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Old 03-02-2001, 09:39 PM   #1
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Join Date: Dec 2000
Location: Springfield, MO, USA
Posts: 1,536
Car: 1986 Trans Am, 1991 Firebird
Engine: 355 TPI, 3.1L V6
Transmission: 700R4 in both

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are the TH350 flywheel and the 700R4 flywheel the same??

About two years ago my 700R4 went out on me and I replaced it with a TH350 turbo since it was cheaper!! Now the TH350 is going out and I'm going to put a 700R4 back in this time!! I need to know if the flywheel I have on there now will work with the 700R4!?! I don't remember changing the flywheel when I put the TH350 in there so I think it's the same flywheel!! Any help would be greatly appreciated!

------------------
1986 Trans AM
305 TPI
200,000+ miles (speedo/odometer non-funtional! Odometer reads 142,000)
4 Wheel Discs
9 bolt Borg Warner Rear (2.77's....oh joy) :P
Completely Stock
Soon to upgrade to a 355 converted from TPI to Carb, Edelbrock 750CFM Carb, Edelbrock Performer RPM Intake, Hedman Shorty Headers, Stock casting pocket ported heads (2.02/1.60 - 65cc), XE268 Cam, Moroso HEI ignition kit with external MSD Blaster II Coil and an MSD 6-AL Box!!
Current project: Keeping my 305 running until I get my income tax returns!
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Old 03-02-2001, 11:42 PM   #2
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Yes the 350 and 700 both use the same flywheel.

------------------
"So many Mustangs, so little time..."
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Old 02-14-2014, 09:55 AM   #3
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Join Date: Dec 2013
Location: bc canada
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Car: 1987/pontiac firebird
Engine: 350 carb
Transmission: 700r4
Axle/Gears: 3.73

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

I have a th350 flywheel and a 700r4 and the center hole in the flywheel is different and won't mount to my 305 v8.

305 came out of an 85 cutlass.
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Old 02-14-2014, 10:50 AM   #4
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Location: Saratoga Area, New York
Posts: 225
Car: 1990 Formula Firebird
Engine: 305 TBI (LO3)
Transmission: WC T-5 out of an 88 T/A
Axle/Gears: 10 bolt, 3.42 & Torsen Posi

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

First, I must scold you for reviving a thread that is 13 years old. Bad!

Second, the flywheel bolt pattern changed on all SBCs in the late 80s, I believe it was 87. Is it possible you have a post 87 flywheel for your pre 87 engine?
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Old 02-14-2014, 11:36 AM   #5
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Car: 1987/pontiac firebird
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Re: are the TH350 flywheel and the 700R4 flywheel the same??

Sorry I couldn't find a way to make a new thread and didnt know this question was that old lol. Yeah the 700r4 flywheel is from an 88 camaro. And the 305 is from an 85 cutlass.

Will I be able to find a flywheel that works?
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Old 02-14-2014, 02:16 PM   #6
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Location: Saratoga Area, New York
Posts: 225
Car: 1990 Formula Firebird
Engine: 305 TBI (LO3)
Transmission: WC T-5 out of an 88 T/A
Axle/Gears: 10 bolt, 3.42 & Torsen Posi

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

That's your problem then. And you should have no what you need finding what you need. FYI, the part you're looking for is actually called a flexplate. Manual transmissions use flywheels, automatics use flexplates. Its a pretty common misconception for them all to be called flywheels tho. You will just need to find a pre 87 flexplate with the same tooth count on the starter ring gear. Did the cutlass engine not come with a flexplate on it?
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Old 02-14-2014, 02:24 PM   #7
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Car: 1987/pontiac firebird
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Re: are the TH350 flywheel and the 700R4 flywheel the same??

Came with the flexplate that was with the motor. Motor was matches up with a th350 trans.

So I just need a flexplate with the same tooth count. Shouldn't be difficult. I'll double check the flexplate that came with the motor and see if it will work.

Thanks for your help!
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Old 02-14-2014, 04:44 PM   #8
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Location: Saratoga Area, New York
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Car: 1990 Formula Firebird
Engine: 305 TBI (LO3)
Transmission: WC T-5 out of an 88 T/A
Axle/Gears: 10 bolt, 3.42 & Torsen Posi

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

The only reason the tooth count matters is for the starter. Different size flexplates have a different number of teeth & therefore different starters.
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Old 02-14-2014, 06:53 PM   #9
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Car: 90 Vette / 67 Camaro / 87 Vette
Engine: 383 SP EFI /383 LT1 /L98 TPI
Transmission: T400 /200R4 /T700
Axle/Gears: 9" 3.90 /12 Bolt 4.11 /D44 3.07

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

Quote:
Originally Posted by tanner-fitz@hot View Post
So I just need a flexplate with the same tooth count.
I'll double check the flexplate that came with the motor and see if it will work.
What you need to be checking is if the flexplate that fits the engine will bolt up to the T700 convertor.

