What RPM @ 100km/h should I expect from an auto Bay?

ratty 63 Custom Title Time!

1,083 posts · joined Oct 2003 · 27 Sep 2009, 10:49 pm

#737722

Hi all,

I finally fitted a tacho to my '78 Auto Bay Kombi (Ex-army) that I have owned for about a year and I think I have discovered why it sounds like it is screaming at 100km/h in comparason with my Brothers '75 Manual Bay Kombi - because it is!

My Tacho shows 4000 RPM @ 100km/h, whilst my Brothers Tacho shows just below 3200 RPM at the same speed.

Now I did expect some difference between the auto and the manual, but is this too much?

Does anyone else have an auto Bay Kombi (2 liter) with stock rims and tyres that has a tacho fitted? What RPM does yours run at 100km/h?

R 🙂

40hp, 6V and ...er... slowly making improvements 😂

It's nice to be important, but it's more important to be nice!

Founding member of the Gold Coast Dub Club Inc. 🙂

dangerous 23 Windows of Awesome

5,901 posts · joined Jan 2005 · 28 Sep 2009, 6:03 am

#737740

Final drive ratio should be 4.09.(NG for late bay or NH code for vanagon)
Most convertors should have a little slippage,
but without factoring this in,
it should equate to 3414 rpm with around a 25" tyre....but 4000 sounds like it is an earlier trans.
Stock 091 bus trans manual trans would be: 4.03=3364rpm.

Earlier bus auto trans have a lower ratio of 4.45 and thus higher rpm,
and the later vanagon trans may be taller, but my book says the 1982 onwards still has the 4.09 ratio.

The 4.45 ratio would be 3708rpm at 100 with a 25" tyre.
Perhaps your tyre is lower diameter than 25"?

westi wrote:That's mad Alan.

ratty 63 Custom Title Time!

1,083 posts · joined Oct 2003 · 28 Sep 2009, 9:00 am

#737760

dangerous wrote:Final drive ratio should be 4.09.(NG for late bay or NH code for vanagon)
Most convertors should have a little slippage,
but without factoring this in,
it should equate to 3414 rpm with around a 25" tyre....but 4000 sounds like it is an earlier trans.
Stock 091 bus trans manual trans would be: 4.03=3364rpm.

Earlier bus auto trans have a lower ratio of 4.45 and thus higher rpm,
and the later vanagon trans may be taller, but my book says the 1982 onwards still has the 4.09 ratio.

The 4.45 ratio would be 3708rpm at 100 with a 25" tyre.
Perhaps your tyre is lower diameter than 25"?

Hi Dave,

Thanks for your reply - that is some interesting info.

Assuming that the Tachos are not 100% accurate it still sounds like I have an early trans in mine .... except it looks like a late trans to me (but I'm no expert). Is it possible to fit parts from the earlier trans in a late case? Would changing the diff, perhaps from an earlier auto, cause this sort of change in RPM?

I'm just wondering if, just like the mechanicals in the rest of the van, someone stuffed the diff or auto in the past and have done a cheap as possible rebuild/repair to get it moving again .... or, did the Army order their vans with a different diff/auto to better suit their needs? Stranger things have happened.

It is fitted with stock 14" rims with new light truck tyres, which, according to me (measured before coffee this morning) measure a fraction over 25".

Perhaps it is time to consider a rebuild on the auto to sort this problem out....

R 🙂

40hp, 6V and ...er... slowly making improvements 😂

It's nice to be important, but it's more important to be nice!

Founding member of the Gold Coast Dub Club Inc. 🙂