Dr Diff Master Cylinder Seals

[djw383]

Does anyone know if you can change the seals between the plastic reservoir and the aluminium? My Doctor Diff one is leaking http://www.doctordiff.com/aluminum-master-cylinder-kit.html .... I think his is the same as the one from Napa....https://www.napaonline.com/napa/en/p/NMAM2373/NMAM2373

Thanks!!!!

[burdar]

The master cylinder he sells aren't anything special except for the 15/16" bore version.  He machines the back of the piston on the 15/16" master to accept a manual brake pushrod retainer.  Have you tried your local parts store to see if a seal kit is available?  You could also call Dr Diff and ask him if you can't find something locally.

[bandt]

I have the same master with the same problem. I went to the wreckers and got a couple oem caps with seals. Problem solved.

Brian

[djw383]

Doctor Diff didn't know the dormant number for the seal needed. It is actually between the reservoir and the aluminium housing.  I was impatient and just bought a AutoZone reman and swapped the seals, so far so good.  I didn't have to bleed the brakes and thankfully I had used silicone fluid. Here is a worthy page to bookmark when searching part stores: http://www.dragstuff.com/techarticles/RacingMasterCylPN.html

[72bluNblu]

The cap seals are Dorman #42081, new caps are #42044 (and come without seals).

The OE seals for those m/c's are crap. They work for like the first 3 or 4 times you open the caps and after that they start leaking. I've done the 15/16" aluminum m/c swap a couple times now, I bleed the brakes with the OE caps/seals and when I'm done I put the dorman caps and seals on, they seem to work pretty well.

[burdar]

Are you using Dr Diffs master or a parts store unit? I've heard some people don't worry about locking the pushrod into the master and run the parts store version. I need to talk to my father-in-law and see if he has the capability to machine the back of the piston. If he can do it, that would save me $60.

[72bluNblu]

I'm running the Dr. Diff version because I wanted a 15/16" bore. The parts store version will be 1-1/32". Plus you need an adaptor anyway, remember that Cass's $95 price tag includes the 4 to 2 bolt adaptor, it's not a straight swap. And Cass is good people, I don't mind spending a little more with him because I know if anything goes sideways he'll take care of it. 

[djw383]

I'm running the Dr. Diff version because I wanted a 15/16" bore. The parts store version will be 1-1/32". Plus you need an adaptor anyway, remember that Cass's $95 price tag includes the 4 to 2 bolt adaptor, it's not a straight swap. And Cass is good people, I don't mind spending a little more with him because I know if anything goes sideways he'll take care of it. 

Agreed.

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[burdar]

I'm running the Dr. Diff version because I wanted a 15/16" bore. The parts store version will be 1-1/32". Plus you need an adaptor anyway, remember that Cass's $95 price tag includes the 4 to 2 bolt adaptor, it's not a straight swap. And Cass is good people, I don't mind spending a little more with him because I know if anything goes sideways he'll take care of it.

Dr Diff's 15/16" master cylinder is $100.  The adapter(which I already have) is an extra $25.  An aluminum master from an 89 Dakota has a 15/16" bore but it isn't machined for the pushrod retainer.  Dr Diff machines the piston for the retainer.  You can buy the Dakota 15/16" master at Rockauto for $40.

[72bluNblu]

Dr Diff's 15/16" master cylinder is $100.  The adapter(which I already have) is an extra $25.  An aluminum master from an 89 Dakota has a 15/16" bore but it isn't machined for the pushrod retainer.  Dr Diff machines the piston for the retainer.  You can buy the Dakota 15/16" master at Rockauto for $40.

I think you'll find that many of those reproduction master cylinders for the Dakota are cast iron now, not aluminum (as they were from the factory). And regardless you still need an adaptor to go from a 4 bolt mount to a 2 bolt mount m/c. Cass has also said over on for A-bodies only that the Dakota m/c will not accept the manual push rod for an A-body, so I doubt it would work in this case either.

The 4 to 2 bolt adaptors are at least $35 everywhere I've seen them if they're purchased separately. Assuming you get the right aluminum 15/16" bore m/c for $40 that's still $75 you've spent and you still need to pay shipping on two separate items. And you probably wouldn't have a way to retain the pushrod in the piston. I don't see how it doesn't make sense to just buy the right one from Cass, knowing everything will fit and work right the first time. Even if it might cost a few extra bucks.