Slant Six Forum :: Realistic options for an overdrive automatic transmission

With luck I might be able to cobble together an A500 setup for $500-$600. Not optimal, but achievable.

Well, no luck at the boneyard. Both A500s were 4wd versions.

I did happen upon a 1985 Volvo 240 station wagon that had a manual trans with the Laycock overdrive. I spent some time under the car looking at the overdrive unit and I think I have a plan.

I need to get a Volvo trans with the overdrive unit and create an adapter that will plug the overdrive unit into the back of a 904. I have some rough ideas of how this could be accomplished, and space and mounting are not an issue for me since I am putting it in a truck. Now to gather parts and learn how to weld properly enough to fabricate something.

Reed,

I think I wasn't clear. The Jeep A904 has a shorter output shaft and tail housing in case you want to make the package shorter. The Jeep main case isn't an asset.

The toughest fabrication bit is probably going to be the trans to overdrive coupler. You'll need to find a good welder and/or machine shop.

Ever since owning a BMW with a ZF 5-speed automatic I've had dreams of one of those behind a slant. Forward ratios are 3.67, 2.00, 1.41, 1.00, 0.74 That's a 5:1 gear spread, twice that of the close-ratio A904 and A727. Reverse is a truck-like 4.1.

Author:	kesteb [ Tue Jul 10, 2018 7:20 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
A Wilcap adapter will eat up most of that budget.

Author:	Reed [ Tue Jul 10, 2018 10:01 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Yeah, that is what I am afraid of. I might be able to find an A500 at picknpull for $100-$200, and maybe build an adapter or buy/trade for one. With luck I might be able to cobble together an A500 setup for $500-$600. Not optimal, but achievable.

Author:	Charrlie_S [ Wed Jul 11, 2018 5:55 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Quote: With luck I might be able to cobble together an A500 setup for $500-$600. Not optimal, but achievable. I'm thinking, any early A-500 you find used, will need to be gone through. They did have their problems That will eat up most of that $500

Author:	Dart270 [ Wed Jul 11, 2018 6:23 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Unless you are hunting a long time, or get lucky, you will have to spend $1200 minimum for a reasonably reliable setup, more like $2500. If you want OD, then an OD 833 stick or adapting a 5spd to a slant bell is probably your best bet economically. I bought my adapter plate in 1991, then found an A500 in 1999 and installed it in 2001 with some home VB mods. Lou

Author:	Reed [ Wed Jul 11, 2018 7:56 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
I have no problem rebuilding an A500 myself, but with prices like these I might just run a 904 and change the rear gear ratio from 3.9 to something higher, like 3.2. I need to just start searching around.

Slant Six Forum https://slantsix.org/forum/

Realistic options for an overdrive automatic transmission https://slantsix.org/forum/viewtopic.php?t=62551	Page 2 of 4

Author:	Reed [ Wed Jul 11, 2018 3:34 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Hmmmm. Hmmmmmmm. http://bmpenterprises.net/blog/2010/01/ ... ter-plate/ My local pick and pull is having a 50% off sale tomorrow. They have a 90 and a 91 Dakota with four speed automatics. That would be $75 plus tax for the trans plus peripherals (OD switch, wires, trans yoke, trans crossmember). Hmmmmmmm. I have an extra V-8 904 case in storage and a bare slant block under my workbench. I also have some big pieces of plexiglass and some Sharpies. I have a drill press and a grinder. Hmmmmmmmm..........

Author:	Reed [ Thu Jul 12, 2018 1:39 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Well, no luck at the boneyard. Both A500s were 4wd versions. I did happen upon a 1985 Volvo 240 station wagon that had a manual trans with the Laycock overdrive. I spent some time under the car looking at the overdrive unit and I think I have a plan. I need to get a Volvo trans with the overdrive unit and create an adapter that will plug the overdrive unit into the back of a 904. I have some rough ideas of how this could be accomplished, and space and mounting are not an issue for me since I am putting it in a truck. Now to gather parts and learn how to weld properly enough to fabricate something.

