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Old 01-29-2003, 12:11:00 AM   #1
Turbo T/A
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Beefing up my TH-350

Well it's almost that time & my bone stock th-350 cant last too long with the new combo & the bottle.

I am turning to you guys to find out what needs to be done to make a reliable th-350. I already have a reverse manual valvebody & a big fat aluminum cooler mounted behind the front grill.

Keep in mind i dont need a killer th-350 with transbrake or anything. I just want to upgrade so it will last. Oh & I need it cheap too lol! Just kidding, but lets try and keep me from shattering the wallet. This buildup was expensive enough!

Thanks in advance

------------------
'81 Viper Blue Z-28
383 Stroker
AFR210cc
Comp XR288HR
Victor Jr
750 Holley
4:10 Rear End
TH-350 10" 3500 stall

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'69 Trans Am, SBC 400" TT, 20" wheels, 3.25 gear, TH400, 3 1/2" full exhaust & interior, 3653#...and carbureted

Old combo:
Race Gas/Pump Gas
Best ET: 8.47 / 9.21
Best MPH: 163.8 / 153.6

Walk softly.... carry a big stick.

New turbo motor in the works
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Old 01-29-2003, 12:45:00 AM   #2
jakeshoe
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I'd say get rid of that reverse manual VB first.
Then add some good clutches (Borg Warner for mild app, reds for street/ strip), a new roller sprag and hardened race.
Set up the clutches with ~.040 on the direct and use a waved plate, forward with .020-.025 and no waved, intermediate with a waved.
Possibly add a clutch to the intermediate and direct.
Use 4L60-E low/reverse steels.
Be sure all the bushings are good, replace pump, rear, stator, direct drum bushings anyways.
Use a TransGo Stage 3 shift kit, adjustable modulator.
A new red lined band.
Be sure pump gears are in good shape and not too deep in pump.

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Old 01-29-2003, 11:22:00 AM   #3
BlownBigBlock
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Your going to need an intermediate sprag unit. Your looking at about $300 for one.

When I was building mine, I talked to 4 tranny companies... TCI, B&M, Coan, and ATI.
They all said the same thing, the weak link of the TH350 is the intermediate sprag assembly.
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Old 01-29-2003, 05:02:00 PM   #4
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Call these guys up and do whatever they tell you
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Old 01-29-2003, 06:11:00 PM   #5
Turbo T/A
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Well here's the word of the day. After talking to many builders in my area, its come to this.

A TH-350 is going to be more expensive to build than a th-400...

Now with this said, what kind of modification do i have to do to fit my car with a 400. My builder actually does transmissions as well including the manufacturing of his own valvebodies ect.... It's going to come with all the trimmings & a reverse manual valvebody.

I think the yoke has to be changed...how bout the driveshaft? Will the headers fit the same? Starter? Flywheel?

Sorry I've always been around th-350's & dont know much about anything else.

------------------
'81 Viper Blue Z-28
383 Stroker
AFR210cc
Comp XR288HR
Victor Jr
750 Holley
4:10 Rear End
TH-350 10" 3500 stall

N.O.S. Cheater 150-250

New Web Site With Pics & Buildup!
__________________
'69 Trans Am, SBC 400" TT, 20" wheels, 3.25 gear, TH400, 3 1/2" full exhaust & interior, 3653#...and carbureted

Old combo:
Race Gas/Pump Gas
Best ET: 8.47 / 9.21
Best MPH: 163.8 / 153.6

Walk softly.... carry a big stick.

New turbo motor in the works
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Old 01-29-2003, 07:47:00 PM   #6
EdgarR
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I have always found that it is more $ to beef up a 350 than just buying a 400 or not that much more. But keep in mind that the 400 does rob a little more power than the 350 but for street/strip not enough to make or break you. You do have to change the yoke, drive shaft and cross member. I know there is a way of using the 350 cross member but not sure how.
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Old 01-29-2003, 08:19:00 PM   #7
Turbo T/A
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More info on this would be greatly appreciated.

I did have a 700R4 in my car for a while last yr & i had to move the crossmember back a bit. Will the TH-400 bolt up to these locations or will i need to make even more holes?

HMM i thought the two driveshafts were the same length but with different yokes?

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'69 Trans Am, SBC 400" TT, 20" wheels, 3.25 gear, TH400, 3 1/2" full exhaust & interior, 3653#...and carbureted

Old combo:
Race Gas/Pump Gas
Best ET: 8.47 / 9.21
Best MPH: 163.8 / 153.6

Walk softly.... carry a big stick.

