I don't remember how it came about but I was thinking of ways to reduce the engine speed on the highway and remember an article somewhere about installing a 3.70 rear end. I have a series V with overdrive and want a little less activity under the hood at 70 mph. I am told that you need a little expertise to change out the ring and pinion and wonder if anyone has done this and how hard was it. I guess you don't find 3.70 rear ends laying around the local junk yard too often.
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3.70 rear end
- Thread starter Thor 1211
- Start date
George Coleman
Gold Level Sponsor
I have a 3.70 in my Alpine with a Toyota 5 speed T50 box, I hade Doug Jennings at Tiger auto did my setup, anyone that dose rearend setups should be able to do it for you.
If your Series V still has its original rear end then it's a 4.22. Even with overdrive you're still making high revs at cruising speed.
The 3.70 would definitely make a huge difference.
I swapped my Series 3's original 3.89 for the 3.70 and now cruise happily along on the highway at 80 miles an hour with overdrive.
I bought a brand new 3.70 gear set from Rootes Post Vintage Spares. Expensive but worth it.
Doug Jennings in Dayton, Ohio also did my set up.
The 3.70 would definitely make a huge difference.
I swapped my Series 3's original 3.89 for the 3.70 and now cruise happily along on the highway at 80 miles an hour with overdrive.
I bought a brand new 3.70 gear set from Rootes Post Vintage Spares. Expensive but worth it.
Doug Jennings in Dayton, Ohio also did my set up.
RootesRooter
Donation Time
There were a fair number of the later, fastback Alpine Couples and GT's sold in Canada. (I'm assuming in you're in that Ontario) The GT model with automatic transmission came with 3.70's. It's a pretty straightforward swap to your Series V. If you know of any fastbacks in local junkyards or currently acting as planters in your neighborhood it might be worth a look there first.
Do you know what ratio you currently have? If its a 4.22, switching to 3.89's would be a lot easier and accomplish most of what you're after. Oh, and if you come across a derelict fastback Alpine that's not an automatic, it has 3.89's that are just as swappable.
Thor, Looking at the replies I see some potential confusion. All the replies make sense, but take different approaches that may not be so clear:
If you have a 4.21 now, swapping to a complete replacement used diff assembly (the pumpkin) you could do it yourself if you found a fairly common 3.89. Or also if you could find a rare 3.70 assembly.
An alternative is to buy a new ring and pinion 3.70 (or 3.89) set from Rootes Post Vintage Spares and have a local rear end shop install that set in your present diff assembly. Actually installing, adjusting , and shimming the gears in a diff requires equipment and expertise above the level of most backyard mechanics.
Tom
If you have a 4.21 now, swapping to a complete replacement used diff assembly (the pumpkin) you could do it yourself if you found a fairly common 3.89. Or also if you could find a rare 3.70 assembly.
An alternative is to buy a new ring and pinion 3.70 (or 3.89) set from Rootes Post Vintage Spares and have a local rear end shop install that set in your present diff assembly. Actually installing, adjusting , and shimming the gears in a diff requires equipment and expertise above the level of most backyard mechanics.
Tom
3.70
Well, I guess my options are clear. First figure out what I have for a rear end. I'm the third guy to go at the drivetrain in this car, so it could be anything in the rear end. Second, I guess I could start scrounging around for an old 67+ fastback and see if I can get a rear end. Finally, I can order the ring and pinion from the guy in Holland (Rootes post vintage spares?)and have Jennings or my local driveline shop install them in my current differential. I'm told it's not the kind of job I can do myself.
First things first, though, I guess I better see what I have. I suspect it's a 4.22 because, even with my wacky instruments, I calculate I'm probably turning 3500 rpm at 60 mph.
Finally, a 3.89 would still be a step up if the current set up is 4.22, so I was wondering how popular 3.89 is and is it worth it for me to go looking around to try and find one of them.
Well, I guess my options are clear. First figure out what I have for a rear end. I'm the third guy to go at the drivetrain in this car, so it could be anything in the rear end. Second, I guess I could start scrounging around for an old 67+ fastback and see if I can get a rear end. Finally, I can order the ring and pinion from the guy in Holland (Rootes post vintage spares?)and have Jennings or my local driveline shop install them in my current differential. I'm told it's not the kind of job I can do myself.
First things first, though, I guess I better see what I have. I suspect it's a 4.22 because, even with my wacky instruments, I calculate I'm probably turning 3500 rpm at 60 mph.
Finally, a 3.89 would still be a step up if the current set up is 4.22, so I was wondering how popular 3.89 is and is it worth it for me to go looking around to try and find one of them.
Thor. Easy to tell what you have. With your car on a driveway, use a piece of chalk to mark your tire at the point it touches the ground. And put a chalk mark at 3:00 on the input drive flange or the drive shaft), Push the car 1 full turn of the wheel. Look at the mark on the drive shaft . It will have turned slightly more than 4 full turns ( 4.22) or less than 4 full turns (3.89) . Be sure you note which direction the shaft turned so you can tell slightly over or slightly under 4 turns.
The 3.89 shouuld be fairly common, even tho most later SVs had 4.22 ,
Tom
The 3.89 shouuld be fairly common, even tho most later SVs had 4.22 ,
Tom
RootesRooter
Donation Time
The 3.89 shouuld be fairly common, even tho most later SVs had 4.22 ,
Almost. The first roughly 10,000 Series V's came with 4.22's, with or without OD. The last 9,000 had 4.22's with OD, 3.89's without OD. Sunbeam Specialties' catalog is a good information source for VIN cutoffs on parts changeovers like this.
