1800: Journey into Overdrive

[Clan]

Have you retained your original Final drive ratio?
I fitted an OD gearbox to a 144 S a long time ago , it was fine in adding a cruising gear , but not very lively in OD .
If i remember correctly , the 120 ( and other ) series had a low axle ratio when OD was specified , so that the first 4 gears were lower making the car lively to drive but tiring driving with revs in 4th gear , hence the OD to give relaxed cruising .

[redcar]

Originally Posted by JP 1800

Hi Gareth I have not heard from you in a while, if you need a hand with the electrics let me know, it is a straight forward install. BTW do you still have my Volvo book as I will be doing some gearbox work soon and the diagrams are useful.

Regards

JP

Hi jp, I still have your book, it's a great read.. The author has that classic 60's tone about him. Real authoritative, lol. But I'm just away on holidays, so when I'm back I'll hook up and return it to you..

Btw, the book is ' Glenns Volvo repair and tune up guide' by Harold T. Glenn. Great read for the Volvo enthusiast...

[redcar]

Originally Posted by Clan

Have you retained your original Final drive ratio?
I fitted an OD gearbox to a 144 S a long time ago , it was fine in adding a cruising gear , but not very lively in OD .
If i remember correctly , the 120 ( and other ) series had a low axle ratio when OD was specified , so that the first 4 gears were lower making the car lively to drive but tiring driving with revs in 4th gear , hence the OD to give relaxed cruising .

Cheers Clan, I plan to keep my existing final drive.. A. Because I ain't going there, and b. I was hoping I might get longer legs adding the OD to it. Dunno if I will, but I can hope.

[swedishandgerman]

This is JUST personal taste and I have read many others who have loved their highly geared rear axle with an overdrive added. However, I found it too high and found that I was frequently switching the overdrive on and off on the hilly roads around here in Devon. I now have an 1800ES axle which is superb and suits the engine far better

All said, putting an overdrive underneath is the single most notable improvement I've done to the old car

[222s]

Adam, I know what you mean about the Devon hills! I suspect that on motorways, the higher geared axle would make more sense. However, for estates, as much as I'd like another gear on top of the o/d 4th, I would recommend against altering the diff ratio when fitting overdrive, as the lower first makes a big difference, e.g. hill starts when heavy laden.

(An estate without overdrive is utterly awful on motorways though, especially if twin carb, as 4th is far too low for high speed cruising)

[Burdekin]

Good tips. I have a sedan diff I was thinking of fitting but will see how the od goes with the estate diff first. Just need to get the od fixed and working.

[swedishandgerman]

Even on motorways, I am definitely finding that a few more revs with my 4.3:1 1800ES diff helps the old car battle along a little more strongly than when I had my 4.1:1 axle. It just suits the engine better altogether

It's better than the 4.56:1 axle in my opinion which is quite revvy through the gears, but more comfortable on the motorway. But the latter suits a twin carb and higher cam than my standard sleepy B20A

[Burdekin]

Just did some rough calcs to work out the different RPM at 70mph (112km/hr) for the different set-ups. I used a tyre diameter of 636mm which I think is what mine is off the top of my head and for ease of calculation I rounded up the circumference to 2m.

No OD fitted and 4th gear of 1:1 which is the M40
4.55:1 diff - 4245rpm
4.3:1 diff - 4012rpm
4.1:1 diff - 3825rpm

With D type OD 0.756:1
4.55:1 diff - 3209rpm
4.3:1 diff - 3033rpm
4.1:1 diff - 2891rpm

[phholden]

Gareth, I book marked this link when I was thinking about OD..it has a wiring diagram
http://volvoamazonpictures.se/guides...o%20Amazon.pdf
cheers
Paul

[redcar]

hey folks,

The weather is crap and i'm not scrabbling under the car in this sh*te, so i'm wondering if you can answer a quickie question..

i just dropped the propshaft (type III i think) in to get refurbed today and noticed the centre bearing has a rubber bushing type thing (ripped to shreds) over it.

i see the bearing can be bought separately, but what is the bush thing that goes over it? in the pic with the gearbox on the pallet, you can just about make it out

In the other pic, which shows my current support bracket. this is the only thing i think i need to take off my current shaft and place on to the new o/d shaft. it has the two little rubber grommets into the chassis for damping.

is there another something rubber between the bearing and the metal support i need to replace?

and is it possible to put this type I support on the type III centre bearing? and is it the same bearing?