700R4 problems (only for Gurus) –Long-
05-15-2003, 06:47 PM
#1
Melting Slicks
Thread Starter
700R4 problems (only for Gurus) –Long-
After many problems with the transmission (swap with another one, teardown, swapped again, new tailhousing) my 700R4 continue to have strange problems.
It shift very well, partial throttle shifts are good ad firmness is good (not weack, not hard).
No slipping, right level of fluid (no burnt smell good red color).
The problem: It shifts too early at WOT. When I say too early I say 3500/3600 rpm. (the stock tach says 4700-4800 rpm. Now with an aftermarket tach I can read correct rpms; I can say correct rpm because every RPM/speed/gear/calculator can confirm every speed at given rpm level with my 2.73 rear end). The other simply related problems is that it do not downshifts at the right speed. (exemple: it do not automatically downshifts to 2 when the speed is above 45 mph)
The very strange thing is that at minimum throttle shift points are right… Minimum throttle shift points are a quite higher compared to others corvetteforum members (expecially 3 to 4).
Here the results at minimum throttle:
1 to 2 12 mph
2 to 3 25 mph
3 to 4 54 mph (!)
My knowledge on automatic trasmissions is low, but when I have a problem I like to collect every information on the web.
Now I know that shift points (partial and full throttle) are affected by at least 3 factor.
1 TV cable adjustment
2 Governor wheights and springs.
3 1-2 2-3 and 3 to 4(overdrive) shift valve springs .
I checked and adjusted few times the TV cable. It seems perfect. It is not stretched, and at every different throttle position the car shifts at differents speed (more pedal gas used, more later the shift occurs and this in a perfect linear increase)
Then I know: (tacken from a fellow member web site)
“The way the govenor works is by adjusting the shift valve pressure.
The shift valves are exposed to both govenor pressure and TV pressure.
If govenor pressure is significantly higher than the TV, the shiftvalve will move and cause an upshift. “
I thoght: “If I change governor weights (lighter) all will be right…. But I need to use very lighter weights to go from the actual 3500/3600 to an acceptable 4800 / 5000 rpm!!!…. and this change will affects also the minimum throttle and partial throttle shifts….I dont want to shift in overdrive with a minimum throttle at 60 – 65 mph !!!”
Maybe If I change governor’s weights all will be right, but I will be always with the feeling of a imbalance between the use of the pressure of the governor in comparison of the use of the pressure of the TV cable for the movement of each shift valve.
Please help me to diagnose the problem, and please try to explain the role of the individual shift valve springs.
(I think that if I change individual shift valve springs I will lower/raise both WOT and partial/minimum throttle shift points). So for what I know now , every operation to raise shift point at WOT will raise also partial / medium throttle shift points.
So the situation will be: Very high minimum/partial throttle shifts (what I don’t really want….and not right) and right WOT shifts (what I really want)
Something in my trans is not right…. And I’m becoming crazy because my primary interest (in all things of my life) is to understand the problems technically ….I’m not satified if something “WORKS” I allways to know why it works.
Thanks
-Beppe-
It shift very well, partial throttle shifts are good ad firmness is good (not weack, not hard).
No slipping, right level of fluid (no burnt smell good red color).
The problem: It shifts too early at WOT. When I say too early I say 3500/3600 rpm. (the stock tach says 4700-4800 rpm. Now with an aftermarket tach I can read correct rpms; I can say correct rpm because every RPM/speed/gear/calculator can confirm every speed at given rpm level with my 2.73 rear end). The other simply related problems is that it do not downshifts at the right speed. (exemple: it do not automatically downshifts to 2 when the speed is above 45 mph)
The very strange thing is that at minimum throttle shift points are right… Minimum throttle shift points are a quite higher compared to others corvetteforum members (expecially 3 to 4).
Here the results at minimum throttle:
1 to 2 12 mph
2 to 3 25 mph
3 to 4 54 mph (!)
My knowledge on automatic trasmissions is low, but when I have a problem I like to collect every information on the web.
Now I know that shift points (partial and full throttle) are affected by at least 3 factor.
