Dorman Vacuum air pump testing Rockauto

WrenchWhore

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So I just ordered a bunch of brake parts to fix my 87 truck. Got a new Vacuum pump, brake booster, and master cylinder. Booster and master were absolute junk. Booster leaked like crazy and the master got sand inside it which clogged one of the lines right off the port.

My issue is the vacuum pump I got was a Dorman part which I know aren't the best but I'm a cheap and didn't think the others parts would be much better unless it was Motorcraft. My issue is it's brand new and puts 17 lbs. of vacuum. Is this ok for a brand new part? I was expecting something like 20 lbs. like others have said. Maybe my gauge is junk but I tested two and both read 17 lbs. The one I replaced was at about 15 lbs. Spending $100 shipped to my door just to gain 2 lbs of vacuum seems dumb but I wanted to hear your guys opinions. After replacing everything it is an absolute night and day difference but I suspect that was mainly from the booster leak and clogged master. Thoughts? Should I send it back and get another one?
 

Cubey

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What transmission? C6 needs a certain amount of vacuum or it'll act up. My vacuum pump started getting weak right after a C6 rebuild, making it act up a little (late 3rd upshifting, noticable downshift when braking).

If you have a manual transmission, I don't think vacuum matters. If the braking is working and you don't have a C6, you might just run it.
 

WrenchWhore

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What transmission? C6 needs a certain amount of vacuum or it'll act up. My vacuum pump started getting weak right after a C6 rebuild, making it act up a little (late 3rd upshifting, noticable downshift when braking).

If you have a manual transmission, I don't think vacuum matters. If the braking is working and you don't have a C6, you might just run it.
I'm running the T19. It's a single cab long bed 4x4 so it's not a crazy heavy crew cab dually.
 

gnathv

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17 is low. This is what I had when I replaced my pump with a used one. Are you checking right out of the pump or at the distribution block?
 

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WrenchWhore

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17 is low. This is what I had when I replaced my pump with a used one. Are you checking right out of the pump or at the distribution block?
I checked right out of the pump hose. I actually have that exact gauge and it's reading just at the bottom of the green at 17 lbs.
 

Cubey

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I hate to tell you, that seems to be how they are now. I just installed a new Dorman 904-808 in my RV and it only has about 20-21 PSI also, with a test gauge going directly do it. I got it from Amazon in the middle of last month, but didn't install it until today.

It has the same exact Dorman part number as the pump I bought in 2017 from O'Reilly, which had 25 PSI when it was new/good. I haven't test driven to see if my C6 behaves properly or not, but I'm guessing it won't. My C6 was acting up when the old pump dropped to about 20 PSI, so yeah.

What a pain to have to pull it back off again, but I'd rather do that, than be stuck with a junk $72 pump. I'll have to put the old pump back on until I get to an O'Reilly to warranty the old lifetime warranty pump, unless I try buying one from the local Napa for $132 and hope it isn't junk too. But there's no guarantee a free replacement one from O'Reilly won't only show 20-21 PSI too.

So, I guess I'll just have to pull the new one off, put the old back on, return the new one as defective, and hope I can get another that shows the right pressure, either from O'Reilly or elsewhere. Makes me wish I had a spare vac pump pulley since that's a good chunk of the labor time, swapping it out. I can't justify spending $60 for one though.
 

WrenchWhore

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Yes, this is at idle, 650rpm
What do you think? Should I just send it back and try to get one that has higher vacuum? If I had a C6 I think it would be a no brainer. Returning can be a hassle but I want it done right and I know these pumps fade over time.
 

Cubey

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What do you think? Should I just send it back and try to get one that has higher vacuum? If I had a C6 I think it would be a no brainer. Returning can be a hassle but I want it done right and I know these pumps fade over time.

You might try buying one of another brand (Napa maybe?) and hope it's better? I'm in the same boat, except at least Amazon does free returns. That's why I bought it from there, since there has been people saying newer vac pumps are bad right out of the box. You might see what RockAuto does for warrantying it too, if they might pay send you another and pay return shipping? Dunno how they do things now. 10 years ago when you could still call them and talk to them on the phone, they were very good about warranty/parts issues.

I might just buy a new Napa one from the local store ($132+tax) and hope it's better since I have time to piddle around here for another month or two.
 

WrenchWhore

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I hate to tell you, that seems to be how they are now. I just installed a new Dorman 904-808 in my RV and it only has about 20-21 PSI also, with a test gauge going directly do it. I got it from Amazon in the middle of last month, but didn't install it until today.

It has the same exact Dorman part number as the pump I bought in 2017 from O'Reilly, which had 25 PSI when it was new/good. I haven't test driven to see if my C6 behaves properly or not, but I'm guessing it won't. My C6 was acting up when the old pump dropped to about 20 PSI, so yeah.

What a pain to have to pull it back off again, but I'd rather do that, than be stuck with a junk $72 pump. I'll have to put the old pump back on until I get to an O'Reilly to warranty the old lifetime warranty pump, unless I try buying one from the local Napa for $132 and hope it isn't junk too. But there's no guarantee a free replacement one from O'Reilly won't only show 20-21 PSI too.

