1/2 ton to 3/4 ton brakes

[RoryH19]

Has anyone changed their k5 or k10 brake calipers to the k20 ones?

I believe this is JB5 to JB7.

I think the rotors are both 1.25 inch but the k20's are larger diameter.

Is this a simple caliper swap or does the booster and master cylinder need to be changed too?

Thanks.

 

[dvdswan]

I put 3/4T axles under my K5 back in the day and never had an issue. I did the rear axle first as I kept breaking the 3.73 geared 12 bolt. I found a 14 bolt with 4.11 gears, I figured I look for a front axle with the same gears would be cheaper than swapping gears. Couple months later I found a 3/4 dana 44 with 4.10 gears for 75 bucks. Never had an issue with brakes.

Give a 17 yo kid a 300 HP 4sp lifted truck that likes to race... rear ends tend to say "I'm done".

 

[RoryH19]

Thanks. Then it sounds like I can keep my same master cylinder and brake booster.
I'm going to compare the caliper sizes at autozone. If they are the same size I'll get the k20 ones.

I hear you on the 17yr old comment. My first car at 16 was a 4sp k20. I drove the wheels off of it.

 

[bucket]

The caliper piston size isn't a big enough difference to need a different master cylinder.

I converted my K10 Burb to K20, even using a rear axle from a 1-ton with the big wide 13 inch drums. The drums are where the master cylinder makes the biggest difference. You had to keep the rear drums adjusted properly so the pedal feel wasn't too squishy. But other than that, I liked the softer pedal feel that the stock K10 cylinder provided.

 

[RoryH19]

Thanks, good to know. Since I want to change the calipers/rotors as they seem original, I'll go with k20 calipers.

 

[Craig 85]

I've done 1/2 to 3/4 ton axle swaps twice. It was cheaper doing axle swaps than re-gearing.

My trucks had the older style metal M/C. I'm not sure if the following statement is correct for 81 and up trucks. I used the same power booster, but switched to the 3/4 M/C. You have to swap the brake lines at the M/C, front becomes the back and back becomes the front. On my '79 K15, I probably should have added an adjustable proportioning valve for the rears due to lock up, but I sold the truck before I did this. I did not have the issue on my '77 K5 as that 14 bolt had the smaller 11" brakes.

 

[RoryH19]

Thanks.
By the time I'm done swapping. I'll have a 14B SF in the rear with 11" brakes and the larger k20 calipers in the front. All using 6 lug axles. My stock k5 rear axle already has 11" brakes so no change there. Already installed a new master cylinder and prop valve for the k5, stock replacements. From the feedback it sounds like I can keep them.

 

[Blue Ox]

If you go to rockauto.com or probably any other auto parts store website you can select the two different possibilities you're considering and see if any part numbers interchange. They will also usually give you some specs like piston diameters so you can see what you'd be changing.

Personally, I wouldn't try to re-engineer a brake system by just swapping parts and seeing if it stops okay, but OTOH I'm sure it's done all the time.

 

[RoryH19]

I looked at RA initially for the calipers. On the k20s it shows both the calipers, ones I already have on my k5 and the ones that are slightly larger.
I also checked the same on AZ.

Should be good to go.

 

[rpcraft]

I thought the difference on the front was that the Caliper is spaced out more to clear for the larger inner size of the rotor (compared to the 6 lug setup, but it was the same caliper (and ultimately the same diameter and thickness of the rotor as well?

 

[bucket]

I thought the difference on the front was that the Caliper is spaced out more to clear for the larger inner size of the rotor (compared to the 6 lug setup, but it was the same caliper (and ultimately the same diameter and thickness of the rotor as well?

Same thickness, different diameter. The calipers are physically the same size and interchange, but some 3/4 tons used a caliper with a little larger piston. IMHO, the larger diameter rotor provides more braking force than the 2mm increase in piston diameter.

 

[RoryH19]

In the big scheme, I'm probably not getting much if any additional stopping power from the slightly larger piston of the k20. It is more of, while I'm replacing should use them instead of the stock k5s.

 

[idahovette]

In the big scheme, I'm probably not getting much if any additional stopping power from the slightly larger piston of the k20. It is more of, while I'm replacing should use them instead of the stock k5s.

What was the cost difference??

 

[RoryH19]

It's actually cheaper to buy k20's on RA and AZ

 

[bucket]

It's actually cheaper to buy k20's on RA and AZ

Seems like a no-brainer to me