D series ford

Hi everyone My name is Lawrie O'neil . I have aquired a D series ford 1974 with 380 motor 6 speed box 2 speed eaton ex masters in perth . . On the diff pinion shaft is 6 / 39 for the number of teeth can anyone tell me the ratio.
I drove the truck and all I can get out of it is 65 kph . with motor screeming. Is there another diff centre that can be fitted to get a bit more
Cheers Lawrie

G'day Lawrie,

Mate 6 pinion teeth
39 Crown wheel teeth

39 divided by 6 =6.5:1

Pretty sure that would be the low range of the 2 speed Diff.

I've got a D series workshop manual
,If you like I'll dig it out & see what I can find out for you.

Goodc luck

Lawrie

Mate - there is a few things in there that don't add up (I reckon).

In simple terms - if the motor is going flat out (Screaming), and your are in top gear, and the diff is in high range (assuming the ratio of 6.5:1 is low range), and it has 9.00 or 10.00 tyres on it - then you HAVE TO be doing more than 65kph.

Trust me - that is simply not possible for it to be anything else but that.

So - you need to confirm the engine is in fact running out to max RPM.

From memory - D Series werent fitted with the combination of a 6 speed box and a 2 speed diff. (I stand correcting on that one). However - assuming I am correct - then that would suggest your diff is not standard.

If that is correct - then has the normal 2 speed diff change over unit been fitted to the speedo?. Conversley - even if the difff is standard - then that speedo change over unit may not be working - hence showing an inaccurate speedo reading. IE: the speedo needle should flick/jump when you change diff ranges. So that all needs confirming.

The first thing I would do - is get someone to pace you in another vehicle - and compare speedo readings. Although you should be able to judge wheter you are only doing 65kph or some where near that without needing a pace car. But do it anyway as part of the elimination process.

The whole thing is a mathamatical excercise. Engine revs (RPM) X by top gear ratio (1:1 with a 6 speed) divided by the diff ratio (the high range ratio / which should be something like 4.8:1) X the tyre circ (in metres) all applied to 1,000 mtrs over so many minutes (RPM).

Sorry I can't make it any more easier to read/understand than that. So if there is a part of my rambling that you don't understand - then please ask.

Oldfulla

I had my car follow me and it peeked at 65kph with 2600 on the rev counter and it does go in hi range
Thanks Lawrie

If the diff is like the one in my Inter the high speed is around 6.54:1 and the low is 8.80 so it is possible that the ratio given is the high speed one. My Inter cruises at around 85-90km/h and the mathematical maximum speed (at 3600 rpm) is around 98 km/h (which it will do on a down-hill run). That is on 8.25-20 tyres.

What size tyres are on the D-Series? It is also possible that if the diff was swapped at some time the drive gear for the speedo (in the gearbox) wasn't so the speedo isn't showing the correct speed.

My XP Ute had that problem. It had the ute rear end (4:1 ) but the speedo read 60mph while covering the ground at 80 km/h. The diff died so I put a 3.5 centre in it and it now reads 60 mph at a fraction over 90 km/h.

So if your diff and speedo drive are mismatched that will put your speedo out.
(edit - written at the same time as the post above)

Gday Lawrie
Just did thet calcs on the specs you provided..
Based on
gearbox 1:1
diff ratio of 6.5:1
rpm 2600
tyres 22.5" (app 498 revs per mile)
( i realise the d series wont be running 22.5's, i used this size for the exercise)

app 77 kph (app 48mph)

so ya wont be far out.....

hope that helps?

chocs

Tyre size 900x20
Lawrie

just over 70kmh would be top speed .. thats sad

G'day Lawrie, great to see you on here, mate, and thanks for the PM last night. Hope you and the family are well.

Sounds like everything is working well even if it is a bit slow. Hope you can find something faster to put under her.

Lawrie & All

I had a fiar bit to do with the D Series Ford truck range back in the times of when trucks like Lawries were new.

Firstly a correction/confirmation re my prev posting.

The 6 to 39 (6.5:1) diff ratio would be in high range and hence make my guess of 4.8ish in high totally incorrect - if the 6.5 was the low range ratio as suggested by someone else. The diff has only one crown & pinion and high range within the 2 speed system is there for a 1:1 ratio.

2ndly - I agree (in principle) with Chocs calculations, however it would be good to see it re done using the 9.00x20 tyre circ. So Lawrie is it possible to measure the rolling circ of one of your drive tyres? Of course - a re cal will in fact reduce the Chocs cal (using the 22.5 tyre circ).

3rdly - can anyone confirm the max RPM of a 380 motor is 2600RPM?

In my experience I have never seen a production D series being geared this slow. And therefore reiterate my prev statment of "there is something wrong' with this vehicle.

I wonder if it has had a diff transplant from a petrol motored vehicle? Lawrie - is there any reference to diff ratio on the complience plate?

I hope that helps to take you in a direction that assists in solving your speed (lack of) issue.

Oldfulla