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1974 Mk1 175 LWB tranny roulette

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1974 Mk1 175 LWB tranny roulette

Postby gromsound » Mon Jul 31, 2017 5:07 pm

Hi transitfriends, here's my second posting :D
After a long night of reading here i think the following conversion plan is feasable. Could you please comment?

i'm looking at a 1974 mk1 LWB double wheels bullnose horsebox (originally a flatbed truck), that already has been fitted long ago with a 205 OHC petrol engine (carb and conventional ignition). Runs fine but the gearbox is RIP -deafening howling in drive, relatively silent in coasting- and also the total reduction incl rear axle is way too high for my use. The thing barely gets to 80 km/h (sorry no mph on this speedo). I need at least 95 km/h (of course without the horsebox that will be removed).

Now i suggested to the seller to put in a 5 speed box to cure two problems in one go (he did that before with his own ex german firebrigade van). And later on we can see whether the final drive has to be changed to a lower ratio, might work with the 5 box replacement only. I have read that the transmission shaft needs to be shortened and balanced, but does the rest fit together? (of course i know about the gear lever position and extra cross member, thats peanuts).

Anyone who can confirm that this is possible? maybe have experience with this combination regarding speed?

thanx in advance,
Andre.
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Re: 1974 Mk1 175 LWB tranny roulette

Postby conrod » Mon Jul 31, 2017 9:14 pm

HI Andre, several options here, all fairly easy.

You could find an overdrive box, bellhousing and crossmember for a Pinto. This is a 4 speed gearbox , with Laycock overdrive bolted on the back. They were an option, and are around, but a bit rare. These give 22% reduction in engine revs, which should hit your target speed.

Another option is the Ford "type 9" 5 speed box. Ultimately not as strong as the combination above, but should be okay behind a Pinto. Best one would be from an early Mk3 Transit (1986-88 I think) as it puts the gearlever in the right place for a Transit. These have a 0.83 top gear from memory, so not as big a step as the overdrive box, but should put you in the ballpark anyway. Would need a custom crossmember and propshaft work.

Third option is the MT75 5 spd box from a petrol Transit. Needs to be from a 2.0 (or possibly a late 2.3??) Really good box, and plenty of info on here about them as many have done this conversion. Similar top gear ratio as the type 9 box. Would also need a custom crossmember and propshaft work.

Tallest rear axle ratio for the dual rear wheel axle is 4.63:1, which with an overdrive or 5 speed box will give you a fairly relaxed 100kph cruising speed at around 3200 rpm.


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Re: 1974 Mk1 175 LWB tranny roulette

Postby gromsound » Tue Aug 01, 2017 4:58 pm

Hi Conr(o/a)d, thanx a lot for the complete info!

Yep i found the mt75 route on your forum, seems the way to go here. Do you think if i fit the low ratio diff (4.63?) i would still be ok in 3d or 4th when hauling loads? I plan to use it as a car transporter for my light classics, max weight 825 kg. If the present high ratio diff (5.83?) would be better or stronger but still gave me 95-100 kph speed i might as well leave it in place.

thanx for your advice :D
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