1975 SquareBody with front drum brakes?

[NeoJuice]

Looking at a project truck. It’s a 1975 with a sbc 350. It’s a nice little project truck for a decent price but it has front drum brakes. Didn’t Chevy make front disc brakes standard in 71? I asked my brother who knows a lot about old classic cars and he’s perplexed as well.

If I was to get the truck I would plan on lowering it so I would need a disc conversion kit. Drop spindles and springs up front. Then the disc conversion kit or do you think I could piece it all together from Napa? It has a booster and master cylinder so it has power assist. In the pictures from the seller I can’t see if it has a prop valve. The truck is about 3hrs away from me and would need to be trailered home.

Any input would be appreciated. This is my first post in the 73-87 forum. I was a regular poster in the 47-52 forum before selling my 52 last summer.

[Keith Seymore]

Nope. No front drums in 1975.

K

[ron350]

Front drum brakes on a 1975 does not sound right.

[Dead Parrot]

Maybe a frankentruck? An awful lot of parts are largely interchangeable over a wide range of years. Possible a PO assembled it out of bits of several other vehicles and it was labeled a 75 due to the cab being a 75.

As long as the frame and body are solid, given your plans, I wouldn't worry too much about the front suspension and brakes being oddball.

My 75 is front disk, rear drum.

[350TacoZilla]

I would wonder if at some point someone pulled the disk setup to swap into an older non disk truck and just threw the leftover parts back under the 75 to keep it moveable. I have bought and built a ton of trucks that were patchwork of different years so it can be interesting what you end up with.

[MJN]

Front disc's were standard in '71- Look at all the bolts and steering parts for signs of them being removed/reinstalled. It does sound like someone took the front end to put disc's on an older vehicle and put the old parts back in this '75.

[NeoJuice]

Thanks for the replies everyone.

Looks to be a frankentruck lol. I'm still making up my mind to buy the truck. Not a big deal because everything up front would be swapped anyway for lowering components.

[kwmech]

show us pics of the drivers side frame rail around the steering box

[NeoJuice]

kwmech,

I can message the seller of the truck. What exactly do you want the seller to take a picture of so I can explain it to him on of the drivers side frame steering box area.

Thanks,

[kwmech]

The steering box mounting. Trying to determine the year of the frame and whether or not it was a cab swap to an older frame

[Pontiac1976]

By chance is it a 4x4 or 4x2 set up.

[NeoJuice]

Sorry for the late response. Its just a regular 1/2 ton pickup.

I put an offer on the truck and going to look at it next weekend. It's about 3hrs from where I live so I'll know a little more next Saturday.

I do plan on lowering the truck probably 5/6-7 with 3" spindles and 2" springs in the front and a flip kit in the rear.

What has me perplexed is what I will need to do for the front end disc swap.

It has a booster/master, in the pictures I cant see were the prop valve is. I'm assuming that master cylinder will need to be swapped out for a disc/drum master and a new prop valve because I'm not sure if they were changed or not for the drum/drum setup.

Or they might not have been changed and be the original master cylinder/prop valve for disc/drum and the truck is running drum/drum.

One other thing he said it has all new brakes/shocks all the way around. I cant find anything online pre-71 for drum brakes online only front disc pads.

We will see.

[RustyPile]

No front drums after 1970. There is absolutely no reason to replace disk brakes with drums, none whatsoever. I suggest you look over that truck very close in person before you agree to a deal. No telling what you might uncover. Compare the partial VIN on the frame to the cab VIN. You may be in for a big hassle getting the title transferred into your name.. IMHO, run away, run far, far away.. There are far too many squarebodys out there to settle for something like this one.

[old Rusty C10]

Originally Posted by Keith Seymore

Nope. No front drums in 1975.

K

wasnt 4 wheel drums if it was manual brakes and power brakes had discs?

[MJN]

Originally Posted by old Rusty C10

wasnt 4 wheel drums if it was manual brakes and power brakes had discs?

No front drums after 1970, no matter if it was manual or power brakes, 2wd or 4wd. This is the Brake info from the 1975 Info packet;
https://www.gm.com/content/dam/compa...olet-Truck.pdf

[NeoJuice]

It's been a while since posting on the forum. What are you using for image hosting because 100kb isn't much for a file to upload now a days.

Where is the VIN on the frame to compare it to the cab VIN.

The more I'm looking at it, it will probably need upper/lower control arms because there different from 73-87 then pre 73 with drums. It will need drop spindles/springs. Then I'll have to piece together rotors, bearings, calipers, brake lines, then possibly master cylinder/prop valve. To put it back properly is going to cost like $2K or more. Even if I find a kit or do tubular control arms it's not going to be cheap.

[Keith Seymore]

Originally Posted by old Rusty C10

wasnt 4 wheel drums if it was manual brakes and power brakes had discs?

Nope.

I'm looking at the brake chart for 1975.

This is the document that the brake design engineer and brake development engineer created to track their parts for the formal release.

All brake information (the parts for production, service, the service manual, the data book, etc) flow down from these documents.

I have them starting in 1969 up through about 2000 model year.