1 TV cable adjustment
2 Governor wheights and springs.
3 1-2 2-3 and 3 to 4(overdrive) shift valve springs .
I checked and adjusted few times the TV cable. It seems perfect. It is not stretched, and at every different throttle position the car shifts at differents speed (more pedal gas used, more later the shift occurs and this in a perfect linear increase)
Then I know: (tacken from a fellow member web site)
“The way the govenor works is by adjusting the shift valve pressure.
The shift valves are exposed to both govenor pressure and TV pressure.
If govenor pressure is significantly higher than the TV, the shiftvalve will move and cause an upshift. “
I thoght: “If I change governor weights (lighter) all will be right…. But I need to use very lighter weights to go from the actual 3500/3600 to an acceptable 4800 / 5000 rpm!!!…. and this change will affects also the minimum throttle and partial throttle shifts….I dont want to shift in overdrive with a minimum throttle at 60 – 65 mph !!!”
Maybe If I change governor’s weights all will be right, but I will be always with the feeling of a imbalance between the use of the pressure of the governor in comparison of the use of the pressure of the TV cable for the movement of each shift valve.
Please help me to diagnose the problem, and please try to explain the role of the individual shift valve springs.
(I think that if I change individual shift valve springs I will lower/raise both WOT and partial/minimum throttle shift points). So for what I know now , every operation to raise shift point at WOT will raise also partial / medium throttle shift points.
So the situation will be: Very high minimum/partial throttle shifts (what I don’t really want….and not right) and right WOT shifts (what I really want)
Something in my trans is not right…. And I’m becoming crazy because my primary interest (in all things of my life) is to understand the problems technically ….I’m not satified if something “WORKS” I allways to know why it works.
Thanks
-Beppe-
05-16-2003, 05:37 PM
#4
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Re: 700R4 problems (only for Gurus) –Long- (conv90)
...
The very strange thing is that at minimum throttle shift points are right… Minimum throttle shift points are a quite higher compared to others corvetteforum members (expecially 3 to 4).
Here the results at minimum throttle:
1 to 2 12 mph
2 to 3 25 mph
3 to 4 54 mph (!) ...
The very strange thing is that at minimum throttle shift points are right… Minimum throttle shift points are a quite higher compared to others corvetteforum members (expecially 3 to 4).
Here the results at minimum throttle:
1 to 2 12 mph
2 to 3 25 mph
3 to 4 54 mph (!) ...
1-2 Min Throttle: between 11-13mph
2-3 Min Throttle: between 19-26mph
3-4 Min Throttle: between 41-51mph
1-2 WOT: between 28-41mph
4-3 Coast Down: between 37-48mph
3-2 Coast Down: between 15-24mph
2-1 Coast Down: between 10-12mph
:thumbs:
05-16-2003, 11:46 PM
#5
Race Director
Re: 700R4 problems (only for Gurus) –Long- (conv90)
Im not a guru at all sorry,but do you have the stock PROM in the computer?
Hows the Torque Converter lock up doing when driving?
Sometimes delaying lock up until 4th gear can improve feel and performance.
Also,what is your TPS voltage at? Just wondering.May not have much to do with the trans shifting but make sure its within specs.It sounds from the other post the tranny may be working correctly,but I notice many cars arent exactly the same when driving.
Hows the Torque Converter lock up doing when driving?
Sometimes delaying lock up until 4th gear can improve feel and performance.
Also,what is your TPS voltage at? Just wondering.May not have much to do with the trans shifting but make sure its within specs.It sounds from the other post the tranny may be working correctly,but I notice many cars arent exactly the same when driving.
05-16-2003, 11:59 PM
#6
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Re: 700R4 problems (only for Gurus) –Long- (conv90)
First off have your new tach calibrated; the stock tach is often off...but face it off by over 1,000rpm is a bit much. It may well be that your WOT upshifts are on the money.
A TransGo shift kit will firm up the WOT shifts quite nicely.
A B&M Governor Reval kit contains springs and smaller weights to set up your shift points. You might use a digital postal scale to help with weight selection.
A TransGo shift kit will firm up the WOT shifts quite nicely.
