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solfly Dork
8/27/22 4:12 p.m.

I've thought about doing some Trans upgrades but aside from some leaks mine seems fine so I've been hesitant.

Opti Dork
8/27/22 10:06 p.m.

In reply to solfly :

If you can ever gets your hands on the sonax valve body with all the upgrades done to it, id strongly recommend it. I didn't even have any symptoms related to the check ball being stuck in the seperator plate. Hoping the upgraded parts get me some extra life out of the trans.

EriktheAwful New Reader
11/11/22 5:23 p.m.

I'm rebuilding my '88 C3500's gauge cluster and was searching for GMT400 sending unit resistances and found this thread. I don't follow the GRM forum as much as I follow the GMT400 forum. After playing with RX-7s and big block Cadillacs, I find GMT400s are incredibly easy to wrench on and dirt cheap for parts.

"Eventually I plan on the jeep steering shaft (ujoints instead of rag joint)"

Sorry to be the bearer of bad news, but it's not compatible with the later GMT400s. You can swap the Jeep joint in, but it adds an additional u-joint to the steering shaft. The additional joint can lock your steering in an emergency situation. Spend the money on a quality shaft like the Cunningham Machine shaft. But, yes, I love the XJ Jeep joint on my '89 Stepside.

I saw a lot of talk in this thread about swapping in a GMT800 master cylinder, and there's some discussion about whether or not it's a good idea. At least two GMT400 forum members scrapped their GMT800 master cylinders after suffering a hard pedal during emergency braking. If you're looking for better brakes, the Raybestos Element3 pads are an excellent upgrade - they seem to come in either GG or HH friction codes depending on which color the moon is when you order them. They're also only $25.

Many of the problems with pedal feel in a GMT400 comes from poor rear brake adjustment, which you've already tackled. Use your parking brake regularly and it'll help keep them in adjustment. The rest of the problems seem to come from improperly bleeding the ABS.  My two trucks are pre-ABS so I don't have much knowledge about that.

Opti Dork
11/27/22 8:15 p.m.

The trucks been putting along serving DD duties since I sold the camaro. Hopefully it doesnt have to do this long, Im looking for another 4th gen Fbody, but until then shes it.

I had a hard 1-2 shift once. Shes been hooked to a trailer a couple times, nothing too heavy though. I lost a 9012 low beam, which is odd, normally I get a pretty long life out of the Phillips 9012/9011s. I got a couple nails in tires, but they were fixable so no big deal.

Only real problem I had was a slow loss of brake fluid. I noticed I had almost no brakes a few months after doing brakes. I looked and the reservoir was empty. I figures I did something stupid and had a leak, checked everything over and didnt find anything. So I filled it up and bled it, and kept an eye on it, about a month later it was low again. Checked again no leaks. I pulled the master back and the booster was dry. Finally I got fed up with it and really went over it and noticed some wetness around the master cylinder reservoir grommets. I cleaned it absolutely spotless and went for a drive and when I got back it had returned. Apparently it was leaking very slowly around the reservoir were it pops in to the master. I wanted a GM master since this is the 2 one thats leaked, but couldnt source one. Ill just have to keep a close eye on the new one.

I had been considering doing the GMT800 master, but I was slightly concerned about the residual pressure (or lack thereof) on the rear drums. I found what I think will be a good compromise. I did the JB7 master cylinder. It is used on the 1 tons without the low drag calipers (which I already swapped out) and the half tons with the hydroboost. It doesnt have the quick take up valve, and has a larger bore than the JB6 master but not as big as the GMT800 bore, plus its made for these front calipers, and a rear drum setup so I figured it was a safe bet. I popped it on this morning, bled the system, went for a drive to engage abs, and came back and rebled it.

Initial response is im pretty happy. The pedal feel seems to be more linear and conventional compared to the OE style master. Stopping seems great. It does still have a pretty small dead spot at the top, its hard to tell if its just OBS Chevy because Ive been driving new vehicles lately or if the rears are out of adjustment. It hasnt been long since Ive adjusted the rear brakes, but Ill give them a check in the next day or two and see if the pedal improves at all, but even if it doesnt, it still feels pretty dang good. This thing was already stopping better than pretty much any GMT400 ive driven, so its getting pretty hard to notice improvements.

I think next Ill probably do a steering linkage. I noticed the outer tie rod end boots are looking pretty haggard, but they still dont have any play in them. I also need to quit being lazy and replace that pass side axle thats been losing grease for like a year.

Opti SuperDork
2/4/23 10:52 a.m.

158,000 mile update.

Truck has been putting around fine. This last week North Texas got hit with a pretty bad ice storm. It may not seem like a big deal to you northerners, but its apocalyptic in Texas. We dont have the support to deal with it, and drivers have no idea how to drive in it. I was out in it everyday taking my wife to work, driving to the grocery story, or going to the gym.

Truck did just fine. A testament to the Firestone Destination AT2s I put on, also 4 high doesnt hurt.

It finally melted off yesterday so I decided to go ahead and do an oil change.

Standard Rotella T6 and a wix filter. Cold Idle oil pressure cam up to 40 from about 35. Looks like I have a small rear main seal leak Im going to keep ignoring. I actually remembered to put an oil change sticker in it this time, so Ill know when to change it.

