hzj 105 1HZ R151 to H151 conversion

Submitted: Saturday, Jul 06, 2013 at 00:40
ThreadID: 103115 Views:39114 Replies:7 FollowUps:5
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I have just converted my HZJ 105 Land Cruiser from the notoriously weak R151 gearbox to the H151 box and thought I would post the details. There is a lot of good info on the subject on the Net but a lot of rubbish from armchair experts as well. I spent a lot of time researching so hopefully you won't have to. I have photos of the whole exercise but this forum wont let me post them, or I don't know how to do it.

If you tow a lot or have an aftermarket turbo fitted to your 1HZ the box will not last long. I know through sad experience. Even if you get yours rebuilt experts say you might only get 30,000 to 50,000k out of it and less if you are hard on it.

Materials:

1x gearbox (with gear lever) and transfer case from 78 or 79 series TURBO land cruiser (very important to get one from a turbo model as the non turbo 78 79 series has the same gearbox as you already have). Mine was from a 1HD FTE engine.
1x transfer case lever and linkage (also the associated bolts and bushes that hold it on) from 80 series
1 x clutch plate for FZJ 75 series Land Cruiser (not HZJ 75)
1 x 15 x 40mm sealed bearing (spigot). NACHI 15BC04S18SSU

The advantage in buying a 78 or 79 series gearbox and transfer is that the transfer case is already PART TIME 4WD like the one you have. If you get one from a petrol or GXL 100 series, most likely it will be a FULL TIME 4WD transfer case and you will have to modify it to part time at a cost of around $550 parts only.

Another advantage over an 80 series box is you can pick up a low km late model box from a 78 79 series in great shape. I did not want to go through all this trouble and find the old box out of an 80 series was worn.

I purchased a low km 2006 78 series H151 gearbox and transfer case from a TURBO model. The bell housing was the same so no need to swap. It bolts directly to the 1HZ. The input gearbox shaft on the H151 is a larger diameter than the R151 and has a larger pilot shaft (the tip of the gearbox input shaft that locates into the spigot bearing when assembled) so you need to replace the pilot/spigot bearing on the end of the crankshaft. The one in it for the R151 is 12mm inside diameter and 40mm outside. You need a 15mm inside and 40 outside (NACHI 15BC04S18SSU). The pilot shaft is a little longer on the H151 so I cut 5mm off the tip with an angle grinder (1mm fiber blade) to prevent it from hitting the crankshaft. You also need to chamfer the tip so it will locate easily into the bearing (google 'how to remove spigot bearing using grease' to show you how to get it out easily) . I think it would have cleared by 2mm but wanted to be safe so I cut the tip off.

You need to replace both gearbox and transfer as the output shaft from the H151 is to big for the input spline socket on the transfer case from the R151.

Clutch.

The shaft on the H151 box is a larger diameter and fewer teeth than the R151 so you have to replace the clutch plate.

There are two options. 1. Try and find (good luck) a flywheel from a factory turbo 1HDT and put it on in place of your old one (it will bolt straight on) and install a new clutch and pressure plate for a 1HDT (expensive). 2. keep your existing flywheel (have it resurfaced if it has grooves or is uneven), Keep your pressure plate if it is in good condition and purchase a clutch plate for a FZJ75 Land Cruiser (14 teeth, 275mm diameter). This clutch plate will slide right onto the H151 shaft and mate perfectly with your original 275mm pressure plate. If your pressure plate is worn, you will need to replace it with one for a HZJ105 (same as the original). I would also replace the thrust bearing (for 78 series TURBO Land Cruiser this time as you have changed the box) and rear engine oil seal while you are at it.

If you can get the 1HDT flywheel and clutch it is the better option as it is a larger diameter 300mm vs 275mm and so is better able to handle high loads.

Transfer case linkage

The lever from the 78 79 series is located on the side of the gearbox where yours is located on top and to the rear of the gearbox (so it won't work). The solution is simple. The transfer lever and linkage from an 80 series will fit onto the new H151 gearbox in exactly the right position (ask for the bolts and little bushes that go with it as well). The top of the H151 box has a place already for you to move the lever to. The transfer lever linkage will fit directly onto the new transfer case now.

