Hello
06-16-2010, 03:31 AM
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Hello
Hi there, I just purchased a 92 camaro, with a 350ci carb and before I go tearing things up, I was wondering if anyone wanted to shed their insight if they had this problem before.
This car listed as having a slipping transmission, 700R4. I went and test drove it, and when I would hit the gas, the speedo and tach would both raise. The car kinda drove, and it shifted ok from p/n/d/, and while driving, it kinda shifted ok, so I am wondering if in fact it is an electrical issue common in these cars, or if perhaps it is the torque converter, or trans.
I probably should try a stall test.
I'm proposing it might be the torque converter since the speedometer and tach move simultaneously when gas is hit at a stand still.
How does the speedometer calculate rotation for the 700R4? Does it have sensors on the input / output shafts?
Thanks!
This car listed as having a slipping transmission, 700R4. I went and test drove it, and when I would hit the gas, the speedo and tach would both raise. The car kinda drove, and it shifted ok from p/n/d/, and while driving, it kinda shifted ok, so I am wondering if in fact it is an electrical issue common in these cars, or if perhaps it is the torque converter, or trans.
I probably should try a stall test.
I'm proposing it might be the torque converter since the speedometer and tach move simultaneously when gas is hit at a stand still.
How does the speedometer calculate rotation for the 700R4? Does it have sensors on the input / output shafts?
Thanks!
Last edited by RyanEricW; 06-16-2010 at 05:03 AM.
06-16-2010, 09:47 AM
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Car: 1992 RS
Engine: Carbed 350
Transmission: 700R4
Axle/Gears: 3.42 posi
Re: Hello
On a 1992, the speedo is electrical, not mechanical.
I'd think you could tell if the tranny was slipping - the engine rpm's will increase alot, but the car moves much slower than you think it should.
The only electrical aspect to a 700R4 is the torque converter lockup function - the rest of the transmission functions are all mechanical, and change with fluid pressures.
What was the car originally equipped with? Was this originally a 305 TBI car?
What carb does it have now?
Things to consider:
1) When I swapped in my 350, my tranny shifted fine, no slipping at all - but after the swap, the increased torque/hp of the 350 let me know really quick that the tranny had been on it's way out, but couldn't tell because of the little 305 in front of it not working it hard - the 350 made it noticeably slip instantly - I had to immediately remove my tranny and have it rebuilt.
2) You want to make sure that the TV cable has been reinstalled correctly with that carb, installed on a nice beefy throttle cable bracket that doesn't flex any during accelleration, and make sure a proper geometry corrector has been used. The older transmissions used a "kickdown" cable for the auto tranny's - the 700R4 uses a "TV Cable" - it's imperative for the transmission that this TV cable is adjusted properly, and that it's installed on the carb with a correct geometry - a small bit off and the pressure changes are different during accelleration sweep of the linkage, thus affecting the transmission pressures differently - the 700R4 is very particular with it's pressures - they have neen known to go out in as short a distance as 2-3 blocks because of incorrect adjustment to the TV cable.
3) Rear Gears - it's quite possible that if a 350 carb swap has been done, that rear gears have changed - stock for a 305 TBI auto car were 2.73 ratio peg leg rear. If gears have been changed, then chances are your speedo is off unless that person changed out the drive and driven gears in the tailshaft of the transmission to correct the speedo. Might want to compare speeds alongside another car you know is correct, to see if your speedo is reading accurate (BEFORE you get that speeding ticket
)
This relates to your speedo questions. There is a plastic gear in a housing on the driver side rear of the tranny. There is another plastic gear on the output shaft in the tailhousing. Speedo is calibrated by changing one or both of these gears to match the rear end gear ratio in the car. The gear on the output shaft spins the gear in the housing, making a pulsing signal electronically that is sent to the speedometer.
4) Has there been a method for locking the torque converter? Stock, the ECM controls TC lockup - but since a carb has been swapped in, there is no ECM, thus no TC lockup.
What happens stock is that in 3rd or 4th gear, when rpm's are lower, the ECM sends a signal to a solenoid inside the tranny that sends more fluid forward to the TC - in essence filling it, and thus there's no difference between engine rpm and transmission rpm since there's too much fluid in the TC to allow the turbine fins inside toturn at a different speed. You can usually tell by watching rpm's on tach - there will be a one last small rpm drop at highway speed - you can watch each gear change (1-2, 2-3, 3-4) and then just barely see another small (maybe 3-400 rpm drop) - that is the TC locking up.
