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Series V Readend

AlpineOh

Donation Time
Hello. Am a first time Alpine owner and have been reading the Forum as I try to bring my recently acquired Alpine back to road readiness. On my first shakedown drive, I found the third member in my car has a very high ratio gearset as the engine rpm(according to the tach) is 4ooo at 50 mph. Does anyone out there know of a rear with more street friendly gear ratio available for sale or trade? Or any suggestions for a possible swap to another read with more rear gear availability. Thanks.
 

Bill Blue

Platinum Level Sponsor
Before going too far, we must establish the following:
Don't trust an unknown Alpine speedometer.
Don't trust an unknown Alpine Tachometer.
Don't trust any unknown Alpine qauge.

The Alpine was available with two rear axle ratios, 3.89 and 4.22. Either could be in your Alpine and neither are what you'd call a "cruiser" ratio. Other Rootes cars used the same axle and some had a 3.70 gearset, which of course, works in the Alpine and is a pretty decent ratio. They are pretty hard to find, but are available from an aftermarket source.

A lot of different rear axles have been used in Alpines, but I don't believe any are what you'd call a "bolt in". A popular choice is the Ford 8", figure it will cost about $500 to get it modified to fit the Alpine. Another possibility is the Dana 44 (I believe) from the Postal Jeep. I know nothing about it other than on paper, it appears to be a good candidate as the physical dimensions and layout are very close to that of the Alpine.

Bill
 

AlsPine

Donation Time
You could also pickup an overdrive transmission. There are two ways to go. There is a person in the UK that sells rebuilt Alpine overdrive transmissions. Many people on this forum have bought one from him including me, and they work very well. Or you can get a conversion kit to use a Toyota 5 speed transmission.
First thing to do is to determine what ratio rear end you have. Unless your Alpine had a OD transmission, and it was replaced with a standard, you should have a 3.89 ratio differential. OD Alpines had the 4.22 ratio. You will have to jack up the car and with the transmission in neutral, turn the drive shaft and count the number of turns it takes to rotate the tire one revolution. If it is a little less than 4 turns, then it is a good bet you have a 3.89 rear end. More than 4 turns, it will be a 4.22.
You can also look at the VIN tag as see it it says OD at the end of the VIN number.
To check your tach, use a dwell meter, it should have a RPM function. You can run up the engine and compare readings.
Have fun with your project.
 

65beam

Donation Time
rear end

if the car is a series 5 and still has the original rearend it's probably a 4:22. almost all series 5's came with the 4:22 gears even without overdrive.
 

Bill Blue

Platinum Level Sponsor
In the early years, it is probably okay to say "your car should have". Later years, especially Series V, it seems the factory stuck any ratio they damn well pleased into any Alpine. That, added to the extreme age these cars are getting too and the number of "restorations" they have undertaken, makes it anybodies guess what a particular car will have.

Better check.

Bill
 

RootesRooter

Donation Time
Check your VIN. Up to # B395010312, Series V's destined for the US or Canada came with 4.22's, with or without OD. The rest came with 3.89's standard, 4.22 with OD. Of course there's always the chance your diff is not original.

If you find you have 4.22's and wish to switch to 3.89's, take the time to search this forum for "crown wheel bolts" tech advice. It's a problem that eventually affects every Alpine.
 

Tom H

Platinum Level Sponsor
Almost surely your tach is reading high
Almost surely you have a 4.22

Recommendations: First determine what you have :
Jack up just one rear wheel and rotate the wheel 2 full rotations. Make a chalk mark on the wheel and on the drive shaft. Best to start with the shaft mark at some easily identified position- like at 3 Oclock. When you have rotated the wheel 2 full turns, you will clearly see that the shaft rotated a little more or a little less than 4 full turns. Just be sure you note which way the shaft was turning so you'll be sure if it went PAST 4 turns or ended SHORT of 4 turns. It will be only about 1/4 turn past the starting point (if a 4.22) or just an 1/8 of a turn short of the starting point (if a 3.89).

Then measure your tire rolling circumference- use a chalk and a tape measure to measure the distance of 2 revolutions rolling down your driveway. Half that dimension is your rolling circumference-should be about 74 inches or so depending on tire size. Divide that into 5280 Ft /mile = about 880 tire revs per mile. Multiply that by the axle ratio e.g.(4.22 x 880 = 3714). so at 3714 engine RPM you should be moving 1 mile in 1 min , or 60 MPH. Take it on the highway with mileposts and run the car at some steady speed or RPM and adjust speed / RPM until you are clocking 1 mile per 60.0 seconds. At that speed, (one mile per 60 seconds) you are going 60 MPH and the RPM is actually 3714 (or whatever you calculated) regardless of what the speedo and tach say. Now you will know how far off your speedo and tach are.

In other words, once you calculate your Revs per mile, based on tire size and axle ratio, that number is also the actual RPM at an actual 60 MPH.