A B&M Governor Reval kit contains springs and smaller weights to set up your shift points. You might use a digital postal scale to help with weight selection.
05-17-2003, 12:29 AM
#7
Safety Car
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Re: 700R4 problems (Bill's86Coupe)
First, I'm not a tranny expert but I stayed at a Holiday In Express last night.
Next, I HAVE worked on mine a good bit and read a book or two about them.
Numero Uno, the TV cable IS NOT used to alter the shift points although as you have found, playing around with it WILL do so because of the pressures the governor experience as you described in your initial post.
Any tranny guy is going to tell you there is only ONE correct adjust point for the TV cable and you'll EASILY find that by adjusting the TV completely to the REAR then pressing the accelerator pedal to the floor. The adjusting mechanism will ratchet forward to the correct position.
The TV cable sets the whole "operating point" pressure level for the transmission.
It's function is to do that and to increase the line pressure with throttle opening to keep the clutchs from slipping in high power/torque situations.
That's about it for the TV cable.
On to shift points.
Any REAL tranny guy will tell you the shift points are controlled by the governor. The weights and springs on the governor to be exact.
You described EXACTLY in your post how the governor works so no need for me to expound on that at all.
You can get a "shift calibration" kit that will come with several weights and springs. With this you can "adjust" shift points to your hearts content.
Instructions come with it and make it clear which springs,etc do what.
On your 90 another thing you may be running into is TCC lockup at times when you don't want to be getting it. Engagement of TCC can feel like the transmission shifting gears. Sometimes it will engage WAY too early for 'some drivers' (ME included) and cause the car to just "fall on it's face".
Mine was doing this until I programmed the EPROM to engage at a faster speed than stock.
One EASY way to disable TCC control while you do the rest of your tranny testing is to purposely misadjust the TCC interupt switch on the brake pedal.
THis will remove one variable from being part of the "equation" as you test for shift speeds.
BTW, if it hasn't been changed in a while, remove your tranny pan, change the filter and fill it back up with fresh tranny fluid.
I just did this to my 91 Vette and it had a DRASTIC and NICE affect on shift smoothness. It will still spin the tires going into second gear but with normal driving it shifts soooo much nicer/smoother now.
(Wish I could get it to spin on the 2-3 shift) :)
Good luck with it.
Next, I HAVE worked on mine a good bit and read a book or two about them.
Numero Uno, the TV cable IS NOT used to alter the shift points although as you have found, playing around with it WILL do so because of the pressures the governor experience as you described in your initial post.
Any tranny guy is going to tell you there is only ONE correct adjust point for the TV cable and you'll EASILY find that by adjusting the TV completely to the REAR then pressing the accelerator pedal to the floor. The adjusting mechanism will ratchet forward to the correct position.
The TV cable sets the whole "operating point" pressure level for the transmission.
It's function is to do that and to increase the line pressure with throttle opening to keep the clutchs from slipping in high power/torque situations.
That's about it for the TV cable.
On to shift points.
Any REAL tranny guy will tell you the shift points are controlled by the governor. The weights and springs on the governor to be exact.
You described EXACTLY in your post how the governor works so no need for me to expound on that at all.
You can get a "shift calibration" kit that will come with several weights and springs. With this you can "adjust" shift points to your hearts content.
Instructions come with it and make it clear which springs,etc do what.
On your 90 another thing you may be running into is TCC lockup at times when you don't want to be getting it. Engagement of TCC can feel like the transmission shifting gears. Sometimes it will engage WAY too early for 'some drivers' (ME included) and cause the car to just "fall on it's face".
Mine was doing this until I programmed the EPROM to engage at a faster speed than stock.
One EASY way to disable TCC control while you do the rest of your tranny testing is to purposely misadjust the TCC interupt switch on the brake pedal.
THis will remove one variable from being part of the "equation" as you test for shift speeds.
BTW, if it hasn't been changed in a while, remove your tranny pan, change the filter and fill it back up with fresh tranny fluid.
I just did this to my 91 Vette and it had a DRASTIC and NICE affect on shift smoothness. It will still spin the tires going into second gear but with normal driving it shifts soooo much nicer/smoother now.
