Power Drive

[1976GMC]

Hello Everyone,
I'm a new member here on the forum, looking for some information. I'm a relatively recent owner of a beautiful 26' 1976 GMC Glenbrook. It is still
pretty new to us and we are in the process of learning all its little quirks and peculiarities.

The coach has a 455 Olds and transmission with the PowerDrive unit. When I first learned about the PowerDrive, I thought it was a modification of some
planetary gears in the transmission to modify output ratio and thus reduce stress on the internal transmission components. However, reading more
about the TH425 transmission, I discovered that the PowerDrive is the modification to the chain drive part of the tranny (the power that goes TO the
planetary gears). As I see it, the PD makes the engine rotate more revolutions in order to make the same number of revolution on the shaft going to
the planetary gears. What is the exact benefit of this? Having PD and the 3.21 final drive ratio makes the engine run at much higher RMPs than I'm
comfortable with - 2,700 RPM at 60MPH. Seems pretty excessive for the giant engine like 455. All my other cars (granted they are all newer) run at
slightly above 1,500-1,700 RPM at the same speed.

When I try to visualize the power transfer in the transmission, it seems that the amount of torque transmitted through the internal components is
actually higher with the Power drive than without PD. This is because engine makes more revolutions per same distance of travel (per same number of
rotations in the transmission). To me that means that internal components (after the chain drive) will receive higher level of stress. Am I wrong
about this? Was PD developed for the 403 engines? To help them with transmitting more power to the ground? Is this setup really beneficial on the
coaches with 455? From reading info on various forums, nearly everyone recommends to have PD if you are towing a toad (which we do).

I would really appreciate your input and advice on this topic. Looking forward to learning form the combined wisdom of all. Please educate me

 

[bill wevers]

Sounds like you have a good set-up.
Most people prefer final drive ratios between 3.50 and 3.70.
The power drive is equivalent to having 3.50.
The 3.21 will bump it up to 3.66 equivalent.

With the 3.07 gears, the carburetor power enrichment circuit
kicks in a lot because of the low manifold vacuum.

--
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose

 

[Jim Hupy]

The TM 425 was originally designed to move a 4000 pound car. We are asking
it to move a 12,000 pound motor home. The same old formula, F x D = Torque
applies in both situations. The motor home is at a three to one
disadvantage weight wise to the cars. Thus, the power drive and different
gearing in the final drives. Manny T sells the power drive and builds
transmissions too. Good guy, knows his stuff. Good friend to the whole GMC
community. The power drive is hell for strong, like the rest of the TM-425.
I wouldn't worry about it.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Sounds like you have a good set-up.
> Most people prefer final drive ratios between 3.50 and 3.70.
> The power drive is equivalent to having 3.50.
> The 3.21 will bump it up to 3.66 equivalent.
>
> With the 3.07 gears, the carburetor power enrichment circuit
> kicks in a lot because of the low manifold vacuum.
>
>
>
> --
> Bill Wevers GMC49ers, GMC Western States
> 1975 Glenbrook - Manny Powerdrive, OneTon
> 455 F Block, G heads
> San Jose
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[jim kanomata1]

> The TM 425 was originally designed to move a 4000 pound car. We are asking
> it to move a 12,000 pound motor home. The same old formula, F x D = Torque
> applies in both situations. The motor home is at a three to one
> disadvantage weight wise to the cars. Thus, the power drive and different
> gearing in the final drives. Manny T sells the power drive and builds
> transmissions too. Good guy, knows his stuff. Good friend to the whole GMC
> community. The power drive is hell for strong, like the rest of the TM-425.
> I wouldn't worry about it.
> Jim Hupy
> Salem, Or
> 78 GMC ROYALE 403
>

