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Old 02-20-2018, 05:45 PM   #1
SnS C10
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Just acquired this 86 k2500 4x4 suburban!

Hey guys long time member. My name is Shaun. I recently traded a toyota corona I had for awhile for this 1986 suburban. its a 2500, 4x4. engine is a crate 350 from Goodwrench with im told 40,000 miles on it and same for the transmission which im told is a th400 although i have not verified this. The engine runs beatifully and sounds great with its dual flowmaster mufflers. its all stock as it needs to pass california smog which it has.

My issue at this point is there is a ticking/knock noise. While in Park it will make the noise but with the slightest raise in rpms, say 100rpm, the noise goes away. There is no noise while driving or revving. Seems to only be right around the park rpm. Kind of sounds like the flexplate tapping against the cover but what do you guys think? I didnt think it sounded like a catastrophic problem and if it were i believe i would hear it more often at different rpm ranges. Thoughts? heres a link to a video

https://www.youtube.com/watch?v=QQvgLrDh0fA
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Old 02-20-2018, 05:47 PM   #2
SnS C10
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Re: Just acquired this 86 k2500 4x4 suburban!

a few pictures too
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Old 02-20-2018, 06:20 PM   #3
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Re: Just acquired this 86 k2500 4x4 suburban!

Couldn't be 100 percent, but i do know the newer 3/4ton (maybe 1/2 ton also) chevys are prone to the flex plates cracking and giving a similar tapping noise.
This might sound like a dumb question also but have you drained the oil to see what it looked like?
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Old 02-20-2018, 06:25 PM   #4
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Re: Just acquired this 86 k2500 4x4 suburban!

i have checked the oil but not drained it. Just picked up the burb yesterday. it does look clean. if it was a rod bearing, i would hear it more often correct?
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Old 02-20-2018, 06:31 PM   #5
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Re: Just acquired this 86 k2500 4x4 suburban!

I would think so, does it have an oil pressure gauge? that appears to be reading properly? I would think an internal engine noise it would continue with raised rpms unless it was somehow oil pressure related. It looks like a nice rig btw, I'm a big fan of suburbans and envy you guys out west that can pick them up with little to no rust
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1995 GMC K1500 Suburban 6" Pro comp 35x12.50R17
LSXburb -Build- 1990 GMC Suburban 6.0 Lq4 4l80e np205 D60 14FF
1988 GMC suburban 350ci Sm465 D60 14FF 8" 39.5x15R15
1969 Pontiac Lemans 400ci Muncie 4 speed
2009 Pontiac G8 Gxp M6
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Old 02-20-2018, 07:10 PM   #6
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Re: Just acquired this 86 k2500 4x4 suburban!

Yes it has a mechanical gauge. Just got off the freeway and it’s idling at about 35 pounds
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Old 02-20-2018, 07:23 PM   #7
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Re: Just acquired this 86 k2500 4x4 suburban!

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Yes it has a mechanical gauge. Just got off the freeway and itís idling at about 35 pounds
Thats impressive, my 95 runs a little lower than that after everything comes up to temp. I would maybe pull the dust shield off of the trans and take a peak at the flex plate if possible
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1995 GMC K1500 Suburban 6" Pro comp 35x12.50R17
LSXburb -Build- 1990 GMC Suburban 6.0 Lq4 4l80e np205 D60 14FF
1988 GMC suburban 350ci Sm465 D60 14FF 8" 39.5x15R15
1969 Pontiac Lemans 400ci Muncie 4 speed
2009 Pontiac G8 Gxp M6
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Old 02-20-2018, 08:58 PM   #8
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Re: Just acquired this 86 k2500 4x4 suburban!

congrats, awesome! Now ditch the running boards haha
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Old 02-21-2018, 10:41 AM   #9
SnS C10
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Re: Just acquired this 86 k2500 4x4 suburban!

strange to me how a slight increase in rpm in park/neutral/drive makes that noise completely disappear

Another questions, the ride on the front end is pretty stiff. Does this have anything to do with the 2 shocks per side in front? Is there a remedy for the stiffness? I thought i read that you can remove one shock per side. Is this advisable and if so which one do i remove?
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Old 02-21-2018, 10:58 AM   #10
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Re: Just acquired this 86 k2500 4x4 suburban!

The stiff ride on a 2500 4x4 is pretty standard. I just drive slower and get used to it.
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Old 02-21-2018, 04:10 PM   #11
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Re: Just acquired this 86 k2500 4x4 suburban!

