Beefing up A500 overdrive

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The A55/42RH and later 42RE are in basic form an A904 with an overdrive. Actually an A999, which was a heavy duty wide ratio 904 with a lockup converter. So a heavy duty rebuild would involve the same parts as the A999. Basically you want the 5 disk front clutch pack if not already equipped. Beyond that, a quality rebuild kit and a shift kit (Trans-go makes one, and would be my pick). Mopar went to plastic servo pistons in the 90's for some reason, and they were crap, really hurting the reputation of the TF, especially in the trucks. Fortunately earlier parts can be used, or Sonnax makes nice billet new ones. The later OD units from the electronic RE transmissions were supposedly better and are interchangeable, so if yours ever causes problems, just grab a later unit from a junkyard. Some later Diesel trucks (48RE) had a stronger planetary in the overdrive, overkill for your purpose. Converters were the same as A999 and came in several stall speeds. Mopar Performance even listed a few for a while. A good converter rebuilder should be able to set one up to suit your needs. Precision of New Hampton has a good reputation, and there are Mopar focused transmission shops for higher performance units. Later units used a different pump drive which was stronger but would require a corresponding pump.

So this is going behind a poly 318? Are you putting a poly in an A-body?!? Polys always had an A727 so an A518/46RH would be a more logical choice, stronger, easier to find, etc.

Keep in mind that the drums and clutches from an A727 based unit A518/46RH/47RH/48RH are not in any way compatible with the A500/42RH, so one can not simply "upgrade" to 46/47/48 spec.
 
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Headintheclouds said:
Not crazy power. 318 poly with 4 barrel Edelbrock. Probably about 250BHP 350lb torque. This is within the original spec of the 42RH but I would like to give myself a bit more leeway for freeway use. The car is being set up for comfortable touring but keeping decent performance.

Most of the control setups for retrofit overdrive drop it out on fairly light throttle. The PACT solution with a vacuum switch and 2 pressure switches drops both lockup and overdrive in one go as the vacuum drops which I don't want.
I plan to have the lockup drop out by vacuum on fairly light application of throttle but have the overdrive held on through a microswitch on the linkage. This should mean I can stay in overdrive for relatively gentle overtakes on the freeway and not have a sudden increase in revs.

If I'm rebuilding the transmission anyway it makes sense to me to upgrade at least to 44 spec. if not 46. I wasn't aware of any real down side so please tell me if I have missed something.

I haven't had the transmission apart yet but I'm guessing my 42RH has 2 steels and 3 friction in the overdrive and 8 lined and 7 steels direct. Upping to 46RH spec would be 3 steels and 4 friction overdrive and 10 lined and 9 steel direct.
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For that level of power the A500 is fine in stock form.
Get a quality rebuilt converter, if you like more clutches/steels, shift kit, and sonnax mod to allow the torque converter to fill in neutral.

Controlling the overdrive and lockup can be done with a toggle switch, or this would be slick with an a/m shifter:

 
RustyRatRod said:
I love it when people talk about power losses in automatic transmissions. You could easily drive one with a Briggs and Stratton single cylinder engine. It wouldn't pull a lot of weight, but the transmission would function fine.
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Never said it wouldn't function fine. Specifically referring to the power loss through the overdrive assembly.
 
junkyardhero said:
when you say "costs a lot of power" how much are the losses on a 500/42 RH?

I'm looking to go this route with a 375hp LA that will either see injection or swap to a G3 down the line. what would be the best course of action- building out an OD unit or go with a gear vendors unit?

currently has a 727 and I'm not racing it
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It depends how much fabrication work you want to do to your car. Obviously with the RE/RH transmission and narrow transmission tunnel the gearvendors will require less fabrication work, and in some case no fabrication is needed.
 
Headintheclouds said:
As far as I'm aware most of the loss in auto transmissions is in the torque converter. Lock up pretty much fixes that.
Overdrive gets the engine working at the most efficient part of the power band but is subjected to high torque at lower revs. This is why I'm looking to strengthen the overdrive, not because I have crazy horsepower.
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maybe so but torque output is directly related to throttle input, ignition timing, and the resistance of the powertrain/vehicle to move and accelerate.

