Hydraulic clutch - The 1947 - Present Chevrolet & GMC Truck Message Board Network

seddons · 05-18-2012, 12:04 PM

I have a 1967 Kaiser M715 with a mid 80's Chevy truck engine SM465 Trans and NP205 TC. I have installed a wildwood ¾” clutch master cylinder and GM factory clutch slave cylinder. This thing is like doing 400 lb. squats to push the clutch in. What have I done wrong? I am at a total loss.

v30crewcab · 05-18-2012, 10:13 PM

sounds like the master is too big. don't recall how big the original one is.

seddons · 05-21-2012, 04:18 PM

The factory master cylinder is .703, the Wilwood one I have is .75 so I am pretty sure that is fine. In fact the only thing that does not match factory specs is the hose. The GM hose will not fit so I used a #3 braded line with #4 ends, could that be the problem?

**Cheng** · 05-21-2012, 05:38 PM

Could have to do with where the master cylinder rod connects to the clutch pedal. If this connection is too far from the pivot point it would greatly reduce your lever arm and then require more effort to push in.

On my 85 K30 with the SM465 hydraulic clutch the master cylinder push rod connects to the clutch pedal ~2.5" below the pivot point & the clutch pedal is ~17" long overall.

So with the original set-up, 20lbs of pedal pressure will generate 136lbs of force acting on the master cylinder.

136lbs acting on the .703 master cylinder will provide 350psi of hydraulic pressure.

136lbs acting on your .75 master cylinder will provide 308psi of hydraulic pressure.

**hatzie** · 05-21-2012, 05:47 PM

You'd be surprised what a difference 0.05" dia will make.

The smaller the bore on the master cylinder, the lighter the pressure you will need to apply.
The price you pay for this is that more travel is required to achieve the same result. You may actually have the travel necessary.

Google Books International Textbook Company Hydraulics

seddons · 05-30-2012, 02:19 PM

Thanks, Wilwood has a .70 and a 5/8" master as well, the .7 is basically the same as stock but before I buy another one, would going to the 5/8" master be better? I should in theory increase pressure even more.

**hatzie** · 05-30-2012, 03:16 PM

Quote:

Originally Posted by seddons

Thanks, Wilwood has a .70 and a 5/8" master as well, the .7 is basically the same as stock but before I buy another one, would going to the 5/8" master be better? I should in theory increase pressure even more.

I'd use a master as close to factory as possible. Travel needed is inversely proportional to the MC diameter. Smaller master = longer pedal travel.

05-18-2012, 12:04 PM	#1
seddons Registered User Join Date: May 2012 Location: Hartford Michigan Posts: 3	Hydraulic clutch I have a 1967 Kaiser M715 with a mid 80's Chevy truck engine SM465 Trans and NP205 TC. I have installed a wildwood ¾” clutch master cylinder and GM factory clutch slave cylinder. This thing is like doing 400 lb. squats to push the clutch in. What have I done wrong? I am at a total loss.

05-18-2012, 10:13 PM	#2
v30crewcab Registered User Join Date: Apr 2012 Location: Chatt Tn Posts: 966	Re: Hydraulic clutch sounds like the master is too big. don't recall how big the original one is. __________________ 88 military v30 crewcab shortbed 5.9 cummins, nv4500, 205 86 k30, 89 diesel burb, 76 gmc pathfinder 71 longbed 5.3 4l80 http://67-72chevytrucks.com/vboard/s...d.php?t=522535

05-21-2012, 05:47 PM	#5
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,941	Re: Hydraulic clutch You'd be surprised what a difference 0.05" dia will make. The smaller the bore on the master cylinder, the lighter the pressure you will need to apply. The price you pay for this is that more travel is required to achieve the same result. You may actually have the travel necessary. Google Books International Textbook Company Hydraulics __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

05-30-2012, 02:19 PM	#6
seddons Registered User Join Date: May 2012 Location: Hartford Michigan Posts: 3	Re: Hydraulic clutch Thanks, Wilwood has a .70 and a 5/8" master as well, the .7 is basically the same as stock but before I buy another one, would going to the 5/8" master be better? I should in theory increase pressure even more.

05-21-2012, 04:18 PM	#3
seddons Registered User Join Date: May 2012 Location: Hartford Michigan Posts: 3	Re: Hydraulic clutch The factory master cylinder is .703, the Wilwood one I have is .75 so I am pretty sure that is fine. In fact the only thing that does not match factory specs is the hose. The GM hose will not fit so I used a #3 braded line with #4 ends, could that be the problem?

05-21-2012, 05:38 PM	#4
Cheng Junior Member Join Date: Dec 2011 Location: Jacksonville, FL Posts: 74	Re: Hydraulic clutch Could have to do with where the master cylinder rod connects to the clutch pedal. If this connection is too far from the pivot point it would greatly reduce your lever arm and then require more effort to push in. On my 85 K30 with the SM465 hydraulic clutch the master cylinder push rod connects to the clutch pedal ~2.5" below the pivot point & the clutch pedal is ~17" long overall. So with the original set-up, 20lbs of pedal pressure will generate 136lbs of force acting on the master cylinder. 136lbs acting on the .703 master cylinder will provide 350psi of hydraulic pressure. 136lbs acting on your .75 master cylinder will provide 308psi of hydraulic pressure. __________________ If it wasn't for the last minute, nothing would ever get done. 1953 3800 - SRW C&C Dump - 216/SM420 1985 K30 Scottsdale - SRW - 6.2/SM465/NP205 (Sold)



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