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Old 05-11-2006, 07:45 PM
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modulator needed?

I have a TH400 with an auto/manual kit and it is going into a mudbog truck offroad only. Can I get rid of the modulator all together if not planning on running in auto?

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Old 05-11-2006, 08:09 PM
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Quote:
Originally Posted by BBCMudbogger
I have a TH400 with an auto/manual kit and it is going into a mudbog truck offroad only. Can I get rid of the modulator all together if not planning on running in auto?
main line pressure will go real high with no modulator ...... 300+ psi usually
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Old 05-12-2006, 05:43 AM
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Is that good or bad?
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Old 05-12-2006, 05:58 AM
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B & M used to make a 'tv cable' style replacement for T400 modulators in the late 70's for blown/turbo applications. I never saw one in the flesh - only magazine articles. Why don't you want a modulator?
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Old 05-12-2006, 06:09 AM
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Quote:
Originally Posted by IanRiordan
B & M used to make a 'tv cable' style replacement for T400 modulators in the late 70's for blown/turbo applications. I never saw one in the flesh - only magazine articles. Why don't you want a modulator?
odds are that with the engine hes probably running, the motor probably wont pull much vacuum... kinda makes a modulator worthless
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Old 05-12-2006, 08:14 AM
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Quote:
Originally Posted by BBCMudbogger
Is that good or bad?

lol ........ bad
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Old 05-14-2006, 08:17 AM
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Vacuum is the issue. Hopefully the motor will be pretty nasty....lol......253/261 duration solid roller.......will be launching at about 3800-4000 I suppose. I am going to get an electric vacuum pump for the brakes. Maybe I can rig something for the modulator, but I don't want to if I don't have to.
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Old 05-14-2006, 11:56 AM
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one item to remember is the auto/manual v-body will only upshift at a higher RPM with no moulator on the tranny or if it is unhooked.

A full manual shift v-body would shift to any gear at any RPM.

There are mods that can be performed to close off the reverse boost circuit to not have a high line pressure problem in R .

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Old 05-15-2006, 04:03 AM
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Check a euro diesel out. Whilst most diesel duallies run a hydraulic booster, Benz's etc run a compact vacuum pump. You could easily rig a pump from a 2000 up M/Benz cdi and a throttle controlled switchover valve from an 81 - 85 300d/td for the trans.
Easy to set up and CHEAP.
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Old 05-17-2006, 03:55 AM
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The switchover valve does what? I am guessing it reduces vacuum at WOT? Thanks for the input.
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Old 05-18-2006, 02:31 AM
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Switch over.

Yes, the switch over valve found on the rocker cover of 81/85 300Ds has 3 vacuum ports - inlet, outlet and bleed off. It's as small as a kickdown switch and could be fitted to most any cable or linkage. Plumb the wot bleed off back to the booster and you will have normal vacuum booster and modulator operation regardless of available vacuum.
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Old 05-18-2006, 03:15 AM
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?????
the modulator is adjustable for vacuum Hg/shift points, 3800 rpm launch is lots of Hg

the brakes have a one way check valve so the booster holds whatever the max Hg is above idle (ex:25Hg on a downshift, excellent check valve will hold it for 2 days with the motor off)

if the idle Hg is so low (below about 12Hg) that the brakes don't work due to the cam, you can't tune the carb

if you want to (????why) be able to turn off the modulator, just add a $5? inline manual on/off barbed valve to the modulator hose

I tried a ten turn fine adjust on/off valve once, to see if I could adjust modulator diaphram reaction time, didn't work on a C4,
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Old 05-19-2006, 03:39 AM
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I'm assuming a BAD roller (260 @ 50 or more) so I treat it like a blown application, if it can find 12 inches then forget everything and run a stock mod.
Im guessing that by the posters name this thing will be run like a light switch - on or off which means no vacuum.
I'm pretty sure the M/Benz sprinters I spoke of are badged as Dodge or Fruitliner vans in the US.
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