TH350C raising 1-2, lowering 2-3 shift
January 17th, 2019, 08:43 AM
#1
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TH350C raising 1-2, lowering 2-3 shift
Ok so I have the B+M weights, #4 and #5, I believe with stock springs. My 1-2 is about 4750 rpm and 2-3 is 5200+, I let off. I would like both around 5000 rpm, slightly over I can live with. Does one weight affect one shift or the other or both? What about springs? I am finding conflicting advice on what they do, some say they just spread the shift, others say raise or lower. I haven't played around much with the TH350 governor. I plan on a Transgo kit set at the firmest shift and Hughes 2500 stall.
Last edited by olds 307 and 403; January 17th, 2019 at 08:48 AM.
January 17th, 2019, 12:00 PM
#2
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I don't know the answer to your questions, but wanted to say that on my car with the original governor the 1-2 and 2-3 shifts are right around 4800 RPM, which has always felt "right" with both the original driveline setup and the current engine/converter/rearend setup. If I want to rev higher I can manually shift.
January 17th, 2019, 12:46 PM
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Might be due to the modulator valve. Load may be different 1-2 then 2-3. Mod valve shifts due to load, gov is rpm. Check into adjusting the Modulator, most have a allen or screw driver lot in the vac line nipple like a vac advance on the distributor. If it has no adjustment you can buy one that's adjustable. If your 2-3 is high and you want it lower, you might need to adjust weight/springs to bring it down and adjust the modulator for shift under load to get you more rpm 1-2.
Last edited by 1970greensupreme; January 17th, 2019 at 12:57 PM.
January 17th, 2019, 06:42 PM
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January 23rd, 2019, 09:21 AM
#8
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It will be interesting to see if the shift points change at all with a shift kit. I could change springs but would raise the 2-3 which I don't really want but can live with. I may see if I have weaker springs around.
January 23rd, 2019, 05:00 PM
#9
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All the modulator does is vary shift points based on engine vacuum. At WOT, there should be no vacuum, at that point the modulator is ineffective.
Changing the weights and springs changes the govenor oil pressure to the shift valves. Govenor pressure is pushing the shift valves towards the upshift position, while spring pressure, detent pressure, modulator pressure, etc tries to keep them in the downshift position. If changing govenor weights does nothing, you may have to start playing with different rate springs in the valve body. TransGo and some of the higher end B&M shift kits include a 2-3 shift valve spring, I think those were included to raise shift points.
If your serious about dialing in the auto shift points, I would suggest getting a bunch of valve bodies, disassemble and organize the springs. Measure free length, wire diameter, and color, hopefully you will end up with a variety of springs. Measure the springs in your valve body, and try a few different springs. Keep detailed notes!!!! It may be best to try a different valve body, that way if you get lost you could always start with a known calibration. Hopefully after a couple spring changes, you will start to see a patter.
Changing the weights and springs changes the govenor oil pressure to the shift valves. Govenor pressure is pushing the shift valves towards the upshift position, while spring pressure, detent pressure, modulator pressure, etc tries to keep them in the downshift position. If changing govenor weights does nothing, you may have to start playing with different rate springs in the valve body. TransGo and some of the higher end B&M shift kits include a 2-3 shift valve spring, I think those were included to raise shift points.
If your serious about dialing in the auto shift points, I would suggest getting a bunch of valve bodies, disassemble and organize the springs. Measure free length, wire diameter, and color, hopefully you will end up with a variety of springs. Measure the springs in your valve body, and try a few different springs. Keep detailed notes!!!! It may be best to try a different valve body, that way if you get lost you could always start with a known calibration. Hopefully after a couple spring changes, you will start to see a patter.
January 26th, 2019, 01:54 PM
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I wondered that and it did help on the 2004R, 300 to 500 rpm. It may be exactly what I need. Like I said, even a couple of hundred rpm should be enough. I will try the Transgo kit and use the shift springs they suggest.
January 26th, 2019, 08:15 PM
#12
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i wouldnt be surprised if some factory transmission calibration already use the spring in the TransGo kit. Maybe the spring included is a duplicate of a performance oriented factory spring? You need to keep in mind there were many, many more grandma-girly man th350 transmissions than high performance versions. TransGo is pretty good about solving issues that occasionally turn up. There had to be a reason for including the spring.
February 3rd, 2019, 05:04 AM
#13
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I would bet my 1986 Caprice TH350C did not have this spring. The 70 trans, I should check the number and see if it is the orginal trans from it, it may not be . I plan on picking up another TH350C as I can't get the converter to lock no matter what I tried. A spare trans is never a bad thing to have around. I will compare the springs when I install the kit. Which is the larger dacron or nylon filter preferred for any sort of performance application? It seems to me the Dacron would filter better, is larger which might make up for being more restrictive but better filter. I am using 10W30 tractor trans hydraulic fluid with Type F for colour. It sure stopped leaks and shifts fine. I may go with the 5W30 synthetic blend and Dexron 6 for colour. Nice to have one old vehicle not leak ATF, all the rest do.
February 3rd, 2019, 09:59 AM
#15
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That is what I was thinking plus the thinner cold weight as well. I may run that combo in my 2004R once the 350 goes back in along with the 2300 stall. I am running coolers on both transmissions already.
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