Servo Questions

[85 Riviera]

1. Is every TH200 or TH200C servo larger then a standard OG 200-4R's servo?

2. Is there some Th200 or TH200C's that have larger servos then others and if so what are the most desireable 200C servos and what are the least desirable TH200 or TH200C servos?

3. Will a larger servo such as the TH200 or TH200C's make the trans shift any firmer/snappier or will it just provide more holding power?

4. Will a larger servo such as the TH200 or TH200C's effect the 2-3 shift in anyway?

Thanks In Advance Guys, this site has never let me down!

 

[chris718]

76 to 78 200s with the vent on the extension housing and the last 3 digits on the piston being 111 or 112.these are the best and the 112 has more area than the superior servo.the smaller one number 111 is very similar to the gn in size but shifts better because of the absense of the litte primary piston present in the later design 2 piece servos.the reason for the extra piston is gm said the larger piston was too slow to react on initial band apply so they incorporated a second primary piston .this piston actually slows down apply by pushing in on and delaying the large pistons apply.these will also undoubtedly firm up 3rd gear due to oil balancing on both sides of the piston that immediately knock off the band in hi gear.seems i started a trend here with this great factory piece.

 

[85 Riviera]

Hey Chris, thanks again! Happy Thanksgiving!

 

[chris718]

same here.

 

[85 Riviera]

76 to 78 200s with the vent on the extension housing

I never looked at one of these yet, What is the "vent in the extension housing". What does it vent and to were? Sorry for this simple Q, your help is a blessing!

 

[chris718]

the vent that allows atmospheric pressure to escape the transmission when filling it or when the transmission is running and positive pressure is generated in the case from crossleaks and normal operation.

 

[85 Riviera]

Oh you meant on the trans case! LoL I was under the impression that the vent had something to do with the servo. Now I understand that you was explaining how to identify the 200 that had the 112 or 111 servo. Stupid me. Hey thanks all your help, I found one of these servos today at my local Pick N Pull. Now I just gotta find time to install it. Its actually going in my 325-4L, I just say its for a 200-4R cause alot of people get side tracked when I ask Q's for the 325-4L. I look at the 325-4L as a FWD verson of the 200-4R, I mean they share the same servo, band, clutches, and basic valve body idea. Anything that improves the shift of the 200-4R will most likely work on the 325-4L or at least thats been my luck so far! Do you have any experiance dealing with these 325-4L's? Mines been behind a 403 Olds with a decent cam, a D5 converter and a 3.36 final drive from a T Type Riviera, its been 8 months and many full throttle blast, the trans is still banging hard. Many told me the trans would not hold up to that kinda power. The mods I used so far on the trans has been> blocked 1-2 and 3-4 acc, blocked line bias valve, stiffer PRV spring, stiffer TV spring and removed 2-3rd acc in servo with bleed hole blocked as well as tuning the governor to desired shift points. So far So good.

 

[77 cruiser]

What`s the cover # on the 112 servo?

Jim

 

[KEhrhardt]

Originally posted by 77 cruiser
What`s the cover # on the 112 servo?

Jim

Piston -> Cover
8628112 -> 8628134
8628111 -> 8628133

From the THM200 Systematic Trouble Shooting Manual

Happy Hunting

Kurt

 

[77 cruiser]

Thanks.

Jim