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Fluid Drive Stumble Help


51_Meadowbrook

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I just don't get it. I've brought this topic up a couple times and haven't found something that works to fix this. In my '51 Dodge Meadowbrook, 3-speed Fluid Drive, if the car is left in gear and stopped the RPMs drop down too low and when I take off it stumbles. The only time that it doesn't drop too low is if I raise the idle stop screw way up, to where the RPMs are around 1000 when idling. I thought it was the fluids so I had changed them, TDH ISO 32 in both. I changed the carburetor from the Stromberg BXV-3 that was on it to the stock Strombrg BXVD-3. It still drops too much. I am inclined to keep working on the dashpot to see if that helps but the RPMs drop way down even when its in Neutral and then you put it in gear and remove the brake. What am I missing that I can try to work on? The car idles and drives beautifully, with the exception of the stumble/stall that it does when in gear without the clutch at take-off.

Edited by 51_Meadowbrook
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If you put the parking brake on, put the car in gear, and let the clutch out, will the car stay stationary?  Or if you have it in gear with the brake on and idling can you have an assistant adjust the idle to about 500 rpm? Then what happens to the idle speed with the car out of gear with the brake on?

Are you getting a good squirt from your accelerator pump, and if so is your step up jet functioning?  Is the account pump stroke adjustable like the carter carb?

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I did exactly what they said in one of the other threads on this site. They said ISO 32 in both. At least that’s what I interpreted them to be saying. What am I supposed to put in that transmission if not ISO 32?

Edited by 51_Meadowbrook
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If the parking brake is on and the car is in gear the parking brake holds it in place. If I adjust the idle speed to 500rpm, with the car in gear and parking brake on, it sends the car over 1000rpm when I push the clutch in. The accelerator pump, as far as I know, is adjustable in 3 settings, Winter Normal and Summer. Winter provides and longer stroke, conversely Summer gives a shorter stroke. The accelerator pump provides a nice stream. The car did the same thing with the first carburetor as it does with this stock carburetor so I’m thinking that isn’t the issue. The carburetor is rebuilt. 

Edited by 51_Meadowbrook
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 For the manual three speed GL 1 gear lube.  NAPA has it in a gallon for about $15.00.   If you have the semi automatic,l will let some one else respond to what is appropriate to them.

 

Maybe try the shorter stroke on the account. pump. The stumble may be from being too rich. What do your spark plugs look like?

Edited by greg g
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The plugs have normal darkness. They are not wet or corroded. I’m assuming the semi automatic is the Gyro-Matic transmission. I do not have that so I would need the GL 1 fluid. What is the viscosity of that fluid? I’m trying to see how much thicker the fluid I put in is from what you recommend. 

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I got 90 weight for my recently installed 1956 three speed with OD.  I think valvoline makes an 80w 100 version but l couldn't locate it locally.  The gear oil will be more viscouse than the hydraulic fluid. Since l don't drive in winter the multi via isn't critical.

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My 47 semi-automatic (TIp-Toe) transmission has a tag that says to use 10 wt oil. 

The gearbox has a hydraulic pump and piston to make the upshifts. 

Someone has said that the ISO 32, which is appropriate for the fluid coupling, is OK for the gearbox (but not for a 3-speed manual.)  

How to tell what you have: 

3-speed manual:  Typical "H" shifting pattern.  No wires running to the transmission (Except to an overdrive unit, if present).

4-speed semi-automatic:  "1st gear" position missing from the "H" pattern.  Wires going to the gearbox.  

 

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The transmission fluid of any weight will not cause idle or stumble issues. 

The Preso-Matic, Gyromatic, Tip-Toe Shift, Vaca-Matic, Hydraulically Operated, and more semi auto transmissions use 10W

Std 3 speeds use GL1 75/90 or close

 

The Fluid Couplings use Fluid Drive fluid (NA) or ISO32 as already mentioned. As long as you didn't fill the coupling with 90W it's not the issue?

So as your car already has fluids that are OK your engine has an issue itself..this because of the poor struggling weak idle in gear..

Maybe check....

1) Valve timing slow...worn timing chain

2) Distributor advance issues..stuck fly weights, springs etc.

3) Compression some what low... needs to be easily 90 lbs or higher IMO with the FD coupling

4) Vacuum gauge test 17-21 HG

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I was reading another thread about transmission fluids. I don't know about them very much, but this was for a Ford and it said to be careful of GL-4 and GL-5 because it is not good for "yellow metals." Do I have to worry about this in these transmissions?

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  • 2 weeks later...

Well, I started using the GL-1 in the transmission. It’s a SAE 90 that I got from tractor supply and it works great. The car doesn’t idle as low when in gear, and when it does it still doesn’t stumble. I can’t believe that for 4 years I have dealt with this and everyone kept telling me it’s fine the way it is and in reality a fluid change corrected the problem. 

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So you are saying that changing the 3 speed  transmission fluid to GL1 90W fixed both your take off stumble and smoothed out your idle  too? 

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My idle was already smooth. I chose the wrong term when I said idle. I was referring to when it is in gear and stopped. But it does seem to have fixed the take off stumble. I knew it wasn’t an accelerator pump issue because both the original carburetor and the replacement stock carburetor I put on recently both had been rebuilt and were working properly. 

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You most certainly were blessed by Jim and Tammy Faye Baker!

  • Haha 1
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No other changes?  Weather, gas, anything?  It just difficult for me to understand how an oil change in the transmission, which isn't even turning idle/standstill could affect the engine.  Not sayin' it's impossible, but impossible for me to understand at the moment.

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Well, its not just oil. Its the transmission fluid. I'm not a scientist and can't say I have this right, but viscosity affects the friction between the gears. As the old fluid lost viscosity as it heated the friction got worse causing the engine to fight the transmission to turn it. The stumble was only at initial acceleration so its kind of like running into a car to push it, the initial contact causes you to temporarily stumble before the car starts moving. Even if that isn't the case with this transmission I like that explanation. And if that isn't what caused it to start working right after 4 years I don't know what it is. The only thing I did was change the fluid from the ISO 32 to the GL-1 and then took it for a drive. The only time it has stumbled was today after I got the distributor wet and then went driving and we had flash floods. Tonight I took it back out and it worked great again.

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