Author:	Joshie225 [ Thu Jul 12, 2018 1:47 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
There is a Jeep 4x4 A904 case if you want to shorten the overall package length. Fopar has one in the dragster. There is the P-Type and J-Type Laycock overdrive in Volvos. I believe the stronger P-Type came in 700/900 series turbo cars. From Wikipedia: "The J-type overdrive was introduced in the late 1960s, and was adapted to fit Volvo, Triumph, Vauxhall/Opel, American Motors and Chrysler motorcars, and Ford Transit vans. The P-type overdrive marked the last updates and included both a Gear Vendors U.S. version and a Volvo version. The Volvo version kept the same package size as the J-type but with the updated 18 element freewheel and stronger splines through the planet carrier. The Gear Vendors U.S. version uses a larger 1.375 outer diameter output shaft for higher capacity and a longer rear case."

Author:	Reed [ Thu Jul 12, 2018 2:24 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Thanks Josh! I actually an not worried about length since the Laycock unit is fairly short, much less than 20 inches. I suspect an engine adapter plate is necessary to mate a slant six to a Jeep 904 case, and if I am going to fabricate an adapter plate I might as well go back to an A500. My thought is to build a completely independent overdrive unit that can slide onto the output shaft of a stock 904 and require only a shorter driveshaft and a mounting bracket to be fully installed. I am watching a J type overdrive on eBay that is complete and comes with a section of output shaft from the Volvo trans to make custom fabrication easier. I will research the J and P type differences and availability. EDIT: Then again, why reinvent the wheel? http://maximum--overdrive.com/products.html

Author:	Tim Keith [ Sun Jul 15, 2018 1:42 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Quote: Well, no luck at the boneyard. Both A500s were 4wd versions. I did happen upon a 1985 Volvo 240 station wagon that had a manual trans with the Laycock overdrive. I spent some time under the car looking at the overdrive unit and I think I have a plan. I need to get a Volvo trans with the overdrive unit and create an adapter that will plug the overdrive unit into the back of a 904. I have some rough ideas of how this could be accomplished, and space and mounting are not an issue for me since I am putting it in a truck. Now to gather parts and learn how to weld properly enough to fabricate something. There are Laycock adapters for the A904, new adapters are costly, a used one might be available. There isn't much to the adapter - it replaces the tailhousing, I think these could be made from steel pipe and a couple machined plates that are welded to the pipe. This would basically be a Gear Vendors. I have a slant 6 to V8 adapter from an A-100. Those are cheap if you can find one. Then, you can use the 42-RE or other A-500 variant. You can beef up the A-500 using the same parts as a 904 uses. I have thought of doing this to my '85 D150. The A500 overdrive unit is the same as the A518 uses If the truck is a long wheelbase model a 'divorced' Laycock might be workable, that needs no special adapter, but you have to attach a front yoke the the Laycock - those are available for $200 or so. This requires a fabricated cross member and a cardan u-joint ( one that doesn't wobble as it rotates ) which is similar to the CV joints in a front drive vehicle. If standard drive u-joints are used there will be a bad vibration. A short wheelbase 1/2 ton might be have adequate length for the divorced Laycock. Contact Glenn at gpyzak@ix.netcom.com for more information - he is one of a few that do this work as a business venture.

Author:	Reed [ Sun Jul 15, 2018 9:58 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Thanks, Tim! I am still putting out feelers and researching the availability of adapters. I sent a parts request to Wildcat and have received no response. I have posted want ads everywhere I can think of and had no response. So, we'll see. I might end up fabricating my own adapter after all.

