1970 LeMans TH350 2nd Gear Slipping

[Dom L]

I have a 1970 LeMans with a 455 and a TH350 3spd auto transmission. Recently, I shifted using the column shifter into 2nd because the kickdown cable is disconnected, and ever since then, 2nd gear has been slipping a lot. So much so that in drive it pretty much just skips second and goes straight to third. It still drives, but I don't want to be left stranded if it breaks completely.

What are my options here? Is it toast? Should I keep driving it? Do I have to rebuild it? Or is there a good and relatively inexpensive replacement option?

I could get another TH350, or I've heard the 200r4 transmission is good because it's a 4speed with an overdrive gear, but those aren't cheap...

If I have to get a new one, where should I look? eBay?

Thanks

[JUSTA6]

Rebuild or replace..... If replacing I'd be lookin for a 400 to go behind the 455.  200R4 was made for taking gobbs of HP from the Buick V6,   NOT the tons of torque from the 455.

[Dom L]

Just now, JUSTA6 said:

Rebuild or replace..... If replacing I'd be lookin for a 400 to go behind the 455.  200R4 was made for taking gobbs of HP from the Buick V6,   NOT the tons of torque from the 455.

Is the TH400 a drop in replacement or would I need to modify the driveshaft?

[B52bombardier1]

The TH400 driveshaft would need to change - different spline count and yoke up front.  Your 200-R4 tranny would also need a "throttle valve cable" and special bracket for precise geometry control of the cable into the R4 case - the cable controls increases in line pressure as torque increases during vehicle acceleration.

Get the mounting and adjustment of this TV cable wrong and your 200-R4 clutch pack friction disk material will be waiting in the fluid pan for the transmission rebuild that will very shortly commence.

Rick

[JUSTA6]

It's the reason I'm having probs with mine. 200R4 Behind my 421 in the GTO.  Need to check adjustment.

[Frosty]

20 hours ago, JUSTA6 said:

Rebuild or replace..... If replacing I'd be lookin for a 400 to go behind the 455.  200R4 was made for taking gobbs of HP from the Buick V6,   NOT the tons of torque from the 455.

I have to disagree with my good buddy JUSTA. A properly built 200 4R can hold the torque of a 455, unless you think you are going to build a high horsepower monster. I drive my Lemans 455 cross country, so I am kicking myself for not getting a 200,4R instead of the 400 I had built. 
 

You can also add a Gear Vendors Overdrive unit to the back of any 400 or 350 TH.

Edited September 28 by Frosty

[64 kiwi boni]

Dom 

what colour is the trans fluid ? Is it nice bright red ? Or dirt brown/red 

smell the oil. Does it smell burnt ? 
brown and burnt smelling tells you it due for a rebuild , red and no burnt smell suggests you have a valve body issue .

either way turbo 350 are a good trans 

and if it was my car I would be keeping it 🍻

And hay ! Has any body told you we love pictures around here 

[Frosty]

Nothing wrong with either the 350 or 400TH. Properly built they will serve you well. So it comes down to what you want and how deep is your wallet.

[Dom L]

6 hours ago, Frosty said:

I have to disagree with my good buddy JUSTA. A properly built 200 4R can hold the torque of a 455, unless you think you are going to build a high horsepower monster. I drive my Lemans 455 cross country, so I am kicking myself for not getting a 200,4R instead of the 400 I had built. 
 

You can also add a Gear Vendors Overdrive unit to the back of any 400 or 350 TH.

Oh cool, maybe if I get the 400 I could do that overdrive unit since I have to modify the driveshaft anyways.

 

5 hours ago, 64 kiwi boni said:

Dom 

what colour is the trans fluid ? Is it nice bright red ? Or dirt brown/red 

smell the oil. Does it smell burnt ? 
brown and burnt smelling tells you it due for a rebuild , red and no burnt smell suggests you have a valve body issue .

either way turbo 350 are a good trans 

and if it was my car I would be keeping it 🍻

And hay ! Has any body told you we love pictures around here 

The fluid looks a bit darker than usual and yeah kind of smells burnt. And since I just changed the fluid and filter like two months ago that's not good...

Here are some pics!

[indymanjoe]

build a th400 its heavy duty and built right is bullet proof. buy once and cry once. 455's can cook a trans.

[Dom L]

6 hours ago, Frosty said:

I have to disagree with my good buddy JUSTA. A properly built 200 4R can hold the torque of a 455, unless you think you are going to build a high horsepower monster. I drive my Lemans 455 cross country, so I am kicking myself for not getting a 200,4R instead of the 400 I had built. 
 

You can also add a Gear Vendors Overdrive unit to the back of any 400 or 350 TH.