New turbo motor in the works
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Old 01-29-2003, 08:39:00 PM   #8
jakeshoe
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Stroked,
OK,
First of all you don't HAVE to have the aftermarket sprag IF you use a VB kit that gives PROPER shift timing. Most aftermarket kits and manual VB's don't take this into consideration and cause the sprag to take a big hit because the clutch locks first, then the sprag and it isn't designed to take that kinda hit. Even the heavy duty, high dollar, high capacity element type sprags will break if your shift timing is wrong. it will take longer but it is still going to happen.
EVEN on a TH400. Believe me. I broke one.
The Th400 stock intermediate roller clutch is not much beefier than a Th350, the old style 16 element sprag type clutch isn't much better either. I broke one of these recently because I was being hard headed and on a budget.
SO that said you can get away fine with using the Th350 if you use the right VB kit. That PROBABLY means you need to get rid of the manual VB BUT if it uses the modulator and doesn't totally bypass the 1-2 accumulator it may be OK.
Next the TH400 IS beefier and is my trans of preference becuase I've built them up to hold 1500 hp and it really doesn't take much other than stock stuff with some HD clutches and bands.
SOMETIMES you can use the same driveshaft with a different yoke. I have done it in a '71 Camaro.
The best way to do the crossmember is to cut the mount off the frount and weld it to the back of the crossmember, usually also have to slightly drop it to retain proper driveline angles.
This keeps it in the stock holes.
There is 6 3/8" difference in the mounting pad location of a short shaft 350 vs 400.
All the other harware is the same, except maybe the dipstick and dust cover. Modulator line needs to be rebent or modded.
TH350 and 400's can use the same converter.
Last,
Not sure where you are at but I have a Th400 with all the bada$$ parts I'll build to your specs if you want. I don't need it as I will soon be pulling my TH400 out and replacing with an overdrive.
So will already have a spare.
It is complete with HD sprag, TransGo VB kit for whatever setup you want, full manual, manual/auto, race, street, whatever.
It would be $550 exchange or $650 outright. I would build it and meet you somewhere if within a reasonable driving distance. 200 miles or so.
It has a deep pan, red clutches, HD band, HD sprag, all clearances blueprinted, all new seals, etc.. Ready to go. 800hp no problem.
email me at jakeshoe@hotmail.com if you need more info or are interested. I'm in north TX.
Also I can modify your crossmember if you bring it to me.
Anyway , enough of the sales pitch.
The TH350 is a good trans and just depends on what you plan to do in the future.
I'm building a Th350 for Old School this weekend for his 10-second 2nd Gen.
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Old 01-29-2003, 08:59:00 PM   #9
craggar
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If you want to go TH400 you really don't need to do much to it, as little as a shift kit.It should be plenty strong enough as long as everything is in good shape.
I haven't done the swap but know that the d/s needs to be shortened,the tranny yoke is different and you can turn your TH350 crossmember around and should be able to reuse 2 of the original holes then drill 2 more.Somebody else on here had to drill all 4 but my friend reused 2.Maybe 2 maybe 4.
IMO the TH400 is more than adequate in stock form for most street cars and alot of race cars.They do weigh more and take more power run which is why some of us run the th350 instead, but if I don't get mine to stop breaking this year I'll be using a th400 soon.
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Old 01-29-2003, 09:12:00 PM   #10
jakeshoe
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craggar,
Just out of curiousity, what is breaking in your trans?
What valve body/kit are you using?
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Old 01-29-2003, 09:14:00 PM   #11
Strkr383
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I am going through this exact issue as we all type. With the power my new motor is going to make, the TH350 is out the door. I've had my share of broken trannys last yr. I picked up a short tail 400 this past weekend for $200 that just came out of a car (yoke incl.) I plan on putting an ATI kit w/ all the goodies to freshen it up.
I have one question, though. Do I need to keep the modulator or does it go away as it did on the 350 manual? I'm talking no speedo, no auto shift. Manual VB w/ limited street.

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Old 01-29-2003, 09:16:00 PM   #12
Doug Jaynes
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hey Jakeshoe

what vb kit do you recomend for a turbo 350 ?
Im very interested in the timing problems you mentioned if you have the wrong shift kit in. any pointers on that ?


I have a t 350 behind my 400. has a hardened race , red clutches and currently a B&M transpac. has a modulator but its not hooked up, kickdown cable also not connected.

this has held up well for a couple years now. but I would like to ditch the kickdown cable and modulator if I need to. the engine only makes 8 or 9" of vac anyway

Thanks a bunch !

