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Does "S" shift position have engine braking? [message #365716]

Tue, 27 July 2021 14:54

6cuda6

Messages: 975
Registered: June 2019

Karma: -6

Senior Member

Curious....do the "S" shift position have engine braking as well, unlike "D" which just seems to freewheel the engine on decel down hill.

Reason i ask is i have a long steep grade that really taxes the brakes and i would prefer to just use the engine to help things.

Rich Mondor, Brockville, ON 77 Hughes 2600

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365718 is a reply to message #365716]

Tue, 27 July 2021 15:01

Keith V

Messages: 2337
Registered: March 2008
Location: Mounds View,MN

Karma: 0

Senior Member

Yes.
Slow the coach with the brakes before putting it in S and then use engine braking to keep you there.
Do not use S to reduce speed, only to maintain it.
IF the coach does start to go faster than you're comfortable with, then apply the brakes to get the speed back under control.
Use the brakes as little as possible but no less.

Keith Vasilakes
Mounds View MN
76 exRoyale
MicroLevel

________________________________
From: 6cuda6@gmail.com
Sent: Tuesday, July 27, 2021 2:54 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Does "S" shift position have engine braking?

Curious....do the "S" shift position have engine braking as well, unlike "D" which just seems to freewheel the engine on decel down hill.

Reason i ask is i have a long steep grade that really taxes the brakes and i would prefer to just use the engine to help things.
--
Rich Mondor,

Brockville, ON

77 Hughes 2600
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My427v8@hotmail.com

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Re: Does "S" shift position have engine braking? [message #365719 is a reply to message #365716]

Tue, 27 July 2021 15:46

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

All gears on the TH 425 have engine braking. It’s just not very noticeable in 3rd. If you switch to a higher numerical gear final drive, all 3 gears will have more engine braking.

John Lebetski
Woodstock, IL
77 Eleganza II

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Re: Does "S" shift position have engine braking? [message #365720 is a reply to message #365716]

Tue, 27 July 2021 15:51

Richard RV

Messages: 631
Registered: July 2012
Location: Full-timer for 12 years, ...

Karma: -17

Senior Member

Rich,

The 1977 Motorhome Operating Manual section on the Automatic Transmission (p18) reads:

SUPER RANGE "S" - Used when super performance is needed for increased acceleration in traffic, hill climbing, or "Engine Braking" down-hill. The selectors lever may be moved from "D" to "S" and Vice verse, under most operating conditions. "SUPER" should not be used at speeds above 75 MPH.

And in the highlighted note:
CAUTION
Before descending a step or long grade, down a mountain or hillside, reduce speed and shift into a lower gear. Use the lower gear ranges to control speed.

It's interesting that the manual states LOW "L" may be used at any speed (it doesn't have the top speed limitation as above), and the transmission only shifts automatically into L below ~40 MPH.

Richard

'77 Birchaven TZE...777; '76 Palm Beach under construction; ‘76 Edgemont waiting its turn

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Re: Does "S" shift position have engine braking? [message #365723 is a reply to message #365720]

Tue, 27 July 2021 18:01

6cuda6

Messages: 975
Registered: June 2019

Karma: -6

Senior Member

Richard RV wrote on Tue, 27 July 2021 16:51

Rich,

The 1977 Motorhome Operating Manual section on the Automatic Transmission (p18) reads:

SUPER RANGE "S" - Used when super performance is needed for increased acceleration in traffic, hill climbing, or "Engine Braking" down-hill. The selectors lever may be moved from "D" to "S" and Vice verse, under most operating conditions. "SUPER" should not be used at speeds above 75 MPH.

And in the highlighted note:
CAUTION
Before descending a step or long grade, down a mountain or hillside, reduce speed and shift into a lower gear. Use the lower gear ranges to control speed.

It's interesting that the manual states LOW "L" may be used at any speed (it doesn't have the top speed limitation as above), and the transmission only shifts automatically into L below ~40 MPH.

Richard

Very interesting....

Rich Mondor, Brockville, ON 77 Hughes 2600

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Re: Does "S" shift position have engine braking? [message #365724 is a reply to message #365716]

Tue, 27 July 2021 18:03

6cuda6

Messages: 975
Registered: June 2019

Karma: -6

Senior Member

Thanks guys...i will for sure downshift after speed reduction....my hope is actually to downshift even before entering the hill as its very close to the entrance to the campsite.

