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TR4/4A TR4A front brake caliper rebuild - grease on rubber seals?

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Popeye

Popeye

Obi Wan
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All,

I am getting ready to re-assemble my front calipers. I split the calipers, removed the pistons and rubber bits, cleaned and painted the halves with hot pink caliper paint. (Kidding... satin black.) I will reassembly with a rebuild kit, SS pistons from TRF, and the caliper seals from Moss.

During re-assembly, I understand I should lubricate the rubber piston seal. As this is a complete restoration, I am replacing all brake lines and plan to use DOT-5 brake fluid.

Can I use Permatex Caliper lube for the piston sea? Or, should i use brake fluid, or something else? (This stuff: https://www.permatex.com/products/l...kes/Permatex-ultra-disc-brake-caliper-lube-4/) There is a "Castrol Red Rubber Grease" that seems perfect, but is unavailable in the US as far as I can tell.

I lean towards using a grease over brake fluid, as I figure during normal driving, fresh brake fluid will only come into contact with the seal edge. The lube is thick, and presumably will last longer than brake fluid.

Finally, is there a preferred brand of DOT-5 brake fluid? (Not intending to start a "flame war" between everyone's favorite brands, just curious if there is a clear winner for our cars.)

Thanks, and have a wonderful weekend! (I will spend it wrenching on my daily driver instead of the TR4A; front brakes and bearings.)
 
With DOT 5, I only use the fluid itself on boots & seals. Seems to work as well as anything, and no worries about contaminating the system with it. The calipers I rebuilt some 30 years ago still work today, and I've never touched the seals since then.

I've not noticed any difference in brands of DOT 5. I buy from TRF just because they seem to have the best price, but didn't notice any difference with the GE DOT 5 I used for awhile (got a bunch of it cheap after GE discontinued it). TRF used to supply "North American" brand, but the last one I got was "Johnson's" or something like that.

Likely you know this, but JIC: There is also a DOT 5.1 standard, which is easier to find in stores. Usually says "Synthetic" on the bottle. But it is NOT silicone and suffers from all the same ills as DOT 3 & 4.
 
Mike,
I have only used brake fluid in this application. That is what I recall they say to use. Of course they also say that you should NOT split the two halves of the calipers. Be sure to get that rubber seal back into place and the two halves torqued down good.
I don't use DOT 5, so no opinion there.
Charley
 
TR3driver said:
Likely you know this, but JIC: There is also a DOT 5.1 standard, which is easier to find in stores. Usually says "Synthetic" on the bottle. But it is NOT silicone and suffers from all the same ills as DOT 3 & 4.
Click to expand...

I did not know that! Thank you!
 
I have used NAPA Sil-Glyde silicone grease (#765-1346) successfully for many years. I lubricate the rubber boots liberally inside and out and coat the piston and it's seals as well. The only place you need brake fluid is in back of the piston. It's too thin to protect rubber over time.
When all is assembled I coat the exterior of the boots right down to the metal caliper housing, which prevents moisture from creeping under the seal and doing it's nasty. The silicone grease both lubricates and protects the rubber and does not cause swelling over time as some other brake lubes do.
They are formulated primarily for metal parts in a high temperature environment, and although they claim to be safe on rubber too, I've heard cases otherwise.
 
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