Transmission Fluid

Carl Stouffer

Carl Stouffer

Well-known member
Jan 15, 2009
4,668
351
83
Tucson, Arizona 85718
I have been using Mobil-1 Full Synthetic transmission fluid in my coach from almost the first time I changed it. I know Manny recommends this fluid
in switch pitch transmissions due to the extra heat they generate. My thinking has been that the additional protection couldn't hurt in a regular
transmission, especially due to the fact that I tow a 3000# Tracker and travel on mountainous roads often.

Since I change the transmission fluid every 15,000 miles or so, I'm wondering if I really need to use the full synthetic, or if I would be safe to use
the much less expensive Mobil-1 semi synthetic. Recognizing that oil is much less expensive than transmissions and engines, I have always tried to
use premium fluids, but I don't want to spend money unnecessarily.

Any opinions or advice?

--
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
 
Carl,

The first question is: Do you have a transmission temperature gauge?
That's one of the first gauges I added to the GMC. There's an appendix to
the P30 Chassis owners' manual, available at
http://www.bdub.net/manuals/index.html, which correlates average
transmission temperature with fluid life. Check that out for an idea of
what to expect. There's lots of other good information throughout that
manual, much of it equally applicable to the GMC as well as the Chevy P30.

Ken H.

> I have been using Mobil-1 Full Synthetic transmission fluid in my coach
> from almost the first time I changed it. I know Manny recommends this fluid
> in switch pitch transmissions due to the extra heat they generate. My
> thinking has been that the additional protection couldn't hurt in a regular
> transmission, especially due to the fact that I tow a 3000# Tracker and
> travel on mountainous roads often.
>
> Since I change the transmission fluid every 15,000 miles or so, I'm
> wondering if I really need to use the full synthetic, or if I would be safe
> to use
> the much less expensive Mobil-1 semi synthetic. Recognizing that oil is
> much less expensive than transmissions and engines, I have always tried to
> use premium fluids, but I don't want to spend money unnecessarily.
>
> Any opinions or advice?
>
>
> --
> 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
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
Carl
You can save money if you don’t change it so frequently. Mobil 1 fully synthetic will last a lot longer than 15,000 miles.
Ask Manny for advice.

Emery Stora

>
> Carl,
>
> The first question is: Do you have a transmission temperature gauge?
> That's one of the first gauges I added to the GMC. There's an appendix to
> the P30 Chassis owners' manual, available at
> http://www.bdub.net/manuals/index.html, which correlates average
> transmission temperature with fluid life. Check that out for an idea of
> what to expect. There's lots of other good information throughout that
> manual, much of it equally applicable to the GMC as well as the Chevy P30.
>
> Ken H.
>

>>
>> I have been using Mobil-1 Full Synthetic transmission fluid in my coach
>> from almost the first time I changed it. I know Manny recommends this fluid
>> in switch pitch transmissions due to the extra heat they generate. My
>> thinking has been that the additional protection couldn't hurt in a regular
>> transmission, especially due to the fact that I tow a 3000# Tracker and
>> travel on mountainous roads often.
>>
>> Since I change the transmission fluid every 15,000 miles or so, I'm
>> wondering if I really need to use the full synthetic, or if I would be safe
>> to use
>> the much less expensive Mobil-1 semi synthetic. Recognizing that oil is
>> much less expensive than transmissions and engines, I have always tried to
>> use premium fluids, but I don't want to spend money unnecessarily.
>>
>> Any opinions or advice?
>>
>>
>> --
>> 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
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
 
Thanks Ken,

I do NOT have a trans temp gauge. That's probably one of the things I really need to add. I HAVE spot checked my aux transmission cooler with an IR
gun, and even under the most extreme conditions (towing the Tracker up a Wyoming mountain at an 8% grade for MILES) it has always been cooler than the
radiator temp.

Emery, I guess I could go longer between transmission services (I think Manny recommends 25,000 miles), but I just feel better keeping the fluid as
clean and fresh as possible. I guess an attitude adjustment might be in order. ;)
--
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
 
Somebody have a schematic on where and what to put where?

