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Tuning a 700R4

40K views 26 replies 8 participants last post by  revspan 
#1 ·
I would like some help tuning my 700R4. Hopefully, someone out there has some ideas to help me.

First, here are the basics of my setup.

350 SBC making 360hp, and 380 ft/lb torque. Max rpm of this engine should be 5800, as the power falls off after that. These are dyno proven numbers.
Engine has a Holley carb, with proper linkage for the trans pressure cable(TV made easy)
700R4 with a 2300rpm stall converter.
Ford 9" with a 4.30 gear, 255-55R16 tires
Vehicle is a 1937 Chevy truck that most likely weighs about 3000-3200lbs.

I have very few miles on this as I have just got it on the road, but for the 30-40 miles that I have driven, I definitely need to work on the transmission shifting.

Currently, I am not happy with the responsiveness that the transmission has in relationship to the throttle. In short, when I add throttle input, I would like to have a linear response to downshifts and later(higher RPM) shifts, which I currently don't have.

As an example,

Mild acceleration: the transmission shifts at maybe 2500rpm, which is fine.
Medium acceleration: The transmission may shift at 3500rpm, which is borderline.
Medium acceleration from a rolling start. Seems that the transmission just does not want to downshift enough, and stays in a higher gear and kind of lugs the engine.
Hard acceleration from a rolling start. Seems that if you REALLY stand on the throttle, that you can get the RPMs up, but then the transmission will "hang" at a high rmp(5500-6000), before it shifts.

So, there is something that I don't have tuned correctly. In an effort to make the medium power upshifts happen sooner, I changed the weights in the governor. The weights that were in there apeared to be stock and weighed 0.45 oz each. I replaced them with weights that were 0.30 and 0.25oz, thinking that that would make all of the shifts happen later. I also put in springs that were the middle two of the kit that I got(Shift technology). The springs that I put in seemed to be a little lighter than what was in there, but I can't be sure as I had no way of measuring them.

Also, I believe that I do have the TV cable set correctly, although I have taken the PSI gauge off the transmission due to the fact that I dropped the truck off today to have the interior installed.

So, any ideas?.... I have the governor kit that I can lighten the weights and springs more if that may help, I also have some fine tuning that could be done on the cable connection on the carb that changes the amount of "pull" in relation to the throttle position.

But......before I do any more testing, could someone give me some theory as to why the trans would behave in this manner? Is it the combination of really light vehicle and really low rear end gear that is making this a challenge?

Any thoughts or discussion would be appreciated.

Thanks



During normal
 
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#2 ·
1. TV cable should be 100% pulled out at max throttle, controls operating pressure as well as shift patttern. Very important to have it right.

2. With the 4.30 gear the governor is turning alot faster at a lower speed than it was designed for with a low to mid 3's ratios. You'll want the lightest weights you can find and springs that will keep the valve from being pushed in too soon.

Take the Garage tour: http://www.youtube.com/watch?v=cZIhuocG2ig
 
#5 ·
the carb is a holley 4150 with a kit from Bow Tie Overdrives.

I just ordered a "Corvette" Governor and will take it apart and weigh the parts, reassemble and see if I can get the shift RPMs up.

As for the hanging RPM, you may be right, because I really have to mash the throttle for it to rev up, and I may be pulling the cable too far.

Here is a question for someone...... If the governor is not calibrated properly(engine speed too low), can the TV force the tranmission to generate a higher RPM? In other words, if the governor isn't properly tuned, does this limit the transmission speed in all conditions?


Thanks for the comments so far.....
 
#6 · (Edited)
Simplified: The governor dumps presssure, when then centrifical force swings the weights out the valve is pushed in blocking off fluid exhaust passages. This causes fluid pressure to "back up" and puts pressure against the shift valves in the valve body and they shuttle against their respective spring pressures thus opening passages for fluid to apply the various clutches and band. You can makes some changes with the governor but with limitations.
Once the gov. valve is 100% in the control action shifts to the valve body.
 
#7 ·
Thanks for that explaination....it helps in understanding what is going on in the transmission.

Anyone replace a governor that is forcing shifts at 2500rpm and direct replace for a "corvette" governor? Wondering what could be expected.

I have seen a few pictures of them, and it looks like they are simply lightened up somewhat to reduce centrifical force.
 
#9 ·
revspan said:
Thanks for that explaination....it helps in understanding what is going on in the transmission.

Anyone replace a governor that is forcing shifts at 2500rpm and direct replace for a "corvette" governor? Wondering what could be expected.

I have seen a few pictures of them, and it looks like they are simply lightened up somewhat to reduce centrifical force.

A photo of a corvette style governor. Please keep in mind that a matching valve body on a vette is calibrated a bit different for this design of governor.


 
#10 ·
wow. Compared to the weights that changed in the tuning kit I have, the changes to the outer weights is HUGE. I weighed the inner weights in my stock governor, and they were 0.45oz. The kit I have as weights that are 0.50, 0.45(stock), 0.35, 0.25, and 0.20oz. It will be interesting to compare the mass of the outer weights.....I bet it will be a lot compared to the small changes in the inner weights.

With this, I am hopefull that I can get the shift points up where they need to be. Unfortunately, I have the truck at the interior shop now and can't make any adjustments.

Thanks again for all of the information! This site rocks!
 
#11 ·
Well, I installed the medium weights and the lightest springs and definitely had an impact in mid throttle response. Actually, under light throttle, the shift points may be a little high, as the trans will now rev to roughly 2800rpm at very light throttle. With a little tuning, I am sure that I will be able to get the mid-throttle shift point where I want with the adjustment kit that I have.

During the one full throttle blast that I did, the transmission downshifted and then proceeded to run right up to thye 5500 RPM rev limiter and hang there until I let off the throttle, at which time it shifted fine.