Unless there's been an aftermarket provision to enable the TC to lock, you'll be getting less mileage on the highway, increased transmission heat, and thus decreased life, and the potential to burn up the 3-4 clutch pack more quickly. So - find out if there's been something installed to control TC lockup - if not you'll want to look into this pretty quickly.
5) Double check your current engine - many folks assume 350 if it's an 8 cylinder car, amny others will state 350 to sell a car, even though it's a 305 - there's no readily visible difference in the block - you have to look on driver side, top of block at the rear, below the rear of the valve cover/head - takes quit a bit to get in there and see it, but the block will be stamped there with numbers - get those and check www.moretec.com. Usually, the stock 305 engines had "5.0L" stamped as well, and alot of the newer 350's had "5.7L" stamped - older blocks just had ~5-8 numbers stamped. That way, you can be asssured of what your dealing with.
Hope any of that helped.
I'd think you could tell if the tranny was slipping - the engine rpm's will increase alot, but the car moves much slower than you think it should.
The only electrical aspect to a 700R4 is the torque converter lockup function - the rest of the transmission functions are all mechanical, and change with fluid pressures.
What was the car originally equipped with? Was this originally a 305 TBI car?
What carb does it have now?
Things to consider:
1) When I swapped in my 350, my tranny shifted fine, no slipping at all - but after the swap, the increased torque/hp of the 350 let me know really quick that the tranny had been on it's way out, but couldn't tell because of the little 305 in front of it not working it hard - the 350 made it noticeably slip instantly - I had to immediately remove my tranny and have it rebuilt.
2) You want to make sure that the TV cable has been reinstalled correctly with that carb, installed on a nice beefy throttle cable bracket that doesn't flex any during accelleration, and make sure a proper geometry corrector has been used. The older transmissions used a "kickdown" cable for the auto tranny's - the 700R4 uses a "TV Cable" - it's imperative for the transmission that this TV cable is adjusted properly, and that it's installed on the carb with a correct geometry - a small bit off and the pressure changes are different during accelleration sweep of the linkage, thus affecting the transmission pressures differently - the 700R4 is very particular with it's pressures - they have neen known to go out in as short a distance as 2-3 blocks because of incorrect adjustment to the TV cable.
3) Rear Gears - it's quite possible that if a 350 carb swap has been done, that rear gears have changed - stock for a 305 TBI auto car were 2.73 ratio peg leg rear. If gears have been changed, then chances are your speedo is off unless that person changed out the drive and driven gears in the tailshaft of the transmission to correct the speedo. Might want to compare speeds alongside another car you know is correct, to see if your speedo is reading accurate (BEFORE you get that speeding ticket
)This relates to your speedo questions. There is a plastic gear in a housing on the driver side rear of the tranny. There is another plastic gear on the output shaft in the tailhousing. Speedo is calibrated by changing one or both of these gears to match the rear end gear ratio in the car. The gear on the output shaft spins the gear in the housing, making a pulsing signal electronically that is sent to the speedometer.
4) Has there been a method for locking the torque converter? Stock, the ECM controls TC lockup - but since a carb has been swapped in, there is no ECM, thus no TC lockup.
What happens stock is that in 3rd or 4th gear, when rpm's are lower, the ECM sends a signal to a solenoid inside the tranny that sends more fluid forward to the TC - in essence filling it, and thus there's no difference between engine rpm and transmission rpm since there's too much fluid in the TC to allow the turbine fins inside toturn at a different speed. You can usually tell by watching rpm's on tach - there will be a one last small rpm drop at highway speed - you can watch each gear change (1-2, 2-3, 3-4) and then just barely see another small (maybe 3-400 rpm drop) - that is the TC locking up.
Unless there's been an aftermarket provision to enable the TC to lock, you'll be getting less mileage on the highway, increased transmission heat, and thus decreased life, and the potential to burn up the 3-4 clutch pack more quickly. So - find out if there's been something installed to control TC lockup - if not you'll want to look into this pretty quickly.
5) Double check your current engine - many folks assume 350 if it's an 8 cylinder car, amny others will state 350 to sell a car, even though it's a 305 - there's no readily visible difference in the block - you have to look on driver side, top of block at the rear, below the rear of the valve cover/head - takes quit a bit to get in there and see it, but the block will be stamped there with numbers - get those and check www.moretec.com. Usually, the stock 305 engines had "5.0L" stamped as well, and alot of the newer 350's had "5.7L" stamped - older blocks just had ~5-8 numbers stamped. That way, you can be asssured of what your dealing with.
Hope any of that helped.