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Originally Posted by SnS C10 View Post
strange to me how a slight increase in rpm in park/neutral/drive makes that noise completely disappear

Another questions, the ride on the front end is pretty stiff. Does this have anything to do with the 2 shocks per side in front? Is there a remedy for the stiffness? I thought i read that you can remove one shock per side. Is this advisable and if so which one do i remove?
I had an 86 K20 that had the dual shocks in the front and it was a rough ride also, Ive heard switching to just single shock set up makes them ride smoother but haven't experienced the change for myself. And what Edahall said could also be the case, 3/4 tons usually aren't known for the best ride quality.
If you were to remove a shock from both you would want to remove the outer shock(i believe) the inner would function the same as a single shock set up, if there is a spacer up top it would probably have to be switched to go inbetween the one shock and the frame. I can take some pictures of my front end later to show the single shock lay out if needed
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1995 GMC K1500 Suburban 6" Pro comp 35x12.50R17
LSXburb -Build- 1990 GMC Suburban 6.0 Lq4 4l80e np205 D60 14FF
1988 GMC suburban 350ci Sm465 D60 14FF 8" 39.5x15R15
1969 Pontiac Lemans 400ci Muncie 4 speed
2009 Pontiac G8 Gxp M6
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Old 02-21-2018, 04:43 PM   #12
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Re: Just acquired this 86 k2500 4x4 suburban!

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I had an 86 K20 that had the dual shocks in the front and it was a rough ride also, Ive heard switching to just single shock set up makes them ride smoother but haven't experienced the change for myself. And what Edahall said could also be the case, 3/4 tons usually aren't known for the best ride quality.
If you were to remove a shock from both you would want to remove the outer shock(i believe) the inner would function the same as a single shock set up, if there is a spacer up top it would probably have to be switched to go inbetween the one shock and the frame. I can take some pictures of my front end later to show the single shock lay out if needed

thanks KeithT712 i would appreciate that!
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Old 02-21-2018, 07:36 PM   #13
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Re: Just acquired this 86 k2500 4x4 suburban!

Heres the pics from my set up(both of mine are the same way) I had been looking into an after market set up for mine but decided against it mostly because of possible clearance issues. Hope these help!
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1995 GMC K1500 Suburban 6" Pro comp 35x12.50R17
LSXburb -Build- 1990 GMC Suburban 6.0 Lq4 4l80e np205 D60 14FF
1988 GMC suburban 350ci Sm465 D60 14FF 8" 39.5x15R15
1969 Pontiac Lemans 400ci Muncie 4 speed
2009 Pontiac G8 Gxp M6
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Old 03-08-2018, 06:29 AM   #14
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Re: Just acquired this 86 k2500 4x4 suburban!

I have a 1990 V2500 Suburban and I initially went to one shock in the front and saw a noticeable improvement in the ride quality. The next step I did was I did a set of 4" lift Deaver Springs (front and Rear Springs) and Bilstein 5100 shocks all around. This made a huge difference in the ride quality of the truck.
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Old 03-11-2018, 06:15 PM   #15
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Re: Just acquired this 86 k2500 4x4 suburban!

Sns C10,

Looks like I have your little brother, 1988 1/2 ton.

Hope you use yours as a DD like I do mine, you'll enjoy every minute of it.

Electricduane, I'm not going to ditch my running boards either. They help the old guy get in/out without wearing out the front seat. ;-)

Enjoy,
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Old 03-12-2018, 10:32 AM   #16
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Re: Just acquired this 86 k2500 4x4 suburban!

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Sns C10,

Looks like I have your little brother, 1988 1/2 ton.

Hope you use yours as a DD like I do mine, you'll enjoy every minute of it.

Electricduane, I'm not going to ditch my running boards either. They help the old guy get in/out without wearing out the front seat. ;-)

Enjoy,
nice looking truck! I go back and forth between driving the suburban and my 2009 toyota tacoma everyday. Currently the suburban is disabled though due to a leaky power steering pump. I did however get the tail lights and reverse lights working yesterday. Found out that my brights are permanently on for my headlights. The switch on the turn signal lever does not seem to be working
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Old 03-12-2018, 10:44 AM   #17
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Re: Just acquired this 86 k2500 4x4 suburban!

hi/low beam switch should be down on the steering column, just above the brake pedal. There is a metal rod that runs from that switch up to the turn signal lever....

This was the one I used on my 89':

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
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Old 03-14-2018, 02:10 PM   #18
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Re: Just acquired this 86 k2500 4x4 suburban!

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hi/low beam switch should be down on the steering column, just above the brake pedal. There is a metal rod that runs from that switch up to the turn signal lever....