You will need to alter switch positions on the gearbox and transfer case. I just move them to match where the existing ones were on the old transfer case. It is hard to describe without pictures (which I have of the whole process but this forum won't allow me to post pictures here). Put simply, look at your old transfer case and move the switches on the new case to the same positions as the old case. It is easy as the cases are the same to look at. Use your existing wiring loom and plug it into the same places as the old one. because the new box is twice the size, a couple of wires on top of the box are a little short and you may have to extend them. Mine were Ok, but tight.

You will need to transfer the cross member rubber mount from the R151 box to the H151 so it will fit the cross member.

I installed the box first and then the transfer case as it was to heavy to do both at once. Also, the new box is MUCH bigger and you may think as I did at first that it won't fit, but it does, you have to wriggle and jiggle it into position, but in the end it fits in fine.

Drive shafts fit perfectly with no mods.
Gear lever form your old box will not fit the new one so make sure you get one to suit the H151 box.

Make sure you get the right oil for the new box and transfer. Ask at you local auto store. It is not the same as the old 80 series box oil. It's an expensive full synthetic and takes 4litres Box and Transfer combined.

I now have a fantastic strong, easy shifting gearbox that I have full confidence in. The only drawback is I have gone from 2400RPM 5th gear at 100 Kmh to 2500Rpm. 1st 2nd and 3rd are similar and I actually like them better.

Good Luck, it is well worth the effort.

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Reply By: Member - MUZBRY(Vic) - Saturday, Jul 06, 2013 at 08:32

Saturday, Jul 06, 2013 at 08:32
Good morning .
If you want, you can send the pictures to me and i'll see if i can put them in for you.
muzbry@yahoo.com.au

Muzbry
Great place to be Mt Blue Rag 27/12/2012

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AnswerID: 514369

Reply By: rumpig - Saturday, Jul 06, 2013 at 08:47

Saturday, Jul 06, 2013 at 08:47
i have read many times of this "weak gearbox" in the 105 series vehicles, can't say i have had a problem with mine so far, i question who "the experts" are saying the boxes only last the klms you have quoted above. my vehicle was turbo'd and intercooled 6 years back, i tow a tradesmans trailer everyday for work aswell as i used to tow a caravan and now a camper trailer when we go on holidays....no issues to date. i tow in 5th gear regularly aswell, just knock back to 4th gear when a decent hill is coming so as not to labour the vehicle up the hills. i know i go against everything people read on the net about how you should drive and what the R151 boxes are like, but this is my daily driver and it works fine IMHO the way it is.
i'm not saying some people haven't damaged the boxes over the years, just saying i wouldn't rush out and change the box for the sake of it myself going on how mine has performed todate.
AnswerID: 514370

Follow Up By: Member - MUZBRY(Vic) - Saturday, Jul 06, 2013 at 08:56

Saturday, Jul 06, 2013 at 08:56
Good morning RumP
My sentiments exactly...
Muzbry
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FollowupID: 793354

Follow Up By: HZJ 105 - Saturday, Jul 06, 2013 at 17:52

Saturday, Jul 06, 2013 at 17:52
Hi, my name is Karl by the way. When my box went my first thought was to get it reconditioned, however after speaking to two leading manual transmission rebuild companies in South Australia and one in QLD specializing in 4WD transmission rebuilds I changed my mind. After telling them my problem (third gear dead and fifth not the best)for two of the companies, their first question to me was "have you put a turbo on it". the second question "how long ago".

To cut a long story short, the experts I referred to are professional transmission rebuilders who repair these boxes. Their advice is that the R151 is OK for naturally aspirated non turbo vehicles, but if you put a turbo on it and/or tow heavy loads a lot it might last as little as what I have stated above. If you do go down the rebuild the R151 track, then ASK THE REBUILD COMPANY ABOUT WARRANTY ON THE BOX IF YOU HAVE PUT A TURBO ON THE 1HZ AND/OR OFTEN TOW HEAVY LOADS. Those I spoke to would not give me one past the roller door of their workshop. But don't take my word for it, make some calls to the professionals.

I tow a trailer with carpentry tools around most days.

