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TH-350C shift points

Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
Ever since I have had the L81 running in the Vette, I have noticed a relatively close shift points on my original tranny. As a result, when in WOT, the Vette is already in 3rd gear by 25 MPH. (1st - 2nd = 15 MPH, and 2nd- 3rd = 25 MPH). It has a shift kit, so when in WOT, the tires would bark when the shift took place.

A couple of weeks ago, I installed a lighter weight and spring on the governor. My hopes was to slightly delay the first shift. Yesterday, the weather was finally nice, and drove it for the first time since the weight change. Yesterday, I got about 17 mph and then second shift at nearly 30. But I lost that bark of the tires. The shift does not seem as crisp.

Today, I replaced the weight again to one even more light, and the 1st-to-2nd shift takes place at 20 mph. The 2nd-to-3rd shift takes place at 35 mph. Some of the force is back, but still no bark of the tires.

I suspect that I need to adjust the modulator somewhat to increase the crispness of the shift, once the weights in the governor are replaced.

Does this seem plausible? Am I confusing something?

I should be able to post some real numbers tomorrow night from my dyno runs on Monday.

GerryLP:cool
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Sorry Gerry, I can't answer your questions, but I can say that those numbers seem really off. You are telling me that you would be in 3rd gear from 35mph (at WOT) all the way to 132 mph? Mine shifts from 1st to 2nd around 45mph and from 2nd to 3rd at around 85mph, and of course stays in 3rd until it tops out. Have you changed your rear gearing? Hope this helps a little.

-Tatortot
 

bill81vette

Moderator
Joined
Jan 17, 2004
Messages
4,321
Location
Troy,NY
Corvette
1981 dark blue metallic
Gerry although I haven't driven mine since October,I know my tranny is in 3rd gear by 35-40 mph(which I don't like).....it seems to sluggish this at this point.1st-2nd is very quick,I end up manually holding the shifter in 2nd till around 45 mph then I let it into 3rd gear
It seems to like it better...I don't know how to change it or if our vettes are just that way....
 
Joined
Mar 26, 2002
Messages
812
Location
Midlothian, VA
Corvette
1981 white/blue interior automatic
Bill,

Are you talking about shifting at WOT, or just normal driving around? Mine will go into 3rd at around 25mph with just light throttle, and yes, it seems sluggish at that point. I too find myself holding it in second.

-Tatortot
 

bossvette

Gone but not forgotten
Joined
May 19, 2003
Messages
3,233
Location
West Unity Ohio
Corvette
1968 1997
you may want to reset your kickdown cable so it stays in gear longer at WOT.
the way I do them and it works for me is with the throttle closed hold the release in and allow/push the outer cable casing to retract all the way towords the firewall, then open the throttle all the way and close the release.
 
Joined
Apr 29, 2001
Messages
2,141
Location
Rio Rancho, NM
Corvette
1981 HD Suspension; ZN1 Option
I purchased a B&M kit long time ago, and it is pretty straight forward to change the shift points with either lighter (to retard the shift point) or heavier (to make the shift point occur sooner) weights, and also to either spread them apart (with lighter springs) or closer together (with stiffer springs). The instructions recommend the trial and error approach at WOT since that is the only way to be consistent with the shift points.

The catch is to make the changes one-at-a-time. Weights first, and the springs.

My concern was the crispness of the shift to disappear with one weight change.

Tatortot, now that you mention it, I do have 3.31:1 in the rear.

Bill, I found that it was more annoying to have the 35 mph shift point for 2nd - 3rd, for once it drops below that speed in normal driving, then the Vette "acts" ready to shift, but it won't until 35 mph. The spread of the shifts points can be changed with lighter springs. EDIT: Bill, I read in the book that the modulator can cause stiff or even sluggish shifts, so before you mess with the gorvernor (if you were at all), you should make sure that the modulator is good. Basically, any kind of fluid coming from the vacuum side is cause for replacement. See page 7A-5 in shop manual.

