high speed rear
- Thread starter cooke
- Start date
Tom Wesenberg
Well-known member
3.78 is standard. 3.54 and 3.27 are the higher speed ratio's available. I'd go with the 3.27 if I was making the change. Also go with the 5.5 Syder's head for more power to push the gears.
The rear end needs to come apart, change gears, and recheck the mesh of the gears. It isn't real hard, but does take time.
The rear end needs to come apart, change gears, and recheck the mesh of the gears. It isn't real hard, but does take time.
Joe K
Well-known member
Stock Model As came in 3.78 and 4.11 rear ends. The 4.11 was used on commercial jobs (like my 29 CC pickup) with 3.78 used for the rest of production.
Today you have 3.78 and 4.11 as option new PLUS you can get 3.54 (been around a while) and 3.27 (fairly new and fairly expensive as befits market demand.)
The 3.54 I installed over the 4.11 made a large difference. Upwards of 10 mph in top speed. Of course the acceleration was slightly challenged using the 3.54.
Some with overbuilt engines (think Cragar or high compression or other speed/horsepoer upgrades) tend to go to the 3.27. Think "speedster" application: a light sports car designed as personal transportation/statement.
Some keep it stock if theirs is a tired engine or used simply as parade vehicle. Or are comfortable with 50 mph and below.
And a few use the 4.11 which is nicely suited to an overdrive, either in the ****** via mitchell or other mods, or in the torque tube or banjo as in borg warner, columbia, others.
Were I to do another Model A of non-overdrive/usual weight/use/highway driving, I would go with the 3.54 again. But it's a compromise. Leaving a stop light with a 3.54 leaves one wondering if the Model A isn't really "roadable" compared to modern cars. But the feeling is temporary - and depends who is honking his horn behind you wanting you to get out of their way. (Kidding - most drivers are patient and enjoy seeing an antique car.)
Installing is not that difficult. If myself as a 24 year old can do it, you certainly can. And doing it has been written up extensively in several sources both online and in the purchase literature. You have plenty of guidance here too. The big thing is to take it a step at a time, get your contact in the right spot (verify using blue layout dye) and have a selection of gaskets and a way to tell bearing preload on that drive shaft/pinion bearing.
Right now I'm collecting parts to assemble another Rear End. Bought in parts starting with a trailer that someone had removed the torque tube and driveshaft and Radius rods. Fortunately for me, the former owner had blanked off the open hole on the torque tube attachment to the banjo and this had preserved the gears within.
I just bought radius rods from a seller off of Swap Meet.
You can NEVER have too many spare parts...
Is there a support group for addict/hoarders of Model A parts?
Joe K
Today you have 3.78 and 4.11 as option new PLUS you can get 3.54 (been around a while) and 3.27 (fairly new and fairly expensive as befits market demand.)
The 3.54 I installed over the 4.11 made a large difference. Upwards of 10 mph in top speed. Of course the acceleration was slightly challenged using the 3.54.
Some with overbuilt engines (think Cragar or high compression or other speed/horsepoer upgrades) tend to go to the 3.27. Think "speedster" application: a light sports car designed as personal transportation/statement.
Some keep it stock if theirs is a tired engine or used simply as parade vehicle. Or are comfortable with 50 mph and below.
And a few use the 4.11 which is nicely suited to an overdrive, either in the ****** via mitchell or other mods, or in the torque tube or banjo as in borg warner, columbia, others.
Were I to do another Model A of non-overdrive/usual weight/use/highway driving, I would go with the 3.54 again. But it's a compromise. Leaving a stop light with a 3.54 leaves one wondering if the Model A isn't really "roadable" compared to modern cars. But the feeling is temporary - and depends who is honking his horn behind you wanting you to get out of their way. (Kidding - most drivers are patient and enjoy seeing an antique car.)
Installing is not that difficult. If myself as a 24 year old can do it, you certainly can. And doing it has been written up extensively in several sources both online and in the purchase literature. You have plenty of guidance here too. The big thing is to take it a step at a time, get your contact in the right spot (verify using blue layout dye) and have a selection of gaskets and a way to tell bearing preload on that drive shaft/pinion bearing.
Right now I'm collecting parts to assemble another Rear End. Bought in parts starting with a trailer that someone had removed the torque tube and driveshaft and Radius rods. Fortunately for me, the former owner had blanked off the open hole on the torque tube attachment to the banjo and this had preserved the gears within.