Doug

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Old 01-29-2003, 11:18:00 PM   #13
jakeshoe
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Leaving a modulator unhooked or bypassed forces the trans to keep maximum line pressure. This itself isn't ALL bad BUT it causes the converter to push the crank into the thrust bearing and premature failure will result.
Lets put it this way,
Do you have a basic understanding of hydraulics?
What psi does your engine oil system run at?
65psi max I would guess for most applications when warm.
A STOCK trans will have 50-120 psi line pressure in all gears with a modulator hooked up. Unhook the modulator and these pressures go to 150-280 psi.
Add a heavier Pressure regulator spring in the trans and this goes up even more, sometimes ALOT.
So the transmission is making much more pressure than the engine and this is forcing the crank into the thrust.
I have used the B&M Transpak in the Th350 and would not recommend blocking off the modulator. It is there for a reason and still has some effect even on the low vacuum applications.
If you wish to permanently position the detent cable like the B&M kit does it shouldn't hurt anything but all shifts will be HIGH rpm. So driving back to the pits after a run it will be rapped up before it shifts to another gear, then it will kick back down as sson as you let off. I had my bracket car set up this way and wouldn't do it again.
I recommend the TransGo kits on TH350's and 400's as well as most other trannies. They fix weak spots in the particular trans you are working on.
I have done a write up several times on the shift timing/intermediate sprag problem. I'll try to cut and paste it here in a bit.
The problems with most of the manual VB is that they override all modulator function, governor funtion, accumulator etc.. So the trans is basically in WOT pressure mode at all times. This additional pressure may help clutches hold better when you are WOT but are unnecessary at idle and part throttle and just causes undue wear.
Now I'm sure that there are some manufacturers manual VB's that address these issues. I would look for a kit/VB that maintains modulator function and accumulator function, and MAYBE governor function.
The gov. is used for auto operation but eliminating it may cause some problems. TransGo manual kits keep the GOV but effectively make it a manual device by locking the gov. weights. You can achieve the same effect with a couple of small pieces of hose.
If you want a "manual" trans you can place small sections of hose in the gov weights.
This makes the trans want to take off in DRIVE, not 1st gear. So you will have to manually select the gear of choice.
The TransGo kit comes with something a little more "engineered" here but same effect.
It won't however give you manual downshift without some other easy mods. It will let you downshift but if the speed is too far off it will wait until it goes to the lower gear.
This will work on a bone stock transmission so if you think you want a manual shift TH350 try it.
Stroker383,
Hope this answers some questions for you as well.
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Old 01-29-2003, 11:36:00 PM   #14
Turbo T/A
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Jackshoe,

My engine builder here in Ottawa, Ontario is going to equip me with a beefed up TH-400. he mentioned something about a 34 element sprag, and he manufactures his own reverse manual valvebodies. He said the transmission should hold much more than I am going to put towards it. This is all said & done for $1200CAD without converter. I realize you have a good deal for me there & if we werent so distant i would definetly be jumping on it. Thank you very much for the offer & suggestions!!!!! I plan to have this tranny built within the next month or so. I'll keep you guys updated on how it goes!

-Carm

------------------
'81 Viper Blue Z-28
383 Stroker
AFR210cc
Comp XR288HR
Victor Jr
750 Holley
4:10 Rear End
TH-350 10" 3500 stall

N.O.S. Cheater 150-250

New Web Site With Pics & Buildup!
__________________
'69 Trans Am, SBC 400" TT, 20" wheels, 3.25 gear, TH400, 3 1/2" full exhaust & interior, 3653#...and carbureted

Old combo:
Race Gas/Pump Gas
Best ET: 8.47 / 9.21
Best MPH: 163.8 / 153.6

Walk softly.... carry a big stick.

New turbo motor in the works
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Old 01-30-2003, 10:55:00 PM   #15
craggar
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Quote:
<font face="Arial,Verdana" size="2">Originally posted by jakeshoe:
craggar,
Just out of curiousity, what is breaking in your trans?
What valve body/kit are you using?
</font>

The sprague is my biggest problem which you have already given me some info about the modulator that may help me out.I printed your post and gave it to my friend to see what he says but haven't had a chance to talk with him this week yet.The v/b is unknown and could be homemade since the guy I got the tranny from builds his own but he's sure it came to him like that.

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86GN What to do with it?
85GN begging for a SB
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