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| Powerglide [message #230583] |
Wed, 20 November 2013 22:30  |
Bullitthead
Messages: 1411
Registered: November 2013
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Not for the GMC, for the 57 BelAir on the trailer behind it. Do any of the gearheads out there know of an adjustment on the OUTSIDE of a cast iron powerglide that will eliminate second gear slippage? I don't want to take it out, and the PO said it has already been rebuilt about 10 years ago and has only traveled about 200 miles since then.
Is there anything I can do to the TH425 in the GMC to get less slippage on takeoff from a dead stop? Sure seems to be wasting a lot of engine torque. Not looking to burn tires, just a better connection to the front wheels.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Powerglide [message #230593 is a reply to message #230583] |
Wed, 20 November 2013 23:47  |
jim kanomata
Messages: 257
Registered: March 2007
Location: fremont,ca
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Back in 1985 we played with different torque converter stall speeds.
I don't think anyone really found anything that was much better than the stock.
Shortly after that the lower gear final drives became the rage, and is still going on.
3.07 is way too high.
Jim Kanomata
Applied/GMC, Fremont,CA
jimk@appliedairfilters.com
http://www.appliedgmc.com
1-800-752-7502
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| Re: Powerglide [message #230595 is a reply to message #230593] |
Thu, 21 November 2013 00:08 |
Bullitthead
Messages: 1411
Registered: November 2013
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I'm pretty sure the PO did not change the diff, so it probably has the 3.07 in there. Don't the 3.70s cut the mileage a little? I like the low RPM torque of the 455 and it's quiet going down the road. When I get it raised up again I will look for the tag on the cover (if it has one). I was hoping for a governor modification or possibly a fluid additive. I've used the Lucas ATF additive in Fords and Chryslers with surprisingly good results in increased power transfer and shift timing improvement. It also slowed down a leak at the shift shaft where the seal was stiff from an exhaust leak heating it up. Haven't needed to try it in any GM transmissions yet.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] Powerglide [message #230620 is a reply to message #230583] |
Thu, 21 November 2013 06:06 |
Steven Ferguson
Messages: 3447
Registered: May 2006
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PG band adjustments can be accomplished with the transmission in place. No
need to remove it, common procedure.
Steve F.
On Wed, Nov 20, 2013 at 9:30 PM, Terry <mrbullitt@verizon.net> wrote:
>
>
> Not for the GMC, for the 57 BelAir on the trailer behind it. Do any of the
> gearheads out there know of an adjustment on the OUTSIDE of a cast iron
> powerglide that will eliminate second gear slippage? I don't want to take
> it out, and the PO said it has already been rebuilt about 10 years ago and
> has only traveled about 200 miles since then.
>
> Is there anything I can do to the TH425 in the GMC to get less slippage on
> takeoff from a dead stop? Sure seems to be wasting a lot of engine torque.
> Not looking to burn tires, just a better connection to the front wheels.
> --
> Terry Kelpien
> 73 Glacier 260
> Smithfield, Va.
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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--
Take care,
Steve
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| Re: Powerglide [message #230624 is a reply to message #230583] |
Thu, 21 November 2013 07:32 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
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If the PG is just soft at shift apply you could try driving it more. It probably needs that band re adjustment as part of the break in which hasn't fully even happened in 200. If slipping in 2nd as you drive, adjust first. There should be no slippage in the 425 in a given gear. That's just torque converter working with misatch in engine/vehicle speed on a heavy vehicle with only 3 speeds, a 3.07 and a fairly tall 1st gear.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: Powerglide [message #230643 is a reply to message #230583] |
Thu, 21 November 2013 09:23 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Bullitthead wrote on Wed, 20 November 2013 21:30 |
Not for the GMC, for the 57 BelAir on the trailer behind it. Do any of the gearheads out there know of an adjustment on the OUTSIDE of a cast iron powerglide that will eliminate second gear slippage? I don't want to take it out, and the PO said it has already been rebuilt about 10 years ago and has only traveled about 200 miles since then.
Is there anything I can do to the TH425 in the GMC to get less slippage on takeoff from a dead stop? Sure seems to be wasting a lot of engine torque. Not looking to burn tires, just a better connection to the front wheels.
