When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
The cause was a missfunction of my automatic transmission. I was roling down a hill on the Swiss-Autobahn in the third gear and once I hit the pedal to drive, the transmission was shifting in the second gear and won't go to the third again.
In addition now its making a noise like I have turbo installed, no matter if in neutral or in drive.
Looks like have to repair now the TH400 or update to a TH 200 4R.
I would need some help which road to go and how an upgrade would work and what exactly on extraparts and modification is needed to install it.
Maybe a cost comparison would also be interesting ?
I'd repair/rebuild the TH400 and keep the car original unless you have a real need for overdrive. If you switch, the rear gearing will probably need to be changed to better accommodate the 200R4 gear ratios. That plus all the bits and pieces to make the new trans work correctly will reall add to the cost. It's your money, so do as you want.
Having had this conversion this year I say it improves the drivability of the car considerably. I see you are in Germany so the overdrive in the 200R4 would improve your autobahn driving and the better gear spread 1st - 2nd is a bonus as well. If you have a numbers matching car you could keep the original trans to stay with the car as swapping back from a 200R4 to TH400 is straightforward because you don't have to modify the driveshaft (except for fitting a TH350 out put shaft to the trans and convertor universal joint TH350- TH400) or the trans crossmember to fit the 200R4 (at least I didn't).
You will need to modify the gear selector if you want to be able to manually engage 1st gear, this can be achieved by grinding a little out of the gate so that the lever will move further or you can buy a kit.
The most critical part is adding the TV cable to your carb and making sure it is set up correctly, there are kits for this also.
The lock up torque converter needs some means of engaging and disengaging. I used a Painless transmission kit for this as well as having a manual override switch in the car.
You may have to change the gear ratio in your differential, 3:55 seems to be a popular pick. I am still running the 3:08 behind a mostly stock 350 and it can cope but you have to lock it into 3rd for around town driving, eventually I'd like to fit the 3:55 ratio though.
My 200R4 didn't have a speedo drive fitted when I got it, make sure they supply one as the TH350 - 400 one wont fit (but the cable will).
There is plenty of info on the forum about this conversion and a lot of good info on BowTie overdrives site and others, I used BowTies TV valve spring because it increased the oil pressure in the trans by over 40 psi.
I'm sure that you are wanting to drive the car on some fairly long trips in the future. If so, I would suggest that you have the THM-400 rebuilt and retain it for 'posterity' and any possible future sale of the car.
And, I would highly recommend that you replace that unit with a 200-4R transmission that has been upgraded to handle the level of power available from your engine. The 200-4R will do nicely to drop into your vehicle without the need to replace or 'significantly' modify the transmission cross-member. You will have to do some minor modification of the exhaust system. I believe that you can still use your stock driveshaft 'as is'...at worst, it might need to be shortened just a bit, also.
This conversion will require the addition of a Throttle Valve (TV) cable to help regulate shift points (the vacuum modulator in the 400 will no longer be available) and there will be some adaptation for the oil filler tube for the transmission. If you wish, you can modify the shifter plate to provide a notch for a 'first gear hold' position. But, it is unnecessary for normal operation of the transmission.
Installing an overdrive trans into your vehicle will not only improve fuel mileage by 20%+ (at highway cruising speeds), but it will also reduce the work effort of the engine and make driving the car much more comfortable.
The 700R transmission could also be used, but this conversion from the THM-400 would be more extensive and somewhat more costly.
I'd repair/rebuild the TH400 and keep the car original unless you have a real need for overdrive. If you switch, the rear gearing will probably need to be changed to better accommodate the 200R4 gear ratios. That plus all the bits and pieces to make the new trans work correctly will reall add to the cost. It's your money, so do as you want.
I agree on repairing the turbo 400, stout automatics that stood up the horsepower of the big block C3 Corvettes of the late 60's and 70's.
My 1970 with 350/300 is still going strong after 160K miles.
Your decision may come down to cost. For those of us in North America we can get donor transmissions from the auto dismantling yards; how common are they in your part of Germany? I think, if it was me, I would have your stock 400 repaired (it may be a simple repair) and consider the upgrade when you have more time to source the parts.
