TH425 Ratios

[Ken H.]

When I bought the GMC in '98, it came with a 3" notebook full of old GMCMI
newsletters starting with No.1. I stumbled across that a few days ago and
began reading them. The link below is to an interesting article from the
Summer '85 (Vol.3 No.4) issue announcing higher ratio internal gear sets
for the TH-425 -- the first I've heard of those. Apparently the "Art Car"
in the company name is for Art Carr, a long-time Hot Rod transmission
expert. I've requested more information from his current company in
Huntington Beach, CA.
https://photos.app.goo.gl/C2GcPqZKHU5DXWqE9

Ken H.

 

[marsh wilkes]

Hi Ken,

Sounds very interesting, especially for hill country.
My first coach "Smokey" must have had taller than 3.07
gearing in the differential, I never had a tach on it. I once pulled
a boat To Santeetlah lake near Robbinsville NC. and I had to have some one
launch the boat for me. I had checked on a similar incline in the parking
lot
and I knew that if I backed down the boat ramp the coach would have never
pulled up the ramp.
In a past life it seems like I have a faint memory
of a different gear set for the Turbo 400. I wonder
what Manny knows, also if the fire is threatening him?

Marsh (never post) Wilkes
Perry Florida

-----Original Message-----
From: Ken Henderson via Gmclist
Sent: Friday, August 21, 2020 1:48 PM
To: GMC Mail List
Cc: Ken Henderson
Subject: Re: [GMCnet] TH425 Ratios

When I bought the GMC in '98, it came with a 3" notebook full of old GMCMI
newsletters starting with No.1. I stumbled across that a few days ago and
began reading them. The link below is to an interesting article from the
Summer '85 (Vol.3 No.4) issue announcing higher ratio internal gear sets
for the TH-425 -- the first I've heard of those. Apparently the "Art Car"
in the company name is for Art Carr, a long-time Hot Rod transmission
expert. I've requested more information from his current company in
Huntington Beach, CA.
https://photos.app.goo.gl/C2GcPqZKHU5DXWqE9

Ken H.
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[Ken H.]

Marsh,

I just 10 minutes ago sent Manny a note of concern about the fires. He's
about 1/2 mile outside the perimeter of the San Jose Evacuation Zone,
according to the map I looked at. I've had word from others out that way
that he's cleared a lot of brush and trees and is not worried. It never
occurred to me to ask him about the different ratios. I suspect there
were parts for TH-400's that could be used in the TH-425, but finding
someone these days to do it would probably be difficult. I just threw it
out there to see what the ripples looked like -- getting back in touch with
you is one of the good ones.

Y'All stay safe -- wear that mask! We're just hangin' around on our 3+
acres & going for groceries now and then.

Ken

On Fri, Aug 21, 2020 at 6:55 PM Marsh Wilkes via Gmclist <

> Hi Ken,
>
> Sounds very interesting, especially for hill country.
> My first coach "Smokey" must have had taller than 3.07
> gearing in the differential, I never had a tach on it. I once pulled
> a boat To Santeetlah lake near Robbinsville NC. and I had to have some one
> launch the boat for me. I had checked on a similar incline in the parking
> lot
> and I knew that if I backed down the boat ramp the coach would have never
> pulled up the ramp.
> In a past life it seems like I have a faint memory
> of a different gear set for the Turbo 400. I wonder
> what Manny knows, also if the fire is threatening him?
>
> Marsh (never post) Wilkes
> Perry Florida
>
>
>
> -----Original Message-----
> From: Ken Henderson via Gmclist
> Sent: Friday, August 21, 2020 1:48 PM
> To: GMC Mail List
> Cc: Ken Henderson
> Subject: Re: [GMCnet] TH425 Ratios
>
> When I bought the GMC in '98, it came with a 3" notebook full of old GMCMI
> newsletters starting with No.1. I stumbled across that a few days ago and
> began reading them. The link below is to an interesting article from the
> Summer '85 (Vol.3 No.4) issue announcing higher ratio internal gear sets
> for the TH-425 -- the first I've heard of those. Apparently the "Art Car"
> in the company name is for Art Carr, a long-time Hot Rod transmission
> expert. I've requested more information from his current company in
> Huntington Beach, CA.
> https://photos.app.goo.gl/C2GcPqZKHU5DXWqE9
>
> Ken H.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[richard h staples]