Randy Hecht
Roswell, GA

1974 Canyon Lands GMC Motor-coach

>
> Thanks Ken,
>
> I do NOT have a trans temp gauge. That's probably one of the things I really need to add. I HAVE spot checked my aux transmission cooler with an IR
> gun, and even under the most extreme conditions (towing the Tracker up a Wyoming mountain at an 8% grade for MILES) it has always been cooler than the
> radiator temp.
>
> Emery, I guess I could go longer between transmission services (I think Manny recommends 25,000 miles), but I just feel better keeping the fluid as
> clean and fresh as possible. I guess an attitude adjustment might be in order. ;)
> --
> 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
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
 
My theory is to use Dex/Merc which is closest available today to the mid 70s time stamp Dexron II products. 400/425 was not built around synthetic
fluids. Today’s transmissions are. I could be wrong but I don’t want anything slipperier in there on the clutch packs than it was designed for. At
first sign of color change I suck out what I can through the dip tube with my Mityvac extractor, about 4+ quarts and replace with fresh Dec/Merc.
Repeat as necessary and didn’t even get dirt under the nails. I try to drive such that I don’t heat the fluid past the cook point, but that is not
always possible in the mountains. The average temp may be safe but fluid molecules in critical areas may exceed that, hence a gradual color change
seen after such service. Also removing fluid removes micro abrasives along with it. Leaving Mobil 1 in for long times does not.
For a great series on THM history and Dexron fluids there is a whole
series by this Weber State auto professor. Hours of info.
https://youtu.be/ygkRuwCpKxU
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
Service manual says Dex3 so thats what it gets until its no longer commercially available....i know fluids are generally backwards compatible but the
materials in these old transmissions are not forwards compatible so......jhmo
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
When Manny T rebuilds these transmissions, he uses all updated clutch packs
that are 100% compatible with Synthetic Transmission fluids. It is what he
recommends that we use in his remanufactured and updated units. I
personally use Valvoline Synthetic in manner rebuilt. You all can do as you
wish.
Just don't call me from the black list in dire straits because you
didn't use what he says and you have cooked one of his rebuilds. I have a
Ragusa Ribbed aluminum transmission pan on my coach, and that is where my
sending unit for the gage is installed. Most of the time, It runs cooler
than the engine coolant does. Works for me. That Synthetic fluid will last
a very long time at 240° or less.
Jim Hupy
Salem, Oregon

On Fri, Aug 6, 2021, 4:25 PM John R. Lebetski
wrote:

> Where /what brand Dexron III are you finding these days?
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
> Where /what brand Dexron III are you finding these days?

I get it from the local tractor supply by my house.

--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
I installed a tranny temp gauge a year late.

It is amazing how fast the. Tranny temp jumps when under load(stop and go and hills). I just installed a bigger cooler and so far 2 trips temps are
way cooler and I have not seen that quick jump from 150 to 200+. Like I seen with the smaller cooler.

One thing about the tranny temp gauge with the sender installed in the pan. The sender will double as a drain plug.

--
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
 
> When Manny T rebuilds these transmissions, he uses all updated clutch packs
> that are 100% compatible with Synthetic Transmission fluids. It is what he
> recommends that we use in his remanufactured and updated units. I
> personally use Valvoline Synthetic in manner rebuilt. You all can do as you
> wish.
> Just don't call me from the black list in dire straits because you
> didn't use what he says and you have cooked one of his rebuilds. I have a
> Ragusa Ribbed aluminum transmission pan on my coach, and that is where my
> sending unit for the gage is installed. Most of the time, It runs cooler
> than the engine coolant does. Works for me. That Synthetic fluid will last
> a very long time at 240° or less.
> Jim Hupy
> Salem, Oregon
>
> On Fri, Aug 6, 2021, 4:25 PM John R. Lebetski

>
> > Where /what brand Dexron III are you finding these days?
> > --
> > John Lebetski
> > Woodstock, IL
> > 77 Eleganza II
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:

Not to worry on my end as the trans in mine is OEM still....when it decides to give up the ghost and get 40 year newer internals then ill switch to
modern fluids.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
 
My PO installed a temp sender in the Ragusa pan. One of many upgrades.