>
> > Sounds like you have a good set-up.
> > Most people prefer final drive ratios between 3.50 and 3.70.
> > The power drive is equivalent to having 3.50.
> > The 3.21 will bump it up to 3.66 equivalent.
> >
> > With the 3.07 gears, the carburetor power enrichment circuit
> > kicks in a lot because of the low manifold vacuum.
> >
> >
> >
> > --
> > Bill Wevers GMC49ers, GMC Western States
> > 1975 Glenbrook - Manny Powerdrive, OneTon
> > 455 F Block, G heads
> > San Jose
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >why don't you go back to 3.07 then tell me your experience.

some have done that but too proud to admit the mistake.
All the RV units that use chassis from suppliers run 4.11 /4.55 using the
same wheel and tire.GM , Ford and Chrysler know more than us

>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
http://list.gmcnet.org/mailman/listinfo/
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org B

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502

 

[1976GMC]

> Sounds like you have a good set-up.
> Most people prefer final drive ratios between 3.50 and 3.70.
> The power drive is equivalent to having 3.50.
> The 3.21 will bump it up to 3.66 equivalent.
>
> With the 3.07 gears, the carburetor power enrichment circuit
> kicks in a lot because of the low manifold vacuum.

I must admit that carburetors are a mystery to me... I feel much easier with computers and fuel injection (conversion project is going to happen some
day). Would it be beneficial to change a final drive ratio to bring it closer to a 3.55 combined number?

 

[1976GMC]

[quote

some have done that but too proud to admit the mistake.
All the RV units that use chassis from suppliers run 4.11 /4.55 using the
same wheel and tire.GM , Ford and Chrysler know more than us

[/quote]

Are you referring to making a mistake of lowering final drive ratio on the GMC?
As far as box RVs - yes, they run a much higher final drive ratios, but that it because output shaft on transmission comes out at a very different
speed from what we have going on in our GMCs

 

[john phillips]

some have done that but too proud to admit the mistake.
All the RV units that use chassis from suppliers run 4.11 /4.55 using the
same wheel and tire.GM, Ford, and Chrysler know more than us

[/quote]

Are you referring to making a mistake of lowering final drive ratio on the GMC?
As far as box RVs - yes, they run a much higher final drive ratios, but that it because output shaft on transmission comes out at a very different
speed from what we have going on in our GMCs[/quote]

Are you saying that both transmissions do not have a 1 to 1 ratio in high gear?
--
Johnd01
John Phillips
Avion A2600 TZE064V101164
Rancho Cordova, CA (Sacramento)

 

[Ken H.]

Vadim,

After having a GMC for 19 years, variously equipped with standard, Power
Drive, and higher ratio final drives; and having talked to and listened
here to literally hundreds of other GMCers, including every expert in the
community, I have an opinion. That opinion is that the Power Drive+3.21 is
as close to the ideal drive train as one can get for the GMC. Yes, the
Power Drive DOES increase the torque load on the TH-425, which can easily
withstand the increase; I'd have no qualms about using it with my Cad500.

Keep it as it is unless you just want to experiment with others -- but
don't let go of the pieces, 'cause you'll probably want to go back.

Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, Troy-Bilt APU, etc., etc., etc.
www.gmcwipersetc.com

On Sat, Dec 16, 2017 at 11:21 PM, Vadim Jitkov
wrote:

> Hello Everyone,
> I'm a new member here on the forum, looking for some information. I'm a
> relatively recent owner of a beautiful 26' 1976 GMC Glenbrook. It is still
> pretty new to us and we are in the process of learning all its little
> quirks and peculiarities.
>
> The coach has a 455 Olds and transmission with the PowerDrive unit. When I
> first learned about the PowerDrive, I thought it was a modification of some
> ​...
>
>

 

[Matt Colie]

NGG,

Welcome to the group, family, cult, asylum....

Education of new owners is something we make a serious issue of here. All of us here have been witness to enough mistakes to make for a massive
experience base.

