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Old 02-12-2007, 09:56 PM
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81 chevy turbo 400 C20 4x4

I am trying to raise the shift point on a turbo 400. The shift point is between 38 and 3900 RPM's . I would like to see the shift point between 4900 and 5000 RPM's during wide open throttle acceleration. I want an automatic shift point (not manual). I have a stage two Transgo shift kit and valve body in the trans . I have tried a B & M adjustable modulator ( no help ). I have disconected the vacuum line to the trans entirely (not good) shift point went up, would stay in low gear until pressure bypass would popoff, then it would shift, I have not messed with the governor yet.I need help (please)

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Old 02-13-2007, 07:40 AM
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81 chevy turbo 400 c20 4x4

Removing metal from the governor weights is what you need to do.

This is not an exact science and can be quite frustrating at times.

Remove the nails at the bottom of the governor, grind a little metal from the inner [secondary] weights a little bit at a time,maybe 1/8th to 3/16 off each side, [not the side where the nails go thru], then reassemble the governor,using 6 penny finishing nails,if I remember correctly.

If you have access to a torch, heat the ends of the nails up [sharp ends],then smack them with a hammer,so the nails will stay in, of course.

Reinstall the governor, then take her for a drive.

Then bring it back,pull the governor back out,and repeat the procedure,unless your just plain lucky,and you happen to have ground off just the right amount of metal the first time[not likely].

The more weight you take off, the later the shift points will be. Good luck,and don't forget to remind yourself how much fun you will have once you have accomplished your goal!
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Old 02-15-2007, 08:23 AM
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you have to change the govenor springs
i have mine set at 65oo at full throttle so no i don not manualy shift at the track i just leave it in drive
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Old 02-15-2007, 09:16 AM
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Shift point

Thank You Bigblockbill,
I will be working on the shift point next week.Just ordered a spring kit yesterday,it will be here Tuesday. I'll probably start on it late tuesday afternoon. I'll let you know how it turns out. Thanks, Ted
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Old 02-15-2007, 09:18 AM
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[QUOTE=4x4mud]Thank You Bigblockbill,
I will be working on the shift point next week.Just ordered a spring kit yesterday,it will be here Tuesday. I'll probably start on it late tuesday afternoon. I'll let you know how it turns out. Thanks, Ted
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Old 02-15-2007, 09:48 AM
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you know its a K-20 and not a C-20 right

C-20 is a 2wd 3/4 ton


good luck
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Old 02-15-2007, 02:38 PM
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81 Chevy K20 4x4

Thanks D,
You are right, on some vehicle's the letter means a huge difference, Mud dragging here the body could be completely deferent in a week. It depends on how rough the track gets and how bad a person wants to win. Oh yea i almost forgot, how soon the next race, and how much money do i have to fix what is broken. I wish I had found Hotrodders Bulletin Board years ago, this is great. All i need to do now is learn to use a keyboard. Have a great day, Ted
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Old 02-15-2007, 02:50 PM
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Quote:
Originally Posted by 4x4mud
I am trying to raise the shift point on a turbo 400. The shift point is between 38 and 3900 RPM's .

would stay in low gear until pressure bypass would popoff, then it would shift, I have not messed with the governor yet.I need help (please)

That bypass popoff is the governor shifting it. That is the max rpm that the governor is set for now.

The modulator makes it shift sooner by overriding the governor. If it is shifting at 3900 that is a modulator problem. When you hold full throttle, zero vacuum, the modulator should not be doing anything against the governor.

Changing the springs or weights might be advisable if your "popoff" point is not what you want.
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Old 02-16-2007, 10:12 AM
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81 Chevy 4x4

I ordered a governor spring kit a couple of days ago. Do you know what color stripe on the modulators is indicating? Is it the partial throttle or high vacuum shift point? Colors white, blue, orange, ect,ect. After I install the spring kit will the trans shift under wide open throttle when the RPMs open the governor and the modulator control the shift under partial throttle. I am happy with partial throttle shift point,I need 1000 RPMs at the top to get up on the cam, maybe more when I add in ratio spread. I would like to shift have land close to the top of the torque curve, deep mud creates lot of resistance, need more speed, Thanks, Ted
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Old 02-16-2007, 02:36 PM
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81 chevy turbo 400 k20 4x4

If your Transgo shift kit provided you with a 1-2 shift valve,along with a cup plug for the valve body[1-2 shift valve train exhaust hole], you will be able to obtain automatic max throttle upshifts above 4500 RPMs, by working with the governor.

Since spring force has a static affect on the governor, just changing springs will not likely produce your desired results.

Centrifugal force acts on the weights in a governor,therefore the effect is more dynamic.

The final drive ratio is also a major consideration, when calibrating governors.

Higher numerical differentials will cause the governor to react differently than a lower [numerical] final drive.

For example,your gov in a vehicle with a 3.55 final drive, may produce 30 psi of governor pressure at 25 mph.

Put your governor in a vehicle with a 4.11 final drive,it may produce 30 psi of governor pressure at 15-20 mph.

Since governor pressure is acting against shift valve spring force,and tv pressure[modulator] to stroke the shift valves,you can see why reducing that governor pressure will raise your shift points.
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Old 02-16-2007, 05:31 PM
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81Chevy K20 4x4

Briscoe,
I am not sure if I understand all of what you are saying, and in my head trying to figure the final ratios is quite a project. Figuring in resistance weight and drag , then adding distance it is very complicated. Tire height 38.5 inches, differental ratio is 488 to 1 , turbo 400 ratio 1st. gear 2.52 I think or close to it, 2nd. gear 1.52 I think or close to it, 3rd. gear is 1 to 1 and then it goes to a new process 208 transfer case that is 2.61 to 1 in low range.
Tracks range in length from 100 to 400 feet. Many between 150 and 200 feet. The tranny has a stage 2 transgo shift kit in it at this time, I do not know about the plug, It has different springs , the valve body plate has been drilled and thats what I remember about the shift kit, I read the paperwork, did what it said put it back together and refilled the trans with B&M Trick Shift. I am ready to change the weights and springs as soon as they get here,I guess I need more direction about that plug your referring to. Thanks,Ted
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Old 02-19-2007, 08:18 AM
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82 chevy turbo 400 k20 4x4

Ted the 1-2 shift valve will stroke all by itself,and make a 1-2 upshift, even in manual low,[at RPMs over 4500] because governor pressure will be too great. Unless.

The 1-2 shift was provided in your transgo kit.Along with a cup plug for the valve body.

Or you modify[grind off metal] the 1-2 shift valve,and install a cup plug in the valve body to block off the exhaust passage,[1-2 shift valve train].

Grinding the lands of the valve allows line pressure on the back side of the 1-2 shift valve,to oppose the enormous amount of governor pressure you will be creating. Blocking off the exhaust hole, keeps that fluid on the 1-2 shift valve.

Ted if you have access to a fax machine,I would be glad to help you with this. If so, please send me a private message. Dana
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Old 02-22-2007, 02:16 PM
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81 Chevy 4x4

Briscoe,
Sure could use your help,had to work few days sorry about delay in response.
Sent a private message, still trying to figure out bulletin board, hope it went ok, about ready to get started again. Race on March 3rd. cancelled, have more time, not so much pressure. Thanks Ted
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