Rich Mondor, Brockville, ON 77 Hughes 2600

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Re: Does "S" shift position have engine braking? [message #365725 is a reply to message #365716]

Tue, 27 July 2021 18:20

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

I remember from TH400 Corvettes you could try to grab first manually at speeds above the 1-2 shift point but it would lock you out until speed was acceptable. The TH350s would not lock you out. The TH425 is of course kin to the 400.

John Lebetski
Woodstock, IL
77 Eleganza II

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365726 is a reply to message #365725]

Tue, 27 July 2021 18:22

Keith V

Messages: 2337
Registered: March 2008
Location: Mounds View,MN

Karma: 0

Senior Member

I do t know, i remember getting reverse at 60mph. That was exciting!
________________________________
From: John R.Lebetski
Sent: Tuesday, July 27, 2021 6:20:13 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Re: Does "S" shift position have engine braking?

I remember from TH400 Corvettes you could try to grab first manually at speeds above the 1-2 shift point but it would lock you out until speed was
acceptable. The TH350s would not lock you out. The TH425 is of course kin to the 400.
--
John Lebetski
Woodstock, IL
77 Eleganza II
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Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
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My427v8@hotmail.com

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Re: [GMCnet] Re: Does "S" shift position have engine braking? [message #365727 is a reply to message #365726]

Tue, 27 July 2021 19:02

Richard RV

Messages: 631
Registered: July 2012
Location: Full-timer for 12 years, ...

Karma: -17

Senior Member

Keith V wrote on Tue, 27 July 2021 16:22

I do t know, i remember getting reverse at 60mph. That was exciting!

Don't leave a guy hanging, Keith - what the hell happened???

Richard

'77 Birchaven TZE...777; '76 Palm Beach under construction; ‘76 Edgemont waiting its turn

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365734 is a reply to message #365727]

Tue, 27 July 2021 21:24

Keith V

Messages: 2337
Registered: March 2008
Location: Mounds View,MN

Karma: 0

Senior Member

Ha ha ha, the Olds 442 did a LOT of engine braking, the rear tires squealed like nothing Ive ever heard before.
But the transmission and all parts seemed no worse for wear!
________________________________
From: Richard
Sent: Tuesday, July 27, 2021 7:02 PM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Re: Does "S" shift position have engine braking?

Keith V wrote on Tue, 27 July 2021 16:22
> I do t know, i remember getting reverse at 60mph. That was exciting!

Don't leave a guy hanging, Keith - what the hell happened???

Richard

--
'77 Birchaven TZE...777;
'76 Palm Beach under construction;
‘76 Edgemonte waiting its turn
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Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
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My427v8@hotmail.com

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365736 is a reply to message #365734]

Tue, 27 July 2021 22:01

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Originally the 442 indicated 4 barrel, 4 speed, and dual exhausts. Or
something like that. And yes indeed, it would turn the tires. Worked on a
bunch of those. That 4 speed was almost indestructible. Hell for strong.
Jim Hupy
Salem, Oregon

On Tue, Jul 27, 2021, 7:24 PM Keith V wrote:

> Ha ha ha, the Olds 442 did a LOT of engine braking, the rear tires
> squealed like nothing Ive ever heard before.
> But the transmission and all parts seemed no worse for wear!
> ________________________________
> From: Richard
> Sent: Tuesday, July 27, 2021 7:02 PM
> To: gmclist@list.gmcnet.org
> Subject: [GMCnet] Re: Does "S" shift position have engine braking?
>
> Keith V wrote on Tue, 27 July 2021 16:22
>> I do t know, i remember getting reverse at 60mph. That was exciting!
>
> Don't leave a guy hanging, Keith - what the hell happened???
>
> Richard
>
> --
> '77 Birchaven TZE...777;
> '76 Palm Beach under construction;
> ‘76 Edgemonte waiting its turn
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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[GMCnet] Re: Does "S" shift position have engine braking? [message #365739 is a reply to message #365736]

Wed, 28 July 2021 08:15

k2gkk

Messages: 4452
Registered: November 2009

Karma: -8

Senior Member

I seem to remember that someone on this list
posted that the transmissions were tested during
development by jamming them into reverse at
highway speed. Development continued until the
transmissions would survive that treatment.

D C "Mac" Macdonald
Amateur Radio K2GKK
Since 30 November '53
USAF and FAA, Retired
Member GMCMI & Classics
Oklahoma City, OK
"The Money Pit"
TZE166V101966
'76 ex-Palm Beach
k2gkk + hotmail dot com

________________________________
From: James Hupy
Sent: Tuesday, July 27, 2021 22:01
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Re: Does "S" shift position have engine braking?

