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350 trans with a plug and vacuum?

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80malibucoup
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350 trans with a plug and vacuum?

Post by 80malibucoup » Thu Feb 09, 2012 12:54 am

I bought a 81 malibu stock v6/350 trans. I'm puzzled on the trans,it has a plug like a 700r4 and a vacumm module. Can anyone tell me about this trans? What is the plug for? Does this trans have a lock-up converter?Can I use this in a hi-performance application?? I need pros and cons on this one,for I know nothing about this trans.

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Re: 350 trans with a plug and vacuum?

Post by timo22 » Thu Feb 09, 2012 11:18 am

if it is an electric plug, more than likely it has a lock-up converter. I know in the late 70s they had an electric switch that dealt with spark advance for emissions. In either case , you are better off getting a std. non-electric 350. These transmissions are a very durable unit for a strip/street car. The modulator helps define shift points by engine vacuum (engine load) in conjunction with the governor(road speed). The kick-down cable not only downshifts for passing gear but increases line pressure to the clutch packs for increased hold on the clutches.

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80malibucoup
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Re: 350 trans with a plug and vacuum?

Post by 80malibucoup » Thu Feb 09, 2012 4:14 pm

I know about the vacuum and the cable,it's the plug that got me puzzled. I've never seen a 350 trans with one.What's good about a lock-up converter? Thanks for the info.

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Re: 350 trans with a plug and vacuum?

Post by timo22 » Thu Feb 09, 2012 4:39 pm

For our purposes a lock-up converter is no good. Basically it locks up the converter to engine rpm. An auto transmission always has slippage between the flywheel and the input shaft.(via the torque converter) By "locking the converter" you have essentially direct drive. This was for improved gas mileage. However there were problems. Sometimes the the converter would go in and out of lock-up causing an erratic ride. I don't think you are worried about gas mileage otherwise we'd be talking about a geo or something! lol

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80malibucoup
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Re: 350 trans with a plug and vacuum?

Post by 80malibucoup » Thu Feb 09, 2012 6:31 pm

I understand putting a lock-up in a 700,but a 350?That makes no sense.

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Re: 350 trans with a plug and vacuum?

Post by timo22 » Thu Feb 09, 2012 10:43 pm

Actually,the reason guys put 700s in their cars is that it is a 4 speed trans. It has a low 1st gear and an overdrive gear. Typically you would use a non lock up 700.this way you have a low 1st gear for taking off and an od gear for cruising on the highway.honestly I would think that most guys that run 700s do not use the lock up 700.l know that I put in a 700 in my 81,I made sure to get a non lock up core to build. Gm realized the way to better fuel economy was to build an overdrive trans. Instead of putting a lock up converter on the 350 which they were phrasing out.

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Re: 350 trans with a plug and vacuum?

Post by axisg » Fri Feb 10, 2012 9:50 am

Sounds like you have the 350c trans ( had one in my 84ss ). They were used in passenger cars and half tonne trucks in the late 70's - mid 80's. Lockup was controlled by either a vacuum switch on the firewall or the OBD1 computer. I bypassed mine and wired to a simple toggle switch

From what I researched its mostly the guts of a TH350 trans with a lockup TC. That was good for a 100-200 rpm drop on the highway when I flipped the switch locking the TC. They are fairly durable AFAIK and there are parts availbale to beef it up, the PO of my car had installed a shift kit which pulled the car around very well with firms shifts even with the 305. However I swapped it in favour of the 200-4r to get Overdrive and swap to lower rear gears.

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Re: 350 trans with a plug and vacuum?

Post by Pete@Hughes » Fri Feb 10, 2012 10:16 am

We offer performance lock-up TH350C torque converters with higher stall speed ratings (2,000 / 2,500 / 3,000 / 3,500) if you're interested in using that transmission and would like to have a performance-oriented torque converter to use with it.

The TH350C can be built into good performing and durable transmission for a street or mild street/strip car. All the commonly available performance friction materials and intermediate sprag upgrades for the TH350 also fit the TH350C. TransGo offers a valve body reprogramming kit that works well and provides dramatically improved shift quality and transmission durability. You can install a toggle switch to manually control the converter lock-up feature so that you can control the engagement/disengagement. Also, the TH350C can be converted to a non-lock-up transmission if necessary with the installation of the earlier style TH350 front pump, input shaft/forward drum, and valve body.

The lock-up feature is actually a pretty neat thing to have when using a high stall torque converter on the street. If you have a combination that requires higher stall speed (3,000+ RPM) and you want to drive it on a regular or even daily basis, especially regular freeway/highway use, the lock-up feature will allow you to have all of the performance advantages of a high stall converter while also having improved fuel efficiency over a non-locking converter as well as reduced transmission operating temperature.

Also, for the 200-4R and 700R-4 guys, I wouldn't ever run a non-lock-up torque converter in a street car unless you were running an OE-style low stall torque converter or running a mismatched overall combination with a 2-series rear gear ratio and a large cam profile and/or large runner cylinder heads/single plane intake manifold. A lock-up torque converter does not offer any significant performance disadvantages in a street or mild street/strip car so there really isn't any point in giving up the additional fuel efficiency and reduced operating temperature.
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80malibucoup
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Re: 350 trans with a plug and vacuum?

Post by 80malibucoup » Fri Feb 10, 2012 11:17 am

OK,I'm running a aluminum head 202,160,flat top piston,11.1 compression, 408sbc,about 415-420 hp,GN rear with stock 342 gear,may go to a 373 later on. Cam is a comp cam flat tappet,507 intake,510 exhast,duration @.50 240in, 246ex. My car is a full interior car. I want to have a nice street/strip car. Would this trans be a good choice or the 700??

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hypeboy
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Re: 350 trans with a plug and vacuum?

Post by hypeboy » Mon Sep 17, 2012 1:45 am

80malibucoup wrote:I bought a 81 malibu stock v6/350 trans. I'm puzzled on the trans,it has a plug like a 700r4 and a vacumm module. Can anyone tell me about this trans? What is the plug for? Does this trans have a lock-up converter?Can I use this in a hi-performance application?? I need pros and cons on this one,for I know nothing about this trans.


I know im late with this. Personally im using PEAK PERFORMANCE VACUUM as well as trans. I actually have a 1987 350 TBI with a TH350 transmission but often failed and was rebuilt many times. I want to assure I have everything right to got it re-installed.

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