I haven't had to buy a set of 3.89's in a while. What do they go for these days? There was a 3.89 diff listed three times on eBay over the last couple of months that never got an opening bid at $160 (including shipping). But you never know with an auction like this, it could turn out to be a 'howler,' with no recourse to the buyer.
Almost. The first roughly 10,000 Series V's came with 4.22's, with or without OD. The last 9,000 had 4.22's with OD, 3.89's without OD. Sunbeam Specialties' catalog is a good information source for VIN cutoffs on parts changeovers like this.
I haven't had to buy a set of 3.89's in a while. What do they go for these days? There was a 3.89 diff listed three times on eBay over the last couple of months that never got an opening bid at $160 (including shipping). But you never know with an auction like this, it could turn out to be a 'howler,' with no recourse to the buyer.
DanR
Diamond Level Sponsor
Thor 1211
I have a '65 SIV that had the Original BW 35 Automatic Transmission. I am replacing the rear axle assy with a SV assembly because it will be getting Jose's V6 Conversion to the 2.8 V6 MustangII engne.
If you are interested in purchasing the complete rear axle assy it's available. Has the wire hubs.
I'll sell it for $200.00 if it has the 3.70 gear you need. Problem I see is shipping cost. But, I just used a site for shipping a Hard Top from Vt to SC and was pleased with the service. www.uship.com
Thanks,
I have a '65 SIV that had the Original BW 35 Automatic Transmission. I am replacing the rear axle assy with a SV assembly because it will be getting Jose's V6 Conversion to the 2.8 V6 MustangII engne.
If you are interested in purchasing the complete rear axle assy it's available. Has the wire hubs.
I'll sell it for $200.00 if it has the 3.70 gear you need. Problem I see is shipping cost. But, I just used a site for shipping a Hard Top from Vt to SC and was pleased with the service. www.uship.com
Thanks,
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Dan raises a good point. What ratio was standard on the SIV Automatics? Inquiring minds want to know.
John W
Bronze Level Sponsor
No way the automatic has the 3.7 in it. Thor, I have the 3.89 from my SIV automatic in my SV overdrive and previously had the buzzy 4.22, and you need to go to Rootes Post Vintage Spares and get the 3.7 and have Doug or someone like Irby Goff (803) 754-2425 (no relation) install it. I've mentioned the 3.7 to Irby for my SV and Irby said the only thing that concerned him from any replacement set would be the quality of the metal. Maybe someone can speak to the quality of the metal of Post Vintage Spares.
Dan, If you and thor don't work out a deal, I think I'd like to talk to you about the SIV wires...DO you also have useable wheels?
Thor, dang if it don't sound like I'm trying to step in on a deal...So I'll add that if you have the 4.22, the 3.89 is much better and I know from twisting the unassembled axle that Dan mentions that's the tightest rear end I've seen anywhere off a car, and the reason for my interest, other than to have wires on my SIV auto.
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alpine_64
Donation Time
The SIV Autos used the 3.89 diff.
3.70
Well, John, I am working on a deal with Dan but don't worry, what will be will be.
One of the things I am just trying to find out is if a regular driveline shop can put the ring and pinion in (to save having to ship it half way across America). The guy at Rootes Post Vintage Spares seems to think it requires special tools and experience.
As a final alternative I could just try to get Irby or Doug to do it.
I have a 4 wire wheels if you want them (one has a couple broken spokes- but my car seemed to ride ok with them) Make me an offer.
Well, John, I am working on a deal with Dan but don't worry, what will be will be.
One of the things I am just trying to find out is if a regular driveline shop can put the ring and pinion in (to save having to ship it half way across America). The guy at Rootes Post Vintage Spares seems to think it requires special tools and experience.
As a final alternative I could just try to get Irby or Doug to do it.
I have a 4 wire wheels if you want them (one has a couple broken spokes- but my car seemed to ride ok with them) Make me an offer.
George Coleman
Gold Level Sponsor
The Roots post Vintage 3.70 ring gear and pinion are working good for me so far but they seem to be a little noisy from stock thats the only beef I have. Roots post may not have the 3.70 any more?
DanR
Diamond Level Sponsor
OK Guys! Here is what I found.
I rotated the wheel and watched the Pinon gear Flang turn.
I marked both the tire/wheel and the Flange where the drive shaft bolts .
It was one (1) revolution of the tire/wheel to two (2) revolutions of the Pinon Gear Flange.
It was so close to exactspots from beginning till the completion of the revolution (s) that I could not tell if there is any difference other than 2 to 1 (Flange to Wheel).
What that means in ratio I have not yet determined.
Will post on the Forum and see what we get....
DanR
I rotated the wheel and watched the Pinon gear Flang turn.
I marked both the tire/wheel and the Flange where the drive shaft bolts .
It was one (1) revolution of the tire/wheel to two (2) revolutions of the Pinon Gear Flange.
It was so close to exactspots from beginning till the completion of the revolution (s) that I could not tell if there is any difference other than 2 to 1 (Flange to Wheel).
What that means in ratio I have not yet determined.
Will post on the Forum and see what we get....
DanR
RootesRooter
Donation Time
Dan, it was only the later, 4-seater Alpine GT fastback automatics that came with 3.70's. If original, your Ser IV would have 3.89's.
RootesRacer
Donation Time
Not enough resolution of rotational angle to determine what the ratio is.
Turn the pinion 10 times and note the number of wheel rotations (to nearest 1/8th or a turn or better).