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Re: [GMCnet] Power Drive [message #327271 is a reply to message #327269]

Mon, 18 December 2017 22:24

NextGenGMC

Messages: 146
Registered: December 2017
Location: Washington State

Karma: -1

Senior Member

I'm really glad I posted this question here. All your replies and personal experiences have significantly calmed my anxiety about running the engine at what I perceived were high RPMs. I've read some additional threads on the forum with people towing fairly heavy trailers with the same setup as I have and traveling at highway speed limits without any issue for the engine and transmission. I feel much better now. Thank you all Smile

Here is a follow up question (let me know if I need to start a new thread for this):
from the point of view of transmission, what is the best way to tackle hills on the road? In the area where I live, we have significant grades on nearly all our roads. We've got multiple grades of 3-4% in any direction we get going and some very steep grades of 6-7%. I've read that its best to slow down and downshift to "S" gear for tackling the grades. Should this be done on all climbs or just on those very hard 6-7% grades? What about driving in town (again lots of hills, but driving at 25-35 MPH)?

Carl S. wrote on Mon, 18 December 2017 17:38

Vadim,

I have a 3.70 final drive in my '75 26 footer and I normally drive between 62 and 65 MPH with no problems. Most 3/4 ton pickups of the same era had 4.10 rear end gears and most 1-Ton pickups were equipped with 4.56 gears, with essentially the same size tires as our GMCs.

The main difference between then and now is the overdrive transmissions on the newer cars. Prior to that, trucks, motorhomes, etc ran at higher RPMs than they do now. Of course, we were lucky to get much more than 100,000 miles out of those older vehicles, but that is only one of the reasons the newer ones last longer.

Vadim Jitkov '76 Glenbrook 26' Pullman, WA

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Re: [GMCnet] Power Drive [message #327273 is a reply to message #327271]

Tue, 19 December 2017 00:15

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Vadim,

I would suggest you download and review these two Operator Manuals for your 1976 GMC as they were written by the guys that built the
vehicle and it is reasonable to assume they knew how to operate them. :-)

Select the appropriate manual depending on the VIN number of your Glenbrook:

Up to TZE166V100877:

http://www.bdub.net/manuals/X7621A.zip

TZE166V100878 and later:

http://www.bdub.net/manuals/X7680B.zip

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@list.gmcnet.org] On Behalf Of Vadim Jitkov
Sent: Tuesday, December 19, 2017 3:24 PM
To: gmclist@list.gmcnet.org
Subject: Re: [GMCnet] Power Drive

I'm really glad I posted this question here. All your replies and personal experiences have significantly calmed my anxiety about
running the engine at what I perceived were high RPMs. I've read some additional threads on the forum with people towing fairly
heavy trailers with the same setup as I have and traveling at highway speed limits without any issue for the engine and
transmission. I feel much better now. Thank you all :)

Here is a follow up question (let me know if I need to start a new thread for this): from the point of view of transmission, what is
the best way to tackle hills on the road? In the area where I live, we have significant grades on nearly all our roads. We've got
multiple grades of 3-4% in any direction we get going and some very steep grades of 6-7%. I've read that its best to slow down and
downshift to "S" gear for tackling the grades. Should this be done on all climbs or just on those very hard 6-7% grades? What about
driving in town (again lots of hills, but driving at 25-35 MPH)?

Vadim Jitkov
'76 Glenbrook 26'
Pullman, WA

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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Re: [GMCnet] Power Drive [message #327277 is a reply to message #327271]

Tue, 19 December 2017 07:34

Richard Denney

Messages: 920
Registered: April 2010

Karma: 9

Senior Member

1. Don't use the automatic kickdown to choose a lower gear when climbing.
Shift down manually. This will maintain higher pressure on the clutches in
the transmission. Manny (the foremost TH425 expert) doesn't install
kickdown switches in his rebuilds.

2. Don't try to make real power at low RPMs, particularly below 2000.
Choose a lower gear. As Dick Paterson says to justify this recommendation,
the oil pump is only moving at half the speed of the engine.

3. Therefore, if the grade is so steep that you can't maintain RPMs in the
power band (2400 to 3600 RPMs, or thereabouts), slow down, manually
downshift, and keep the engine in the power band.

4. At low speeds and while accelerating, the transmission will do the right
thing.

5. From a stop, the stall slip of the torque converter will do what needs
to be done.

6. The GMC isn't a race car.

Rick "we have to be the drivetrain control computer" Denney

On Mon, Dec 18, 2017 at 11:25 PM Vadim Jitkov
wrote:

>
>
> Here is a follow up question (let me know if I need to start a new thread
> for this):
> from the point of view of transmission, what is the best way to tackle
> hills on the road? In the area where I live, we have significant grades on
> nearly all our roads. We've got multiple grades of 3-4% in any direction
> we get going and some very steep grades of 6-7%. I've read that its best to
> slow down and downshift to "S" gear for tackling the grades. Should this
> be done on all climbs or just on those very hard 6-7% grades? What about
> driving in town (again lots of hills, but driving at 25-35 MPH)?
>

> --
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
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Re: [GMCnet] Power Drive [message #327286 is a reply to message #327277]

Tue, 19 December 2017 09:53

NextGenGMC

Messages: 146
Registered: December 2017
Location: Washington State

Karma: -1

Senior Member

This makes perfect sense. Again it all comes down to engine RPMs on these big block engines. Just need to get comfortable at running it differently than what I'm used to.

