Transmission Fluid Unknown Age

M

Melbo

Member
Aug 19, 2018
155
10
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75
The GMC was started for the first time today since I bought it. It has new timing chain and gears new water pump new fan clutch new fan new fan
shroud all new fuel lines new fuel filters electric fuel pump and the starter alternator and radiator have been gone through. New belts and hoses. I
changed the oil and pulled the dizzy and ran the pump. New antifreeze. New power steering pump and new belts. I have some more new parts to install
but I was at a point where I could see if it was going to run and it fired right up and runs nice and smooth. I am wondering if moving it (this is my
first opportunity to do so it was towed in and parked) with the old transmission fluid is a good idea or if I should change it as well before putting
it in gear. Any opinions would be greatly appreciated.

Thanks

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
Change the transmission fluid and the final drive oil and the power steering fluid. You should also consider flushing the brake fluid. Some might also advise replacing the headlight oil :).

Emery

>
> appreciated.
 
I was checking the maintenance manuals. I'm guessing 90 wt for the final drive and Dexron for the trans. Any advice on this (I know I'm opening a
can of worms but a sense of direction is helpful) would be greatly appreciated.

TIA

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
Melbo,
I've published this several times but not int he last several years, so...her goes again for the newbie'e and others that have not seen it.

You can take it to a "Jiffy Lube" type place to have them change the fluid, and to my way of thinking that is the only way to
*completely* change all of the fluid, as long as you have the filter changed also. The only catch is, the last couple of times I
stopped at a "Jiffy Lube" type place, they were *not* offering synthetic fluids as a change option. So you may have to make a sort
of deal with the owner/manager to use synthetic fluid. That being said, you can get most of the oil out using the following
procedure. Keep in mind, there are several...perhaps many... that would not do this (including IIRC Manny). I've done it many
times with no ill results. Sooooooo.....

This is a very messy procedure...you're gonna spill fluid, so be prepared with Oil dry, rags and the like to clean-up afterwards.

1. Do this with the trans cold. Wait at least over night.

2. Raise the coach high enough to get a 5 gal pail under it with room to spare.

3. Disconnect both trans lines at the radiator, and be prepared to catch the fluid coming out of the cooler in the radiator.

4. Attach hose extensions to the lines and drop the lines into the 5 gal pail.

5. Using two people, start the motor for only couple of seconds. Do this to identify which line the fluid will come out of. Now
you know which line you *must* keep in the bucket.

6. Again, using two people, (one to run the motor, the other to watch the fluid) start the motor.

7. Run the motor until the fluid line begins spurting air. Shut motor off immediately!! The fluid will get quite frothy.

8. Allow to stand without the motor running for 4-5 minutes. This will let excess fluid in the trans drain down into the pan.

9. Start the motor again for no more than 5 seconds. Shut off the motor, This will pump out that last little bit in the pan and
make dropping the pan a lot less messy.

10. Let the oil lines drip into the pail while you drop the trans pan.

11. Drop the trans pan, and replace the filter using two (2) "O" rings at the filter.

12. Hook up the two trans lines to the oil cooler at the radiator.

13. Fill the trans with about 7 qts of trans fluid.

14. Start the motor and allow it to idle for about 30 seconds or so before checking fluid level.

15. Check fluid level and add accordingly.

16. Once full, drive until normal operating temp is reached, and recheck fluid level. Add fluid to bring to "Full".

I've used this procedure on every auto trans that I've owned for....well....forever. This is just the way I do it....your mileage
may vary.

Just my relatively informed, off the cuff, back yard mechanic, gut level, eyeball it up and guesstimate, way of doing
things....that's all...

--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Larry

Thank you for the "plan" however you did not give any advice on which fluids to use. My coach is up in the air and I have oil pans to catch
everything I will plan on Dexron and 90 wt.

Thanks

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
> Larry
>
> Thank you for the "plan" however you did not give any advice on which fluids to use. My coach is up in the air and I have oil pans to catch
> everything I will plan on Dexron and 90 wt.
>
> Thanks
>
> Melbo

Other than cost, I can see no reason to use anything but synthetics. Personally would not mix synthetic brands. They all claim mixability. But I have
personally experienced a trans failure. When the trans was taken apart all of the seals had swelled to the point that many were hard to remove. The
person doing the rebuild said the only time he had seen this when someone mixed some of the transmission "fixes in a bottle". Problem is, I never use
any of those chemicals. I did however use Amsoil synthetic fluid and at 20K miles drained 4 qts and added 4 qts of Mobil One. So I am suspicious of
mixing those two. Start with a brand, stay with it. JWIT
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Thanks to Emery for the headlamp oil replacement reminder. It is amazing how many people forget/by pass this scheduled maintenance procedure. Another
often overlooked recommended update is the addition of a inert gas additive to Co2 whistle Running any tire different than a 16.5. Methane gas from a
grain only farm animal is most desirable, but honestly, any captured gas from animals ingesting any alfalfa products should work in a emergency
situation. as long as it was humanly recovered. Could be the difference between life or breath....
Stand by for next weeks update...."how to use your toe nail clippings to modify your tires for winter use"...
Scott.

--
Scott Nutter
1978 Royale Center Kitchen, Patterson 455, switch pitch tranny, 3.21 final drive, Quad bags, tankless water heater, everything Lenzi. Alex Ferrera
installed MSD Atomic EFI
Houston, Texas
 
My transmission advice is DO NOT FLUSH. Change what you can get out by suction device through dipstick tube or the messy way dropping pan. I got out
about 6.5 quarts after sitting a long time and torque converter drained back to the centerline. Drive it and do it again in a month or some miles
later. After several changes it will appear clean. Many old varnished transmissions fail shortly after a full transfusion as the fresh fluid
additives suddenly do too much cleaning. There are many "failed shortly after flush" stories on line. I have never had a failure using the gentle
method. GM does not mention the flush method in service manual ( did not exist back then). The current most correct fluid to buy is the Dec/merc. Not
ATF! I buy the Valvoline Dex/merc in gallons. As far as filter goes, if unsure of the Chinese filter, better to stay with used correct sized old
one(.075 tube) than ruin trans with defective new filter. Or buy new one from a vendor that has screened them as good. Check level engine running,
warm in Park.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
I have to agree with John about doing a full system flush. Draining what is in the pan and replacing with new partially dilutes the new oil. This reduces the concentration of fresh additives and detergents that can upset and dislodge crud and varnish build-up. Such crud is often found in high mileage and/or neglected transmissions.

I just finished up the overhaul of 2 Identical VW automatic transmissions. Both had similar mileage, and similar use. I noted how one was spotless inside while the other had substantial sludge build-up in the clutch apply piston areas. These areas Have a tendancy to collect crud due to their design and function. Doing a full flush could cause that sludge and crud to come loose and circulate, possibly causing damaged piston seals and/or sticking valve body function that often leads to clutches that slip and burn.

I wonder if Trans shops that recommend a flush do so intentionally knowing that they might be doing more harm than good.

Les Burt
Montreal
'75 Eleganza 26'

>
 
I think it is a generally good idea to get a baseline on any new to you vehicle by changing all the fluids as soon as it is convenient to do so. The
transmission fluid/filter is only a little bit more complicated than doing an oil change, same with the final drive.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
Also-- I'd never let anyone hook up a shop trans flusher machine to any vehicle I own. Who has been on the machine before you and was it
properly"sanitized" of sludge and particulate matter that can ruin a valve body are the unknowns.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
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