4.11s to 3.73s

[torqueluvr]

So I've been reading much on swapping out gears lately. I have an 87 JDM BJ74 auto, which I think is the A440F. The gearing on this tranny blows. Plus i'm running 31s and plan to put on 33s in the future. Right now, the gearing is gross. Overdrive kicks in at 65 km/h in the city and it bogs really bad.

Now I would like to, if the funds permitted, switch to a H55F, but theres no way I could afford it. So my other option is to re-gear the Cruiser. Now, if my math is right with smaller gears I can run bigger tires without the RPMs completely bogging down, correct?

And, if I do switch from 4.11s (Im pretty sure thats what my truck has, how do I check?) to 3.73s, is this just changing the gears in the diffs? Or is it tranny work?

Also, I've heard of some people running 3.08 Marks gears from John at Radd, that's quite a low ratio.

Info on switching gears and the mechanics would be great. Also, can I buy 3.73s new? How much? Can I find used? Where? How much?

Thanks boys.

TP

edit: I think my math is backwards. I need to go the other way in gear ratios to have better low and power right? And my 13BT is ugly sluggish in first. ANyone else with a 13BT auto and 31s have the same problem?

 

[PhrogsPhorever]

What year truck? Regular or HP front?

 

[torqueluvr]

my first post indicated its an 87. What do you mean by HP front? The truck is stock.

 

[PhrogsPhorever]

Oops

You should have 4:11s on an '87.

As far as the front, I was referring to a high pinion diffrential, like the 80 series, has the 8" gears vice the 9.5" which are a little harder to find in the flavor you might want. But, you should be Ok as I think they went to the HP front diff in 90, or 91. I think a set of late model 40 or 60 Series thirds with the gearing you want would work also, pretty sure same spline count. Not 100% though, still learning on the 70 series.

For the DIY, the FSM should suffice for instructions for swapping the gears, not too difficult. Just need the tools and the time. And I'm sure for a few the guys in your local club would hook a brother up and hep you with the re-build.

 

[Whistler74]

You caught yourself: as you said your math was backwards. You probably would want 4:56 gears to raise the rpm and stay in the powerband.

I have 32" tires and yes, the gearing sucks. Much more driveable with 29" diameter which is closer to stock. I haven't figured out the best way yet but it won't be cheap - diffs, Marks, or H55 will all be a sizeable chunk of cash.

In the meantime, when you're driving around under 80kmh keep it in third to avoid the drop into OD. Some very knowledgeable people here recommend an Extreme Valve Body (again, $$$) but I have no personal experience.

Hope to hear what you decide - good luck.

 

[ForealBoreal]

put 255/85/16s on it and leave it.
Its a land cruiser not a subaru.

 

[Radd Cruisers]

The autos are indeed a dog with the tall overdrive and the stock 4.11s. I think a move to 4.56s would be quite a good one, and you would get back a lot of what you have lost... but really, 31" tires (if they even measure 31" tall) are pretty small in the scheme of things.

I'm running 255s on mine and that's much taller than what you have at a true 33.3" tall.

Mark's underdrive gears will give you about an 8% change in gearing - or put another way - it would turn your 4.11s into effectively 4.439s - which might make just the kind if difference you're looking for.

Or, put another way, it would make your 31s feel more like a set of 28.5s...

And you would get lower t'case gears in the deal as well (along with some gear whine).

~John

 

[Tapage]

I would put more 4.56 than marks underdrive gears .. coz that would be a lot of reduction for ya in low .. dunno if you really need coz marks gears are not cheap at all ..

Anycase and to be honest I don't think you really need re gear a 4.11 Cruiser with 13BT engine on it .. or your tranny it's just plain wasting too much powa from your engine ..

 

[torqueluvr]

Thanks for all the advice. My 13BT isn't near as strong as it should be I think. Its really slow and it really bogs. I'm working on the turbo (boost controller, boost gauge and pyro) in the coming weeks. Next would be maybe a valve adjustment and an injector rebuild (285000 km, 100000km of that on veggie by the previous owner). I'll keep you all posted. All your input is great. Thanks again guys.

TP

 

[crushers]

do a compression test and see what the results are.
change the fuel filter and see if any change.
are you still running veggie or straight diesel?
run some injector cleaner through and see if that helps.

i would start cheap and work up.

 

[torqueluvr]

Hey Crushers.

The veggie is on the backburner right now as I need to replace a pollack valve; its been on straight diesel for 6 months now. I'll run some injector cleaner through it tomorrow. I've heard prices on testing injectors, are they difficult to remove yourself? If I could save a couple hun taking them out myself, I'll do it.

 

[crushers]

nah, if you can change a spark plug then you can pull an injector, just be careful of the fuel return rail nuts. sometimes they can be on so tight they twist the rail. that rail is obsolete now so be careful.