(Wish I could get it to spin on the 2-3 shift) :)
Good luck with it.
05-17-2003, 12:33 AM
#8
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Re: 700R4 problems (only for Gurus) –Long- (conv90)
BTW.
On your 90 transmission, the only thing controlled by the ECM is the TCC lockup. No shift speeds or shift firmness, line pressure or anything else.
Just the TCC.
Over and out.
On your 90 transmission, the only thing controlled by the ECM is the TCC lockup. No shift speeds or shift firmness, line pressure or anything else.
Just the TCC.
Over and out.
05-17-2003, 08:53 AM
#9
Melting Slicks
Thread Starter
Re: 700R4 problems (VetBoy89)
The very strange thing is that at minimum throttle shift points are right… Minimum throttle shift points are a quite higher compared to others corvetteforum members (expecially 3 to 4).
Here the results at minimum throttle:
1 to 2 12 mph
2 to 3 25 mph
3 to 4 54 mph (!) ...
Sounds like you’re trans is working fine. Here are the shift points at from my Helm’s service manual.
...
1-2 Min Throttle: between 11-13mph
2-3 Min Throttle: between 19-26mph
3-4 Min Throttle: between 41-51mph
1-2 WOT: between 28-41mph
4-3 Coast Down: between 37-48mph
3-2 Coast Down: between 15-24mph
2-1 Coast Down: between 10-12mph
:thumbs:
1-2 Min Throttle: between 11-13mph
2-3 Min Throttle: between 19-26mph
3-4 Min Throttle: between 41-51mph
1-2 WOT: between 28-41mph
4-3 Coast Down: between 37-48mph
3-2 Coast Down: between 15-24mph
2-1 Coast Down: between 10-12mph
:thumbs:
If I change governor weights in order to raise WOT shift points, these min. throttle shift point will be higer and this is not good...
-Beppe-
05-17-2003, 08:56 AM
#10
Melting Slicks
Thread Starter
Re: 700R4 problems (65Z01)
First off have your new tach calibrated; the stock tach is often off...but face it off by over 1,000rpm is a bit much. It may well be that your WOT upshifts are on the money.
A TransGo shift kit will firm up the WOT shifts quite nicely.
A B&M Governor Reval kit contains springs and smaller weights to set up your shift points. You might use a digital postal scale to help with weight selection.
A TransGo shift kit will firm up the WOT shifts quite nicely.
A B&M Governor Reval kit contains springs and smaller weights to set up your shift points. You might use a digital postal scale to help with weight selection.
05-17-2003, 09:00 AM
#11
Melting Slicks
Thread Starter
Re: 700R4 problems (conv90)
I need to add that my TCC lock is at exactly 42 mph and I don't want to delay it. I like like this.
I have a B&M governor recalibration kit ...
I'm waiting to use it .....whaiting for some your answer saying I'm correct to try to use it as first try...
-Thanks to all
-Beppe-
I have a B&M governor recalibration kit ...
I'm waiting to use it .....whaiting for some your answer saying I'm correct to try to use it as first try...
-Thanks to all
-Beppe-
05-17-2003, 09:04 PM
#12
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Re: 700R4 problems (only for Gurus) –Long- (conv90)
thought about an auto. to 6-speed conversion? :yesnod:
05-19-2003, 01:24 PM
#15
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Re: 700R4 problems (conv90)
Dont worry my budget is tight as well, but it WILL be changed over to a 6-speed at some point in time. I already have the clutch pedal installed and the bellhousing ready to go. Now if i could just find the 3400 bucks for Richmond.
:cheers:
:cheers:
05-21-2003, 07:20 AM
#16
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Re: 700R4 problems (IBEAM700)
If you have the standard V-8 governor, then the change to a Corvette style, this will get you what you want, easier downshifts and later WOT shifts. It will have very little effect on part throttle shifts.
05-23-2003, 03:59 PM
#17
Melting Slicks
Thread Starter
Re: 700R4 problems (Probuilt)
If you have the standard V-8 governor, then the change to a Corvette style, this will get you what you want, easier downshifts and later WOT shifts. It will have very little effect on part throttle shifts.
-Beppe-