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I'm pretty sure the Powerglide has an external band adjustment that may help. As far as the GMC, that churning sure is aggravated by the final drive ratio and the stall speed of the convertor. The selection of convertors for our coaches is limited. Convertors have stall ratios, extension co-efficients, stall sppeds and most can be controlled independently.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Powerglide [message #230668 is a reply to message #230624] |
Thu, 21 November 2013 11:18 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| JohnL455 wrote on Thu, 21 November 2013 06:32 |
If the PG is just soft at shift apply you could try driving it more. It probably needs that band re adjustment as part of the break in which hasn't fully even happened in 200. If slipping in 2nd as you drive, adjust first. There should be no slippage in the 425 in a given gear. That's just torque converter working with misatch in engine/vehicle speed on a heavy vehicle with only 3 speeds, a 3.07 and a fairly tall 1st gear.
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Although my trans temp runs relatively cool, the highest temps I see are in city driving due to the torque converter. Even mountain driving stays relatively cool due to minimal slip at those RPM's.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Powerglide [message #230711 is a reply to message #230634] |
Thu, 21 November 2013 17:29 |
winter
Messages: 247
Registered: September 2007
Location: MPLS MN
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Read and remember what JimK said, "3.07 is too high" (for a TZE coach). Believe him. The reason a 3.55 or better yet for a 26' a 3.70 does not cost you fuel rate is that the engine is finally matched to the load and no lugging.
Matt
[/quote]
Would installing a "RV" cam or advancing the cam over stock to move the torque peak down lower also be solution to the load mismatch?
How much of the lack of fuel consumption increase could also be due to less torque converter slip at higher RPMs with the lower gears? The BSFC probably decreases around the torque peak but should also increase with the reduction in load. As long as the higher load wasn't putting the carb into power enrichment mode.
Most of what I've read suggests that a 403 should run a 3.55 or 3.70, a 455 should run a 3.21 or 3.43. A 500 should probably then run a 3.07 or 3.21 with a lower stall torque converter.
Jerrod Winter
1977 Palm Beach
Green Jelly Bean
Twin Cities, Minnesota
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| Re: Powerglide [message #230731 is a reply to message #230711] |
Fri, 22 November 2013 00:32 |
Bullitthead
Messages: 1411
Registered: November 2013
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I don't see any adjustment on this CAST IRON powerglide. I've seen it on the aluminum one but never messed with it because that one was working fine. My 1969 "MOTORS" manual details the ALUMINUM powerglide low band adjustment, but doesn't even acknowledge the cast iron case ever existed. More books to look at and people to call tomorrow.
If I make it to California with a functioning GMC, I'll check with Jim about the 3.7 diff gears. I just like the low rpm cruise on the flatlands, but sooner or later I'm going to have to go up a hill.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: Powerglide [message #230758 is a reply to message #230731] |
Fri, 22 November 2013 07:04 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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""If I make it to California with a functioning GMC, I'll check with Jim about the 3.7 diff gears. I just like the low rpm cruise on the flatlands, but sooner or later I'm going to have to go up a hill.
Terry Kelpien 73 Glacier 260 Smithfield, Va.
""
Terry, I still run the 3:07 mostly in the mountains around AZ. If My diff required attention, I sure would switch, but frankly, with the right ratio spread between the lower gears, the 3:07 does quite well. There's nothing detrimental about running 2 cnd and even 1 st up and down the hills.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: Powerglide [message #230760 is a reply to message #230583] |
Fri, 22 November 2013 08:21 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
Karma: 7
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Torque converters use redirection of fluid to multiply torque. Variables include the diameter of the converter and the pitch of the stator blades. Unlike a slipper clutch, they actualy multiply the availible torque and are more efficient especially moving heavy loads. The converter will flash to a higher RPM [ different from stall speed] which is also closer to the engine torque peak. In drag racing, converters are typicly used that stall near to peak torque for maximum acceleration but would obviously be too high for everyday use. The amount of slippage in a given converter is affected by the vehicle weight, engine load, torque and the gear ratio.
At a constant speed on level ground, the slippage is ~ 300 rpm.
Changing the converter slippage isnt practical short of going to a switch pitch converter.
