Home » Public Forums » GMCnet » Any way to know what my final drive ratio is?
Any way to know what my final drive ratio is? [message #371348] |
Sun, 21 May 2023 09:35 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Hi all, I just got back from a trip and once again all was well with the coach. Now that all things are in order of course I have to be concerned about SOMETHING -so I was wondering whether or not my PO had changed the final drive.
The coach is a 77 with a 403 and seems to have lots of oomph on hills, rolling along pretty good at speed too ...so my question is can a person tell if the coach has the original 3.07 simply from the performance -or- in other words where does the 3.07 fall flat compared to other options?
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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Re: Any way to know what my final drive ratio is? [message #371349 is a reply to message #371348] |
Sun, 21 May 2023 10:43 |
lqqkatjon
Messages: 2324 Registered: October 2010 Location: St. Cloud, MN
Karma: 5
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You can try to check rpm and compare to mph. But my experience is pretty tricky to be accurate with that method.
Otherwise the only guarantee way is to pull cover and count teeth.
Sometimes paint(applied i think painted some blue?). But really still guessing.
If someone switched to a 3.21 final, that has 8 bolt cover. But pretty rare.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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Re: Any way to know what my final drive ratio is? [message #371353 is a reply to message #371350] |
Sun, 21 May 2023 15:20 |
Carl S.
Messages: 4186 Registered: January 2009 Location: Tucson, AZ.
Karma: 13
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If you have a tach, this chart from Applied might help:
https://www.gmcrvparts.com/product-p/gm1-1.001.1.htm
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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Re: Any way to know what my final drive ratio is? [message #371354 is a reply to message #371353] |
Sun, 21 May 2023 16:35 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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Carl S. wrote on Sun, 21 May 2023 13:20If you have a tach, this chart from Applied might help:
https://www.gmcrvparts.com/product-p/gm1-1.001.1.htm
I'll have to get a tach hooked up, thanks!
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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Re: Any way to know what my final drive ratio is? [message #371355 is a reply to message #371350] |
Sun, 21 May 2023 16:38 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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seeburg220 wrote on Sun, 21 May 2023 09:00I also have a '77 403 w/stock 3.07, and it's a pig.
Can you elaborate what you mean by "pig"? Slow off the line? Top speed lacking? no uphill pulling power? Just wondering.
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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Re: Any way to know what my final drive ratio is? [message #371358 is a reply to message #371348] |
Sun, 21 May 2023 18:59 |
Tilerpep
Messages: 404 Registered: June 2013 Location: Raleigh, NC
Karma: 7
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Two things I can think of
If your gps speed does not match your indicated speed, then some math might tell you how off, then the ratio of available options that would make you that much off.
And in that vein, if you have a speedometer fixer box it would indicate someone put in final. It is a little gear box inline where speedo goes in tranny on mine.
1975 Glenbrook, 1978 Royale rear bath
Raleigh, NC
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Re: Any way to know what my final drive ratio is? [message #371359 is a reply to message #371355] |
Sun, 21 May 2023 20:57 |
seeburg220
Messages: 18 Registered: April 2009
Karma: 0
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boybach wrote on Sun, 21 May 2023 17:38
Can you elaborate what you mean by "pig"? Slow off the line? Top speed lacking? no uphill pulling power? Just wondering.
Mostly just really slow off the line. Merging onto a highway was interesting. (I will say that part of the problem until recently, was the gas pedal rod was bent, so if you floored it, the carb wasn't opening all the way. Bending the gas pedal rod back up helped quite a bit.) Regardless, it just feels like you can feel all 12k lbs it's trying to pull. With my 3.55 coach, it got up and went.
Currently '77 403 Palm Beach.
Formerly '78 403 Kingsley.
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Re: Any way to know what my final drive ratio is? [message #371360 is a reply to message #371359] |
Sun, 21 May 2023 22:47 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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seeburg220 wrote on Sun, 21 May 2023 18:57boybach wrote on Sun, 21 May 2023 17:38
Can you elaborate what you mean by "pig"? Slow off the line? Top speed lacking? no uphill pulling power? Just wondering.
Mostly just really slow off the line. Merging onto a highway was interesting. (I will say that part of the problem until recently, was the gas pedal rod was bent, so if you floored it, the carb wasn't opening all the way. Bending the gas pedal rod back up helped quite a bit.) Regardless, it just feels like you can feel all 12k lbs it's trying to pull. With my 3.55 coach, it got up and went.
Well mine is pretty slow getting away at the lights so I guess I probably do have the 3.07 ...however, that isn't a deal breaker for me -plus I very rarely would have to merge into fast traffic or tow anything at the moment. I guess I'll just drive it like the 46 yr old thing it is and suck it up.
thanks!
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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Re: Any way to know what my final drive ratio is? [message #371364 is a reply to message #371348] |
Mon, 22 May 2023 10:27 |
JohnL455
Messages: 4447 Registered: October 2006 Location: Woodstock, IL
Karma: 12
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I had a 10 hour drive Sat (traffic and construction around Chicago and N In). Had originally had a 3.07. Only great above 70 with no wind or tail wind. I now have Cinnabar USA 3.42 and with a 455 think it’s the best (least downsides) option. Better in stop and go. Better on hills up and down (important as I use gears) in mountains. I cruised at 75 and at times did 80 due to truck traffic speeds. I would not want higher 3 gears as this is how driving is now.
If you have a friend with a known ratio, and are musical, could do side by side 60 MPH and find the note on a guitar and fine tune to it. Then take it to your coach, do same speed and if pitch is same you have same gears (if same size tires). No tach needed.
John Lebetski
Woodstock, IL
77 Eleganza II
[Updated on: Mon, 22 May 2023 10:28] Report message to a moderator
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Re: Any way to know what my final drive ratio is? [message #371365 is a reply to message #371364] |
Mon, 22 May 2023 11:25 |
boybach
Messages: 566 Registered: December 2020 Location: Vancouver Island
Karma: 4
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I don't find the coach slow or lugging on hills however when things get steeper and it drops down to about 45mph I put it into second and it roars up quite contentedly often changing back up to third. Also I rarely go over 65 although I feel the coach would certainly go faster if I floored it.
Mostly drive around 55 and have no problems keeping up with traffic. On trips up the west coast on rural and dirt roads where the average speed is probably around 35-40mph, I'm the envy of friends that drive C-class rigs and have to wait for them the top of the big climbs (or pretty much any hills).
Hwy speed limits in my neck of the woods are in the 80-90 kph (50-55mph) range with the odd stretch at 110 (68mph).
I guess if I was traveling on the interstate or towing perhaps I'd need to change something - for now though, I can't think how things could be improved enough to warrant the swap. And who knows, maybe I do have a different ratio because there's no way I'd describe the performance as sluggish or like a pig!
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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Re: Any way to know what my final drive ratio is? [message #371374 is a reply to message #371365] |
Thu, 25 May 2023 14:27 |
Keith V
Messages: 2337 Registered: March 2008 Location: Mounds View,MN
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Look for a speedo correction box on the speedo cable down by the transmission.
If it has one you know it's not stock. Maybe it says what the correction is?
I have 3.70's behind my 455, it's awesome. I like to drive the secondary roads and it's very happy at 50/55
Of course even on the freeway I rarely exceed 60.
3.42 MIGHT be better if you do all freeway and like to go 70.
Keith Vasilakes
Mounds View. MN
75 ex Royale GMC
ask me about MicroLevel
Cell, 763-732-3419
My427v8@hotmail.com
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