Topic: Changing rear end ratio


voced    -- 01-07-2015 @ 2:51 PM
  I have a 2:78 ring and pinion (I think out of a 46) to put in my 35 pickup that has a 4:11. After getting it apart I notice that the number of pinion splines are not the same and the carrier bearings are larger on the 2:78. What can I do to make this work? Jerry


Stroker    -- 01-07-2015 @ 3:15 PM
  I'm thinking that you actually have a 3.78:1 gearset, as 2.78 is not a Ford ratio. Having said that, I'd look for a compatible earlier 3.78 gearset. Here's a link to all the differences between years: http://www.flatheadv8.org/fordrear.htm


ken ct.    -- 01-07-2015 @ 3:16 PM
  You will not be happy with a 2.78 RE in a flathead.Not enough motor to pull that ratio.Dont believe FH's came with that low a ratio. 3.78 would be much better. ken ct.


ford38v8    -- 01-07-2015 @ 3:50 PM
  Use the later center section, and a 6 to 10 tooth spline adapter.

Alan


voced    -- 01-07-2015 @ 5:12 PM
  Yes I meant it is a 3:78 not 2:78
Sorry


MICHV8    -- 01-08-2015 @ 6:25 AM
  Stroker...
What a great article! Thanks for posting the link. What is different about 33-34 axles? The author briefly mentions the narrow center section, but doesn't seem to go into detail like the other years...

This message was edited by MICHV8 on 1-8-15 @ 6:29 AM


Stroker    -- 01-08-2015 @ 2:24 PM
  MICHV8: I don't have any personal experience with 33-34 axles, so I can't address your question. I'm sure there are many Forum members who can enlighten both of us. As for the link, I should give credit to Golden Gate RG#1, as that's where I sourced it. Many of our Regional Groups have great tech links, and you can source them right here on this site.

vocd: I believe you would be better for you to find a ca 33-34 gearset as 3.78:1 was a common ratio even then. The Green Book may help with compatibility/interchange issues.

This message was edited by Stroker on 1-8-15 @ 2:29 PM


voced    -- 01-08-2015 @ 6:26 PM
  The rear end is in my 1935 pickup. It also has the large inside pipe type drive shaft (not the solid shaft type)and not sure how a 10 to 6 spline adapter will work. Also, do any of you know what type speedometer gears I will need for the 3:78 ratio.



ford38v8    -- 01-08-2015 @ 9:35 PM
  I think a spline adapter would have to be welded onto a hollow shaft, not sure on that. #3.78 gearing would take a 19 turtle gear.

Alan


40 Coupe    -- 01-09-2015 @ 4:12 AM
  The 10 spline pinion is typical of the late 32 & 33-34 fords. I am sure it may have been carried over to 35. I believe someone is making an adapter from 10 to 6 spline, try the stores that specialize in the gearing.
The 10 spline pinion is slightly shorter than the 6, your drive shaft may have to be shortened. You will have to use the bearings for the 10 spline so the diameter of the 6 spline pinion has to be reduced and you need a spacer for the threads. The gear head of the 3:78 is too large to pass through the differential case so the case can be opened slightly or the OD of the gear head reduced to pass. Some of the cases have slight interference to the 3:78 ring gear which can be ground out.


JM    -- 01-10-2015 @ 7:46 PM
  Voced, 3.78 gear sets with 10 spline pinions can be found that will drop right in your '35 pu rear. These are not to be confused with the '34 and earlier gear sets. I swapped 4.11, 10 spline pinion gears with 3.78, 10 spline pinion gears in my '35 fordor sedan (same rear as in your pu) two years ago. I am very happy with that conversion. I am now getting ready to swap 4.11 10 spline gears with 3.54 10 spline gears in my '35 coupe.
You can use a 6 spline gear set in your '35 pu, but you must remove the 10 spline end on your hollow/tubular driveshaft and replace it by welding in a 6 splined end. I would recommend finding a reputable driveline shop to do that job for you and have them check alignment and balance of final driveshaft assembly.

John

This message was edited by JM on 1-11-15 @ 1:01 PM


ken ct.    -- 01-10-2015 @ 9:26 PM
  You can also change the complete 37 RE for the 36 which I have done on my 36. Lots of 37's had that ratio. Use the 36 backing plates and drill 1 hole for the rear brake rod support brackets on each side and slightly grind a little off the top of the BR clevis so it will pass under the axel tubes when brakes are applied. All there is to it.Works great. ken ct.


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