On the other hand, if the trans itself is mechanicly slipping, thats another matter entirely.
76 Glenbrook
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| Re: Powerglide [message #230766 is a reply to message #230760] |
Fri, 22 November 2013 08:44 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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| Chris Tyler wrote on Fri, 22 November 2013 07:21 |
Torque converters use redirection of fluid to multiply torque. Variables include the diameter of the converter and the pitch of the stator blades. Unlike a slipper clutch, they actualy multiply the availible torque and are more efficient especially moving heavy loads. The converter will flash to a higher RPM [ different from stall speed] which is also closer to the engine torque peak. In drag racing, converters are typicly used that stall near to peak torque for maximum acceleration but would obviously be too high for everyday use. The amount of slippage in a given converter is affected by the vehicle weight, engine load, torque and the gear ratio.
At a constant speed on level ground, the slippage is ~ 300 rpm.
Changing the converter slippage isnt practical short of going to a switch pitch converter.
On the other hand, if the trans itself is mechanicly slipping, thats another matter entirely.
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A typical torque converter has a stall ratio of about 2.2 to 1 but they are available as high as 2.6 to 1 in automotive applications. Extension is how long that multiplication lasts. Typically a higher stall ratio has less extension. They are amazing machines and much more complicated than most people realize. The old twin and triple turbine dynaflow converters were really interesting. They harnessed the torque converter turbines to drive the planetary gearsets so that in effect they gave you a CVT.
Bob de Kruyff
78 Eleganza
Chandler, AZ
[Updated on: Fri, 22 November 2013 08:44] Report message to a moderator |
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| Re: Powerglide [message #230769 is a reply to message #230711] |
Fri, 22 November 2013 09:00 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
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| winter wrote on Thu, 21 November 2013 18:29 |
Would installing a "RV" cam or advancing the cam over stock to move the torque peak down lower also be solution to the load mismatch?
How much of the lack of fuel consumption increase could also be due to less torque converter slip at higher RPMs with the lower gears? The BSFC probably decreases around the torque peak but should also increase with the reduction in load. As long as the higher load wasn't putting the carb into power enrichment mode.
Most of what I've read suggests that a 403 should run a 3.55 or 3.70, a 455 should run a 3.21 or 3.43. A 500 should probably then run a 3.07 or 3.21 with a lower stall torque converter.
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Jerrod,
Your questions and points are completely valid and I will try to cover them as best I can.
For starters, always remember that air equals horsepower and not much else matters in the long run.
An "RV" cam, if done correctly could be a very good thing, but without seeing the actual data that was created from a hot run with said cam, I can't provide an opinion that is more than a guess. There are so many things that can happen with camshafts that it can be hard to separate them for evaluation.
When one takes a single engine with a single camshaft and changes the base timing, it is very seldom that the actual torque peak changes. The top 10% may move some, but from my experience, the engines torque curve sort of "rocks" on the torque peak (for lack of a better description). The torque peak of any engine is a function of its volumetric efficiency and that is much more a result of the ports and cylinder head shapes. The valve events don't have a great effect until you change them a lot.
While a lower slip torque converter is a good thing for fuel economy, it has its own issues. If the stall is too far below the engine's torque peak, then the vehicle will be a dog "across the line". This can unsell a vehicle line in a heart beat. Detroit tried that a lot during the first oil embargo. It also has a tendency to hard on the transmission itself.
I wish I had a set of the data that we would develop and use during initial phases of an engine program. Best BSFC ends up being an island at the WOT torque peak in the middle of a sea of data. Any direction you go from that island the BSFC increases (higher fuel consumption/lower MPG). How much and how fast is very engine specific. There is one of these pictures for each manifold pressure, but the BSFC never gets better than it is at WOT, but it can be close enough so the reduced pumping loss can make up the difference.
I have a 9500# 23' coach, the reason I would rather have a 3.55 than a 3.42 is that I can get a 3.55 from a known reliable supplier and I might even be able to get it with limited slip. As to what the Cad 500 guys do, you will have to ask them. I suspect that they are enough bigger than a 455 that they would be comfortable with a 3.07 either.
That is my take on this whole thing.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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