Any ideas?

I do have an aftermarked good quality dipstick, but was wondering if fluid level could impact this.

Not sure where to go as this really needs to be worked out.

Thanks
 
#14 · (Edited)
This might not help. Made a chart after calibrating my 85 c10 with a 3.73 rear and th350c. 1st 3.08 number/ 2nd 3.73 both 28" tire.

B&M governor calibration kit for WOT.....AN APPROXIMATION!!
GM#24202127 = 4400 rpm
Blue&Yellow 2 & 3 = 4900 rpm C10 tried good torque jump to 2nd at 4300
GM#24202117 = 5000 rpm
Blue & Yellow 4 & 3 = 5100 rpm 4500 chirp 2nd
GM#24202122 = 5200 rpm
Blue & Yellow 2 & 5 = 5300 rpm C10 tried revs out till done at 4700
Blue & Yellow 5 & 3 = 5500 rpm
Blue & Green 4 & 5 = 5600 rpm c10 revs 5000 full pull, hard kickdown
Blue & Green 3 & 5 = 5600 to 5700 rpm with 3.08 and 4700 with 4.10 s10 v6 +500rpm from stock
 
#18 ·
Well, the transmission is working fine at part and mid throttle. Unfortunately, at WOT, it still hangs at the rev limiter(5500RPM).

I think that I may pull that limiter chip and replace it with a 6000rpm chip to see if it may shift after 5500rpm. The engine has been dynoed and power falls off after about 5300, hence the 5500 limit that I had in the ignition system.

As I understand, WOT shifts are controlled via valve body......Is this for sure?......is there anything else that could impact WOT shift RPM?

Looking for a knob to turn

Thanks!!!!
 
#19 ·
O
Another update. Made a small adjustment on the TV cable...slight loosening. From a dead stop, at WOT, it would rev to 6000....bounce the rev limiter. Then when revving up, it runs right up to 5800, shifts fine and then is on to 3rd, which goes fine too.

So, I am thinking that I can make a small adjustment in the springs and weights to do the final tuning.

One other issue is that I would like to solve is a shift from 1-2, under light throttle, that is too quick. Could this be due to the light weight, and the 4.30 gear? Is there a fix for this? I already have the lightest springs in the governor.....

Any ideas?
 
#20 ·
another update

Ok...I have now pulled the governor and added weight.

Before and after RPM shift points

1-2 shift. Was 6000 RPM, which is on the rev limiter. Need to let off to shift
2-3 shift. Was 5900 and stayed right at 5900.
3-4 shift. Was 5900, and dropped to 4700.

So.....I am not sure how I can use the governor to move all of the shift points. Seems that the governor is having a big effect on higher gears. If I continue to add weight, I will lose a reasonable shift point in the 3-4 shift.

Also, I "could" simply lift a little during the 1-2 shift, but I plan on a nitrous shot that will rely on a micro switch detecting WOT, so lifting isn't what I would like to do.

Really looking for some ideas here... Thanks in advance.
 
#21 ·
Starting over

Well, bit the bullet and dropped a new "corvette" governor in. Wot shifts are now:
1-2. 4000
2-3. 4300
3-4. 3700

So, I still have some variation in shift points, but I am back under the rev limiter.

Tomorrow I will "sneak" up on an rpm that will keep me around 5500rpm

BTW, I did get advice from a local transmission shop owner that said to forget the governor kit, and simply grind mass off of the existing weights. He said tha the kits work for th350s, but are more trouble on the 700r4.
 
#22 ·
Well, the mystery is solved. I got so frustrated after 18 random tries that I took the time measure the spring pressure of all the springs and spent time studying all of the combinations that I had tried. After all this work, here are the conclusions that anyone doing this MUST take into consideration.
1) springs can impact shift RPM just as well as weights. Don't make the mistake that weights alone determine rpms.
2) springs must be matched to weights. For example, you can have two weights and two springs that will behave MUCH different if you simply switch the springs and keep the weights the same.


In the end, I got my combination right on with a 1-2 shift at 5700 and a 2-3 shift at 5800. I started with 4000 rpm wot shifts and made most of my improvements by changing springs and dropping one of the weights.

Hope this helps someone...
 
#23 ·
In the end, I got my combination right on with a 1-2 shift at 5700 and a 2-3 shift at 5800. I started with 4000 rpm wot shifts and made most of my improvements by changing springs and dropping one of the weights.

Hope this helps someone...
Been following your thread, glad you got it ironed out. Could you possible post what springs and weights you wound up using?

Thanks
Vince
 
#27 ·
NP...here is the final combination that I used. For the sake of addressing variation in different kits, I will also give some of the values that I measured for comparison.

Regarding springs. I took two measurements. First was at a compressed height of 0.25, second was at a compressed height of 0.35.

I used:
.25" .35"
Green spring 450g 350g
and
Black spring 1050g 850g

FWIW, stock "corvette" springs at 0.25" are 380g and 1400g. The kit has springs range from 290g to 1050g.

I would recommend that anyone tuning their governor find a small scale and measure their springs BEFORE they change them.....otherwise you could, will be flying blind.


Weights:

Stock, which is 0.5oz/14.2g
"B" weight from kit which is 0.45oz/12.75g

FWIW, weights from the kit ranges from 5.6g to 14.2g

Final combination had Green spring with "B" weight, and Black spring with stock weight.

I can't stress enough that you need to keep good notes during tests. It took some work to see the patterns in what needed to be changed to get this right. Now the thing drives like a dream!

So, in the end, I increased pressure of light spring, reduced pressure of the heavy spring to solve the problem of drastic differences in shift points from 1-2 to 2-3 shifts.

again.....if you don't know where you are starting, you are going to get frusterated. I sure was!
 
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