Richard Denney wrote on Tue, 19 December 2017 05:34

1. Don't use the automatic kickdown to choose a lower gear when climbing.
Shift down manually. This will maintain higher pressure on the clutches in
the transmission. Manny (the foremost TH425 expert) doesn't install
kickdown switches in his rebuilds.

2. Don't try to make real power at low RPMs, particularly below 2000.
Choose a lower gear. As Dick Paterson says to justify this recommendation,
the oil pump is only moving at half the speed of the engine.

3. Therefore, if the grade is so steep that you can't maintain RPMs in the
power band (2400 to 3600 RPMs, or thereabouts), slow down, manually
downshift, and keep the engine in the power band.

4. At low speeds and while accelerating, the transmission will do the right
thing.

5. From a stop, the stall slip of the torque converter will do what needs
to be done.

6. The GMC isn't a race car.

Rick "we have to be the drivetrain control computer" Denney

On Mon, Dec 18, 2017 at 11:25 PM Vadim Jitkov
wrote:

>
>
> Here is a follow up question (let me know if I need to start a new thread
> for this):
> from the point of view of transmission, what is the best way to tackle
> hills on the road? In the area where I live, we have significant grades on
> nearly all our roads. We've got multiple grades of 3-4% in any direction
> we get going and some very steep grades of 6-7%. I've read that its best to
> slow down and downshift to "S" gear for tackling the grades. Should this
> be done on all climbs or just on those very hard 6-7% grades? What about
> driving in town (again lots of hills, but driving at 25-35 MPH)?
>

> --
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
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Vadim Jitkov '76 Glenbrook 26' Pullman, WA

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Re: [GMCnet] Power Drive [message #327288 is a reply to message #327286]

Tue, 19 December 2017 10:26

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Sometimes, it is the exhaust note that gets our attention in a GMC. Some of
them are quite "raspy" compared to our sound deadening environment in
modern automobiles. I compare modern automobiles to appliances. Open the
door, the light comes on. No driving pleasure here. Cars should not have
automatic transmissions or self starters or power windows. Wipers, ok.
Heaters, ok. Entertainment centers, nah. If you can't crank it, you don't
need to be driving it. (Grin)
Jim Hupy

On Dec 19, 2017 7:53 AM, "Vadim Jitkov" wrote:

> This makes perfect sense. Again it all comes down to engine RPMs on these
> big block engines. Just need to get comfortable at running it differently
> than what I'm used to.
>
>
> Richard Denney wrote on Tue, 19 December 2017 05:34
>> 1. Don't use the automatic kickdown to choose a lower gear when climbing.
>> Shift down manually. This will maintain higher pressure on the clutches
> in
>> the transmission. Manny (the foremost TH425 expert) doesn't install
>> kickdown switches in his rebuilds.
>>
>> 2. Don't try to make real power at low RPMs, particularly below 2000.
>> Choose a lower gear. As Dick Paterson says to justify this
> recommendation,
>> the oil pump is only moving at half the speed of the engine.
>>
>> 3. Therefore, if the grade is so steep that you can't maintain RPMs in
> the
>> power band (2400 to 3600 RPMs, or thereabouts), slow down, manually
>> downshift, and keep the engine in the power band.
>>
>> 4. At low speeds and while accelerating, the transmission will do the
> right
>> thing.
>>
>> 5. From a stop, the stall slip of the torque converter will do what needs
>> to be done.
>>
>> 6. The GMC isn't a race car.
>>
>> Rick "we have to be the drivetrain control computer" Denney
>>
>> On Mon, Dec 18, 2017 at 11:25 PM Vadim Jitkov
>> wrote:
>>
>>>
>>>
>>> Here is a follow up question (let me know if I need to start a new
> thread
>>> for this):
>>> from the point of view of transmission, what is the best way to tackle
>>> hills on the road? In the area where I live, we have significant
> grades on
>>> nearly all our roads. We've got multiple grades of 3-4% in any
> direction
>>> we get going and some very steep grades of 6-7%. I've read that its
> best to
>>> slow down and downshift to "S" gear for tackling the grades. Should
> this
>>> be done on all climbs or just on those very hard 6-7% grades? What
> about
>>> driving in town (again lots of hills, but driving at 25-35 MPH)?
>>>
>>
>>> --
>> 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
>
>
> --
> 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
>
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Re: Power Drive [message #327311 is a reply to message #327191]

Tue, 19 December 2017 17:39

bwevers

Messages: 597
Registered: October 2010
Location: San Jose

Karma: 5

Senior Member

Someone here once said, "Never go downhill in a GMC faster than you went up the hill..."
Meaning: don't let your downhill speed get away from you.

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

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Re: [GMCnet] Power Drive [message #327313 is a reply to message #327311]

Tue, 19 December 2017 17:48

Ken Henderson

Messages: 8726
Registered: March 2004
Location: Americus, GA

Karma: 9

Senior Member

And generally go down in the same gear you went up (or would have to).
Also, if you're going down too fast, use the brakes briskly to slow below
the desired speed, THEN downshift to the gear that's needed to control the
speed.

Ken
, Living in Flat Country but Been Up & Down Lots of Mountains,
H.

On Tue, Dec 19, 2017 at 6:39 PM, Bill Wevers wrote:

> Someone here once said, "Never go downhill in a GMC faster than you went
> up the hill..."
> Meaning: don't let your downhill speed get away from you.
> --
> 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
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach

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