Trimatic overdrive

**Puzzigully** · 03-01-2019, 06:38 PM

Hi,

has anyone heard of an overdrive for a Trimatic?
I'm not talking about the gearvendor ones..

Web search pops up volvos fitted with trimatics with overdrive and a "laycock" conversion..

I dont want to change the transmission to a T400/700 etc

any pointers welcomed

**HXsman** · 03-01-2019, 09:25 PM

Interested too, what diff ratio are you running Russ ?

**Kiwivan** · 04-01-2019, 06:11 PM

Have been thinking changing to an auto box in the future

Cheers Kiwivan

**Puzzigully** · 05-01-2019, 07:15 PM

I'm pretty sure it's a 3.55 (or similar) as I'm spinning over 3,000 rpm at 100 km/h
I need to confirm exactly.

The other option that I can see you're alluding to, is to swap out the diff ratio to a 2.78 or similar.

That's certainly on the cards, but thought I'd like to explore the O/D option so I keep the "traffic light" acceleration ;)

I can see that it's been talked about, but not been able to find any detailed info of who/where sells it.

Worst case, i just change diff ratio.....certainly cheaper than a Gear Vendors unit!!! lol

**Sandaro** · 05-01-2019, 10:04 PM

Had use of a MGB at one stage, that had a laycock overdrive unit I believe, electronically operated by the flick of a toggle switch.

Just googled and Overdrive spares in UK are doing Laycocks for all types of cars (Aston Martins, Rolls etg) so should be strong enough to handle. Maybe an idea to email them direct for an idea of cost and size of tunnel needed.

They are a separate unit that I imagine could be mounted to back of gearbox or even in front of diff, either way with short connecting shaft and modified tailshaft for rest

**Valencia** · 05-01-2019, 10:41 PM

Try a 3.08 ratio best of both words imho

**Puzzigully** · 06-01-2019, 04:24 PM

What tyre size are you running with the 3.08?
With that combo, what rpm are you getting at 100 km/h?

Thanks

**Dr Terry** · 06-01-2019, 05:16 PM

GM did make a 4-sp version of the Trimatic but it wasn't fitted to Holdens sold in Australia. It was used in a few export versions.

It was however seen in many BMWs sold here during the 90s.

The GM name for it was the 4L30 (there was also a 4L30E electronic control type).

My guess is that you would need to make a new bell housing using the front half of a Holden unit
& the rear half of a BMW unit.

Dr Terry