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Discussion Starter · #1 ·
How about a debate on the ultimate servo? It's been argued that the H is the stout, HD standard of the servo line. It has the largest release possible at 3.785" it uses the case bore and it has a fairly large apply at 2.960".
Mario has said he's had great success with the R servo with its small release. Noone has said much about the O with a small apply and the largest release. What is your opinion and why? If you were going to do a billet one, what sizes would you use?

SERVO SIZES
Sizes
'A' 2.825" apply 3.785" release
'B' 2.710" apply 3.785" release
‘C’ 3.120” apply 3.785" release
'H' 2.960" apply 3.785" release
'K' 2.375" apply 3.355" release
'N' 2.560" apply 3.785" release
'O' 2.460” apply 3.785” release
'R' 2.820" apply 3.265" release
'W' 2.375" apply 3.300" release
'Z' 2.500" apply 3.335" release
 

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I am using "H" and it works very well in my mid 10 second car. Shifting is quick and firm in all gears. I will stick with it.

I have used an "R" servo and had a band start slipping going into second. I can't explain why exactly other than the apply bore may have not been sealing well. . Third shift was good. I changed it for the "H" and put in a new band. It has been fine ever since.

I have a buddy using an "A" servo which has the apply size of and "R" and the release size of an "H". He has had no problems and the shifts are firm in a 428CJ running low 11-high 10.

Other than these 3 sizes, I probably wouldn't use another size except "C" in a serious car. I wouldn't want a smaller apply piston.
 

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I have been usin the 'R's for a while now. I always did like them but based on Kent 89coupes and Mario's sucess with them i stuck with them.I never have had any issues with 2-3 flare using these servo's. Maybe that could be the small release??
I have also used the A and never had any issues ,i have one in one of my cars now.
I have 2 H servo's but never tried them yet.Should one day i suppose.
Used a few B servo's just in stock rebuilds .

I have a B in a daily driver i got and if you try real hard you can get it to do a 2-3 at just the right spot,like light throttle and shift to 3 .It has the high gear clutch set up at .030 too.I put it down to the large release side of the B servo.
A guy here in OZ that i have got a few V/B's from is looking at modifying an R servo so i cant wait to see how. He sets up his manual v/b to suit the R servo too.
Lets get the debate going..
 

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Installing a "H" servo in place of a "A" cured a part throttle 2-3 flare but had no affect on full throttle shifts. The "H" isn't too hard to find at Pic A Part but I've yet to see a "R". What did the "R" come in?
 

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Discussion Starter · #7 ·
I thought the C servo came in the hipo cars. That's what the eBay vendors claim anyway.
I don't necessarily put any faith in what is said on eBay.
In my limited experience the H servo seems to be the van/truck servo. The truck C4s I've seen with the short tailshaft housing and the yoke have had H servos.
 

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The "R" with it's small release area allows for quick 2-3 shifts, right? Why didn't the aftermarket copy it instead of the "H"? Is this an oversight on there part?

Gerald.
 

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I think they got hung on the idea "bigger is better" theory....the more apply pressure the better....
 

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Nothing wrong with a lot of apply pressure. For real high HP applications its the only thing thats going to keep the drum from running away. Of course to keep the apply speed the same as the smaller servo's you'll have to increase line pressure and that can be its own can of worms. For over 500 HP I'd rather have a large servo and considerably higher than normal line pressure. Over 700 HP and theres no way I'd run with anything other than a full bore servo.
 

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Makes you wonder how these other (non Ford) transmissions cope with serious HP and generally alot smaller apply servo's?? Alittle more and surface area sure....but its not alot of difference.
 
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