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Transmissions and Rear Ends Three on the tree or four in the floor? Shift it all here.

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  #1  
Old August 6th, 2018, 08:09 AM
WE7X WE7X is offline
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Default 1970 RM7500 clutch slave cylinder question

I have seem listings for a clutch slave cylinder for a '65-66 3500 series that looks like the one on my 1970 RM7500 (rear engine) chassis ( 401M motor) and Clarke 5/2 transmission. Rock Auto for one...in Wagner and Dorman brands.
I am wondering if anyone has a way to determine if there might be some minor differences in one for a 1970. Mine sat for several years, and the piston is now seized at the bottom of the bore. The bore is so rusty that I do not think it is repairable, and I might not even be able to salvage the piston. I have a second slave cylinder, but it is in the same sorry condition.
I can have it bored and sleeved if necessary, but if the '65-66 is the came cylinder, I want to go that way
I see two listings, which show slightly different bore sizes ( 1.063 and ?0.96? or something similar) I have not tried to measure the bore of the original quite yet., but I see a '15/16' cast into the Delco housing, so i know it is a nominal 1" bore....give or take a lot of rust.
Any input is helpful.
or call (425) 466-0884
Rod Johnson
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Old August 7th, 2018, 03:53 PM
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LEWISMATKIN LEWISMATKIN is offline
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Default Re: 1970 RM7500 clutch slave cylinder question

Use the ".96" listed cylinder--15/16" is .937" so the ".96" cylinder will be closest to the original. If you go with the larger bore--"1.063"=1 1/16" can cause a fluid displacement problem especially if the bore of the master cyl. is smaller than the slave cylinder. I hope this helps you in your decision.
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Old August 7th, 2018, 08:19 PM
WE7X WE7X is offline
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Default Re: 1970 RM7500 clutch slave cylinder question

Lewis,
Thank you for that input, and I agree with the diameter vs. fluid transfer issue.
I found a Wagner SC45289 listed at Rock Auto; as fitting a '64 or '65 3000 series, and the picture looks correct. The alternate item ( Dorman CS36124 ) has the slightly larger bore, and the input fitting location is on the top, vs. on the bottom in my particular setup.
I then found a source one at Centric, and a bit less expensive than Rock Auto.
It has been ordered.
I would have been fine with having the local shop putting a sleeve my old cylinder (which they would do for the same cost), but we had not yet found a replacement piston. I am sure both of my original pistons will be in pretty bad shape if I can even get one of them out in one piece.
Now off to the local NAPA for some new supply ( remote reservoir setup in this rear engine chassis) ) and return hoses, and to get a new pressure hose fabricated.
It seems to very rare for any place to have any parts listings or information on anything bigger than a 4000 series chassis in a roughly 50 year old GMC. Rod J
Issaquah, WA
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