WOW that overdrive unit is expensive! $3200 isn't worth it at all for what I'm doing

[Dom L]

31 minutes ago, indymanjoe said:

build a th400 its heavy duty and built right is bullet proof. buy once and cry once. 455's can cook a trans.

I'm looking into what I'll have to do, it looks like it needs a new crossmember and transmission mount, with new holes drilled? Then new yoke and shorten the driveshaft, and reuse the converter?

Will a built 350 hold up to the 455 or is it just not strong enough? That would be the easier (and cheaper) route it seems.

[B52bombardier1]

If you ALWAYS have the self-discipline to never ever tempt fate using your right foot with the TH350, it'll be fine.  But then, what's the point of having a 455?

Rick

 

[64 kiwi boni]

i am the same as the guys, a well built 400 will never let you down.

but !!!

the turbo 350 will be fine if this is your cruiser, and no mucking around with changing things !!!

wow !! its a cool car Dom !!!! well done and i see my other fav next to it !!! watch out frosty will see the challenger !!! 

they look gooooood parked to each other !!!!

[Frosty]

Kiwi is correct. So it begs the question, what do you plan to do with the motor and the car itself? Is it going to be a cruiser? A street/strip combo? Or an all out race car?

A 350 is good for cruising, you can’t beat a 400 for performance.

Food for thought, the GV Overdrive is $3200 but it if you source a 200 4R, it will cost around $2000-2800 to have it built up too. So that is the price of overdrive.

If you go with a new used transmission, you have to get ones with the BOP bolt pattern (Buick-Olds-Pontiac) on the bell housing and not the Chevy bolt pattern. A good rebuilt 400 is still around $2000 or more. 

Kiwi - I see the Challenger! I’m done with black cars! 

[TWO LANE BLACK TOP]

Dom...

Does the Turbo 350 Trans..Have the  short or long Tail shaft..?? The reason I ask...If you Decide to go to a Turbo 400... Justa Be sure that that the Tail shaft is the Same Length...If the 350 in your car has the short tail shaft...Be Sure to use the short shaft 400..If you have a long shaft 350...Use the long tail shaft version of the 400...

The Turbo 350/400 Transmissions are dimensionally the Same...With that being Said...

The Crossmembers are also the Same...The only thing You would have to do is Justa slide it back...It is More Than likely that there are Already Factory holes predrilled in the Frame for the Turbo 400... Crossmember Location...As far as the drive shaft goes...If the Tailshafts...(long vs Short) are the Same...The Only Modification Required would be to Change the Front yoke...The Flexplate Would have to be Changed out Also...As the bolt pattern on the T H 400 Torque Converter is different from the 350...justa be sure that you use a SFI approved Flexplate...(it is very cheap insurance against any future issues)...Something to be very aware of...Most Venders will sell the Chevrolet Flexplate for all GM applications...The Chevy Flexplate Will bolt right on the Pontiac engine..Using the Chevy Flexplate instead of using a Pontiac specific Flexplate Can Cause...Starter Alignment/Grinding issues...As there is a very slight difference between the Pontiac Specific and The Chevy Flexplate Outer Ring gear Location....But enough that it can cause the issue I Mentioned Earlier...Other than that It should be a Straight Forward Installation...That's Justa my two cents...

TLBT...

Edited September 29 by TWO LANE BLACK TOP

[Dom L]

14 hours ago, 64 kiwi boni said:

i am the same as the guys, a well built 400 will never let you down.

but !!!

the turbo 350 will be fine if this is your cruiser, and no mucking around with changing things !!!

wow !! its a cool car Dom !!!! well done and i see my other fav next to it !!! watch out frosty will see the challenger !!! 

they look gooooood parked to each other !!!!

Haha the challenger is my daily, but sadly only a v6. Good gas mileage though and it looks good

8 hours ago, Frosty said:

Kiwi is correct. So it begs the question, what do you plan to do with the motor and the car itself? Is it going to be a cruiser? A street/strip combo? Or an all out race car?

A 350 is good for cruising, you can’t beat a 400 for performance.

Food for thought, the GV Overdrive is $3200 but it if you source a 200 4R, it will cost around $2000-2800 to have it built up too. So that is the price of overdrive.

If you go with a new used transmission, you have to get ones with the BOP bolt pattern (Buick-Olds-Pontiac) on the bell housing and not the Chevy bolt pattern. A good rebuilt 400 is still around $2000 or more. 

Kiwi - I see the Challenger! I’m done with black cars! 

I don't plan on doing a lot of strip with it, but maybe one or two runs just for fun? I just don't want it to explode again basically.

