Noisy cruising ex-Army 1.7 diesel

[lowtimeppl]

Hi all
My new acquisition is an LHD ex-German Army 1.7D (non turbo) and the 4th gear is (from what I have gathered) designed for towing and rough roads - so at 50mph it runs out of puff a bit, but mainly I’m struggling to hear myself think. Having said that, the bus has no interior at present so that won’t help the volume.
I have asked various Claude various questions and it advises a gearbox swap but is not super specific about which one to seek out; or to have some surgery to replace the upper gear(s).
The gearbox is an ABF code. I have standard 14 inch wheels.
At some point would like to fit 15” wheels of a particular type, so whatever I do now with the gearbox should be compatible with changing the wheels and potentially lowering 30mm. I’m not looking for miracles of 70mph, I know that’s not going to happen, but I’d like reduce the rpm and the noise.
I am trying to run theoretical numbers from the various websites and calculators but I am also looking for real-world lived experiences.
Thanks for any input.
Rob.

[mioba]

An empty panel van is a very noisy van.
expecting 70mph is a joke esp for cruising speeds. 55-60 is the sweet spot.
You might well be better replacing the engine with a better lump if its performance you want.

[lowtimeppl]

I explicitly stated I wasn’t looking for 70mph and that I was looking to cut down the screaming. It’s not a panel van, I never said it was. It has factory windows, I said ‘bus’.

[silverbullet]

Bus and van are pretty much interchangeable terms but anyway...not everyone appreciates that the Bundeswehr used Caravelle type minibus vehicles as well as kombis.

Asking some LLM bot about a specialist topic like this us a waste of time, human experience is the best tool even if it can be somewhat subjective.

Do you need to keep it as a diesel? A 2 litre 8v petrol will give similar mpg afaik, be happier with the gearing (3.5-4k light throttle cruising on motorway) pretty much a direct swap, a lot smoother and quieter if you get the exhaust right (long downpipes around 42-45mm)

More recent engines are also a more costly option because of the architectural changes but if its based on the EA827 block with the oil pump bulge and jackshaft to drive the dissy/vacuum pump it bolts up VW Lego style.

HTH

[Aidan]

If you are keeping the engine then any of the diesel water cooled era (1983 model year on) 4 speed gearboxes apart from the ABH and ABS (1.6 TD 4 speeds) will work - going to a 5.83 or 5.86 final drive will mean it will cope with larger tyres (15" rims do not necessarily mean larger diameter tyres, I have 205/65/15 tyres which are actually slightly smaller diameter than stock and it runs on -30mm springs)
With the original engine you will struggle to pull longer gearing/reduce revs, the 1.7s were geared to keep up round town with traffic, be quick up through the gears using the torque but don't have the power to do much more than 55mph especially when loaded up (or towing)
Without stripping the box it is not possible to know why it is so noisy, it could be wear to the 4th gearset, wear to main bearings or wear to crown and pinion, chances are it has been neglected and run hard with old oil or the wrong oil.

USEFUL GEARBOX CODE INFORMATION

[lowtimeppl]

Thanks both. I wasn’t being snarky in my first response just clarifying.

Yep asking AI was just curiosity really to see when it came up with. A lot of it sounded sensible and lot cited this forum as sources. Anyway…

Engine swap to a petrol sounds interesting in theory, I don’t have a workshop or extensive tools, or the facilities to fabricate an exhaust, the mounts etc. and I wouldn’t know what engine would be the right one to use? The bus is actually my daily driver so downtime is a consideration.

The noise is the engine high revving, not so much transmission noises. I just want to to be revving lower whilst pootling along at 55 than it does now, howling in protest.
It’s 55k original miles in fantastic condition, never needed any welding, except for one tiny spot beneath one of the side windows. Absolutely solid underneath. Been used mainly at shows etc.
Thanks for the useful information, I will research compatible gearbox codes, as that seems to be the least painful swap.

[mioba]

Have you checked your rpm at idle. Iirc It should be about 850.

To reduce the noise. Insulation. Closed cell and fibre insulation.

[silverbullet]

The original T3 diesels were sourced from the contemporary fwd VW car range, basically the JX is a Mk2 Golf td engine.
So essentially if the donor car petrol engine is a transverse installation, thats the one that will use the same pickup points for the T3 inline engine mounts, bars, the coolant hoses will match up because thats what they are designed to match and the sump will fit.
Broadly speaking.
With experienced helping hands and some thorough prep its doable in a weekend but ypu will need access to an engine crane, trolley jack, wheel ramps etc

[lowtimeppl]

Have you checked your rpm at idle. Iirc It should be about 850.

To reduce the noise. Insulation. Closed cell and fibre insulation.

Good idea, that's in the plan for the volume, now just need to slow the rpm at speed. Ta.
 

[Aidan]

only way to reduce the revs is to have an engine that produces more power at lower revs
VW (et al) went TDi, clever fuel injection direct into combustion chamber with a turbo to give it the air to burn more fuel more efficiently
And mate that to a gearbox with more ratios closer together so the engine is always in its happy spot
there is no simple cheap shortcut that magically makes a 70s/80s technology vehicle drive like a 2000s one - and it is cheaper to buy a T5 that already has that technology if that is what you want
as the Irish saying goes " if you want to get to there, then I wouldn't be starting from here"