If your goal is fuel-economy;
with 3.23s and .69od, your cruise rpm works out to about 65=1800 which is a little on the low side..... because you just cannot, without a computer, give the engine enough ignition timing.
If you are really interested in fuel economy and are really gonna cruise with 3.23s at 65=1800 in overdrive/LU, then you will need a stand-alone timing computer to optimize the cruise timing, AND you will need a spreadbore carb with tiny primaries, (triple-booster is better) and a matching hi-velocity intake, AND a sharp tune. To make the 250BHP, with these restrictions, you may need a solid-lifter cam, and a free-flowing dual exhaust. A decent cylinder pressure close to 155/160 psi would be a bonus.


On my dash I have a variable timing retard switch with a range of 15 degrees. My Idle-timing is usually set to 12 to 14 degrees, with the device set in such a manner that I can advance up to 6, and retard up to 9. With it fully retarded the Idle-timing drops to about 4/5 degrees. This is just enough to keep the engine running, while in first gear (manual trans with an over-all starter gear of 10.97), at about 550 rpm, with the throttle closed, idling thru the parking lot. Any less rpm and the engine is dangerously close to stalling. But if I nail the gaspedal, all hell breaks loose, lol.
The point is between the minimum and the maximum torque that your engine can produce, you control it with throttle opening, and to some degree, with ignition timing.

With the factory-type un-modified distributor, at the factory timing spec, you'd be lucky to get 24* of cruise timing@1800. If you modify it and kick in a bunch of Idle-timing, maybe you get 46 degrees@1800, which is not likely gonna be enough. But it's a pretty good start. In the end, your engine at cruise, is likely to want 54 to 60 degrees, can't say exactly, cuz I've never had a Poly and never tuned one...

Having said the above; 2200 to 2400rpm is a good cruise target, for optimizing the timing.. With 27" tires and .69overdrive, this maths to,
3.91s for 65=2180 in overdrive.
This will get you a starter gear of 10.71, a very nice tire-spinning number.
and the bonus is 55= 2700 in Drive/locked up, and perhaps 3000 unlocked at WOT, perfect for passing slowpokes.
I have driven this combo for several years in a second generation Dodge Dakota and I liked it very much.
For your application, I would not consider the GearVendor, even tho I have one in my HotRod and like it too.
Ima liking post #20
 
WIT Transmissions modifies drums for more clutches and steels. Might get in touch with them.
 
"Keep in mind that the drums and clutches from an A727 based unit A518/46RH/47RH/48RH are not in any way compatible with the A500/42RH, so one can not simply "upgrade" to 46/47/48 spec." INCORRECT.
 
"WIT Transmissions modifies drums for more clutches and steels. Might get in touch with them." WHAT?? It's easy to put five Red Eagles in ANY 727 direct drum using stock steels and pressure plate.
 
volaredon said:
Um yeah, trans fluid that's in the converter, the clutch packs and all the other moving parts as it runs ....
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The clutch packs are NOT "immersed in fluid". No wonder nobody wants to answer any more of your questions about "parasitic drag"..they already did, you just don't like the answers. Your remind me of the guy who posted that a C6 robs 60 horsepower to operate.
 
Duster346 said:
It depends how much fabrication work you want to do to your car. Obviously with the RE/RH transmission and narrow transmission tunnel the gearvendors will require less fabrication work, and in some case no fabrication is needed.
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thank you for the invaluable input.

in your opinion does either one have any distinct advantages over the other?

if going with the 42RH are there any "must have" upgrades that you would suggest?
 
Once upon a long time ago, I put too much fluid in a trans; because the stick was wrong, which I did not know at the time. The spinning parts in there musta whipped the fluid up pretty good and some of it blew out the vent. Eventually it "sorta found it's own level". Sure made a mess tho.

BTW
In Neutral, anybody can turn the driveshaft, whether or not the engine is running, even counter-rotating (engine off) ..... think about that. Obviously, at idle, the back half takes a lot less than one manpower.
On the bench, you can easily turn the front half with a plier.
But, I guess, Powering up the pump will take some power: can't be much tho, cuz even the smallest slanty will idle down to~450 in gear..........
My guess is that the power-loss gets sucked up in the TC, which is slipping all the time, converting horsepower into heat. can't be much tho cuz I have run my 904 without an oilcooler 3-seasons ........ with a 2800 .......for five years. And after that, it ran fine in my son's truck for another 5 or more, without a freshening. In the truck, tho, we plumbed the cooler in.
The only thing in that trans, that has to be and stay immersed, is the VB.
 