Craig, I will try that. It seems to make sense. I wonder what kind of effect it has on the changed governor settings.

GerryLP:cool
 

bill81vette

Moderator
Joined
Jan 17, 2004
Messages
4,321
Location
Troy,NY
Corvette
1981 dark blue metallic
Bill,

Are you talking about shifting at WOT, or just normal driving around? Mine will go into 3rd at around 25mph with just light throttle, and yes, it seems sluggish at that point. I too find myself holding it in second.

-Tatortot
mine is just normal driving....I don't do the WOT to awful much...
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Sorry Gerry, my TH350C has the "in all gears neutral syndrome" and needs to be rebuild. I don't know if a 350 has in a sense the same throttle valve as a 700? I read that when the throttle valve leaks oil, the transmission will shift earlier because there is a early buildup of oil pressure.? (something like that..) Maybe you want to take a look at that..

Groeten Peter.
 

zachh

Well-known member
Joined
Aug 1, 2005
Messages
221
Location
virginia beach, va
Corvette
1979 black 'n' silver L82 1978 Trans Am Y88
Sorry Gerry, my TH350C has the "in all gears neutral syndrome" and needs to be rebuild. I don't know if a 350 has in a sense the same throttle valve as a 700? I read that when the throttle valve leaks oil, the transmission will shift earlier because there is a early buildup of oil pressure.? (something like that..) Maybe you want to take a look at that..

Groeten Peter.
Turbo 350s dont have throttle valves.. They have kickdown cables... or something like that... I dont think they are adjustable, if they are, i dont know how to do it. Throttle valves are on 700r4s and 200r4s. Throttle valves work by pulling a cable which opens a plunger which allows a certain amount of fluid for the rpm the engines at. When the throttle moves far enough, there is enough fluid pressure and volume to make the transmission shift. So if it leaks oil, it will change your fluid(shift) settings. I dont know how much, but itll do something. Thats the principle behind the thing.
Good Luck
zachh
 

Peer81

Well-known member
Joined
May 21, 2003
Messages
2,497
Location
Netherlands
Corvette
'81 Black
Thanks Zachh, so no need to look for throttle valves in Gerrys 350..:ugh

Groeten Peter.
 
7

76 Sting

Guest
I purchased a B&M kit long time ago, and it is pretty straight forward to change the shift points with either lighter (to retard the shift point) or heavier (to make the shift point occur sooner) weights, and also to either spread them apart (with lighter springs) or closer together (with stiffer springs). The instructions recommend the trial and error approach at WOT since that is the only way to be consistent with the shift points.

The catch is to make the changes one-at-a-time. Weights first, and the springs.

My concern was the crispness of the shift to disappear with one weight change.

Tatortot, now that you mention it, I do have 3.31:1 in the rear.

Bill, I found that it was more annoying to have the 35 mph shift point for 2nd - 3rd, for once it drops below that speed in normal driving, then the Vette "acts" ready to shift, but it won't until 35 mph. The spread of the shifts points can be changed with lighter springs. EDIT: Bill, I read in the book that the modulator can cause stiff or even sluggish shifts, so before you mess with the gorvernor (if you were at all), you should make sure that the modulator is good. Basically, any kind of fluid coming from the vacuum side is cause for replacement. See page 7A-5 in shop manual.

Craig, I will try that. It seems to make sense. I wonder what kind of effect it has on the changed governor settings.

GerryLP:cool

Gerry I concur!!! the shift points stink!! The modifications sound simple enough do you still have the install sheet? I would love to make the same changes as you have and play around until I get the performance that I prefer.

Is it asking to much to send me a copy of the install sheet so I can see just how easy this is or maybe scan it in and send it over in an e-mail? If you can't do you know where I could find a copy or the instructions?

Please keep this post going if you can, I find this extremely interesting and would like to hear more about your success.

:beer
 
7

76 Sting

Guest
Gerry,

Thanks PM sent back... Any more luck with the configuration?
 

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