You are largely correct about the powerdrive being a less than optimum solution, and if the TH425 were a weaker beast, it would be. It was a much
better solution than GM came up with 3 years too late. The stock 3.07 was chosen because it was all that GM had. It was actually for the towing
package for the Oldsmobile Toronado. It is not that bad if you have a light 23' and cruise at 70+. That was the plan in 1973 and that died fast with
the first Arab Oil Embargo (that really made only political complications) and the 55MPH national speed limit. The fact is that the only torque that
can be transmitted through the transmission is what it takes to accelerate and move the vehicle. So, the powerdrive cannot vastly effect that
transmitted torque.

How tough is a TH425? Lots of owners have put Cadillac 500s on them and have no more trouble than the rest of us. Then there is Jim Kanomata
(Applied GMC => put them in your speed dial) that has a twin turbo 540 and the only thing that he does not break all the time is the transmission.
So, don't sweat that one.

GMs recommended solution was the 3.41. That is just enough to keep the carburetor out of power enrichment is most cases. But for my money (I am only
a couple of kinds of engineer and worked in as with automotive for decades) the 3.55 is a better choice. I know you are looking at 2700 at 60, but do
not try to relate this to a modern much lighter vehicle. That is just wrong in so many ways. Our coach with a 3.07 is running a 19~2100 at ~60MPH,
and the intake depression (vacuum) is disturbingly low and this is with a 9600# coach.

So, for the near term, leave it alone. Learn to drive and maintain her and enjoy what she brings you. If you are going to make the change to EFI,
you are in the right place. There are many here with very successful installations. This forum can be searched and so can both GMCMI and GMCWS for
more information. When you have learned enough to frame a question, come back here for the right answer. We have people writing here with literally
millions of miles and many decades of experience. Me? Yeah, I'm a ship's engineer by training and other things, but I have only had a GMC for 12
years and 70K, that makes me young in this group. Yes, I write long answers, but they are simply because most serious questions cannot be covered
with a simple answer. I don't mind as I am trying real hard to pass along what many very patient people have taken the time to teach me.

There are other GMC Motorhome places on the web. There are multiple on FaceBook, but technical answers there should be checked as I have seen several
occasions of wrong and dangerous answers. That does not mean stay away. It a great social forum. There is also a group at RVillage.com. I know, I
started it and so far it has little value.

Before too long, do us all a favor. You are running the forum, so, go to and scroll down to the place that you can
fill in a sigfile. Please put in a real name (so when other GMCers meet you, they will know who you are), Short about the coach (you did say 76
Glenbrook in the first, but some E-mail readers only see one post at a time) and a geographic reference (the header the e-mail readers never see does
say Washington) but try to be a little specific and I will tell you why later. This will be a help to both you and us, and again there is a reason.
Remember to scroll down to when you are done.

You bought a coach and found your way here, that is good, but what you may not realize is that the coach is more than just a new big toy because it
connects you to this community. You are now part of a community like very few others. It is filled with helping and supportive people that really do
want you to enjoy both the coach and what she can bring to you. To this end, they can do just amazing things. If you hang around here, you will get
to read some incredible but very real stories. The only other community like this that I know of is that of the watermen that are my world. For that
reason, I have taken to welcoming new owners here much as any new owner or vessel would be welcomed there. So,

May the Good Lord bless this coach and all those that set forth within her.

Welcome Vadim

Matt

--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit

 

[Bob Dunahugh]