Also a month or two ago there was finally an end to the master cylinder debacle. The brakes felt good with the JB7 master but it still leaked at the grommets. I called a buddy of mine who works on a bunch of these and he said hes seen the same problem a couple times on aftermarket masters, and he always solved it with a delco or GM master. I couldnt get ahold of the GM JB7 master very quickly, so I just picked up the standard GM master. Brakes feel great and a month later I havent lost any brake fluid. Think im finally done with the brakes.

Next up is steering linkage and front axles. I keep meaning to order them and keep forgetting. I was getting a little noise from the axles when in 4wd, so maybe that will motivate me to finally order them.

Opti SuperDork
3/23/23 2:29 p.m.

Decided to give the OBS some love so I cleaned it up today. I broke the glovebox right when I got the truck and have just left it closed and ignored it since then.

A buddy went to put something in it yesterday and it just fell off so I decided I should probably see if I can repair it.

You can see the lower mounting/pivot point is broken off.

Add a little of this

Filled up the void and put a little on top and this is how it turned out.

Letting it cure right now, but after the initial 10 minute set up it seems pretty strong. We will see if it holds up. Next up is some type of repair for the center console. Ive been looking for a used once since i bought the truck. The closest Ive got is a blue one.

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) GRM+ Memberand UltimaDork
3/23/23 2:41 p.m.

I don't think you can own a GMT 400 without some epoxy somewhere in the interior plastic.

AngryCorvair (Forum Supporter)
AngryCorvair (Forum Supporter) GRM+ Memberand MegaDork
3/23/23 3:06 p.m.

i bet if you popped the reservoirs off those masters, you'd find that the grommets are dimensionally identical, so you could swap your good grommets into your larger MC and have a non-leaker with better pedal feel.

Opti SuperDork
3/23/23 4:21 p.m.

In reply to AngryCorvair (Forum Supporter) :

a friend said the same thing. I'm over it. The truck always had a good pedal for an OBS, I was just trying to make it feel like a modern truck. I pulled a trailer today and it felt good, as I'm done with it


onemanarmy Reader
3/24/23 10:55 a.m.

Love this thread....the GMT400s could very well be the best trucks ever made (mayeb gmt800?....but its close)

Opti SuperDork
5/27/23 3:31 p.m.

Started a new job and my commute became a good bit longer. I noticed a little shoulder wear on the outside of the front tires, so figured it was time to quit putting off the tie rods.

I ran moog adjusters and Mevotech TTX tie rod ends. I love these things, I've had much better luck than the moog parts lately and the hardware is awesome. Aligned it and it drives much better.

Plan on trying my hand at tinting the windows this weekend so I went ahead and stripped the windows. Had two layers of tint. It was old at this point it was mostly clear with a slight purple color.

Opti SuperDork
5/28/23 4:50 p.m.

Got the tint on. It went okay. Better than the last time I tried about 15 years ago. I think ive got it down enough to do frameless windows like on the front of the Camaro. Ill keep trying on stuff I think I can do, until I actually get a little better and have some confidence.

Did 30%. I think the limit in Texas is 25% for the front windows. I like all the windows to match otherwise it makes my OCD flare up. Ill have them redone by a professional, or I might retry the front two windows, they both have small creases. Im torn I want to get better, but I also want get tint. Ill definitely do the front two on the camaro. Anyways It made a big difference. Its a little hot today, and I made about a hour drive to the parents house and it makes it seem like the AC is working much better.

I will do the windshield in 80%. Couple friends have done it and told me its legal (need to verify) but it made a huge difference on their trucks.

I went and cleaned her up, so she was pretty. I love this truck.

Opti SuperDork
6/4/23 12:15 p.m.

163,300 Mile Update.

Time for an oil change. I never even pulled the dipstick over the last drain interval. Truck was right at the bottom of the safe zone. I dont recall where it was after the last oil change. Regardless it means I lost/burned less than a quart over a 5K OCI. Im happy with that on a SBC thats always wet, no drips, but it stays "wet." Also at the end of the OCI hot and cold oil pressure had not changed at all compared to the brand new oil.

Standard stuff. Rotella T6.

Also had a failure. Lost a tail light circuit board on the passenger side. its already been changed before, and Im surprised this was my first circuit board failure, they never seemed to last very long on the other GMT400s. No turn signal made my commute pretty rough

Doing this made me look at the tail lights and realize they look like hell. I will probably order some cheap repops. They are cheap enough I dont know if I feel like spending the time polishing these up.

Also my glovebox repair lasted like 10 openings. I been keeping an eye on eBay for a glovebox and center console. Ive seena  couple glove boxes for 2-300 dollars, and I havent wanted one that bad, and last week one popped up for 32 dollars. I went ahead and ordered it. The outside isnt as nice as mine, but it has both hinges. I may swap the outside from mine onto this one I bought, but for now it works.

I also decided to see if I can find another Dale Earnhardt Chevrolet Dealer badge. I found you can buy the new ones from the dealer but they are different now. Maybe I can try and refinish this one, but I cant find any pictures of the older style. If anyone is a better internet sleuth than me and can find an older one for sale or even a picture of one, Id be gratefule. Here is mine.

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