Or use the calculator Kevin has posted on his site:
http://mysite.verizon.net/vze3rjzs/images/tire-speed-calculator-v2.xls

Then you can swap in one or some of the following :
3.89 ring gear (from several sources new and used)
3.70 ring gear (from Rootes post vintage spares)
Rebuilt OD tranny from Jeff Howarth in the UK or ????
5 speed Toyota tranny - used
Repair and recal your tach

Good luck. Lots of people here have done the above swaps

Tom
 

mattinoz

Donation Time
would be great if there was a metric version of Kevin spreadsheet for those of us that measure distance and speed in kilometres(ph).
 

mattinoz

Donation Time
Thanks Michael, yes I'm aware of the dual scales, however I know my speedo is reading fast so it would be useful to know by how much. I might be just tyres or the wrong speedo for an my OD box. I have confirmed I have a 4.22 diff and I'm running Firestone F570's 165/70 R13's
 

alpine_64

Donation Time
Thanks Michael, yes I'm aware of the dual scales, however I know my speedo is reading fast so it would be useful to know by how much. I might be just tyres or the wrong speedo for an my OD box. I have confirmed I have a 4.22 diff and I'm running Firestone F570's 165/70 R13's

Matt,

You rolling radius is probably a little smaller than stock which will change the speedo, currently you will be:

100kph = 3218 RPM
60kph = 1930 RPM
50kph = 1609 RPM

which is about 104% of stock.
 

todd reid

Gold Level Sponsor
Series V rear end

I had the same perceived issues when I bought my car many years ago. Over a period of years, I did the following;

1. Found out my tach was reading 1,000 rpm high (indicated 4,000 was really only 3,000 prm).

2. Swapped in a used 3.89 rear. Helped at highway speeds, and I really didn't notice an effect on acceleration.

3. Upgraded to 14" wheels.

The combination of all 3 changes made for a nice all around car.
 

Ron67Alpine

Silver Level Sponsor
...Then you can swap in one or some of the following :
3.89 ring gear (from several sources new and used)
3.70 ring gear (from Rootes post vintage spares)
Rebuilt OD tranny from Jeff Howarth in the UK or ????
5 speed Toyota tranny - used
Repair and recal your tach
Good luck. Lots of people here have done the above swaps
Tom

Just to be clear, is it just a matter of changing the ring gear, to get a better hiway ratio? It's not necessesary to replace the entire rear end? And is the 3.70 better than the 3.89?
Thanks
Ron
 

RootesRacer

Donation Time
Just to be clear, is it just a matter of changing the ring gear, to get a better hiway ratio? It's not necessesary to replace the entire rear end? And is the 3.70 better than the 3.89?
Thanks
Ron

You pull the pumpkin and R&R the ring and pinion.
You also need to have the gears setup by a competent mechanic.

Its been said the 3.70 is weaker than the 3.89.
The 3.70 was used on automatic arrows, so strength was probably not an issue.

Also its been reported that the new 3.70s that are available arent very quiet in operation, but that may be a fluke of too few data points.
 

RootesRooter

Donation Time
3.70's were used on automatic twin-carbed Alpine GT's and the Weber-ized Hillman GT's in the UK. I don't think they were used on any U.S.-bound Arrow sedans. I autocrossed the heck out of a set of 3.70's and couldn't break it over a dozen years. It finally succumbed to a worn front bearing that allowed the oil to drain out and fry the unit. I really miss that 4% on the freeway.


You pull the pumpkin and R&R the ring and pinion.
You also need to have the gears setup by a competent mechanic.

Its been said the 3.70 is weaker than the 3.89.
The 3.70 was used on automatic arrows, so strength was probably not an issue.

Also its been reported that the new 3.70s that are available arent very quiet in operation, but that may be a fluke of too few data points.
 

65beam

Donation Time
ear end

rootes rooter,
my white 69GT now has a 3:70 in it thanks to another automatic GT that had terminal rust. all my literature shows the arrow with the 3:89 even with the auto box. the minx and hunters sedans also had 3:89 gears. the specification book supplied to the dealers in 1970 for the salesman to use shows all the fastbacks with 3:89 gears. the literature shows different. that doesn't surprise me since chrysler was in charge at that time. many years back i also set the entire 3:70 pumpkin from another GT in my series 4. it's a great car to drive with the close ratio all syncro box and the 3:70 gears. the original 3:70 gears are very quiet.
 

alpine_64

Donation Time
You pull the pumpkin and R&R the ring and pinion.
You also need to have the gears setup by a competent mechanic.

Its been said the 3.70 is weaker than the 3.89.
The 3.70 was used on automatic arrows, so strength was probably not an issue.

Also its been reported that the new 3.70s that are available arent very quiet in operation, but that may be a fluke of too few data points.

Jarrid,

Didnt the H120 rapiers and the Hunter GTS (both the weber DCOE equiped holbay engined cars) run the 3.70 as standard. They also used the later stronger O/D as standard on those models too IIRC.
 

RootesRacer

Donation Time
Jarrid,

Didnt the H120 rapiers and the Hunter GTS (both the weber DCOE equiped holbay engined cars) run the 3.70 as standard. They also used the later stronger O/D as standard on those models too IIRC.

I dont know, they didnt send any to the US, so factory 3.70s are very rare here.

The rationale for what I read was that the 10 teeth they put on the pinion made the gear itself not as deep at the 9 teeth units on the 3.89.

Strength is perhaps relative, but sounds like it wasnt weak by 100hp standards.

200hp may be a different story though.
 

65beam

Donation Time
rear end

i pulled out a couple of my H120 dealer literature and both show a 3:89 rear end gear. 1st gear ratio was 12.14:1, 2nd was 7.75:1, 3rd was 5.04:1 (OD 3rd 4.05:1), 4th 3:89 (OD 4th 3.12:1) i wonder where the name H120 came from?
 
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