Vadim. You covered the subject well. The T425 with a 3:07 FD, 14 inch tires=
, and a 4,000 lbs car was a good combination. GM had the peak HP for the 4=
27, and 455 reached in the 3,600 to 4,200 RPM range. So higher RPM's in the=
4200 range, and above isn't an issue. We have 16 inch tires, and 12,000 lb=
s as you covered. And a different cam profile. That's another can of worms.=
Till about 2003 we only had the 3:07, and 3:21. I think there was a 3:42 f=
rom Cinnabar? So the Power Drive was a way to get the RPM's up to get out =
of luging our engines years ago. But as you mentioned. The PD is adding mor=
e load on the T425. Then Jim K at Applied GMC came out with some great FD r=
atio choices up to a 4:10 ratio. These ratios ended the luging. And allow t=
he engine/trans to work more efficiently. Some say the PD,or a lower FD ra=
tio are the same. No. Not at all. Is the PD bad? No. It's better then nothi=
ng. In your situation. I'd leave things as they are till you have trans is=
sues. Then change the FD ratio. I'm thinking of going to 4:10 from my 3:70.=
Towing, or not. I'd recommend 3:70. When I'm pulling my enclosed trailer w=
ith a car in it. A 78 Royale 403, and the 3:70 FD. My GVW is about 21,000lb=
s. As a side note. My mileage went up with the 3:70. As to newer engines a=
t 1500 RPM's at 65 MPH. Their design is another kind of animal. Bob Dunah=
ugh Member GMCMI.

 

[Glenn Giere]

I've had one in mine for years. Works great. Can't find any disadvantage. No need to mess with spedo error as its ratio to rear end is unchanged.
--
Glenn Giere, Portland OR, K7GAG
'73 "Moby the Motorhome" 26'

 

[powwerjon]

I think that I have had almost every different drive ratio setups in the GM=
C=E2=80=99s that we have owned in the last 18 years. Our first was a 77 EL=
II with a 403 and a stock 3.07 ratio final drive. It was cruising at 2280=
RRPM as 64 MPH. It was lacking in performance at anything under 75 MPH. =
Above that it got up on the cam and pulled and ran well. The first change=
we did was go with a 3.55 final drive. Running at 64 MPH the RPM moved up=
to 2880 RPM and would run well and really pull when doing a pass. Our cur=
rent GMC is a 30=E2=80=9D Buskirk Stretch with a 461 Jasper Olds with MPFI,=
3.21 final and a 3.50 chain drive giving a effective 3.66 final ratio. Un=
derstand that the coach weighs14,800# pulling a loaded as a trailer Honda C=
RV at 3800# with a total of 18600# when we travel to and from Tucson. We r=
un 65 MPH and pull most grades without problems. The one grade that is mor=
e difficult is the grade up the mountain from White Sands to Los Cruses a v=
ery long climb. Have done both ways and they both work well. J.R. Wri=
ght GMC GreatLakerTech Editor 78 Buskirk 30' Stretch 75 Avion Under R=
econstruction Michigan (On Location in Tucson) > On Dec 17, 2017, a=
t 12:19 PM, Glenn Giere wrote: > > I've had one=
in mine for years. Works great. Can't find any disadvantage. No need to me=
ss with spedo error as its ratio to rear end is unchanged. > -- > Glen=
n Giere, Portland OR, K7GAG > '73 "Moby the Motorhome" 26' > > _____=
__________________________________________ > GMCnet mailing list > Unsu=
bscribe or Change List Options: > http://list.gmcnet.org/mailman/listinfo=
/gmclist_list.gmcnet.org

 

[1976GMC]

Thank you everyone for the warm welcome and for your replies. This is exactly the information I was looking for. I'm just trying to better understand
the purpose of some of the modifications that are on this unit. That way i will know better what its doing and why when we are on the road...
The answer I hear from the members - leave it as is, slow down to 55 (maybe 60) MPH, chill out and enjoy the scenery I plan on doing exactly
that.

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA

 

[Jim Hupy]

You won't hurt that 455 if you keep the rpm's under 4200 or so.
Jim Hupy
Salem, Or
78 GMC Royale 403

> Thank you everyone for the warm welcome and for your replies. This is
> exactly the information I was looking for. I'm just trying to better
> understand
> the purpose of some of the modifications that are on this unit. That way i
> will know better what its doing and why when we are on the road...
> The answer I hear from the members - leave it as is, slow down to 55
> (maybe 60) MPH, chill out and enjoy the scenery I plan on doing exactly
> that.
>
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Ken H.]