Originally the 442 indicated 4 barrel, 4 speed, and dual exhausts. Or
something like that. And yes indeed, it would turn the tires. Worked on a
bunch of those. That 4 speed was almost indestructible. Hell for strong.
Jim Hupy
Salem, Oregon

On Tue, Jul 27, 2021, 7:24 PM Keith V wrote:

> Ha ha ha, the Olds 442 did a LOT of engine braking, the rear tires
> squealed like nothing Ive ever heard before.
> But the transmission and all parts seemed no worse for wear!
> ________________________________
> From: Richard
> Sent: Tuesday, July 27, 2021 7:02 PM
> To: gmclist@list.gmcnet.org
> Subject: [GMCnet] Re: Does "S" shift position have engine braking?
>
> Keith V wrote on Tue, 27 July 2021 16:22
>> I do t know, i remember getting reverse at 60mph. That was exciting!
>
> Don't leave a guy hanging, Keith - what the hell happened???
>
> Richard
>
> --
> '77 Birchaven TZE...777;
> '76 Palm Beach under construction;
> ‘76 Edgemonte waiting its turn
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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Re: Does "S" shift position have engine braking? [message #365742 is a reply to message #365716]

Wed, 28 July 2021 11:18

Larry

Messages: 2875
Registered: January 2004
Location: Menomonie, WI

Karma: 10

Senior Member

A number of years ago I talked to trans expert Manny Travao about this issue. He spoke to the parts in the trans that transmission braking can be hard on. (can't remember what they are anymore) He advised me that brakes are cheaper and easier than transmissions to replace. So what I've done since is, on long downhill interstate grades, I start at the top at 55mph and allow the coach to get to 65mph. I then brake to 55 and let it coast to 65. That intermitant braking allows the brakes to cool between braking episodes while keeping speed reasonable. On long steep 2 lane grades, depending on the grade and how winding the road is where I have to slow to low speeds, I will then use the trans to assist braking. JWID

Larry

Smile

78 Royale w/500 Caddy
Menomonie, WI.

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Re: Does "S" shift position have engine braking? [message #365747 is a reply to message #365742]

Wed, 28 July 2021 14:47

6cuda6

Messages: 975
Registered: June 2019

Karma: -6

Senior Member

Larry wrote on Wed, 28 July 2021 12:18

A number of years ago I talked to trans expert Manny Travao about this issue. He spoke to the parts in the trans that transmission braking can be hard on. (can't remember what they are anymore) He advised me that brakes are cheaper and easier than transmissions to replace. So what I've done since is, on long downhill interstate grades, I start at the top at 55mph and allow the coach to get to 65mph. I then brake to 55 and let it coast to 65. That intermitant braking allows the brakes to cool between braking episodes while keeping speed reasonable. On long steep 2 lane grades, depending on the grade and how winding the road is where I have to slow to low speeds, I will then use the trans to assist braking. JWID

Been doing that as well but this hill is a bad one.....its about 2.5 miles down and 14% grade.

Rich Mondor, Brockville, ON 77 Hughes 2600

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Re: Does "S" shift position have engine braking? [message #365754 is a reply to message #365716]

Wed, 28 July 2021 22:36

Rick Staples

Messages: 126
Registered: May 2014
Location: Johnstown, Colorado, USA

Karma: -1

Senior Member

Yes.

The THM400/425 has:

No engine braking in 1st gear drive range.
Engine braking in 1st gear Low range.
No engine braking in 2nd gear drive range.
Engine braking in 2nd gear "S" range
Engine braking (slightly) in 3rd gear.

HTH

Rick Staples, '75 Eleganza, Johnstown, CO "Advice is a dangerous gift, even from the Wise to the Wise, and all paths may run ill." -Tolkien

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Re: Does "S" shift position have engine braking? [message #365755 is a reply to message #365716]

Wed, 28 July 2021 22:57

bwevers

Messages: 597
Registered: October 2010
Location: San Jose

Karma: 5

Senior Member

According to my sources, putting the transmission in "S" engages
the band holding 2nd gear and elevates the hydraulic pressure.
Normally in "Drive" when shifting to second, there is a sprague
that engages in the forward direction(no engine braking).

When shifting to 3rd the sprague overruns and the direct clutch
holds the input and output shaft together.

