73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: travisr1988 on July 23, 2015, 05:22:14 pm
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Does anyone have any recommendations for a new or remanufactured/rebuilt transmission? 700r4 or th350 to replace my bad th350. If I go with a 700r4 what else needs changed? I believe mine is the short tail as it is in place of a 3 on the tree standard transmission.
Thank you in advance
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Your driveshaft will have to be shortened, 700R4's are longer. You will also need lockup provisions. Unless you do a lot of highway driving I would stay with a TH350 My $.02
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I live 20 miles from work, so I see highway a lot. However with my gear ratio (3.42:1) my cruise rpm is something like 2500, and would drop to 1800 or so with overdrive and no lock up, so it would probably be something like 1500 with lock up right? Where should it be for best mileage?
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Final drive with a 3.42 would be 2.50. Lugging the engine may yield worse gas mileage and unless a 700R4 is set up perfectly with the TV cable those transmissions can fry in a heartbeat. Google rpm calculator to see rpm's at mph. The 700R4 has a .73 OD.
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You wouldn't happen to know what stall would be best for the lunati voodoo 60101 cam would you?
Cam card: http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60101
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We have a resident cam expert here, he will chime in when he see's it. I just know from experience in stock applications that sometimes a 700R4 when geared wrong in back is not something you want to do unless you have expert help. They are so easy to burn up if not done right. I put a 700R4 in place of a TH350C in a 1985 with a 305 and 2.73 rear gears. OD was useless until you were going faster than the speed limit. Transmission wanted to downshift on the least bit of an incline.
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When I changed out my engine and transmission a couple of years ago, I went with a TCI Street Rodder TH350 (paired with a GM 350 Crate Engine), and I have been very happy with it so far. I did a "package" deal with them and got everything I needed - Transmission, Torque Converter, External Transmission Cooler (upgraded version), Detent Cable, Dipstick, and 3-Gallons of their Racing Transmission Fluid - all for around $1350, including truck freight. I had to go back and order a new speedo gear later to get that set properly (additional $20 w/shipping), and I also ordered a new yoke ($92) from them because my original had a weep hole, and their transmissions do not include the cup and o-ring, so it leaked. They told me I could plug the hole in my existing yoke, but I opted to order a new solid one instead.
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You wouldn't happen to know what stall would be best for the lunati voodoo 60101 cam would you?
Cam card: http://www.lunatipower.com/CamSpecCard.aspx?partNumber=60101
That's sort of a higher lift version of the Comp XE256H (12-234-2), and so it is a good choice. You should have about 300 lbft at 1000 rpm and 350 lbft at 1500 rpm, so the stock torque converter will work fine. Note advertised range on the cam card of 1000-5500. So you're good with the stock torque converter. Higher stall rpm won't help you, but it will be harder on the transmission.
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Thank you Rich. So stock stall it is. Yeah I chose that cam after taking your information into account and I wanted to be different, plus desktop dyno says my combo should put out 420+ ftlbs at 2000rpm and peaks at 439 at 3000 or 3500 if I recall correctly. So I did as Zieg said and the numbers come out to 1882rpm in overdrive @ 65mph, 1738rpm @ 60mph, with th350 it's 2576rpm @ 65mph and 2377rpm @ 60mph. Most of my highway use is 60-65mph, some 55 some 45. So 2179rpm @ 55mph and 1783rpm @ 45 with th350. So what range would I want to keep the rpm in?
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I think most people on the forums have said 2000-ish rpm at highway cruise (60-65) is best. Above that you get a lot more air resistance and need more hp on tap. 1700-1900 rpm at 60-65 is low. And 700R4s don't like to be lugged. I would think stick with the TH350 and the 3.42 gears, or go with the 700R4 and step up at least to the 3.73 gears, which would get you to 1900-2100 at 60-65.
Basically, the TH350 is pretty bulletproof and long-lived up to its torque limits. I think the highest torque in which the TH350 was the factory trans was 410 lbft. The TH400 has higher torque limits (500+ lbft), but is less bulletproof than the TH350 and doesn't last as long. It also has some interesting failure modes (cf shrapnel). And the 700R4 is the pickiest. If the TV cable is not set up right you can dynamite the 700R4 within a few miles, and it doesn't like to be lugged.
My own decision was to stick with the TH350 because 1) switching would be a PITA on a lifted shortbed K truck (all those driveshafts and U-joints and stuff), 2) for torque in the 420-430 lbft range, I was probably better off with the TH350 as long as I didn't do brake-starts and rev-it-up-and-drop-it-in-drive nonsense, and 3) the 700R4 just seemed too finicky to me.