I just bought radius rods from a seller off of Swap Meet.
You can NEVER have too many spare parts...
Is there a support group for addict/hoarders of Model A parts?
Joe K
1931 flamingo
Well-known member
3:78 was usually standard, a 3;54 considered hi-speed. I believe it's a 6-7 mph diff.
R/end banjo needs to come apart to install, pre-load on brgs set and r/pinion b/lash set. Try doing a search, there are details in several threads.
Paul in CT
We all must have been typing at the same time......................
R/end banjo needs to come apart to install, pre-load on brgs set and r/pinion b/lash set. Try doing a search, there are details in several threads.
Paul in CT
We all must have been typing at the same time......................
Last edited:
Joe K
Well-known member
All within one minute.
Fine minds think alike.
So do crummy minds - but we don't have to admit to that.
Call it random occurrence.
Joe K
It's not that difficult... a process of disassembly, cleaning, inspecting/restoring to what it needs to be. Unless the axle was recently restored properly I would count on doing everything (replacing bearings,races,seals, cleaning,checking axles for issues.. etc). The other half is the proper setup of preload for the carrier bearings and backlash of the pinion to ring gear mesh. I would read the article in the early volume 1 or 2 of How to Restore you Model A , rear end article in the front... and/or also Les Andrews procedure in the Repair manuals authored by him is good as well. Pay attention to your preloads/lash, and all details. Even one nick on something can cause you issues. I have changed out a gear set in a recently done rear in 2-4 hours, but if it needs everything plan on some time. After doing about 100 + I have the KRW tools and have them down to my own science... if you take your time and pay attention to detail you will do fine. One caveat. If you've never dealt with a rear spring before please be sure you use a good spring spreader and be safe. The rear springs have great tension on them.. and must be removed at the precise spread distance for the shackle to come out undamaged as well as yourself to remain undamaged. Please heed this warning (only said to ensure you know that they can be dangerous) as I have your safety in mind.
I think the guys above have the ratio questions well covered.
Good luck!!
Larry Shepard
I think the guys above have the ratio questions well covered.
Good luck!!
Larry Shepard
Skibb
Well-known member
Our A just got a 3.54 rear and Snyder's 5.5 HC head. In our case there was lots to do with bearings and all besides the ring and pinion. The rear added 4 to 5 mph and the head gives more power. The car runs great now. We'll try it out on the Blue Ridge Tour in May as we live in a hill less part of the Fla.
hardtimes
Well-known member
Hey cooke,
What year/model A you dealing with
As said 3:27 is 'highest' that I know of. In 1930, Ford put the first 3:54 in the his '30 roadster....to make it act a bit more 'peppy' and attractive to buyers! As the roadster is the lightest of Fords creations, he created a winner, as it 'cruised' along at a little higher speed with less engine rpm. I think that a lot of cars...heavier and light use the 3:54 nowadays, as it's a good choice!
Tom Wesenberg
Well-known member
Unless you live in a very hilly area I think you'd like the 3.27. I installed one in my friend's 31 pickup.
hardtimes
Well-known member
Hey cooke,
Yeah , that info helps! If stock with better head , as you have, a 3:27 would probably make you happy driver
! Recently, I sold a sport coupe with a new 3:27 and stock trans/rear gearing. It was nice to drive and engine took respite from high rpm!
Mikeinnj
Well-known member
Cooke, Do yourself a favor and read Tom Endy's very well written article on rebuilding a Model A Ford differential then decide if you are up to the job and the expense involved. Here is the link to download the pdf document.
http://www.ocmafc.org/techarticles/Tom%20Endy%27s%20Special%20Topics/Differential%20Seminar%20-%20Re-Edited.pdf
Mikeinnj
Well-known member
Larry, You forgot to mention adjusting the pre-load for the pinion gear.
I have just completed the Coromandel Rally in New Zealand with a 3.54 diff in my otherwise stock 29 RPU. On several steep hills with a long gradual climb I found a disappointing loss of power, with other A's accumulating behind me and a couple passing me still in top gear. I put it down to the high ratio diff although there are of course many other possible reasons. I will check the compression to see if that is causing it.
Tom Wesenberg
Well-known member
The Snyder's 5.5 head should more than make up for the difference.
