BJ40 4 Speed to 5 Speed Conversion (1 Viewer)

[OffRoad911]

Would like to hear from anyone who has successfully completed a 4-speed gearbox conversion into a 5-speed gearbox.
If so, what was the improvement and are there any long term issues with any of the components used to align the system?.
What speed difference has been noted on the B Type Diesel engine?

 

[bikersmurf]

You might be better off posting in the diesel forum. I can’t comment much on a diesel or a five speed.

What I do know. You’ll need to massage the floor a bit to clear the 5 speed. If it’s from a 60 series, the hole through the tunnel is further back.

 

[Disasterman]

I have a 3B in a ‘74 with a 5 speed. Although I didn’t do the build I can tell you that highway driving 60-75 is comfortable if the rest of your chassis is Squared away. Floor mod is a must.

 

[robstar]

I believe you can achieve similar results by changing the final gear ratios of both the front
and rear differentials. For example, if the original final gear ratio was 4.1, go to 3.7.

 

[bikersmurf]

I believe you can achieve similar results by changing the final gear ratios of both the front
and rear differentials. For example, if the original final gear ratio was 4.1, go to 3.7.

The combination of 33s & 3.70s will turn 4th into a nice overdrive. I really like it with a SBC and don’t miss the gearing increase at low speed a bit. It does make starting off in third harder though.

 

[John in Utah]

The combination of 33s & 3.70s will turn 4th into a nice overdrive. I really like it with a SBC and don’t miss the gearing increase at low speed a bit. It does make starting off in third harder though.

You might miss that gearing with a B engine though. I really like the combo of 31s & 4.11 with a 5 speed, 4th gear will still climb well at 55 mph @3k rpms. Maybe the combo of turbo & big tires is easier/cheaper than a 5 speed swap?

 

[Splangy]

The combination of 33s & 3.70s will turn 4th into a nice overdrive. I really like it with a SBC and don’t miss the gearing increase at low speed a bit. It does make starting off in third harder though.

You can get away with that a lot easier with a SBC than he’s going to with a 90hp B engine.

The 5th gear is really nice with a turbo, but you may not get much use out of it without a turbo if you live in the hills.

 

[gerg]

Turbo makes everything better! Gears don't replace horsepower unfortunately.
Turbo, 3.7S and 5spd makes for a very nice Hwy vehicle.

 

[John in Utah]

Don’t tempt me @gerg. I’ve had my eye on your turbo kit for awhile now

 

[gerg]

Bahh! I'm a bad salesman. Not trying to tempt anybody, sorry for that. Tires are by far the biggest bang for your buck to make it driveable. Ive never done a gear swap but I'm thinking 3.7s are cheaper all in all than a 5spd? Could just do 60 series axle swap at the same time? People do that I'm learning. I just got a bj40 few weeks ago so I'm a bit behind on the cool 40 things to do.

 

[OffRoad911]

Bahh! I'm a bad salesman. Not trying to tempt anybody, sorry for that. Tires are by far the biggest bang for your buck to make it driveable. Ive never done a gear swap but I'm thinking 3.7s are cheaper all in all than a 5spd? Could just do 60 series axle swap at the same time? People do that I'm learning. I just got a bj40 few weeks ago so I'm a bit behind on the cool 40 things to do.

I like this solution too.

 

[Casey E]

I run 3.7 gears 2F and a 5spd in my daily driver and love it, I know not a diesel but still an awesome upgrade.

 

[OffRoad911]

Is the Diesel engine that bad? Is it that slow that mating it with a 5 speed won’t help? I have driven a 4 speed and the maximum I achieved was 50mph. The vehicle started loosing its power and speed while climbing too. I put it down to an old tired engine but not sure if an overhaul of the engine would have made any difference.

 

[David70FJ40]

1970 FJ40, stock rear gears, 4:11 I believe, installed the H55 two years ago and it made a world of difference. On the straight and somewhat level I can keep up with traffic, hills are a bit of a problem but I can usually get by in 4th. Along with power steering and the disc brakes, the H55 is money well spent!

 

[Splangy]

Is the Diesel engine that bad? Is it that slow that mating it with a 5 speed won’t help? I have driven a 4 speed and the maximum I achieved was 50mph. The vehicle started loosing its power and speed while climbing too. I put it down to an old tired engine but not sure if an overhaul of the engine would have made any difference.

Is it because you're too high in the RPM range or because you're running out of power? The 5th gear is only going to help keep your revs lower. If you don't have enough power to get past 50mph then shifting to 5th will only make it worse.

 

[Varty Yo]

TURBO!!!!!!

 

[OffRoad911]

Is there a good 40 series mechanic in the North West, UK? Someone who can add on a Turbo and help with a new suspension kit?

 

[OffRoad911]

Is it because you're too high in the RPM range or because you're running out of power? The 5th gear is only going to help keep your revs lower. If you don't have enough power to get past 50mph then shifting to 5th will only make it worse.

Yes, I get that. I know it will help reduce engine noise and probably add a little speed. My experience driving a friends BJ40 wasn't that good. His BJ bottomed out at around 50mph and getting it to go any faster was a struggle. Not had the pleasure of driving a very good BJ40 with a decent engine. Mine, is still sitting far away in Sunny Pakistan and waiting to have its hard top conversion, H55f fitted and also all the AC/Heater pipework redone.

 

[OffRoad911]

A quick update, picked up a used H55f today and the workshop is busy overhauling the gearbox. Will appreciate if you guys can suggest if I should make any other alterations to the gearing.

 

[Splangy]

Alterations to what gearing? The trans and transfer? Not much you can alter besides a low range kit for the transfer. If you meant the final drive ratio, that’s going to depend on your tire size and anticipated driving style/speed. For example, 3:70’s and bigger tires can make that 90hp engine feel even more sluggish than it already is.

Unless you live in a very flat area, I’d start looking for a turbo if you want to use that 5th gear much.