On the other side of the coin, I am glad yours is going fine and hope it keeps going for you. I posted the details of my R151 to H151 conversion in the hope of saving others the many hours of research I put in.

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FollowupID: 793388

Follow Up By: rumpig - Sunday, Jul 07, 2013 at 10:07

Sunday, Jul 07, 2013 at 10:07
Hi Karl
mate i'm not going to dispute that's what they've told you, just saying it's not my personel experience with this gearbox. i would certainly look at the option of changing the box should i possibly have a drama somewhere down the track (as i'll possibly do an engine swap in the future also), but i thought i'd put in my original post in to show those who might be concerned about their vehicle with the same gearbox, that it's not something they need to rush out and change out of fear that its about to fail on them.
cheers
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FollowupID: 793431

Follow Up By: HZJ 105 - Sunday, Jul 07, 2013 at 17:28

Sunday, Jul 07, 2013 at 17:28
Hi Rumpig, your argument is a fair one, I probably shouldn't have generalized my comments to all R151's. Like yours, I am sure there are many R151's going fine and if it aint broke, why fix it. I too would like to change the engine to 1HD FTE but at 10k for the bits, It will have to wait.

On another note, there is one significant error I made in the conversion description. Probably because I wrote it at midnight.
You do need to get the bell housing with the new gearbox/transfer case as the gearbox end of the R151 bell housing is the wrong size for the H151 gearbox. The front faces are the same though.
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FollowupID: 793457

Reply By: Member - PJR (NSW) - Saturday, Jul 06, 2013 at 08:51

Saturday, Jul 06, 2013 at 08:51
Good post what ever you name is.

A few (shhh decades back) I changed the box in a Kin.....d to a different model and it took weeks to get all the information, specifications and parts together. I can just imagine it these days. There is more to it than I did. That post mate should save anyone wishing to do the same a whole bunch of headaches.

Good post

Phil
AnswerID: 514371

Reply By: pop2jocem - Saturday, Jul 06, 2013 at 11:02

Saturday, Jul 06, 2013 at 11:02
Good post HZJ 75.

Just a suggestion with the flywheel. The original flywheel can have the PCD for the 300 mm pressure plate bolts and dowels machined to suit. The flywheels are the same outside diameter so machining is possible.
I fitted a H151 box to my 75 series when I replaced the old 1HZ with a 1HD-FT ex a wrecked 1997 80 series. The box and flywheel are from a 2003 1HD-FTE ute. I got the flywheel with gearbox but could have used the original and machined it for the larger clutch.
Mine being a 75 the transfer lever was pretty close to the right location but as you have noted needs changing if using that box for a wagon.
As you said, a lot easier with piccies. I think you have to be a member to post them, not sure.

Cheers
Pop
AnswerID: 514380

Reply By: fisho64 - Saturday, Jul 06, 2013 at 11:56

Saturday, Jul 06, 2013 at 11:56
top post mate, one that will be referred back to by many people in the future.
AnswerID: 514382

Reply By: Member - DingoBlue(WA) - Saturday, Jul 06, 2013 at 18:29

Saturday, Jul 06, 2013 at 18:29
Can purchase a brand new box and clutch for the 105 for $2600 incl gst. Why would you bother rebuilding or replacing with another box?
Rather a bottle in front of me than a frontal lobotomy!

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AnswerID: 514396

Follow Up By: fisho64 - Monday, Jul 08, 2013 at 02:22

Monday, Jul 08, 2013 at 02:22
if your box has failed, why would you bother to spend $2600 on another that wasnt strong enough in the first place?
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FollowupID: 793497

Reply By: Member - Phil G (SA) - Saturday, Jul 06, 2013 at 19:29

Saturday, Jul 06, 2013 at 19:29
Nice writeup Karl and well worth doing if you plan on keeping the vehicle a long time.
Almost seems a shame to take the gearbox and leave the 1HD-FTE back at the wreckers!
I'm guessing you may have already seen the 5 page "sticky" on LCOOL for the H150/H151 conversion, which might be useful for those going the same way:
http://www.lcool.org/forum/viewtopic.php?t=11641&postdays=0&postorder=asc&start=0

Cheers
Phil
AnswerID: 514400

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