Your decision may come down to cost. For those of us in North America we can get donor transmissions from the auto dismantling yards; how common are they in your part of Germany? I think, if it was me, I would have your stock 400 repaired (it may be a simple repair) and consider the upgrade when you have more time to source the parts.
its my understanding the only additional parts one would need is a th350 yoke , a tv cable and a regular switch for the lockup....otherswise the 200r4 fits perfect...
I am also considering the same upgrade since the 4 speed OD is superior that heavy 3speed with todays speed limits and fuel prices (dont start with the "you shouldnt be concerned with fuel economy" bit... its not the deciding factor but its one just the same especially when limited to high octane stuff ) It would be nice not having the engine whining at 3,000+ rpm on the thruway all the time...
200R4 for sure! Not all TQ converters are created equal. So shopping for a stall speed is not equal. Cheaper large 11 inch TC's slip up to their rated stall speed. So in the past I had a powerful Big Block with a 3000 stall. I think it was a B&M Saturday night special. Driving down the highway in 3rd gear it was always doing 3000 rpm unless of course I went faster. Very inefficient and just turning power into heat.
On the other end there are highly efficient smaller diameter like 9.5 inch. They only slip up to the stall rating when you have your gas pedal on the floor. So you can then buy higher stall ratings and have the best of both worlds. With or without lockup you can run 3500 stall.
This all depends on your engine and cam choice and when the power band comes in.... I agree that 2000-2200 is the best guess choice... its what they had stock and what I have behind my 350-400hp 355 build.
I made this conversion a couple of years ago. I removed my fully functioning TH400, sold it and never looked back. I bought a used transmission and made some upgrades to the shift calibration and it has served me well so far.
What rear gear ratio do you have? I have 3.55 and would almost consider this the minimum for me. The Monte Carlo SS that the 200-4R was removed from had 3.73
Will you go with a performance rebuilt unit shipped from USA or try to buy a used one local and have it rebuilt? How easy is it to find a core for you?
Will you be doing any of the work yourself? This conversion is almost plug and play but not quit. Moreover, it will require sourcing different parts and kits to fully adapt the unit. I had fun, you might too.
The highway driving is night and day. There are roads around me that are 120 kph. At that speed the car is only turning 2300 rpm. The converter is also a lock-up style.
Tranny and heat are a problem. It is dumb to run exhaust pipes right next to any tranny using the stock holes on a cross member. Buy the cross member that has a pass under exhaust like the BTO
I found a real competent shop here in Germany which made me an interesting offer:
He will make a fair price for the repair including everything and he also offers me to install a TH700 R4 for a reasonable price.
My questin now, I have the stock Differential , with 3.08 as I remember.
What exactly is the disadvantage with a TH700 and a 3.08, and what would be the best ?
I mean I drive a lot here with around 80-90 miles per hour on the Autobahn, but also will not be the slowest when we drive up the Alps or other mountains
High range gear in the overdrive transmission is a .67:1.00 ratio. At 100 kph, your THM-400 might be turning 2700 rpm; with the overdrive transmission, your engine will only be turning 1800-1900 rpm. That isn't a problem at highway speeds, as the C3 engines have plenty of low-speed torque.
But, at lower speeds (ie, 50 kph) your engine would be "lugging" at less than 1000 rpm, if you put the shifter in high range. So, you just need to run the transmission in 3rd gear for low-speed driving and then put it in high range for highway speeds.
Again, if you install the O/D trans, it will have a lockup clutch which will provide even higher efficiency when at steady speeds. However, you really need a good lockup clutch controller to make the decisions of when it should be ON and when it should be OFF. If the lockup clutch is left ON when the engine is loaded, the clutch can be damaged very quickly. Some folks just use a simple toggle switch for activating the L/U clutch. But, if you forget to flip it off, your clutch might quickly become "toast". Get a controller and be done with it.
The small white tube on top is a vent. Needs nothing connected to it. Three are several companies that make a shift kit for the 200-4R. My preference is Trans-Go, but there are others that are good as well.
08-18-2014, 12:37 PM
Repair the TH400 or update to THM200-4R
Not all TQ converters are created equal. So shopping for a stall speed is not equal. Cheaper large 11 inch TC's slip up to their rated stall speed. So in the past I had a powerful Big Block with a 3000 stall. I think it was a B&M Saturday night special. Driving down the highway in 3rd gear it was always doing 3000 rpm unless of course I went faster. Very inefficient and just turning power into heat.