The GV overdrive would be good if I didn't have to get another trans on top of that, so then it's $2000-2800 for a TH400 then another $3200 for overdrive which is a $5k setup.

2 hours ago, TWO LANE BLACK TOP said:

Dom...

Does the Turbo 350 Trans..Have the  short or long Tail shaft..?? The reason I ask...If you Decide to go to a Turbo 400... Justa Be sure that that the Tail shaft is the Same Length...If the 350 in your car has the short tail shaft...Be Sure to use the short shaft 400..If you have a long shaft 350...Use the long tail shaft version of the 400...

The Turbo 350/400 Transmissions are dimensionally the Same...With that being Said...

The Crossmembers are also the Same...The only thing You would have to do is Justa slide it back...It is More Than likely that there are Already Factory holes predrilled in the Frame for the Turbo 400... Crossmember Location...As far as the drive shaft goes...If the Tailshafts...(long vs Short) are the Same...The Only Modification Required would be to Change the Front yoke...The Flexplate Would have to be Changed out Also...As the bolt pattern on the T H 400 Torque Converter is different from the 350...justa be sure that you use a SFI approved Flexplate...(it is very cheap insurance against any future issues)...Something to be very aware of...Most Venders will sell the Chevrolet Flexplate for all GM applications...The Chevy Flexplate Will bolt right on the Pontiac engine..Using the Chevy Flexplate instead of using a Pontiac specific Flexplate Can Cause...Starter Alignment/Grinding issues...As there is a very slight difference between the Pontiac Specific and The Chevy Flexplate Outer Ring gear Location....But enough that it can cause the issue I Mentioned Earlier...Other than that It should be a Straight Forward Installation...That's Justa my two cents...

TLBT...

I think it's the short tail shaft but I haven't researched it too close yet. but isn't the short TH400 still like 6in longer than the 350?

Also, isn't it possible to use the 350 torque converter on the 400 so the flexplate can stay the same?

 

Btw thanks for the feedback guys!

[Frosty]

I see you have two choices if you are planning to spend $2000-2500 on a new-to-you transmission.

Option #1 - build a reliable 400TH - 3-speed

Option #2 - build a reliable 200 4R and have overdrive.

The 200 4R is two inches longer than a 400. So you may need to drill new holes in the frame for the tranny crossmember to bolt to. You will obviously need to shorten your driveshaft and change the front yoke.

The decision is this, are you going to do a lot of freeway driving to make the OD transmission worth your while? As much highway driving I do with Lucy, a 200 makes more sense for me, in hindsight. That said, my 400 is quite reliable.

Edited October 2 by Frosty

[Dom L]

On 10/1/2024 at 10:44 PM, Frosty said:

I see you have two choices if you are planning to spend $2000-2500 on a new-to-you transmission.

Option #1 - build a reliable 400TH - 3-speed

Option #2 - build a reliable 200 4R and have overdrive.

The 200 4R is two inches longer than a 400. So you may need to drill new holes in the frame for the tranny crossmember to bolt to. You will obviously need to shorten your driveshaft and change the front yoke.

The decision is this, are you going to do a lot of freeway driving to make the OD transmission worth your while? As much highway driving I do with Lucy, a 200 makes more sense for me, in hindsight. That said, my 400 is quite reliable.

With either of those options, I need a new yoke, new crossmember, and shortened driveshaft... And I don't do a ton of highway driving but I'd like the option to I guess. It's not a daily commuter or anything. Are 200r4s possible to build to take 500lbft of torque? Not that I have the traction anyway, but still. I just don't want to break another one down the line. I've also heard the 200 has a cable that connects to the throttle pedal or something that will burn out the transmission if disconnected, though I don't know much about that.

I would like a 4 speed though if it's reliable enough.

[Frosty]

A TV cable connects to the carb linkage, essentially replacing the 400's kickdown cable. The TV cable controls line pressure, shift points, shift feel, part throttle downshifts, and detent (full throttle) downshifts. So if the TV cable is not adjusted properly, it can cause numerous transmission problems.

You can buy a new crossmember for the 200 4R, but you might be able to re-use the stock one by drilling new holes in the chassis 2 inches past the 400 holes.

Yes a 200 4R can be built to withstand 500HP. You can go online and find folks that build and sell them regularly (yes, they can be pricey for the uber-high HP ones). That said, if you have a local transmission shop you trust, talk them about building one for 500HP. I suspect they can do it, the price difference is probably the cost of the more durable parts needed to withstand that HP load.

