Diff Info

[mezzmo]

Hey fellow Bedowines!

I need some information on Diff ratios's please. My 76 has a 173 or 179 (not sure which) and 3 speed auto, the motor is strong, the tranny is solid but my god is it sluggish and screams in top gear!! Question:: has anyone any information as to what ratio i would need to quiet down and substantially reduce the top end high revs and what would i sacrifice with the replacement - as the theory goes - every action has a reaction! but i cant imagine it could be any worse than what i have.

I have actually purchased a VN to do a transplant to a V6, but to be honest, i would be perfectly happy to retain the old red if i can fix this issue.

All help greatly appreciated - (also please keep in mind that i dont possess an ounce of mechanical ability so please explain in english if possible!!!)

Mezz

[Warren]

Mezz

Basiclly the diff ratio is a number that represents the number of revolutions (turns) the tail shaft (and thus motor) has to spin to turn the wheel one full turn.

Bedfords origanally came with a high ratio diff 4.2:1 that was good for round town weight carrying in England. Not really designed for Oz conditions.

Common ratios for beddys and holdens in Oz are aprox 3.5:1, 3.25, 3.08:1 2.75:1, you often see these refered to as Highway diffs.

In your situation it seems you more than likely have a original ratio diff (4.2:1).

You can either get the diff center replaced with a different crown wheel and pinion or find a replacement diff.

If you do a search on this site there are quite a few threads on Diff ratio's.

Try looking at This One for a start.

Note that these ratio numbers are from memory, and may not be 100% correct, but you should get the idea.


Warren



 

[mezzmo]

Cheers Warren - really helpful info on that link.

[Bas NZ]

Mezz, have found the 3.5 to be the best behind a 202 the cresta gears fits straight into the centre of the beddy centre if you can get hold of one the Auto cresta has the 3.5 gears only, it is a easy swap even to line up the gears is no problem with a bit of grease on the teeth. For a 179 or 186 I have a mate that has a 3.7 diff this is dead right for this size motor. If you are lucky enough to pick up a trimatic 3 speed with overdrive on it as I did the standard 4.2 (or what ever it is) Bedford diff is just right.

[JOE RYAN]

Mezz

I have a 186 with a 3speed trimatic and I installed a hz diff with a ration of 3.5. I had the diff in before I converted to auto. Installing the auto added about an extra 300 rpm at 100 klm,at present at 100 klm revs are 3100 rpm. Still seems to be screeming too much for my liking

Joe

[restoreid]

Hi Joe what size tyres do you have & what is the overall diameter cheers Reid

[Bas NZ]

Reid, good question, never gave the tyre size a thought but must play a big part, glad to see someone is with it. I run 15s on back and now that I think of it it did make a big differance.

[ben]

Installing the auto added about an extra 300 rpm at 100 klm

hey joe.. the final drive on both gearboxes are the same ratio so it should not have altered your revs at 100km.. only thing i can think of is that the speedo gear ratio is different and your tacho reads differently.. is this possible? cause different final drive is same for both trimatic and 3 speed.

ben

[hotrod]

Been a few year since I put a tacho on
 but they are electronic and work off the motor nothing to do with speedo drive


Plus there is this

http://www.sciforums.com/Manual-Transmission-power-loss-vs-Auto-t-43079.html

[ben]

Been a few year since I put a tacho on
 but they are electronic and work off the motor nothing to do with speedo drive Huh Huh Huh

oh yeh duh!! that was really silly..

anyway the article explians that autos suck more power than manuals.. but how does that effect your engine revs at 100 clicks?

my van still does 3000 revs at 100 after ive done 200,000 + kms on the motor.. fair bit more tired and loss of power but still same amount of revs as when i first got her..

ben