The "L" works the same way only for first gear.
Here's a link to a diagram of the TH400 which is similar:
http://www.turbo-mopar.com/forums/attachment.php?attachmentid=39900&d=1338520896

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

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Re: Does "S" shift position have engine braking? [message #365756 is a reply to message #365716]

Thu, 29 July 2021 09:12

JohnL455

Messages: 4447
Registered: October 2006
Location: Woodstock, IL

Karma: 12

Senior Member

TH425 has no energy saving era freewheel clutches so it is engaged in all gears, except for converter slip The friction material wear occurs only during the shift events. Once in a lower gear, there should be no friction material slip. I drive it as if it were a manual in mountains. If you rely on brakes and you use them up with heat soak, then what? I choose the lower gear preemptively, then apply brakes only as needed to limit engine overspeed with very short applies and long off intervals. I beg to disagree with Manny here (and on disconnecting the GM designed kickdown which I have connected as stock) as overheating brakes can warp drums and rotors and break down grease leading to future fails. Remember that even Mobil 1 grease is only rated to 305F by Mobil. My trans has just past 100K mark no problems.
The long grade you speak of at 14% is a first gear grade taken below 30 MPH. In S it will run away.

John Lebetski
Woodstock, IL
77 Eleganza II

[Updated on: Thu, 29 July 2021 09:18]

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365757 is a reply to message #365756]

Thu, 29 July 2021 09:59

Keith V

Messages: 2337
Registered: March 2008
Location: Mounds View,MN

Karma: 0

Senior Member

This is a good explaination.
I also think that manny means don't use the transmission to slow the vehicle from say 65 to 40, I don't think hes saying to use S to stay at 40mph
________________________________
From: John R.Lebetski
Sent: Thursday, July 29, 2021 9:12 AM
To: gmclist@list.gmcnet.org
Subject: [GMCnet] Re: Does "S" shift position have engine braking?

TH425 has no energy saving era freewheel clutches so it is engaged in all gears, except for converter slip The friction material wear occurs only
during the shift events. Once in a lower gear, there should be no friction material slip i drive it as if it were a manual in mountains. If you rely
on brakes and you use them up with heat soak, then what? I choose the lower gear preemptively, then apply brakes only as needed to limit engine
overspeed with very short applies and long off intervals. I beg to disagree with Manny here (and on disconnecting the GM designed kickdown which I
have connected as stock) as overheating brakes can warp drums and rotors and break down grease leading to future fails. Remember that even Mobil 1
grease is only rated to 305F by Mobil. My trans has just past 100K mark no problems.
The long grade you speak of at 14% is a first gear grade taken below 30 MPH. In S it will run away.
--
John Lebetski
Woodstock, IL
77 Eleganza II
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Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com

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[GMCnet] Re: Does "S" shift position have engine braking? [message #365758 is a reply to message #365756]

Thu, 29 July 2021 09:59

James Hupy

Messages: 6806
Registered: May 2010

Karma: -62

Senior Member

Wear on the "S" clutches can be limited somewhat by matching engine RPM'S
to approximately what they would be in "S" before you engage the
transmission manually.
If your coach lurches and rpm's climb suddenly, you just wore off some
clutch lining. Try to minimize that if possible.
Jim Hupy
Salem, Oregon

On Thu, Jul 29, 2021, 7:25 AM John R. Lebetski
wrote:

> TH425 has no energy saving era freewheel clutches so it is engaged in all
> gears, except for converter slip The friction material wear occurs only
> during the shift events. Once in a lower gear, there should be no friction
> material slip i drive it as if it were a manual in mountains. If you rely
> on brakes and you use them up with heat soak, then what? I choose the
> lower gear preemptively, then apply brakes only as needed to limit engine
> overspeed with very short applies and long off intervals. I beg to
> disagree with Manny here (and on disconnecting the GM designed kickdown
> which I
> have connected as stock) as overheating brakes can warp drums and rotors
> and break down grease leading to future fails. Remember that even Mobil 1
> grease is only rated to 305F by Mobil. My trans has just past 100K mark
> no problems.
> The long grade you speak of at 14% is a first gear grade taken below 30
> MPH. In S it will run away.
> --
> John Lebetski
> Woodstock, IL
> 77 Eleganza II
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
>
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Re: Does "S" shift position have engine braking? [message #365760 is a reply to message #365716]

Thu, 29 July 2021 11:43

boybach

Messages: 566
Registered: December 2020
Location: Vancouver Island

Karma: 4

Senior Member

When I go downhill in S using engine braking, it's a bit disconcerting listening to the pop-pop-pop from the engine ...normal or not?

Larry

Larry - Victoria BC - 1977 ex-Palm Beach "Ol' Leaky" 40,000 miles, PO said everything working but forgot the word NOT. Atwood helium fridge, water heater & furnace. SS exhaust system, Onan, Iota Converter, R134A, New fuel lines & heat exchange hoses

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