Or, if you HAVE to get on a freeway, and it makes you more comfortable,
stay with the traffic. The GMC should still be comfortable at 75-80. :-}

​Just what I do -- but, then, there are some who advise against caravaning
with me. :-{​

Ken H.

On Sun, Dec 17, 2017 at 9:44 PM, Vadim Jitkov
wrote:

> Thank you everyone for the warm welcome and for your replies. This is
> exactly the information I was looking for. I'm just trying to better
> understand
> the purpose of some of the modifications that are on this unit. That way i
> will know better what its doing and why when we are on the road...
> The answer I hear from the members - leave it as is, slow down to 55
> (maybe 60) MPH, chill out and enjoy the scenery I plan on doing exactly
> that.
>
> --
> Vadim Jitkov
> '76 Glenbrook 26'
> Pullman, WA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[Rdenney]

Only the Redhead, when punching a hole through Atlanta traffic at 70 mph on
a congested freeway, but I actually think it was Manny the Maniac that was
driving your coach.

Rick "who needed that big margarita after that one" Denney

On Sun, Dec 17, 2017 at 9:57 PM Ken Henderson
wrote:

> Or, if you HAVE to get on a freeway, and it makes you more comfortable,
> stay with the traffic. The GMC should still be comfortable at 75-80. :-}
>
> ​Just what I do -- but, then, there are some who advise against caravaning
> with me. :-{​
>
> Ken H.

--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com

 

[kingsley coach]

Ken

I've followed Kerry Tandy through El Paso in the outside lane at 4:30 doing
75 + ...Clearly a student of your driving school !

Mike in Las Cruces

https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon
Virus-free.
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> Only the Redhead, when punching a hole through Atlanta traffic at 70 mph on
> a congested freeway, but I actually think it was Manny the Maniac that was
> driving your coach.
>
> Rick "who needed that big margarita after that one" Denney
>
> On Sun, Dec 17, 2017 at 9:57 PM Ken Henderson

>
> > Or, if you HAVE to get on a freeway, and it makes you more comfortable,
> > stay with the traffic. The GMC should still be comfortable at 75-80.
> :-}
> >
> > ​Just what I do -- but, then, there are some who advise against
> caravaning
> > with me. :-{​
> >
> > Ken H.
>
> --
> Rick Denney
> 73 x-Glacier 230 "Jaws"
> Off-list email to rick at rickdenney dot com
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Michael Beaton
1977 Kingsley 26-11
1977 Eleganza II 26-3
Antigonish, NS

Life is too short to hold a grudge; slash some tires and call it even !

 

[kingsley coach]

Vadim

When you get a chance, could you connect with John Shotwell and record your
TZE number so we know where these machines are living
And there is also the Black List for you to get on...help for the GMC owner
when on the road. If you need more info on finding these, let us know.
Thanks for the sig addition to your posting....

Mike in NM

On Mon, Dec 18, 2017 at 1:14 AM, Kingsley Coach
wrote:

> Ken
>
> I've followed Kerry Tandy through El Paso in the outside lane at 4:30
> doing 75 + ...Clearly a student of your driving school !
>
> Mike in Las Cruces
>
>
> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon Virus-free.
> www.avast.com
> https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link
>
>
> On Mon, Dec 18, 2017 at 12:24 AM, Richard Denney

>
>> Only the Redhead, when punching a hole through Atlanta traffic at 70 mph
>> on
>> a congested freeway, but I actually think it was Manny the Maniac that was
>> driving your coach.
>>
>> Rick "who needed that big margarita after that one" Denney
>>
>> On Sun, Dec 17, 2017 at 9:57 PM Ken Henderson

>>
>> > Or, if you HAVE to get on a freeway, and it makes you more comfortable,
>> > stay with the traffic. The GMC should still be comfortable at 75-80.
>> :-}
>> >
>> > ​Just what I do -- but, then, there are some who advise against
>> caravaning
>> > with me. :-{​
>> >
>> > Ken H.
>>
>> --
>> Rick Denney
>> 73 x-Glacier 230 "Jaws"
>> Off-list email to rick at rickdenney dot com
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
>
> --
> Michael Beaton
> 1977 Kingsley 26-11
> 1977 Eleganza II 26-3
> Antigonish, NS
>
> Life is too short to hold a grudge; slash some tires and call it even !
>
>
>

--
Michael Beaton
1977 Kingsley 26-11
1977 Eleganza II 26-3
Antigonish, NS

Life is too short to hold a grudge; slash some tires and call it even !

