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| | | | Joined: Mar 2010 Posts: 10,310 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,310 | I need to replace a 12 bolt 6 lug 3.08 GM rear end in my '49 3100.
(I have a 6 lug 3.64 Nissan Xterra rear end in my '50 3100 behind a T5 transmission with .72 overdrive which was a breeze to adapt to these trucks. It has drum brakes.)
My '49 has a TH400 (no overdrive) so I need a rear ratio in the low 3s.
2005 and later Xterras have 3.13 ratio gears but they came with disc brakes.
I have brand new Huck brakes on the front wheels on this truck and want to know if I can run them with disc brakes on the rear, and can I use the original style '49 master cylinder with this setup?
Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Feb 2004 Posts: 29,885 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,885 | The disc brake calipers will probably need more volume than the original equipment master cylinder can provide, plus discs usually need a power booster to function properly. Pairing up a disc brake with Huck fronts would be interesting, for sure!
I'd suggest working up a "dual diagonal" setup, where one rear disc and one front drum brake on the opposite corner of the vehicle is operated by each chamber of a dual-outlet master cylinder. That should equalize the fluid volume from each chamber and might avoid having a bad mismatch from one portion of the master cylinder to the other.
Jerry
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| | | | | Joined: Mar 2010 Posts: 10,310 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,310 | I am heading to the pick-n-pull tomorrow to see if I can find one with drums and a low 3s gear ratio. Nissan Xterra is not an option. When they went from drums to discs, they went from 4.64 to 3.13. The width is a perfect fit.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: Apr 2005 Posts: 2,832 'Bolter | | 'Bolter Joined: Apr 2005 Posts: 2,832 | You can probably get by without a booster for the brakes on the rear of a pickup. What I would do is put an inline residual pressure valve (2#) in the rear brake line to keep the caliper pad close to the rotor and cut down on the volume of fluid needed to engage the rear brakes. Then one will need an adjustable proportioning valve to dial in the front to back bias so neither locks up before the other. As stated it's interesting.
Evan
| | | | | Joined: Mar 2010 Posts: 10,310 Renaissance Man | | Renaissance Man Joined: Mar 2010 Posts: 10,310 | Thanks all.
I am going to try to rebuild the 12 bolt 3.08. The guts don't look bad.
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
| | | | | Joined: May 2005 Posts: 8,878 . | | . Joined: May 2005 Posts: 8,878 | I've always heard it's not wise to have disc in the rear without first or also having front disc.
Can you think of any factory vehicle with front drums and rear disc? Not to say what the manufacturers do is the only way, but what they do is a good guide and pretty much will be safe. | | | | | Joined: May 2015 Posts: 11,181 Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums | | Housekeeping (Moderator) Making a Stovebolt Bed & Paint and Body Shop Forums Joined: May 2015 Posts: 11,181 | I've always heard it's not wise to have disc in the rear without first or also having front disc. Yep, Front brakes do most of the work, so if you have discs on the rear, they're likely to lock up even under moderate braking. You don't want to be swapping ends when some yahoo pulls out in front of you. Like Jerry said, it's probably going to be tough to get setup correctly. I have a friend with a '63 Corvette and he's replacing the rear trailing arms and installing rear discs but can't afford to upgrade the front drums yet. He talked with Willwood and they said they see that all the time for the same reason as my buddy. They say to put a proportioning valve on the rears and spend about a day setting it up so the braking force is equalized.
Kevin 1951 Chevy 3100 work truckFollow this saga in Project JournalPhotos 1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car) Busting rust since the mid-60's If you're smart enough to take it apart, you darn well better be smart enough to put it back together. | | | | | Joined: May 2006 Posts: 8,351 'Bolter | | 'Bolter Joined: May 2006 Posts: 8,351 | I've always heard it's not wise to have disc in the rear without first or also having front disc.
Can you think of any factory vehicle with front drums and rear disc? Not to say what the manufacturers do is the only way, but what they do is a good guide and pretty much will be safe. I can only think of 1 off the top of my head, the 1984 Yamaha Moto-4 ATV. It had drums on both front wheels, and a single disk on the rear axle. I had one back in the '80s, almost never used the front brakes, as the rear was sufficient to stop it most of the time. Of course this really isn't a good comparison to trying it on a full size truck.
Bill Burmeister
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