Someone else who knows more about transmissions can offer more, but that's my take on it.
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Hey Rich, I got another question, my brothers truck has a 700r4, 350 .040 over, 64cc camel humps from summit, 9.5:1 and a grower torque beast cam 00904. He says it needs a 3500rpm stall, so being as my cam is higher lift and slightly lower duration @.050 213/219 his is 214/224, wouldn't he be overdoing it with a 3500 stall? Wouldn't a 2000-2400 stall be better suited? Then again his best time was in the high 14s and he says it can do 12s, so he may be just full of bull.
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"torque beast cam" and 3500rpm stall??? Poser country. Somebody saw that some monster hp tune on a cammed up fueler they saw on Mecum auctions had a 3000 rpm stall, so they figger bigger is better, MINE needs 3500.
Which is BS. A torquey engine should work with a stock stall, or it's not a torquey engine. I mean, torquey to me means more torque than stock. The reason to go to a high rpm torque converter is that your engine build traded torque away to get mucho horsepower up top -- which is certainly a good trade for a drag car -- and you need to get the engine rpms up to where the horsepower starts before you launch.
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That's what I thought, anyway desktop drag shows his does not respond as well to higher stalls, it shows mine gets quicker than his past 2000rpm stall. His combo isn't very well matched either, his cam is 1800-5500rpm, his intake is 1500-6500rpm, his heads are summit camel humps and he's running lower compression. Either way mine pulls noticably better than his with a bad tranny, whereas his is a built 700r4. His cam says it works with stock converter as well.
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Back on topic, TCI as 76longbox mentioned had a combo for $1400 shipped. I think this is the better route so far.
http://www.tciauto.com/tc/street-roddertm-th350-trans-package-1969-79-6-tailshaft-small-big-block-chevyhtml
Summit also has a package http://m.summitracing.com/parts/cmb-13-0056
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Go with the 700R4 and put some better gearing in for your final.
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Vile, I considered that, but that would mean new driveshaft, carrier, ring and pinion, brackets, etc on top of new transmission and torque converter. I need more cost effective for now. Eventually, when finances allow, I'll build a 383 and back it with a 700r4 and 4.10/4.11 rear gears.
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There are a bazillion of these trucks in junk yards with that configurations and all of the parts you need. I can't see spending any money on a TH350 or 3 speed anything these days.
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I have a question on th350 transmissions. Why would summit and jegs branded th350s not have provisions for kickdown cables? wouldn't I want a kickdown?
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When you get on the throttle, intake manifold vacuum falls, the vacuum line to the transmission releases the diaphragm on the vacuum modulator, which increases hydraulic pressure to the governor, which has to spin faster for the centrifugal weights to overcome the piston pressure on the valve and open the valve to enable the shift.
What the kickdown cable (or kickdown switch) does is cut the modulator out of the circuit -- basically it bypasses it -- providing full pressure to the governor. This will require the governor to go to its programmed (by the selection of weights and springs) highest-rpm shift point.
The benefit of the kickdown switch is that it happens faster than the vacuum signal to the modulator, so the shift happens quicker. Also, the modulator at 0 vacuum does not provide full pressure to the governor.
I think some modulators can be adjusted to give earlier downshifts/later upshifts, but I prefer having the kickdown to bypass the modulator entirely and run the shifts right off the governor at WOT.
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Thank you Rich, it definitely sounds like I want a kickdown. Does anyone know any good transmission builders in the north Austin area who back there work?
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So, I parked the truck some time ago when the tranny started acting up and only started it every couple weeks and moved it around a little. Now it loses very little fluid as opposed to the 2 quarts daily or more, and doesn't seem to have any problems shifting, although I haven't been on the highway or above maybe 40mph, could it have been trash in there somewhere causing the problems and leaks and it cleared up? It showed signs of failing front pump, failing governor, and was making awful noise, shifting really late at light (almost idle) throttle (sometimes wouldn't shift unless I snapped the throttle) and leaked like crazy.
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The governor is stupid simple, and its only common failure mode is a trashed nylon gear. Pull it and look at it. 5 minutes. It's behind a cap secured with a bail on the side of the transmission. You might leak an ounce of ATF when you pull it.
(http://www.dragracingonline.com/technical/images/0409/gov2.jpg)
Sounds more like the regulator is shot. Also an easy replacement.