Fitting an auto trans behind the Perkins in the Ok

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01 Nov 2012 14:53 #1 by dandjcr
dandjcr created the topic: Fitting an auto trans behind the Perkins in the Ok
Forum Home > On the Road > Fitting an auto trans behind the Perkins in the Oka.

Peter & Sandra James Oka 374
Member
Posts: 412
In response to a few queries I'll post the basic details here but I have written an in depth document which I'll put up as a document that can be downloaded.
I was pretty happy with the way the Perkins goes, it suits the truck and we're in no great rush these days anyway plus 374 has only done 98,000km so is only just run in.
But I really hated the Rockwell transfer case with its noise, heat and that useless handbrake configuration. The Spicer gearbox wasn't far behind either despite 374 being on its third gearbox in under 100k, the current one had only done 40k. The biggest problem was though that after driving an auto in the Humvee for the last 9 years I was over changing gears for good. Initial inquiries revealed that an early Allison auto would bolt straight up but only had 3 gears and no overdrive or torque converter lockup so that wasn't on. Then Pete Furlong found an adapter in the US that allowed a GM auto to be bolted to the back of the Perky and then a wide variety of New Process transfercases could be bolted to it. The biggest problem was then the lack of a handbrake setup on most of the NP transfers. So it was decided to fit a GU Nissan Patrol transfer case to the back of the transmission which provided an excellent rear tailshaft handbrake.
So what I did was to remove the existing drivetrain from the engine back. Also removed the clutch pedal, master cylinder and all the associated stuff as well as the gearshift assembly from the centre console.
Then a Perkins industrial SAE3 flywheel housing was bolted to the engine, followed by a Perkins stepped industrial flywheel. An adapter ring was then bolted to the flywheel housing to mount the GM 4L80E auto trans to. There is also an adapter to connect the flywheel to a GM350 flexplate which is then bolted to the torque converter. Once the auto is bolted up then a Marks 4wd adapter is used to connect the auto to the Nissan transfer case. Tailshafts are made up of the Nissan transfer case ends and sliding joint (with excellent rubber boots) and the Oka outer ends.
A B& M Sportshifter was mounted where the gearshift was and the transmission is controlled by a Compushift II aftermarket controller which works very well, I've been running a Compushift in the Humvee for over 200k and 7 years with zero problems.
So far we've only done about 200 kms but the setup works pretty well, the auto lets the Perky get on boost pretty quickly and it stays on boost all the way up through the gears, as the top gear is still the same engine revs at touring speeds are still the same. It is much more relaxing to drive especially in traffic and in towns and there doesn't seem to be too much difference economy wise. The Compushift has paddle shifters so gear selection can be done manually rather than burying the welly and the torque converter can be locked in any gear at any speed so low range downhill preformance is still the same. I also fitted 2.86 : 1 low range gears to the transfer case which helps enormously.
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Oka 374 LT Van

March 11, 2012 at 6:49 PM Flag Quote & Reply

Pete Fox
Member
Posts: 140
Thanks for that Peter.
I already have a Nissan transfer case mated to the 5 speed manual trans, so all the tailshaft and handbrake work has been done (apart from tube length). I am a confirmed manual driver, but I really hate this wide ratio setup.
I am looking forward to your document.
Pete
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Peter Fox

OKA 266 Multi-cab.

Photobucket album



March 11, 2012 at 8:11 PM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
The document is up in the contributions section.

www.oka4wd.com/apps/documents/?&page=5

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Oka 374 LT Van

March 13, 2012 at 6:50 PM Flag Quote & Reply

Pete Fox
Member
Posts: 140
Thanks Peter for a really well structured and informative article.
Please excuse my ignorance but I have four questions I hope you can answer.
I have trawled the net looking for the SAE 3 housing and stepped flywheel, but there is very little out there. Where do you suggest I start looking?
Also there is the reverse information situation with the 4L80E transmission, information overload from American sites with beefed up 1200 hp versions crammed with aftermarket goodies for lots of $$$. Most of this goes over my head because they are speaking a new language. Finding a rebuilt transmission without all this stuff is not easy either probably because in my ignorance I don't know what is required. Realistically, for the Oka application how much of this really necessary, i.e. what upgrades are needed/recommended?
Computer-less manual shifting is an option for the 4L80E. This appeals to my manual focussed brain and my aversion to little black boxes. Are there any negatives to going this way?
GM flexplates that I can find have either 153 or 168 teeth. which one is correct?
Thanks, Pete
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Peter Fox

OKA 266 Multi-cab.