This was the one I used on my 89':

https://smile.amazon.com/gp/product/...?ie=UTF8&psc=1
thank you for the info! I will check out the metal rod when i can free up some time.

Also, my turbo 400 trans does not down shift. In fact when in drive, it seems to upshift too early. For example i may be doing 20mph in 3rd gear and not be in any kind of power band for the engine. The wire coming out of the side of the trans is connected to the switch at the gas pedal. What could be going on here? Maybe the switch is bad? Can the shift speed/rpm be adjusted?
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Old 03-14-2018, 02:42 PM   #19
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Re: Just acquired this 86 k2500 4x4 suburban!

I'm not familiar with the TH400 but with a little research, it looks like there is some type of actuator/valve thing either on the carb or on the tranny itself. I was first thinking about adjusting the TV cable, but I guess yours doesn't have it (700R4 has one).

Bring to tranny shop. Sounds like there may be some adjustments that could be had....
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Old 03-14-2018, 02:52 PM   #20
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Re: Just acquired this 86 k2500 4x4 suburban!

From what I understood there is either a switch at the carb or at the gas pedal which is where mine is. Hoping that this is an easy fix rather than spending money at the trans shop
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Old 03-19-2018, 09:26 PM   #21
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Re: Just acquired this 86 k2500 4x4 suburban!

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From what I understood there is either a switch at the carb or at the gas pedal which is where mine is. Hoping that this is an easy fix rather than spending money at the trans shop
You need to make sure you have 12 volts to the "switch" at the throttle pedal in the cab. It is actually a variable resistor and varies the voltage to the transmission based on throttle position and handles the upshifts and downshifts.
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Old 03-19-2018, 09:46 PM   #22
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Re: Just acquired this 86 k2500 4x4 suburban!

I did test the voltage and I have 12 volts at the switch with the key on and also 12 volts when I apply the pedal to the switch which activated the wire running to the switch on the trans
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Old 03-22-2018, 11:16 AM   #23
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Re: Just acquired this 86 k2500 4x4 suburban!

replaced the power steering pump yesterday and took it for a drive. The trans is not downshifting at all. Since I have power at the switch by the pedal, should i assume the switch on the trans is bad?
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Old 03-22-2018, 11:34 AM   #24
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Re: Just acquired this 86 k2500 4x4 suburban!

Switch inside the pan, or it somehow got unplugged internally. The switch does not control the shifting on a T400. It just controls the down shift when you stab on the pedal. (If teh governor is working correctly) Early up shifting could be a vacuum modulator out of adjustment, a small vacuum leak in the hose coming to the modulator or the governor out of calibration. I've seen the rear bushing in the trans walk out of the case and strip the nylon gear on the governor rendering it useless. Pull the 4, 5/16'' bolts out of the small steel plate (3x3) near the back of the trans and pull out the governor. You will have a slight amount of oil come out. If the gear looks good, look at the valve internally and see if it goes up and down when you move the fly weights.


If all that looks good, then move on to the vacuum modulator for an adjustment.


Actually try adjusting the modulator first, pull the vacuum hose off and with a small flat blade screwdriver go inside the hole and tighten the screw about a 1/4 turn then take it for a drive and see if it makes a difference, repeat as necessary. When you pull the hose off and get even a slight amount of trans oil, you've found your problem, replace the modulator then adjust
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Old 03-23-2018, 01:18 PM   #25
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Re: Just acquired this 86 k2500 4x4 suburban!

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Switch inside the pan, or it somehow got unplugged internally. The switch does not control the shifting on a T400. It just controls the down shift when you stab on the pedal. (If teh governor is working correctly) Early up shifting could be a vacuum modulator out of adjustment, a small vacuum leak in the hose coming to the modulator or the governor out of calibration. I've seen the rear bushing in the trans walk out of the case and strip the nylon gear on the governor rendering it useless. Pull the 4, 5/16'' bolts out of the small steel plate (3x3) near the back of the trans and pull out the governor. You will have a slight amount of oil come out. If the gear looks good, look at the valve internally and see if it goes up and down when you move the fly weights.


If all that looks good, then move on to the vacuum modulator for an adjustment.


Actually try adjusting the modulator first, pull the vacuum hose off and with a small flat blade screwdriver go inside the hole and tighten the screw about a 1/4 turn then take it for a drive and see if it makes a difference, repeat as necessary. When you pull the hose off and get even a slight amount of trans oil, you've found your problem, replace the modulator then adjust
i did what you said except i bottomed out the screw then backed it off 1.5 turns. The burb does downshift now and shift slightly better but not anywhere near it should. Better though. Will try to screw it in a little more but its already almost bottom out. May be time for a new modulator
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