So, I guess I'll just have to pull the new one off, put the old back on, return the new one as defective, and hope I can get another that shows the right pressure, either from O'Reilly or elsewhere. Makes me wish I had a spare vac pump pulley since that's a good chunk of the labor time, swapping it out. I can't justify spending $60 for one though.
Yeah this is definitely annoying since I just got it all hooked back up and it's almost the same as the old one. I need to double check and maybe triple check my vacuum readings that it is in fact low on vacuum.
I'm not surprised that the cheapest air pump on Rockauto isn't working like I thought. Especially for this old dinosaur technology. I really didn't want to spend that extra money for a Napa brand but maybe this is "you get what you pay for" kind of situation.

I figured once I got this air pump working better that maybe my Cruise control would start working again and they are still inoperative. It's never worked since I got the truck. Not sure if it's the weak vacuum pump or something else out of adjustment but the fact that it still not working really infuriates me.
 

WrenchWhore

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You might try buying one of another brand (Napa maybe?) and hope it's better? I'm in the same boat, except at least Amazon does free returns. That's why I bought it from there, since there has been people saying newer vac pumps are bad right out of the box. You might see what RockAuto does for warrantying it too, if they might pay send you another and pay return shipping? Dunno how they do things now. 10 years ago when you could still call them and talk to them on the phone, they were very good about warranty/parts issues.

I might just buy a new Napa one from the local store ($132+tax) and hope it's better since I have time to piddle around here for another month or two.
I sure hope rockauto has good returns. I dislike Amazon but when it comes to returning and getting another one they're awesome. They kinda have to considering they sell a lot of junk sometimes. It's the luck of the draw sometimes with parts no matter where you get them. I agree though. I just want it done and fixed so I can work on another fix that needs attention like my power steering leaking more than the Exxon Valdez...
 

Cubey

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Yeah this is definitely annoying since I just got it all hooked back up and it's almost the same as the old one. I need to double check and maybe triple check my vacuum readings that it is in fact low on vacuum.
I'm not surprised that the cheapest air pump on Rockauto isn't working like I thought. Especially for this old dinosaur technology. I really didn't want to spend that extra money for a Napa brand but maybe this is "you get what you pay for" kind of situation.

I figured once I got this air pump working better that maybe my Cruise control would start working again and they are still inoperative. It's never worked since I got the truck. Not sure if it's the weak vacuum pump or something else out of adjustment but the fact that it still not working really infuriates me.

I have an in cab vacuum gauge and it dropped about 5 max reading right when the C6 started acting up, and that gauge is also showing the new pump being about the same as the old pump. I guess Dorman changed something in the pumps and it has caused a 5psi drop vs the ones being made 5 years ago. The bolts that assemble the pumps used to be cap head screws, now they are cheaper hex head bolts.

This is what the in cab gauge show showed right after the C6 rebuild, and before the pump went weak:
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Now it shows about 15-17. But also testing the pump directly shows it being weak. Unless the main hose coming from the vacuum pump is suddenly damaged... nothing has changed.

I do have two cruise control vac lines totally undone because I don't trust 37 year old mechanical cruise control; one of the barbs is capped off on the distribution tree, and the other is feeding the in cab gauge. So, with a properly working pump, the in cab gauge should be showing about 20 and the pump without anything on it should show 25, at least on my RV.

Edit: yes the in cab gauge shows In.Hg not PSI but it's still a good indicator. I have a HFT test gauge that shows PSI which is what I use to test the pumps directly. Plus I think it's actually showing PSI, not In.Hg
 
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WrenchWhore

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Thank you for this info Cubey. If anyone needs a great working vacuum pump it's you with that motorhome. Where it could be a life or death situation and you need all the braking pressure you can get. I'm going to head outside and do some more test. Most likely i'm going to get another vacuum pump and cross my fingers maybe i'll just send it back to Rockauto and go direct to my Napa down the street and stop pinching pennies. The time it takes for things to ship from Rockauto to my part of AZ is also an annoyance. Keep us posted about your findings.
 

Cubey

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i'll just send it back to Rockauto and go direct to my Napa down the street and stop pinching pennies.

I know the feeling. But again, the pump it was replacing was the same brand and model number.... and I can tell that they have changed things about the build since 2017. And Napa ones might be rebranded Dorman for all we know.

That's how replacement parts are these days... one or two companies make all of the parts and it gets dozens of brand names slapped on it. The AutoZone in-house brand FSV I bought (for the lifetime warranty) came with SMP/Pollak branded instructions.

And yes I can get a free replacement from O'Reilly in a few months, but, it'll be the same stupid thing I got from Amazon and you got from RockAuto, unless we got counterfeits.

The brakes were ok with the old pump but the C6 was acting up, due to not having enough vacuum at the vacuum modulator.

In late 2019, the alternator belt get lost (before I had the in cab gauge) and I didn't notice until I started braking a few times coming up to a turn. Thankfully no one was ahead of me, I was braking plenty early and I was able to limp to a truck stop to let it cool off overnight. I had a spare belt to put on, but being v-belts, the AC and PS belts had to come off first to put on the ALT belt. I was stomping the brake pedal with both feet, lifting myself off of the seat.
 
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