Photobucket album



March 15, 2012 at 9:46 AM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
Can't help on the flexplate, wouldn't think it would matter as you are only using it to join the drive adapter to the torque converter, the ring gear isn't used.
As I said in the doc the Compushift is/has been extremely reliable in the Humvee over 8 years and over a 100k kms over the worst roads and tracks in Oz and has NEVER given a problem. There are three other Humvee's that I know of running the same setup again with zero problems. You would still have to change gears if it was manualised, you'd just be getting rid of the clutch basically.
As far as the actual 4L80E is concerned you want a heavy duty 4wd version which has a short output shaft, typically what is/was fitted to a Chev 2500HD ute or a civilian hummer H1. Bullet engines in Qld have the correct trans brand new and also the Compushift.
The SAE3 bellhousing is found at truck and tractor wreckers and the flywheel likewise. One place to try is "The Rock" tractor wreckers out of Wagga. They should be available at pretty much anywhere that has Massey ferguson tractors, that is where mine came from.
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Oka 374 LT Van

March 15, 2012 at 5:00 PM Flag Quote & Reply

Rick Whitworth
Member
Posts: 74
Peter,
Great info on your well planned auto conversion
Suspect $$ were pretty high but any option that ditches that noisy Rockwell will cost
thanks for great article
Rick

March 16, 2012 at 9:52 AM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
Rick, yes not much change out of $9k but I did buy a brand new trans, wouldn't like to pay for my labour either, took about 6 weeks, prob a good 10 to 14 days solid would see it done if you had everything on hand before starting, I spent nearly a week waiting for a starter motor right at the end. Was very disappointing after hooking everything up and sitting in the driver seat, cranking it to hear the starter whirring away without engaging!
There is no other way of starting an auto except with the starter when its in the shed. I guess on the road if you had abige enough hill and the torque converter can be locked right from the start then you could clutch it ;-))
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Oka 374 LT Van

March 17, 2012 at 8:29 AM Flag Quote & Reply

James & Usha (THEByleDuct)
Administrator
Posts: 161
Peter in your document you link to www.hpg.com which is an accounting firm. Am I right in presuming you are refering to the Hummer Parts Guy whose website is www.hummerpartsguy.com ? Entering in the part number you provide for transmission piping and hose goes to a TUBE, TRANSMISSION TO COOLER (REAR) which appears to be right.
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OKA #072

July 14, 2012 at 6:48 PM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
Yes it is the Hummer Parts Guy and the part is a special small tube which fits into the trans fittings and allows connection of a flexible rubber trans hose. When I replaced the Humvee's TH400 3 speed auto with a 4L80E I couldn't get those metal lines anywhere, had to buy late model Commodore ones from GM and cut the rest off, not cheap at $120 each whereas the Hummer ones were only a few dollars each.
I usually cut and paste links from tha actual website so must have stuffed that one up, will see if I can correct it or maybe the mods may have to.
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Oka 374 LT Van

July 15, 2012 at 7:13 AM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
The link in the doc is fixed now.
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Oka 374 LT Van

July 15, 2012 at 7:22 AM Flag Quote & Reply

James & Usha (THEByleDuct)
Administrator
Posts: 161
Thanks for that Peter. I'm looking at doing the conversion to an auto as per your instructions although keeping the NP205.
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OKA #072

July 15, 2012 at 1:28 PM Flag Quote & Reply

Peter & Sandra James Oka 374
Member
Posts: 412
James that will work ok as the Np205 will bolt straight on if it has the chev pattern adapter and the correct input spline. If it is the Oka NP205 currently fitted then you won't have to worry about handbrake etc as it will already be fitted. That was what stopped me fitting an NP205, the handbrake.
The biggest problem with the NP205 as I see it is the relatively high low range ratio of 1.9:1 which coupled with the auto will have adecided lack of engine braking. The GU transfer case can be geared down using the Gearmaster gears.
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Oka 374 LT Van

July 15, 2012 at 5:54 PM

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