Apparently Art Carr sold his design/business to ATI, a fairly large performance transmission company which is still around. They offered a low
first-gear planetary set for the THM400 (which should work in the THM425 as the gears are the same). It replaced the original 2.48:1 first gear with
a 2.75:1 ratio, which would help a little getting started up steep grades over 10,000 ft. altitude. (I once had to back down a shelf road about 1/4
mile. Not fun.)

In my notes I found the gearset was going for $649 direct from ATI and $750 from Summit racing a few years ago. ATI even listed a gearset with a
2.9:1 first gear for a short time. However, apparently they had some quality problems, with one unhappy customer complaining his new planetary gears
were full of metal chips, including in the needle bearings. Now the the THM400 low gears are no longer listed on the ATI site, so we may be out of
luck. I should have bought them when I could. Maybe they'll reappear some day.

That's what I know.

Rick Staples

--
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

 

[Ken H.]

I haven't heard back from Art Carr, but I DID hear from a prominent GMCer
who says he's been running those 1st & 2nd gear ratios ahead of a 3.21 FD
for 35 years! lt'd be a sad day if we didn't learn something new!

Ken H.

On Fri, Aug 21, 2020 at 10:34 PM Richard H Staples via Gmclist <

> Apparently Art Carr sold his design/business to ATI, a fairly large
> performance transmission company which is still around. They offered a low
> first-gear planetary set for the THM400 (which should work in the THM425
> as the gears are the same). It replaced the original 2.48:1 first gear with
> a 2.75:1 ratio, which would help a little getting started up steep grades
> over 10,000 ft. altitude. (I once had to back down a shelf road about 1/4
> mile. Not fun.)
>
> In my notes I found the gearset was going for $649 direct from ATI and
> $750 from Summit racing a few years ago. ATI even listed a gearset with a
> 2.9:1 first gear for a short time. However, apparently they had some
> quality problems, with one unhappy customer complaining his new planetary
> gears
> were full of metal chips, including in the needle bearings. Now the the
> THM400 low gears are no longer listed on the ATI site, so we may be out of
> luck. I should have bought them when I could. Maybe they'll reappear
> some day.
>
> That's what I know.
>
> Rick Staples
>
> --
> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[hal stclair]

There is a 2.97 first gear available for the 4l80e which should fit the 400/425 transmissions. A 1.57 second gear vs the 1.48 stock gear is also
available. TCI used to carry both.
Hal
--
"I enjoy talking to you. Your mind appeals to me. It resembles my own mind, except you happen to be insane."

1977 Royale 101348,

1977 Royale 101586, Diesel powered,

1974 Eagle Bus 45',w/slideout,

Rio Rancho, NM

 

[john r. lebetski]

Art was huge in the TH 2004R Buick turbo racing world back in the day. The stock somewhat tall first gear is not great in stop and go. However, going
to a steeper first gear would be the worst choice for the mountains you could do. On grades over 6% where you need to use 1st and second gears back
and forth, the RPM drop going into S is ALREADY too much. That is to say, you wind it out as high as you dare in 1st then shift to 2nd and are at the
very bottom of the power band, barely in it. Going to to steeper first would make that worse.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[bill wevers]

I once had a discussion with Manny about the lower gear ratios. He said that
he used them, but they broke and left him stranded. He said that they weld the
gears together. They're build up from the planetary set from a smaller GM transmission,
probably from the TH200 or TH350. They are not as strong as the TH400 gears.

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