[JUSTA6]

If your going that far away from period correct parts, look into the 700R4 overdrive that was made to go behind a V8.  I have a 200 in my GTO behind the 421.  (keep in mind the 200 was designed to go into the Buick Grand National V6) When working it's awesome, have a ton of $$ tied up in rebuild and problems since.  The car is down now because it won't shift out of 1st. Last time I had it in the shop, the guy closed his door behind me, loaded up his tools and closed his business.  Learned that when I tried to get ahold of him about the STILL leaking issue, a couple days later.  Upgrades include new input snout, heavy duty 1st and 2nd gears.  Have to keep a drip pan under the car and usually add some fluid before putting the car away and it's up to operating temp.  You have options to check out.  Without having to deal with by-pass the computer issues, the 400 would be my choice, but it's up to you.

[Frosty]

JUSTA - the 200 4R was put behind both V6 and V8 applications from 1981-1990. Like the 700 R4, the 200 is not computer driven.

The THM200-4R can be found in the following GM vehicles:

• 1981–90 B-bodies
• 1981–84 C-bodies
• 1983–88 G-bodies
• 1985–90 D-bodies
• 1989 Pontiac Firebird Trans Am Indy Pace car (with the turbocharged LD5 Buick V6 and a turbocharger)

This includes both V6s and V8s. Granted these V8s were not larger than 350, mostly less than 307 C.I. None of these engines were much over 300 HP in the day. Just because the Grand National GSX, and the Pace Car TAs were the highest production HP motors bolted behind the 200, doesn't mean it cannot support a 421 or 455. IT needs to be beefed up.

I tend to favor the 200 4R over the 700 R4 for one basic reason. The 200 was the only overdrive transmission made using the BOP bolt pattern. Using a 700, 4L60, 4L80, etc. requires an adaptor kit because these trannies use the Chevy bolt pattern.

Clearly you got taken for a ride by your tranny mechanic. He screwed you big time.

JUSTA is correct, you need to do your homework.

[Dom L]

6 hours ago, Frosty said:

JUSTA - the 200 4R was put behind both V6 and V8 applications from 1981-1990. Like the 700 R4, the 200 is not computer driven.

The THM200-4R can be found in the following GM vehicles:

• 1981–90 B-bodies
• 1981–84 C-bodies
• 1983–88 G-bodies
• 1985–90 D-bodies
• 1989 Pontiac Firebird Trans Am Indy Pace car (with the turbocharged LD5 Buick V6 and a turbocharger)

This includes both V6s and V8s. Granted these V8s were not larger than 350, mostly less than 307 C.I. None of these engines were much over 300 HP in the day. Just because the Grand National GSX, and the Pace Car TAs were the highest production HP motors bolted behind the 200, doesn't mean it cannot support a 421 or 455. IT needs to be beefed up.

I tend to favor the 200 4R over the 700 R4 for one basic reason. The 200 was the only overdrive transmission made using the BOP bolt pattern. Using a 700, 4L60, 4L80, etc. requires an adaptor kit because these trannies use the Chevy bolt pattern.

Clearly you got taken for a ride by your tranny mechanic. He screwed you big time.

JUSTA is correct, you need to do your homework.

Hm... Still, I don't want to worry about the transmission again, so I might just go with the 400 for peace of mind. I found someone locally who supplies cores and builds them, so I'll probably go that route. Should I ask for a stock build or upgraded? If so, what upgrades should I go for?

[B52bombardier1]

I have them rebuild for longevity and durability., not necessarily snappy shifting performance.  You might consider having them plumb in the lines for an external stacked plate transmission cooler and install the cooler to keep radiator water out of your trans and transmission fluid out of your radiator coolant.  This occurs with failures inside the radiator sub tank of trans fluid and will never be considered as a warranty repair item by the shop.

For my El Camino 4L60E rebuild and for my upcoming Catalina 4L60E rebuild I told and will tell them that I will pay extra for any wear items that are questionable.  Always, always get the torque converter cleaned out internally and rebuilt - make sure the TC "neck" is not grooved - she's a leaker, if grooved.  Rebuilt transmissions should be run on a dynamometer if the shop is well equipped.

Get their warranty in writing up front. Get what they are actually going to perform during this rebuild written down up front.  There is a big chance of variability in what constitutes the rebuild of a transmission.  Will they ream the valve body for bushings if it needs it?  Whose manufacturer rebuild kit - Sonnax and Transgo are well known choices.  Any hard parts replaced and will these cost extra? Stock steels and friction disks or Kolene upgrades? Do they recommend "hardened" hard parts for the shell, the planets, and input shaft - maybe even other upgraded hard parts?

I'm probably missing something but at least this is a start.

Rick

[Frosty]

There is nothing wrong with the 400 for sure. B52bombardier1 has some excellent points too.