Larry Davick

>

>> When Manny T rebuilds these transmissions, he uses all updated clutch packs
>> that are 100% compatible with Synthetic Transmission fluids. It is what he
>> recommends that we use in his remanufactured and updated units. I
>> personally use Valvoline Synthetic in manner rebuilt. You all can do as you
>> wish.
>> Just don't call me from the black list in dire straits because you
>> didn't use what he says and you have cooked one of his rebuilds. I have a
>> Ragusa Ribbed aluminum transmission pan on my coach, and that is where my
>> sending unit for the gage is installed. Most of the time, It runs cooler
>> than the engine coolant does. Works for me. That Synthetic fluid will last
>> a very long time at 240° or less.
>> Jim Hupy
>> Salem, Oregon
>>
>>> On Fri, Aug 6, 2021, 4:25 PM John R. Lebetski

>>>
>>> Where /what brand Dexron III are you finding these days?
>>> --
>>> John Lebetski
>>> Woodstock, IL
>>> 77 Eleganza II
>>> _______________________________________________
>>> GMCnet mailing list
>>> Unsubscribe or Change List Options:
>>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>
> Not to worry on my end as the trans in mine is OEM still....when it decides to give up the ghost and get 40 year newer internals then ill switch to
> modern fluids.
> --
> Rich Mondor,
>
> Brockville, ON
>
> 77 Hughes 2600
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
 
My transmission has 'blue racing clutches', Kolene steels, Kevlar bands, a Ragusa finned aluminum pan, etc. I'm sure it will handle updated
transmission fluid. I'm just questioning the need for the expensive full synthetic fluid.

Maybe my best course of action would be to just extend my service interval (I already did, from 12,000 miles to 15,000 miles).
--
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
 
Lots of references to Manny trans and front ends etc.
Simple question, who the hell is he?

Larry :p
--
Larry - Victoria BC -

1977 Palm Beach 40,000 miles, PO said everything working but forgot the word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
 
He is not from Hell, I assure you. His name is Manny Trovao. Name is
Portugal in origin. He, like his father before him worked in a General
Motors assembly plant in Central California.
Manny showed great promise and GM sent him to Michigan to M.I.T. to
get his engineering degree. This was after he had worked on a GM assembly
line for a number of years, so he knew the value in hard work. After
getting his degree, GM wanted him to remain in Detroit and work there.
But, Manny was a California boy, wore shorts all the time (still does)
and was not well suited for Michigan Winters. So, he and GM parted ways,
and he now is on his own. Still works long hours, at a feverish pace. He
and his wife Deo live in San Jose, California. They have a GMC coach with a
slide-out. And he rebuilds transmissions for GMC's, along with disc brakes
for the rear ends, and 1 ton conversions, etc. One very Busy guy. And I
might add, from personal experience with him, that he doesn't suffer
foolish people well. (Grin)
In my personal opinion, he is one of the "GMC HERO'S" that these
coaches seem to attract. Great guy.
Jim Hupy
Salem,Oregon

> Lots of references to Manny trans and front ends etc.
> Simple question, who the hell is he?
>
> Larry :p
> --
> Larry - Victoria BC -
>
> 1977 Palm Beach 40,000 miles, PO said everything working but forgot the
> word NOT. New Atwood fridge, water heater & furnace. New SS exhaust system,
> 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange hoses
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
And (along with Deo!) loves being on cruise ships! Haha.

He mentioned that they have another river cruise coming up soon - I wish *we* were as ready to travel as they are! Hopefully soon for us...

Rob
Victoria, BC
76 Royale - Rear Twins/Dry Bath

>
> He is not from Hell, I assure you. His name is Manny Trovao. Name is
> Portugal in origin. He, like his father before him worked in a General
> Motors assembly plant in Central California.
> Manny showed great promise and GM sent him to Michigan to M.I.T. to
> get his engineering degree. This was after he had worked on a GM assembly
> line for a number of years, so he knew the value in hard work. After
> getting his degree, GM wanted him to remain in Detroit and work there.
> But, Manny was a California boy, wore shorts all the time (still does)
> and was not well suited for Michigan Winters. So, he and GM parted ways,
> and he now is on his own. Still works long hours, at a feverish pace. He
> and his wife Deo live in San Jose, California. They have a GMC coach with a
> slide-out. And he rebuilds transmissions for GMC's, along with disc brakes
> for the rear ends, and 1 ton conversions, etc. One very Busy guy. And I
> might add, from personal experience with him, that he doesn't suffer
> foolish people well. (Grin)
> In my personal opinion, he is one of the "GMC HERO'S" that these
> coaches seem to attract. Great guy.
> Jim Hupy
> Salem,Oregon
 
Manny: Ditto Jim H.'s comments. Manny's been trying to wind down some of
his activities, spending more time travelling with his travel agent wife,
Deo. In years past he'd travel around the country, rebuilding
transmissions and leaving them in place as replacements for those in need.
Places I know he did that: Jim B's Coop in Orlando, Jeff Sirum's in
Okeechobee, and here (3 times, leaving 5 rebuilt transmissions each trip);
I think he's eliminated all that -- I know he hasn't been here for over 3
years.