K

[RustyPile]

Originally Posted by NeoJuice

Where is the VIN on the frame to compare it to the cab VIN.

One of 2 places depending on the actual year of production. On top of the frame rail near the steering gear mounting point.. On top of the frame rail under the cab.

[SCOTI]

Originally Posted by NeoJuice

It's been a while since posting on the forum. What are you using for image hosting because 100kb isn't much for a file to upload now a days.

Where is the VIN on the frame to compare it to the cab VIN.

The more I'm looking at it, it will probably need upper/lower control arms because there different from 73-87 then pre 73 with drums. It will need drop spindles/springs. Then I'll have to piece together rotors, bearings, calipers, brake lines, then possibly master cylinder/prop valve. To put it back properly is going to cost like $2K or more. Even if I find a kit or do tubular control arms it's not going to be cheap.

There's nothing wrong w/the earlier 63-72 A-arms as far as function vs the 73-87's. If they're in decent shape, they can still be used w/a dropped suspension set-up.

You might find a 1/2 ton squarebody for the brake stuff @ a local wrecking yard as they still show up occasionally.

[NeoJuice]

SCOTI,

The information that I found online said the 73-87 were different from 63-72 and should be swapped. But as you said if they were in decent shape and I didn't have to swap them that would be even better.

I would just need to Look for the RPO code if the truck still has the label in the glove box (e.g., JB3, JB5, JB6 can indicate brake package). 1.00" rotor thickness vs 1.25" thickness.

But again since it has front drums and I would be swapping to disc I can determine that myself and purchase the proper rotors and proper calipers for the 1.00" or 1.25" rotor thickness.

I haven't even seen the truck in person yet until Saturday to see if I even want to buy it. Getting kind of worked up about nothing lol.

[Keith Seymore]

Judging by the chart I posted JB1, JB3 and JB5 all get the same rotor: 11.86 x 1.28".

The smaller 1" rotor must have been a later model thing; perhaps cost or mass reduction.

JB6 is a 3/4 ton brake system and is not relevant.

K

[NeoJuice]

I went and looked at the truck on the weekend. I put a deposit down on it and will pick it up on the 24th. Talked with the guy and he didn't really know squat either then it had drum brakes on the front. I'll post an update once I get it home and organized. It was a little rougher in person but not bad for the price. I'm not looking for a show truck just a something to cruise around in.

[SCOTI]

Originally Posted by NeoJuice

SCOTI,

The information that I found online said the 73-87 were different from 63-72 and should be swapped. But as you said if they were in decent shape and I didn't have to swap them that would be even better.

I would just need to Look for the RPO code if the truck still has the label in the glove box (e.g., JB3, JB5, JB6 can indicate brake package). 1.00" rotor thickness vs 1.25" thickness.

But again since it has front drums and I would be swapping to disc I can determine that myself and purchase the proper rotors and proper calipers for the 1.00" or 1.25" rotor thickness.

I haven't even seen the truck in person yet until Saturday to see if I even want to buy it. Getting kind of worked up about nothing lol.

Think of the earlier 63-72 arms as a primitive 'Delrin' style of bushing. It's basically like a rubber lined steel screw that allows pivoting up/down via the threads of the screw.

Then, automotive manufacturers started down the path of making the 'standard duty' trucks more compliant (& comfortable) like cars w/the porky rubber bushed bushings.

Heavy Duty trucks kept those same 63-72 style of bushings through the end of the C/20/30 body style ('91?) because they were effective. The car style rubber bushings were compliant & helped isolate the suspension, but their movement came from twisting/distorting that porky rubber insert vs allowing the a-arms to pivot w/less bind. Over time they'll deteriorate, crack, & harden. That's where 'Poly' bushings came into play & are supposed to be an 'improvement' (a subjective assessment @ best). Delrin came along as the improved answer to Poly as it allows more freedom to pivot w/o the binding but they're also more expensive parts that do the same thing as those old school drum brake 63-70 a-arm bushings.

There is no Caster/Camber advantage using the 73-87 vs 63-72 a-arms. I'd pop fresh BJ's in place for a disc brake spindle & use the existing 63-70 a-arms w/o hesitation.

[cwcarpenter98]

Originally Posted by SCOTI

I'd pop fresh BJ's in place for a disc brake spindle & use the existing 63-70 a-arms w/o hesitation.

I would do the same thing. When I was replacing the original rubber bushings on my 81, I had to really fight them. If I had a set of 63-72 arms sitting around, I totally would have just used those instead of trying to replace the rubber bushings.

My 63 is running the original 63 control arms, stock height squarebody 1.25" spindles, and stock ball joints for a squarebody. No modifications were needed for this combo

[NeoJuice]

SCOTI, cwcarpenter98,

From what I understand, you're suggesting that I keep the existing upper and lower control arms, but replace the ball joints and control arm bushings. After that, I can install the drop spindles and lowering springs. Then I’ll just need to gather all the components for the disc brake conversion—rotors, bearings, seals, backing plate, calipers, and brake lines.

I'll have the truck home on the 24th and will be able to get some pictures after that to verify what's actually going on out front. I did look under the truck and it did have a front sway bar.