Granny help!
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Junior User
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Granny help!
O.K. first off, I have done some reading in the past on the rear end subject and I just did a search and now I am totally confused.
I have the granny gear (and a 2wd). I must, because I don't use first unless I'm on a steep hill.
I jacked the rear end up( both rear tires), put the tranny in neutral, painted the tread of the tire and a point on the drive shaft, turned the tire and counted the driveshaft revolutions.
'2-revolutions exactly'. What does that mean?
This truck needs some speed and I'm not too interested in hauling much right now. What gear do I want for my 4 speed?
Thank You
I have the granny gear (and a 2wd). I must, because I don't use first unless I'm on a steep hill.
I jacked the rear end up( both rear tires), put the tranny in neutral, painted the tread of the tire and a point on the drive shaft, turned the tire and counted the driveshaft revolutions.
'2-revolutions exactly'. What does that mean?
This truck needs some speed and I'm not too interested in hauling much right now. What gear do I want for my 4 speed?
Thank You
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Joined: Mar 2002
Posts: 135
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From: USA
Granny help!
The easiest thing to do would to crack open the diff, count the number of teeth on the pinion, and then count the number of teeth on the ring gear. Then divide the pinion into the ring gear and that will tell you what you got. I read once how to do the driveshaft method like you did but I don't remember how it was done. Maybe someone else will. Here's another way, if you've got a tach, measure you're tires from top to bottom to get a diameter. Now this sounds hard but its pretty easy, it'll let you take any gear ratio and see what rpm you'll be running at any speed. All you gotta do is take the mph x gear ratio x 336, and divide that number by your tire diameter and that will tell you what rpm you'll be running at what ever speed you put in. Hope this helps.
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Granny help!
Appreciate help!! Maybe somebody knows the tire rotation test out here; meanwhile- When I check the yards, what is the ratio I want for low torque- fast truck? Or is there a search key word on ebay?
I know these 390's are bad ,but I don't pull stumps any more!
I know these 390's are bad ,but I don't pull stumps any more!
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Joined: Mar 2002
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From: USA
Granny help!
I'm not sure about the e-bay, I never touch the stuff myself, but there are alot of gears out there. Such as 3.50,3.53,3.08's etc. What year and model is your truck? I know you said you had a four speed. If you can give me the v.i.n. tag info off the door jamb I could tell you what gear etc. it has in it if its stock. Let me know when you get it and I'll try and help you if I can.
Fleet Owner
Joined: Jun 1999
Posts: 24,552
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From: Creedmoor, North Carolina
Granny help!
Kevin, read my post on the Strangeness thread for counting your ratio. If you have a 390 the 3.00 is a good ratio. 3.25 should put a little more torque in there and still be fast. Both the 3.00 & 3.25 are very common and everybody is looking for 3.50 or 3.70 posi, (just had two 3.25s for sale in a swap meet) so you might be able to pick one of those up for $50.00 and if you have a shorter gear to swap, the classifieds might render you one with a little jingle for your jeans. 
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Granny help!
[updated:LAST EDITED ON 01-Apr-02 AT 06:24 PM (EST)]Curtis thanks for the help. Here you go: VIN= F25YRG33775. axle=38. trans=F. body=3,4. It's a 1970
Wierd, I had my friend who is an expert machinist rebuild it and he insists it is a 390 and all the parts I bought including headers were 390 as well. However, the lmc truck catalog says it's a 360 for this vin. Maybe it was changed out.
Jo- I will look up your thread, thanks.
kevin
Wierd, I had my friend who is an expert machinist rebuild it and he insists it is a 390 and all the parts I bought including headers were 390 as well. However, the lmc truck catalog says it's a 360 for this vin. Maybe it was changed out.
Jo- I will look up your thread, thanks.
kevin
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From: USA
Granny help!
Kevin I found your truck is an F-250, 360 c.i.d., it was built in San Jose in August of 1969, the tranny's a 4 speed syn. Warner T-18, The axle code threw me, my book doesn't show a 38 for that year. It does however have a 28 which is a Dana 70 with 4.56's. That sound about right if you got that low of a gear. Double check your axle code and let me know if I'm wrong.
. Oh and by the way my 70 Sport Custom vin said it was a 390 too, But there should be a little tag attached to the distributor right on top of the manifold that will have 360 on it . Threw me for a loop too!!
. Oh and by the way my 70 Sport Custom vin said it was a 390 too, But there should be a little tag attached to the distributor right on top of the manifold that will have 360 on it . Threw me for a loop too!!Trending Topics
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Granny help!
[updated:LAST EDITED ON 02-Apr-02 AT 09:11 PM (EST)]"The axle code threw me, my book doesn't show a 38 for that year. It does however have a 28 which is a Dana 70 with 4.56's"
Well maybe that other thread mentioning that -if you don't have posi traction you need to double the rotations- is correct. That would mean that if I counted 2 rotaions the real answer is something like 4.00 and 4.56 is not that far off.
Well maybe that other thread mentioning that -if you don't have posi traction you need to double the rotations- is correct. That would mean that if I counted 2 rotaions the real answer is something like 4.00 and 4.56 is not that far off.
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