CudaFactHackJob said:
The clutch packs are NOT "immersed in fluid". No wonder nobody wants to answer any more of your questions about "parasitic drag"..they already did, you just don't like the answers. Your remind me of the guy who posted that a C6 robs 60 horsepower to operate.
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Wrong. I never seen anything, other than alot of beating around the bush about the subject.
You saying centrifugal force and running in fluid is a non factor in the amount of power a given trans takes to operate? And that it doesn't take fluid pressure, from pumped-in fluid, to keep a clutch pack engaged?
 
my 2 pennies worth. i have a buddy with a 3/4 ton 4x4 diesel. he had a bad vibration and it was u joints. it finally cracked the o/d housing and he got 1 off ebay. i got the diesel o/d unit and went into my auto trans parts book comparing o/d parts. there are a couple plates that are different between the diesel/gas. getting the diesel plates and extra clutches should, i say should allow building the o/d to diesel specs. then problem solved. change for a nickel please.
 
Do you still have the part numbers to hand? It would be useful to have a list to compare the different parts.
 
i use mopar parts giant as my source. it is the same parts lookup as the dealerships use. it is free. put in year of truck trans came out of and what truck it came out of and look up trans parts. go to the overdrive unit section.
 
volaredon said:
Wrong. I never seen anything, other than alot of beating around the bush about the subject.
You saying centrifugal force and running in fluid is a non factor in the amount of power a given trans takes to operate? And that it doesn't take fluid pressure, from pumped-in fluid, to keep a clutch pack engaged?
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Going from memory, the pump is relieved at ~275psi. All circuits are independently pressure regulated, except reverse, which runs wide open. Generally, the line pressure operates in the range of 55 to 90 psi. The TC at 30 to 75, lower in Neutral/Park. The lube line runs ~5 to 30psi. The governor at UP TO line pressure. Of all these circuits, only the lube-circuit is a designed-in controlled leak.
When the parts are new, there is very little oil leakage out of the power-pistons and or servos. The clutches are lubed by a different circuit thru tiny orifices running at modest pressures. When a clutch is disengaged the fluid is relaxed into the manual valve, about IDK say 1.3 inches from the bottom of the stock pan.... well below the spinning parts. The servos dump at a similar height. The bulk of the fluid that is being flung about is that which is semi-continuously leaking from the lube circuit, that has done it's job of lubing, including lubing the clutches, and which exits the drums, and mostly when the packs are relaxed.That exiting oil becomes splash-fluid for the bands, as they receive no other.
The pump and the TC are the only parts that are connected to the crank, until a clutch is engaged.
So you are correct;
It takes power to spin these parts up, just as it takes power to accelerate the vehicle;
But not much power is required to maintain speed, such as when cruising.

IMO
the power loss to the fluid is minimal, and not much can be done about it, anyway.
I think, the Convertor is the power sucking monster, lol, and the loss is directly related to the rpm and the load. After all, it is not coupled to the driveshaft in any way, but by anything other than the friction between the oil molecules.
For the OP none of this matters.
 
Spot on. The only reason for beefing up the trans for me would be to add design improvements from later models and improve reliability. If I'm already rebuilding the trans it won't cost much to add a few clutches, change to kevlar band and replace plastic pistons with billet. I just need to make sure there isn't a down side to any of this. I have already bought the Sonnax valves to allow fill in Park.
 
CudaFactHackJob said:
"WIT Transmissions modifies drums for more clutches and steels. Might get in touch with them." WHAT?? It's easy to put five Red Eagles in ANY 727 direct drum using stock steels and pressure plate.
Click to expand...
Just lettin him know about another option.
 