A truly great GMCer/Person who I'm hoping will come again for a non-working
visit!

Ken H.

> He is not from Hell, I assure you. His name is Manny Trovao. Name is
> Portugal in origin. He, like his father before him worked in a General
> Motors assembly plant in Central California.
> Manny showed great promise and GM sent him to Michigan to M.I.T. to
> get his engineering degree. This was after he had worked on a GM assembly
> line for a number of years, so he knew the value in hard work. After
> getting his degree, GM wanted him to remain in Detroit and work there.
> But, Manny was a California boy, wore shorts all the time (still does)
> and was not well suited for Michigan Winters. So, he and GM parted ways,
> and he now is on his own. Still works long hours, at a feverish pace. He
> and his wife Deo live in San Jose, California. They have a GMC coach with a
> slide-out. And he rebuilds transmissions for GMC's, along with disc brakes
> for the rear ends, and 1 ton conversions, etc. One very Busy guy. And I
> might add, from personal experience with him, that he doesn't suffer
> foolish people well. (Grin)
> In my personal opinion, he is one of the "GMC HERO'S" that these
> coaches seem to attract. Great guy.
> Jim Hupy
> Salem,Oregon
>

>
> > Lots of references to Manny trans and front ends etc.
> > Simple question, who the hell is he?
> >
> > Larry :p
> > --
> > Larry - Victoria BC -
> >
> > 1977 Palm Beach 40,000 miles, PO said everything working but forgot the
> > word NOT. New Atwood fridge, water heater & furnace. New SS exhaust
> system,
> > 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange
> hoses
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
Fastest trans rnr guy period and all around great guy.

Sully
Bellevue wa

> Manny: Ditto Jim H.'s comments. Manny's been trying to wind down some of
> his activities, spending more time travelling with his travel agent wife,
> Deo. In years past he'd travel around the country, rebuilding
> transmissions and leaving them in place as replacements for those in need.
> Places I know he did that: Jim B's Coop in Orlando, Jeff Sirum's in
> Okeechobee, and here (3 times, leaving 5 rebuilt transmissions each trip);
> I think he's eliminated all that -- I know he hasn't been here for over 3
> years.
>
> A truly great GMCer/Person who I'm hoping will come again for a non-working
> visit!
>
> Ken H.
>

>
> > He is not from Hell, I assure you. His name is Manny Trovao. Name is
> > Portugal in origin. He, like his father before him worked in a General
> > Motors assembly plant in Central California.
> > Manny showed great promise and GM sent him to Michigan to M.I.T. to
> > get his engineering degree. This was after he had worked on a GM assembly
> > line for a number of years, so he knew the value in hard work. After
> > getting his degree, GM wanted him to remain in Detroit and work there.
> > But, Manny was a California boy, wore shorts all the time (still
> does)
> > and was not well suited for Michigan Winters. So, he and GM parted ways,
> > and he now is on his own. Still works long hours, at a feverish pace. He
> > and his wife Deo live in San Jose, California. They have a GMC coach
> with a
> > slide-out. And he rebuilds transmissions for GMC's, along with disc
> brakes
> > for the rear ends, and 1 ton conversions, etc. One very Busy guy. And I
> > might add, from personal experience with him, that he doesn't suffer
> > foolish people well. (Grin)
> > In my personal opinion, he is one of the "GMC HERO'S" that these
> > coaches seem to attract. Great guy.
> > Jim Hupy
> > Salem,Oregon
> >

> >
> > > Lots of references to Manny trans and front ends etc.
> > > Simple question, who the hell is he?
> > >
> > > Larry :p
> > > --
> > > Larry - Victoria BC -
> > >
> > > 1977 Palm Beach 40,000 miles, PO said everything working but forgot the
> > > word NOT. New Atwood fridge, water heater & furnace. New SS exhaust
> > system,
> > > 6000w Onan, Iota Converter, R134A A/C, New fuel lines & heat exchange
> > hoses
> > > _______________________________________________
> > > GMCnet mailing list
> > > Unsubscribe or Change List Options:
> > >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
 
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