GM used two different convertor bolt patterns ; 10.75" and 11.50"

Some flexplates have both convertor bolt patterns , some only have one which may be the wrong one for your T700 convertor

You can see this one has both bolt patterns
http://www.summitracing.com/int/part...make/chevrolet
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Old 02-14-2014, 08:18 PM   #10
jmd
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Car: `86 SS / `87 SS
Engine: L69 w/ TPI on top / 305 4bbl
Transmission: `95 T56 \ `88 200-4R

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

Quote:
Originally Posted by tanner-fitz@hot View Post
I have a th350 flywheel and a 700r4 and the center hole in the flywheel is different and won't mount to my 305 v8.

305 came out of an 85 cutlass.
In between 85 and 86 is when balance and bolt pattern changed. If your cutlass had been an 86 it would have worked.
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Old 02-14-2014, 08:37 PM   #11
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Re: are the TH350 flywheel and the 700R4 flywheel the same??

A 86-up 700 flex plate (automatics don't have a flywheel) will almost bolt up to a 350 converter; and a 69-85 350 flex plate will almost bolt up to a 700 converter.

Once you get past the crank flange difference between 85 & 86, the 350/Glide flex plate converter bolt circle is some SAE measurement, and the 700 one is some metric one. They're REAL close; not exact; sometimes they fit, sometimes not; you might have to elongate the converter bolt holes in the flex plate slightly. Around .060" (1/16") or so if memory serves. I don't recall which one has the larger/smaller bolt circle, sorry.

Some of the aftermarket ones have slots instead of round holes to accommodate either bolt pattern.
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Numquam ponenda est pluralitas sine necessitate.
William of Ockham, c. 1330 AD, from Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi

Roughly paraphrased into modern English, and applied to figuring out what's wrong with your car:

The simplest explanation that fits all the facts is probably the right one.
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Old 02-14-2014, 10:55 PM   #12
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Join Date: Dec 2013
Location: bc canada
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Car: 1987/pontiac firebird
Engine: 350 carb
Transmission: 700r4
Axle/Gears: 3.73

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

So basically it is almost impossible to get an 88 700r4 to mount to an 85 305 eh? The flex plate just won't work?

Could I use the th350 flex plate for the 700r4?

The crank diameter is 2 1/2" and the th350 flex plate works with that. But the flex plate that came with the trans (the 88 700r4) has a 2" diameter hole and doesnt fit.
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Old 02-15-2014, 12:15 AM   #13
jmd
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Transmission: `95 T56 \ `88 200-4R

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Re: are the TH350 flywheel and the 700R4 flywheel the same??

Quote:
Originally Posted by tanner-fitz@hot View Post
So basically it is almost impossible to get an 88 700r4 to mount to an 85 305 eh? The flex plate just won't work?
All you need is a 1985 200-4R (B-body, D-body, G-body) or 700-R4 (F-body, B-body) flexplate and of course the right metric bolts. The 700-R4 converter will bolt right up.

And frankly, an 85 Cutlass would have come with a "metric" transmission (TH200-C, TH200-4R) and originally had the exact same flexplate as an 85 Camaro V8. So that's not the original flexplate for the car if a 700-R4 converter doesn't bolt up to it.
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Old 02-15-2014, 08:03 AM   #14
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Re: are the TH350 flywheel and the 700R4 flywheel the same??

A 88 700 will BOLT RIGHT UP TO a 85 305. However the flex plate WILL NOT.

If you have a motor from 85-back, you need a 85-back flex plate, to fit to the crank.

So NO, the 88 flex plate will not attach to the 85 motor, because the 88 flex plate is not from 85-back.

85-back; 86-up.

Once you get that sorted out and quit expecting a 88 flex plate to bolt to a 85 crank, you're almost home free.

You'll also find that there are 2 outer diameters of flex plates. 12.8", with 153 teeth; and 14", with 168 teeth. Either one, IN THE RIGHT YEAR RANGE, will bolt both to the crank, and to the 700. Most but not all 350s, as well as trucks with 700s, came with a 14" one. These cars, as well as most cars with 700s and other "metric" transmissions from about 78 or so on up, AFAIK came with the 12.8" one. If you get the wrong diameter for your starter, you'll have to get a different one of those too, and it's possible that it then will interfere with some other part. (exhaust most likely)

The vehicle look-up choice jmd gave you is GUARANTEED to get you a flex plate that will fit everything you've got. Crank, trans, starter, the whole shebang.
__________________
Numquam ponenda est pluralitas sine necessitate.
William of Ockham, c. 1330 AD, from Quaestiones et decisiones in quattuor libros Sententiarum Petri Lombardi

Roughly paraphrased into modern English, and applied to figuring out what's wrong with your car:

The simplest explanation that fits all the facts is probably the right one.
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Old 02-15-2014, 08:03 AM
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