I just gotta say something here.
To make good use of the Overdrive models, as pertains to fuel economy, with a modest cam; you are sorta married to a final drive of 3.91 x .69=2.77s for 65=2240, which is as low as you dare go and still be able to at least almost give the engine the ignition timing it wants. With this, and the A518, your Roadgears are
9.58- 5.67-3.91-2.77 Whereas with the A999 and 2.76s, they are
xxxxx -7.56-4.25-2.76 So, you get the same ~cruise rpm.
Now check out those numbers. For acceleration;
7.56 is a way better gear than 5.67, as is 4.25 compared to 3.91. So then, the only thing you are loosing is ALL of First gear. But the two next gears are better.
But you can get around some of that first-gear handicap, to some degree, by setting up your engine for more low-rpm torque. And/or you can compromise.
Say you increase your cruise rpm by 10% (to 2460) with a new rear gear of 3.23s. Your new road gears are
*** 8.85-4.97-3.23 , compared to
9.58- 5.67-3.91-2.77
Now, 8.85 is better than half way in between The first two A518 gears. You can easily make up the starting-line difference with stall and or cylinder pressure. From 9.58 to 8.85 is only 8.2% which equates to say 20ftlbs
IMO
this is a reasonable compromise, and is way cheaper, and you don't have any fabrication to do..

Another good compromise is say just 5% more gear (than 2.77) and a higher than factory stall.
From a stall of 2000, to 2800, the 318 might make an extra 20 footpounds, and lets go with 2.94 (cruises at 65=2380 in LU, perhaps 2450 without. Your new Roadgears with the A999 ratios are
xxxx8.06-4.53-2.94 compared to
9.58- 5.67-3.91-2.77 with the A518;
But, the extra 20 ftlbs found by the highstall, are worth perhaps the same 5% so if you factor that in, you get the equivalent performance of;
8.46-4.76-3.09 still not
9.58- 5.67-3.91-2.77, but a reasonable compromise, IMO
BTW, that 8.46 starter gear is with the 2.74 Low gear of the A999. Compared to the A904 with only a 2.45 First gear, this would math to 3.45s in the back...... which, being between 3.23s and 3.55s, is not really all that slow..........
Food for thought; and
we never even talked about cylinder pressure yet.
 
AJ/FormS said:
I just gotta say something here.
To make good use of the Overdrive models, as pertains to fuel economy, with a modest cam; you are sorta married to a final drive of 3.91 x .69=2.77s for 65=2240, which is as low as you dare go and still be able to at least almost give the engine the ignition timing it wants. With this, and the A518, your Roadgears are
9.58- 5.67-3.91-2.77 Whereas with the A999 and 2.76s, they are
xxxxx -7.56-4.25-2.76 So, you get the same ~cruise rpm.
Now check out those numbers. For acceleration;
7.56 is a way better gear than 5.67, as is 4.25 compared to 3.91. So then, the only thing you are loosing is ALL of First gear. But the two next gears are better.
But you can get around some of that first-gear handicap, to some degree, by setting up your engine for more low-rpm torque. And/or you can compromise.
Say you increase your cruise rpm by 10% (to 2460) with a new rear gear of 3.23s. Your new road gears are
*** 8.85-4.97-3.23 , compared to
9.58- 5.67-3.91-2.77
Now, 8.85 is better than half way in between The first two A518 gears. You can easily make up the starting-line difference with stall and or cylinder pressure. From 9.58 to 8.85 is only 8.2% which equates to say 20ftlbs
IMO
this is a reasonable compromise, and is way cheaper, and you don't have any fabrication to do..

Another good compromise is say just 5% more gear (than 2.77) and a higher than factory stall.
From a stall of 2000, to 2800, the 318 might make an extra 20 footpounds, and lets go with 2.94 (cruises at 65=2380 in LU, perhaps 2450 without. Your new Roadgears with the A999 ratios are
xxxx8.06-4.53-2.94 compared to
9.58- 5.67-3.91-2.77 with the A518;
But, the extra 20 ftlbs found by the highstall, are worth perhaps the same 5% so if you factor that in, you get the equivalent performance of;
8.46-4.76-3.09 still not
9.58- 5.67-3.91-2.77, but a reasonable compromise, IMO
BTW, that 8.46 starter gear is with the 2.74 Low gear of the A999. Compared to the A904 with only a 2.45 First gear, this would math to 3.45s in the back...... which, being between 3.23s and 3.55s, is not really all that slow..........
Food for thought; and
we never even talked about cylinder pressure yet.
Click to expand...
You left out the best of both worlds- using the A500 as the OP has said he will do.
 
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