than before but if its the same then I'm suprised I would have drive it like that. what could be the problem? I want to get some ideas before I take it back to the trans shop. Thanks
 

·
Registered
Joined
·
101 Posts
have you checked the modulator valve?

you might try adjusting the modulator valve in one turn and see if that softens the shift. if it feels harder put it back where it started and adjust out one turn. from the factory setting you should have four turns in and out. it is not recommended that you go more than one turn at a time. if your modulator valve is not adjustable it can be replaced with an adjustable one for about 25 bucks.
 

·
Registered
Joined
·
1,806 Posts
Did you mention the hard shifting to the shop that rebuilt your transmission?
Is it the original C4?
What speed is it shifting from 1 to 2?
is the down shift linkage adjusted properly?
Do you have full manifold vacuum to the modulator?
More information will help get you the right answers.
 

·
Registered
Joined
·
56 Posts
Discussion Starter #4
I havent told the shop yet, I want to go in with some sort of knowledge about the problem. this is the original trans, Im unsure of the speed, but I do have full manifold vacuum
 

·
Registered
Joined
·
1,806 Posts
You should have mentioned that it was shifting hard when you took it in for a rebuild. That gives them an opportunity to fix it.
Water under the bridge now.
as for the hard 1 - 2 shift There is an accumulator valve in the transmissions valve body that can be adjusted with different springs or shims. There is also a small rubber disc that is commonly left out to improve the shift (or forgotten). You can install a missing disc to slow the shift down. You are asking me to "undo" the things I normally do to make a C4 shift firmly.
Just so you know a harsh shift is not a bad thing as long as it happens at a low enough speed. My street C4s typically shift 1-2-3 before you cross an standard intersection with light throttle. On the other hand if you have you foot buried in the carpet it will spin the tires on the 1-2 shift at about 40 mph. The 2-3 full throttle shift will typically chirp the tires on dry pavement at 55 to 65 mph. This from a C4 that is built for street use at a cost of about $750 - $760.
The fast shifts, when they happen early, is easier on the transmission and on your fuel mileage. The performance is built in for those times when you need (want) it.
 

·
Registered
Joined
·
56 Posts
Discussion Starter #6
Thanks

Thanks for the help. I was unaware that the way it is shifting could be benifitial. I was worried that the hard shift might hurt the new trans. I guess Im just babying the new rebuild. Thanks again.
 
1 - 6 of 6 Posts
Top