Prestomatic transmission problem HELP!!!

[Guest imported_BaronvonR]

Hi

I am in need of some help on my 1951 DeSoto Custom's prestomatic transmission. It is very hard to get it going forward....almost feels as though the brakes are hanging up, but they are not. The car climbs hills with difficulty, and does fairly well on the straight away. I was told it might be the torque converter or pump. I dont want to tear it apart until I know for sure what the problem is. Does the torque converter have a seperate oil supply from the transmission, perhaps it is low on fluid??? ANY help would be greatly appreciated to diagnose the problem. IF it is the torque converter anyone know who repairs these in the CT area???

[Jon Robinson]

Hello again, BaronvonR:

You specify that it's hard to get the car moving forward. Does it roll easily enough in Reverse?

It's very common for the parking brake drum on the back of the transmission to act in the way you're describing--turning easily in one direction and not the other.

Drop the driveshaft, undo the big nut holding the parking brake drum on, remove the drum, and thoroughly clean all the grime off the drum and the shoes. Use regular spray-style brake parts cleaner.

There are two adjustments on the parking brake as well. One adjusts the shoes nearer for further from the drum, and the other adjusts the parking brake cable in and out of the housing and determines the starting point of the pull whe you apply the parking brake.

If you've noticed any noisy chattering at low speeds, this is a sure sign of the parking brake.

I learned this lesson years ago, and I've helped several friends solve what they thought were transmission problems by cleaning the parking brake. One man was going to have his '53 Chrysler's transmission and rear end rebuilt until I cleaned the parking brake for him. It was perfect.

JON

[Jon Robinson]

Baron:

As for the rest of your questions:

Yes, the torque converter, known more accurately on these cars as a "fluid coupling" or "Fluid Drive unit," does have a separate oil supply from the engine. The Fluid Drive units orginally came with a mineral oil-based fluid under a Mopar trade name, but being that it was a low-viscosity oil meant to grab under cetrifugal force, today's Dextron III or tractor fluid work just fine. Lift up the carpeting on the passenger's side, and you'll see two removeable inspection covers--a big one on the side of the transmission hump near the seat, and one small one higher on the transsmisson hump where the passenger's left foot would normally ride. You fill the Fluid Drive unit through the small inspection cover after you turn the Fluid Drive unit to where the filler plug shows. If you want to change all the fluid in it, you'll have to drop the lower bell housing and drain it.

If the fluid in the Fluid Drive unit is low, the engine would tend to race as if it were not solidly connected to the drive train--something like a slipping clutch. If it feels pretty connected, it's probably not the fluid level.

While you're in there, you might want to pull the large inspecion cover as well just to acquaint yourself with the transmission's electrical components.

JON

[Guest imported_BaronvonR]

Hi Jon,

You are an invaluable source of information. I had the E brake checked and it just fine. Turned out that when I had the torque converter checked there was only 3 quarts of oil in it! I had it drained and refilled it with 10W oil (I hope that was the right oil to use)...it took almost 8 quarts. I then tried the backing it out of the garage and it fairly flew out.....absolutely amazing the difference. How often should this be checked as NO book I have read on the car or on my Imperial mention servicing this unit. I fully intend to have this checked on my Imperial as I spent a considerable amount getting the brakes redone on it....appears to me to be the same problem. Well live and learn. Both have felt like the brakes were dragging when all of the time it was lack of fluid....I have gone ahead and had the governors cleaned as per your suggestion. Thanks so very much for sharing your wisdom...I love my MoPars and want to drive em.

[mopar380]

Hi

A note about the oil you put in the fluid coupling, I would take Jon's advice and put in the Dextrom III fluid rather than the 10W engine oil. In fact I would completely drain out and remove all traces the engine oil, and replace it with the Dextron III which is a mineral based oil. The engine oil may do harm to some of the seals in the unit.

Ian

[Jon Robinson]

Thanks, Ian, for your vote of confidence, and yes Baron, I would get that motor oil out of there. Motor oil is meant to be slippery, which you don't want in a fluid coupling that should be grabbing, and I share Ian's concern about it seeping around the big carbon seal. It's probably not an emerigency, though, and it did answer your question.

JON

[Guest imported_BaronvonR]

Again many thanks for all of the info...I passed the dextron III on to my auto mechanic and he stated that the repair manual called for 10W oil for the unit. I tend to agree with you however and will have it drained out and replaced...any idea where I can get the Dextron III??? Thanks so much!!!