Help 1970 TH400 problem

[Rob]

The problem is bad slipping in Normal drive. So bad that the car wont run above 5mph or so.
This happens all the time, when trans is cold or warm, hitting the gas pedal right off the start from idling. Other selections such as L1 and L2, R work fine. Only the D slips.

I have an original TH400 from a 1970 Fleetwood with a 472cu, in my 1946 Cadillac.

I did drop the pan, changed the filter & fluid, and checked the transmission linkage.
After driving for 10 miles on Low, I dropped and checked the pan again and found a few black rubber chips in the pan... not sure if this is related.
I did check the fluid level many times, warm and idling on P, fluid level is fine and not leaking outside.
Also, when engaging into normal drive, the transmission makes a klung sound and kind of shakes the car harder than other selections.

Any thoughts ?
Thank you.
Rob

[Michael Stamps 19507]

The klung sound might be the idle set too high.  I find that most of these engines are set by ear and tend to be way to high.  Other than that it sounds to me like its time for a rebuild.  

Stampie

PS - Just for Pooter I answered with more than one word.

[Geoff Newcombe #4719]

Yeah ..... you sure are being chatty today Stampie!  
:-)

[Rob]

Any ideas on what can cause this slippage on D only ?
I have the How to work/modify the TurboHM400 great book but it does not list this symptom...

[Bruce Reynolds # 18992]

Gday Rob,

It has to be something internal, but seeing as you have changed the oil and filter, I think it is time that you took a little drive to your local, good, transmission shop, and got their expert advice.

It might be a simple fix, or requiring a complete teardown, but it is better to get it looked at sooner than later.

If it requires a complete teardown, then get a couple of quotes, and check out the previous work of the Transmission Shop.

Sometimes, one has to bite the bellet.

I use a couple of good shops here in Tasmania, but they are a tad too far away from you to be of much assistance.

Bruce,
The Tassie Devil(le),
60 CDV

[Rob]

Bruce, thanks  for your answer.
I am going to take it down myself and swap it with an already rebuilt unit. The tranny shops where I live are just too expensive to consider.
I was hoping for a simpler in-car fix but it looks like its not going to happen.
ROb

[Doug Houston]

Perhaps this was a workable conversion. The transmission was never designed or teated to be used with the 46 engine. That doesnt mean of course, that it wont work. But, there are no experiences that you might seek out to determine what needs to be corrected for proper operation. Probably, the transmission was taken from a junk car that was run ning O.K., and installed in your car without being rebuilt. Thats a common mistake, but a real money saver in the short term.

My gut feeling is that, since the original Hydra-Matic tranmission that was in that car at one time, is about the best operating gearbox that you could have in tha day, or even today, IF the transmission is put in perfect order before going into the car. Perhaps there is a strong feeling about preferring the THM 400, but were I in your shoes, Id find a 46-50 transmission, and install it in the car, and enjoy it.

[Jeffrey Traikoff]

This will be a good oppurtunity for some DIY tranny work.  TH400s are simple as pie and strong as hell.  Rebuild kits are fairly inexpensive and the rebuild should be relativley easy, just make sure you have a good manual handy.  I always thought tranny work was for the elite but i helped rebuild a hydramatic out of a Rolls Royce and then I realized that it isnt as impossible as it may seem! Fun too!  GL

Jeff T.

[Bruce Reynolds # 18992]

Gday Jeff,

I like your reasoning.

By philosophy is that if someone can do it, then there is no reason why I cant do it myself, especially when following instructions.

That is how I taught myself to be a mechanic, amongst other things and now I am into Computers, but, not with greasy fingers.

A jack of all trades, and master of two.

Bruce,
The Tassie devil(le),
60 CDV.

[Geoff Newcombe #4719]

Doug,
He doesnt make it crystal clear, but my take on it is that he put BOTH the 472 and its TH400 in the car.

[Doug Houston]

Sorry about that I take back everything I said.

[Rob]

Yes sorry if I was not clear, it is a 70 472ci attached to the TH400 in place of the orignal engine & tranny.

I also own a 1947 Cadillac with the orginal engine and Hydramatic, vehicle is unrestored but in good condition, and it runs great...engine has less power and tranny shifts a bit harsh but runs great..so far.

The only annoying point with the old tranny is the that it is sometimes hard to select to reverse gears.I had another 47 Cadillac before and it had the same selector issue and gear clash while shifting to reverse at times.

I do however appreciate the sound of the original tranny  and engine, as well as the very classic, heavy sweet-and-sour smell of the exhaust gas...

Rob
46@bigcadillac.com

[Geoff Newcombe #4719]

Rob,
Perhaps this posting by Doug Houston on 8/6/06 will help with your gear clash problem ........

The prewar Hydra-Matics were indeed, tricky into reverse. In addition to having the transmission engage before moving the selector into reverse, THE REAR WHEELS MUST BE TOTALLY STOPPED. This is true on even the post war transmissions through 1950.

The post war transmissions had a reverse blocker built into the control valve body to ensure that the trans. engaged before the selector could even move into reverse.The rule about stopped rear wheels still holds on them. In 1951, a cone clutch device was added to the reverse mechanism. This permits the selector to yanked right into reverse as soon as the engine fires. Its kind of a nice feature. On two of my 41 cadillacs, I have 49 Cadillac transmissions, and on the convertible coupe, I have a 51 Cadillac box. The 2-3 upshift is a bit tough, but that reverse selection is just great!

[bill henry]

if the sprag (roller clutch ) is bad it will slip in D but not 1 or 2