vrv questions

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Apr 9, 2022 | 08:16 PM

Peter A.

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Mountain Pass

Joined: Dec 2016

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vrv questions

Hi guys,
It's been a couple of years since I last had any problems with my 87 dually. The last big problem was a blown head gasket on the old 6.9. The purchase of a 92 donor truck allowed me to upgrade to a 7.3 w/Hypermax turbo. This engine has run flawlessly, since installation. The other day I noticed a hesitation on the upshift from 1st to 2nd gear. The again this morning. It can't be the transmission { C6 with only 90,000 miles on it }. I'm thinking that the vrv cleanup and repair that I did years ago, may have gone bad. Any ideas ???????

Peter

Apr 10, 2022 | 07:06 AM

tjc transport

i ain't rite

Joined: Mar 2005

Posts: 65,569

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From: Marlboro Mental Hospital.

it could be a lot of things.
improper adjusted VRV.
weak vacuum pump.
cracked vacuum line.
failing trans modulator.
failing trans.
low trans fluid.
dirty trans fluid.
dirty trans filter.

Apr 10, 2022 | 10:43 AM

Peter A.

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Mountain Pass

Joined: Dec 2016

Posts: 127

Likes: 2

Yes, I'll be checking all of the obvious this morning. The VRV has been working properly since I cleaned and adjusted when I switched engines. I'm leaning towards a loose or rotted vacuum line. [ hopefully ] It seems to be an intermittent problem. I just came back from a road test, and was able to affect the up-shift by lifting my foot off the pedal for just a split second.
Peter

Apr 10, 2022 | 10:53 AM

tjc transport

i ain't rite

Joined: Mar 2005

Posts: 65,569

Likes: 5,606

From: Marlboro Mental Hospital.

depending on how old the vacuum pump is, i would suspect that first. you want minimum 17 inches vacuum for proper trans functions. the higher the vacuum, the better.
easy way to test pump is put a vacuum gauge on with engine running and quickly hit the brakes two or tree times. vacuum should climb back up almost instantly. if it take a minute or more to get back over 20 inches, the pump is on it's last legs.

Apr 11, 2022 | 06:19 AM

Olds64

Logistics Pro

Joined: Jun 2017

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From: Edmond, OK

Recently my Bullnose was shifting weird and it turned out to be a bad vacuum pump. My power brakes were also acting squirrely. After a run to the parts store and 20 minutes with a wrench the problem was fixed. Good luck.

Apr 11, 2022 | 07:28 AM

rhythim

Cross-Country

Joined: Aug 2015

Posts: 68

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From: Middle TN

All of the above is good info. My '85 started having delayed shifts about a month ago, so I did all the normal checking, had 20" vacuum from the pump, no leaks in the lines, and the diaphragm in the modulator wasn't ruptured, so I figured the VRV was at fault. Bought one of the new replacement units reverse-engineered and built by Nick at https://www.nickpisca.com/diesel/fue...gulator-valve/ and installed it. Truck was much improved, but still not shifting like it ought to have been, even after adjusting the VRV per the factory manual and adjusting the spring tension on the modulator. Finally gave up, spent the $20 and replaced the modulator valve, even though it seemed like it was OK, and that fully cured the issue.

Apr 12, 2022 | 02:47 PM

Peter A.

Thread Starter

Mountain Pass

Joined: Dec 2016

Posts: 127

Likes: 2

It finally stopped raining giving me enough time to check the vacuum pump. !0 to 12 was all that I could getup of it. Crap! more money for Chinese parts. Then I realized that along with the overdrive and other goodies, I also had taken the vacuum pump w/pulley off of the donor truck. After about 20 minutes of looking in the barn I found the pump. Ironically it took less time to find the pump, then it took to change it. The new old pump is fairly consistent at 18 inches. Went on my road test without any transmission or brake issues. I'm just wondering how long we will still be able to scrounge parts for these old relics.
Thanks for your advise and input.
Peter