Author:	Tim Keith [ Sun Jul 15, 2018 11:50 am ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
The reason the "divorced" Laycock can have vibration issues is the transmission is rigidly mounted to the motor, both are supported by flexing rubber mounts. The Laycock o/d is rigidly attached to the frame of the truck with a very short driveshaft connecting to the o/d unit. A traditional U-joint can not account for the flexing with such a short driveshaft. A Cardan u-joint is commonly used to address this. http://www.dana.com/light-vehicles/prod ... fts/cardan. The Laycock o/d has its own oil supply, it is electrically activated. using a reverse lockout switch. I believe there is a one-way sprag clutch that can be damaged if the Laycock is engaged in reverse. The o/d appears to be integral with the Volvo transmission but its a separate unit. With the 'divorced' setup you must add an a driveshaft yoke to the front of the o/d, these are available for a reasonable cost. A machinist that can cut splines on a shaft can make this part, but why not just buy this shaft from a vendor that makes them ? I've seen used Laycock adapters on Ebay. But you can build the divorced Laycock setup without the adapter but you need to use a cardan u-joint or the truck will shake like its falling apart. I believe it is the so called "double" cardan that you'll need. A common y-joint wobbles slightly as it rotates. Having two of these together neutralizes the side to side movement.

Author:	Reed [ Sun Jul 15, 2018 3:22 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
My thought on the Laycock was to build it so it used the front yoke of a 904 compatible driveshaft welded/spliced to the output shaft of a Volvo transmission and fabricate a cone that would bolt to the open end of the Laycock unit (that normally bolts to the trans) and has a input shaft support bearing and seal. The 904 yoke would slip into the tailshaft housing of the 904 like a regular driveshaft. The Volvo output shaft would go into the OD unit. The od unit itself would then be bolted to a mount that would tie it to the trans mount for the 904 and also to the frame rails of the truck. Hopefully that would reduce vibrations and minimize the length of the Laycock unit. If it was built that way it would be fairly quick and simple to install and remove. But now that I think about it, I would have to put a slip joint in there somewhere so the rear axle could go up and down without smashing into the OD unit. Hmmm. And now I have to think about vibrations. Hmmm. I need to finish up a home remodelling project and get my garage back and then start doing some measuring and pondering. I have an extra slant 904 and an extra v-8 904, so I have most of what I need to fabricate either an A500 adapter plate OR a Laycock overdrive unit adapter. I just need some space and time. Either option is doable, I just need to figure out which is more feasible. I have a completely rebuilt and beefed up slant 904 ready to go, so I would like to use that and not have to get an A500 and rebuild that. But adapting the Laycock unit to the 904 would be trickier. I need to have the parts on the workbench in front of me and do some pondering and measuring.

Author:	Joshie225 [ Sun Jul 15, 2018 5:04 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Reed, I think I wasn't clear. The Jeep A904 has a shorter output shaft and tail housing in case you want to make the package shorter. The Jeep main case isn't an asset. The toughest fabrication bit is probably going to be the trans to overdrive coupler. You'll need to find a good welder and/or machine shop. Ever since owning a BMW with a ZF 5-speed automatic I've had dreams of one of those behind a slant. Forward ratios are 3.67, 2.00, 1.41, 1.00, 0.74 That's a 5:1 gear spread, twice that of the close-ratio A904 and A727. Reverse is a truck-like 4.1.

Page 2 of 4	All times are UTC-08:00
Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/

Author:	Tim Keith [ Sun Jul 15, 2018 5:32 pm ]
Post subject:	Re: Realistic options for an overdrive automatic transmission
Quote: Reed, I think I wasn't clear. The Jeep A904 has a shorter output shaft and tail housing in case you want to make the package shorter. The Jeep main case isn't an asset. The toughest fabrication bit is probably going to be the trans to overdrive coupler. You'll need to find a good welder and/or machine shop. Ever since owning a BMW with a ZF 5-speed automatic I've had dreams of one of those behind a slant. Forward ratios are 3.67, 2.00, 1.41, 1.00, 0.74 That's a 5:1 gear spread, twice that of the close-ratio A904 and A727. Reverse is a truck-like 4.1. You can purchase a new shaft that replaces the 904 output shaft and has the correct splines for the Laycock. The so called "adapter" is a 904 tail housing replacement that aligns the new shaft. This is one site that provides these parts. The custom shafts are listed at $245.00. A GM turbo 400 adapter is listed at $395.00, a 904 adapter is probably about the same price. http://maximum--overdrive.com/. Their "Remote Mounted Unit" is what I've been calling a "divorced" Laycock.