 

[Jim Hupy]

Jim K. has that 540 cubic inch dual turbocharged, intercooled, for a
purpose, and he only drives 55 on his way to 80. I have followed him a
couple of times to and from rallies. You need to be on your "A" game to
keep him in view. The 403 is really happy above 3000 rpms. Don't ask me how
I know.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> Ken
>
> I've followed Kerry Tandy through El Paso in the outside lane at 4:30 doing
> 75 + ...Clearly a student of your driving school !
>
> Mike in Las Cruces
>
> source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=icon>
> Virus-free.
> www.avast.com
> source=link&utm_campaign=sig-email&utm_content=webmail&utm_term=link>
>
>
> On Mon, Dec 18, 2017 at 12:24 AM, Richard Denney

>
> > Only the Redhead, when punching a hole through Atlanta traffic at 70 mph
> on
> > a congested freeway, but I actually think it was Manny the Maniac that
> was
> > driving your coach.
> >
> > Rick "who needed that big margarita after that one" Denney
> >
> > On Sun, Dec 17, 2017 at 9:57 PM Ken Henderson

> >
> > > Or, if you HAVE to get on a freeway, and it makes you more comfortable,
> > > stay with the traffic. The GMC should still be comfortable at 75-80.
> > :-}
> > >
> > > ​Just what I do -- but, then, there are some who advise against
> > caravaning
> > > with me. :-{​
> > >
> > > Ken H.
> >
> > --
> > Rick Denney
> > 73 x-Glacier 230 "Jaws"
> > Off-list email to rick at rickdenney dot com
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
> >
>
>
>
> --
> Michael Beaton
> 1977 Kingsley 26-11
> 1977 Eleganza II 26-3
> Antigonish, NS
>
> Life is too short to hold a grudge; slash some tires and call it even !
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[robert mueller]

Vadim,

Double Trouble has a 3.21 to 1 planetary gear final drive. They were OEM equipment in the 1966 & 67 Olds Toronado; GMC "folklore"
notes that they are "bulletproof."

Based on what I've read on the GMC net and my personal experience it's not high speed that will alter the life of a TH425
negatively; it is constantly putting a heavy load on them when you accelerate from a stop.

I do my best to accelerate slowly from a stop up to the speed limit.

I drive whatever the speed limit is; be it 55, 60, 65, 70, or 75.

As noted the Toronado weighed around 4000 lb and the GMC weighs THREE times that much. Once you have the mass in motion the stress
on the transmission drops. Of course it takes more power to move the GMC down the road because of the weight AND the drag.

IIRC I've noted that the RPM's of the 455 with the 3.21 to 1 final drive runs around 2400 at 65 and it loves it! It will cruise at
that rpm range all day long without a hiccup.

Regards,
Rob M.
The Pedantic Mechanic
Sydney, Australia
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
USA '77 Kingsley - TZE 267V100808


-----Original Message-----
From: Gmclist [mailto:gmclist-bounces] On Behalf Of Vadim Jitkov
Sent: Monday, December 18, 2017 1:44 PM
To: gmclist
Subject: Re: [GMCnet] Power Drive

Thank you everyone for the warm welcome and for your replies. This is exactly the information I was looking for. I'm just trying to
better understand the purpose of some of the modifications that are on this unit. That way i will know better what its doing and why
when we are on the road...
The answer I hear from the members - leave it as is, slow down to 55 (maybe 60) MPH, chill out and enjoy the scenery I plan on
doing exactly that.

--
Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA

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