Converting '88 Blazer to '75

[Brian75]

Hello Everyone,

I'm new here and just got an '88. This is a great forum, and I plan to use it a lot! My plans are just to fix what needs it mechanically, brakes, exhaust, leaks, etc.. and then cosmetically make it look like the '75 I used to have.

My questions revolve around what it takes to convert some things. I saved the top and all parts from my '75 and that part looks pretty straight forward from the C/K Forum guy's tech article.

I assume the front end conversion should be pretty easy because guys put the newer nose on the older ones all the time and I already have the fenders and core support. The light wiring I do not think will be a big deal.

My main questions are on the door panels and dash. I want to convert to the '75 door panels. I think the length of the stubs on the window cranks is longer on the '88, so I'll have to change them out, but should the '75 door panels work after that? Will they cover where my '88 covers? Looks like from pics they will, but I would hate to buy them and have them not cover what my '88 does...

My biggest question is on the dash and cluster. I would love to put the '75 dash and guage cluster in my '88 to really complete the conversion. I see I will have to get a '75 style windshield wiper switch and take the wiring from the turn signal stalk and wire up the switch and then relocate the headlight switch. But, I'm concerned about the HVAC controls etc... and if anything else is going to cause a problem.

Has anyone on here ever tried to convert from the newer to the older style?

Thanks for any info, and should I post this in the truck section too?

Here are a couple pics. Sorry the one is sideways... I will be selling this nose after my conversion is complete, but will post that in the for sale forum.

Thanks for any help or advise.

Brian

[Berg]

There's more to the conversion than you think if you'd like it to come out factory looking. For the nose conversion you will have to use the 1975 wiper transmission because the wiper arms sit lower and are meant to hide under the leading edge of the hood instead of sticking up through the cowl sheetmetal panel. You also should make plates that cover up the holes where the 81-91 hood hinges go to keep all the crap out of the cowl assembly. Another overlooked item is the door supports. A 73-75 has internal door supports that stiffen them. You are gonna want to keep those. The doors from 73-76 differ from the 77-91 doors also. Your 75 door panels will not cover the interior trim holes punched into the later-model doors. The top edges where the panels sit are also slightly different and noticeable to me, but maybe not other people. The rocker panels and floor supports also need a rocker box built and added to the truck to stiffen the body. A lot of guys leave that out and the truck will lose its structural integrity after a while. As far as the dash swap and wiring, I personally don't think it would be worth it unless you used EVERYTHING from the 1975 into your 1988 body. The 75 uses an ammeter and 76-up uses a voltmeter. The wiring to the alternator is different for these. The HVAC controls are a totally different animal all together and I'd just leave the 88 stuff in it. You could keep all the 88 dash wiring, gauges and internals and just use the 75 dash pad and bezel, add the wiper switch and figure out which wires control it from the stalk. Chances are, your 88 has delay wipers and the 75 did not. To keep the wiper delay, look for a replacement switch for a 1982 truck with delay wiper option. I never had to convert the wiring so good luck. I'd sit down with both schematics for the 75/82/88 years and figure out how to make it work. The forward light harness isn't too hard to adapt at all.

[Berg]

also, are you keeping the TBI? You'd need the newer style fuse block and fuel pump wiring and whatnot anyway so I'd just stick with all 88 stuff. You could always swap the gauges from your 75 cluster into the 88 cluster but you will have to get an electric oil pressure gauge and a voltmeter from a slightly newer 78-era cluster or around those years so you could get the old style lettering but with the electric sending unit and the voltmeter. I hope this helps before you get rid of stuff you could use back on your rig! Don't forget about the floor-mounted Hi-beam switch too!

[Brian75]

Thanks for the advice guys! I didn't even think about the wiper posts being too long! Most of the other stuff, I have thought about. I do have the inner door supports from the '75, so I'm good there.

I was not certain about the doors/panels, so thanks for the info there. It might be a lot easier to just keep the '88 guages and door panels. The "main" thing I was after was the full convertible conversion and the nose conversion anyway...

Thank you for taking the time to reply. I will post pics as I bring it along.

Brian

[Berg]

hey Brian, any update? How are things coming along? I'm curious to see if you made any progress

[Brian75]

It's been going slow, but I have made some progress. I did a lot of engine work first. Basically just cleaning, painting, and fixing leaks.

I have the front sheet metal prefit, and the next thing I'm doing is the top conversion. As you can see, I have already removed the half-cab. Currently looking for a usable OE hood. I do not want to use aftermarket if I can avoid it.

[Jonboy]

For the doors, if you can find a nice set of 73-76 doors ,you can use them I am guessing you saved the doors from your '75? The '75 door panels will not cover the holes in your '88 doors.

For the gauges, find a '76-78 cluster. It will have a voltage gauge (compatible with your '88 wiring) but give you the look you are after. '76 & '77 have a mechanical oil pressure gauge, 78 is electric. You could always transfer your '75 gauges to the '88 carrier, and source a '78 oil pressure gauge and 76-78 voltage gauge.

With the top cut off, make sure you properly support the rockers. The top stiffens up the tub considerably, and it will flex going down the road if you don't brace them. Since you cut the roof off, you know what kind of bracing is in the top.

[68Timber]

Looks sweet! Love the full vert's but us balding guys appreciate their half cabs. That's my technical contribution.

[riz]

Man does that make me think of having my K5 clip off and painting the engine....



RIZ

[Brian75]

Thanks guys. I did not save the doors from my '75. They were junk.
I have a ton of pictures of rocker boxes and plan on building some. The pics don't show it, but it needs new inner and outer rockers. So, I'm going to build new rocker boxes then.
I do have a '79 cluster with tach, and I'm planning to swap in those gauages. I also have the tach cluster wiring.
Does anyone know where I can hook up my '79 tach wiring to the '88 wiring to get a tach signal? It's not like the old school HEI where you could just plug onto the tach side of the distributor.

[Jonboy]

There is a white plug with a brown end coming off of one of the coil connectors. that is the tach signal lead.

[Brian75]

Great! Thanks for the tip Jonboy! I'm a long way away from getting to the cluster, but now I'll know where to get my tach signal. It's going to be a long winter in the shop of making sparks and dust...

[bL.A.zer90045]

welcome to the club!!! i went "fully topless" bout 3 years ago on my 86 k5 that i used a 74 donor.im in the process now of converting from 4wd to 2wd,and mocking up my 5.3 lm7/4l60e swap! ULTIMATE!!! KEEP THE UPDATES/PROGRESS COMING!!!

[Brian75]

I considered doing an LS/4L swap on this rig, but another project came along sooner than I wanted it to. Don't projects always seem come along at the wrong time? My wife has always wanted a '47 - '53 Chevy truck, and I found an unbelievable barn find that has been sitting in the same place in a concrete floor pole barn for almost 30 years. I'm really fired up to get started on it. It will definitely get an LS, so I decided not to do one on the K5. The drivetrain is fine in this K5 for what I'm using it for anyway...
I have made a little progress, so here are some pics.
I decided to just bite the bullet and replace the whole bed floor rather than just try to patch around on it. I also found a hood and got my doors cut off.