Brandontyler65

well i was talkin to a guy at the transmission shop the other day killing some time and i told him i have a soft shift from 2-3rd gear and he told me to try installing this b4 i get into the valve body TCI Servo so if i do get this do i just unbolt the other one and stick this one in or what and please be specific pics would help to if anyone has done this

THUMPIN455

Since he recomended it, ask him if there is anything else to it. It looks to me as though you install the servo and cover, then adjust the bands.. There is a band adjustment procedure in the FAQ.. Although I have not done one on a C4, we have put servos and a multitude of other parts in Th350s, 400s and GM OD transmissions.

The C4s I have rebuilt have shifted just fine with a stock rebuild.

DGA

No-No-No

If you simply pop the servo you will drop the strut that goes between the band and the servo into the pan.

I have sometimes been skillful enough to accomplish the servo R & R without dropping the band but since you are not familiar with the construction I would hesitate to tell you to try it.

Not sure what you call a 'soft shift' but if a problem does exist I would recommend that you replace the vacumn can first.

Now for the lesson. Both shifts 1-2 and 2-3 occur when the Governor pressure (Created by a device on the output shaft of the transmission) becomes strong enough to move the appropriate shift valve in the valve body.

Governor pressure increases as wheel speed increases.

The valve is held close by a spring assisted by throttle presure. Throttle pressure is controlled by the vacumn can with causes throttle pressure to increase in proportion to engine load

During the 1-2 shift when the valve does move pressure is fed to the apply side piston of the servo which is being held in a release position by a spring.

When the 2-3 shift is called for the 2-3 valve moves and sends pressure to the High Reverse Clutch and to the release piston of the int servo. The apply pressure remains but the piston moves to the release position because the release side piston is larger and also is assisted by the release spring.

Governors either work or they don't---Vacuum cans on the other hand can suffer from various problems.

Since the easist possibility is the vacuum can and it is not very expensive I would start there.

If you feel that the problem is the piston (they do leak) I would simply reseal it. I'm sure that a trans shop has a big supply of seals as many times the servo is not resealed during a so called overhaul/rebuild

Sean W.

noob saves the day!

THUMPIN455

OOOPS! DGA.. I forgot about the struts... My bad.. yeah he is 100% correct... I been readin about TH2004R stuff too much lately.. dang it.

you da man.. Thanks for catchin that before he had to drop the pan and figure out how to get the struts back in..

Brandontyler65

ok i'll give the modulator a try

Soaring

Thanks for your expert advice Don. Sounds like you have been around a block or two with the C4's.

hutchamatic

One question that was not asked is what letter is on the servo. The TCI servo is a modified H piston. This is the largest one that is easiest to find. There was a C servo but they are very hard to find. They have been reproduced but very expensive and not really worth the difference. The reason for the larger servo is in the hyd part. Larger servo more apply area and more pressure on the band. The TCI has an O-ring on the cover to help prevent leaks also. I have replaced many servos and not dropped the band anchor. You will have to have the apply pin lined up horizontal so it will go in. I have never rebuilt one without replacing all the seals. I hope no has seen this done.